Independent High School STEM Project Paper

Tackling Concussions in Football: A Different Approach to Football Helmet Design
Rishi Makkar
STEM Research Project
Massachusetts Academy of Math and Science

Concussions in Football 2
Table of Contents
Abstract 3
Literature Review 4
Research Plan 22
Methodology 25
Results 31
Data Analysis and Discussion 39
Conclusions 44
Applications, Future Experiments, Extensions 46
Literature Cited 54
Acknowledgements 56
Appendix 57

Abstract
Despite improvements in helmet design, concussions in professional football occur at a
higher rate each year. The cumulative effect of multiple instances of brain trauma causes
memory loss, speech dysfunction, vision deterioration, and Alzheimer's disease. Current football
helmets are able to attenuate linear accelerations but are unable to mitigate rotational
accelerations. Prototypes were designed to reduce average impact force as well as linear and
rotational acceleration by dissipating impact energy and extending collision duration. Aluminum
honeycomb and aluminum foam were attached to the exterior shell of an Advanced Combat
Helmet and a Schutt football helmet. In addition, another prototype, which comprises a sheet of
soft neoprene suspended at high tension above the exterior shell, was constructed. All prototypes
were tested individually with a drop tower, and acceleration vs. time was measured with a DAQ
accelerometer. The data suggested that most prototypes produced an increase in collision
duration as well as a decrease in average and peak impact acceleration. The materials and
construction methodology applied in the engineering process can be improved upon for
application in safer helmets.

Introduction
Over an entire career, including high school, college, and professional vocations, a
football athlete can experience over 20,000 hits to the head (Lincoln, 2011). The cumulative
effects of thousands of head impacts have been connected to memory loss, speech dysfunction,
vision deterioration, and Alzheimer’s disease. Many neurologic disorders result from damaged
neurocognitive functioning caused by multiple instances of brain trauma. A concussion, a type of
brain trauma, may sideline a player for only a couple of weeks, but the long term effects appear
many years later. Several years after retirement, a player may become unable to feed or dress
himself, develop vulnerability to emotional outbursts, or lose the ability to maintain basic
memory recollection. Only recently have scientists become aware of the detrimental
repercussions of concussions, and this awareness has inspired competition between football
helmet manufacturers. Nevertheless, the engineering and testing process used by current
manufacturers is inadequate, and therefore a decrease in concussions has not been documented.
Over the past century, football has become integrated with American culture, but recently, the
concussion epidemic has raised serious questions and concerns regarding contact sports.
History
Progress in the development of football helmets has drastically reduced the likelihood of
sustaining traumatic head injury. The first football helmets were made out of leather, which
provided minimal protection against the forces experienced while playing football. With the
implementation of the double bar face mask, although the rate of spine injuries had drastically
decreased, head injuries continued to occur. To address the increased risk of brain trauma, the
National Operating Committee on Standards for Athletic Equipment, NOCSAE, was founded in

1969 to establish safety standards for football helmets (Apuzzo, 2004). The risk of head injury
has been reduced from 55% to 12% since the foundation of NOCSAE, along with a 76%
decrease in fatalities, an 84% decrease in severe head injuries, and a 65% decrease in cranial
fractures (Halstead, 2012). Advanced energy absorbing foams, stronger plastic shells, intricate
faceguards, and various suspension liners have all been implemented and have contributed to the
reduction of sustained head trauma. Through the use of complex ridges, contours, and ventilation
openings, helmets have become increasingly lightweight, durable, and affordable while
absorbing the multitude of forces experienced during football collisions. Over the past 30 years,
the fit of football helmets has improved, and this has also reduced the probability of experiencing
head injuries. Moreover, other pieces of equipment, such as shoulder pads and mouth guards,
also contribute to preventing concussions. However, despite improvements in helmet design,
concussions continue to occur in professional leagues, college, and high school.
Recently, the rate of concussions has increased by approximately 15% every year
(Lincoln, 2011). Perhaps this is due to improvements in the diagnosis of concussions, but at the
very least, this statistic indicates that the likelihood of sustaining a concussion has not decreased.
Currently, the injury incidence rate is an alarming 0.726 concussions per 1000 impacts (Duma,
2012).The various helmet manufacturers, including Riddell, Xenith, and Rawlings, have all
committed to designing safer helmets and have developed an assortment of designs by
implementing various types of foam and applying innovative suspension systems. However,
despite the utilization of different technologies employed by manufacturers, most helmets
receive similar testing results, and do not address the concussion crisis (S. Rowson, personal
communication, December 12, 2013).

Neurobiology
Ongoing concern with brain trauma has yielded insight into the causes and effects of
concussions. A concussion involves a certain degree of damage to the neurons, axons and other
elements that comprise the gray and white matter of the brain. With current football helmets,
concussions are most often caused when brain cells are harmfully strained, stretched, or twisted,
which stimulates chemical imbalances resulting in neurological dysfunction. This type of injury
is sometimes referred to as a diffuse axonal injury. Autopsies of deceased players have revealed
tearing of axons and neural fibers, confirming the occurrence of multiple concussions (Barth,
2001). The violent jerking of the neck, similar to a whiplash type of motion, is responsible for
the exertion of shear forces on the biological components of the brain. These rotational forces
cause not only permanent parenchymal brain damage, but can also result in epidural or subdural
hemorrhage (Andersen, 2012). In addition, the brain may collide against the skull multiple times
after impact, a phenomenon known as a coup and countercoup. Swelling and blood clots result
from this occurrence, and confusion is a common ensuing symptom. Concussions and neck
injuries are both related, because it is not uncommon to sustain a concussion as well as a neck
injury. However, the incidence of a concussion does not definitively indicate a neck injury, and
the incidence of a neck injury does not definitively indicate a concussion. Every region, tissue,
and cell of the brain is connected to and dependent upon each other. Therefore, damage to one
part of the brain can disrupt the functioning of the entire organ. Because of the lack of natural
biological protection, such as bone density or cerebrospinal fluid, the back of the brain is most
vulnerable to damage upon impact. This area of the brain includes regions associated with visual
reception and long term memory, therefore, blurred or clouded vision is an immediate diagnosis
of a concussion, and memory loss is a long term repercussion of a concussion.

Football players are especially vulnerable to multiple instances of head injury because the
accumulation of thousands of minor head impacts damages neurocognitive functioning no less
than the experience of multiple concussions. Because the neurological anatomy and upper
vertebrae structure is different for each individual, the detection of brain trauma after an impact
is almost impossible (Barth, 2001). The goal of completely eliminating the risk of sustaining a
concussion may inconceivable, but even a 20-30% reduction will prove to be a valuable
contribution to the football community (Apuzzo, 2004).
Linear and rotational forces are both experienced in a football collision. Every impact has
a rotational and linear component, and rarely is a purely rotational or a purely linear force
experienced. Only a head-on-head collision, where the crowns of two helmets collide, results in a
purely linear force. Rotational forces are often associated with angular/oblique/tangential
impacts, and linear forces are often associated with radial impacts. However, because the upper
vertebrae have a tendency to rotate after any collision, radial impacts also cause rotational
acceleration. Although the magnitude of linear acceleration is only dependent upon the
Figure 1. Regions of the brain and their respective functions. (Post, 2012)

magnitude of linear force, the magnitude of rotational acceleration is also dependent upon the
radial distance of the exerted force from the neck. This phenomenon is modeled by the equation,
, where the magnitude of torque is directly proportional to the
magnitude of rotational acceleration. The violent jerking of the neck after impact, which was
discussed in the section above, is essentially rotational acceleration experienced after a collision.
Although linear forces are often indentified with skull fractures, both rotational and linear forces
are capable of causing a parenchymal brain trauma. Studies have suggested that when these
forces are exerted together, “linear acceleration is correlated to an intracranial pressure response,
and rotational acceleration is correlated to the strain response of the brain,” (Duma, 2012).
Rotational acceleration causes the harmful stretching and twisting of axons and neurons, while
linear acceleration causes an intense blunt pressure upon the brain. Current helmets are able to
attenuate linear acceleration (Jeffords, 2008), and therefore those forces will not be discussed in
this section of the literature review. Nevertheless, it is worth noting that linear and rotational
acceleration are both correlated. Both are caused by the same magnitude of force upon impact,
however, this force is exerted in different directions (Jeffords, 2008). Therefore, a reduction in
linear acceleration will correspond to a reduction in rotational acceleration. Researchers disagree
on the degree to which these two forces are interrelated.

Biomechanics
Rotational forces, which are dependent upon a combination of impact location, impact
obliquity, and impact energy, can occur along three axes of the skull; the sagittal plane, the
coronal plane, and the transverse plane (S. Rowson, personal communication, December 12,
2013). On impact, the head can move along each axis with a different magnitude of acceleration
(Duma, 2012). Transverse rotation is the most dangerous and damaging rotation, and in severe
cases can result in permanent paralysis. There are millions of different combinations of head
rotation, and each yields a specific amount of brain trauma. The following data might be slightly
skewed and inapplicable because the methods of evaluation, from which the statistics were
derived, simulated a pure rotational force. In reality, as stated before, all impacts also have a
linear component, which is also capable of causing brain trauma (even though current helmets
adequately attenuate linear acceleration). Furthermore, the experiment accumulated data of
rotation along a single plane at a time, while in actuality, as stated before, rotational acceleration
Figure 2. Relationship between rotational and linear acceleration (Rowson, 2012)

is experienced along all three planes at once. Moreover, precaution should be taken before
assigning data of rhesus monkeys to human athletes. Nevertheless, the data provides a basic
benchmark that helmet manufacturers should strive to attain. The average magnitude of
rotational acceleration capable of causing concussions was determined to be approximately 6432
rad/s2
, with an average velocity of 36.5 rad/s (Duma, 2012).
Figure 3. Examples of football collisions and motion of the upper vertebrae. Illustration ‘a’
depicts sagittal rotational acceleration, and illustration ‘b’ depicts transverse rotational
acceleration. Coronal rotational acceleration is not depicted, however, this form of
acceleration occurs along the remaining axis. Illustration ‘c’ depicts an impact capable of
producing linear acceleration as well as rotational acceleration, which in this case would
mainly occur along the sagittal axis. Illustration ‘d’ depicts a collision capable of causing
linear acceleration and rotational acceleration along multiple axis (Jordan, 2013).

After the magnitude of rotational acceleration exceeds 6000 rad/s2
, the chances of
experiencing brain trauma increases exponentially. A magnitude of rotational acceleration
beyond 10000 rad/s2
was determined to nearly guarantee a concussion (Duma, 2012). As stated
before, transverse rotational acceleration causes the most brain damage, therefore its maximum
threshold, the least magnitude of acceleration required to cause a concussion, is significantly
lower than the threshold along the other axes. For coronal plane rotation, the maximum threshold
was determined to be approximately 16000 rad/s2
, with an average velocity of 46.5 rad/s (Duma,
2012). The threshold for rearward sagittal rotational acceleration was determined to be
approximately 10000 rad/s2
with an average velocity of 19 rad/s, while the threshold for forward
sagittal rotational acceleration was determined to be approximately 4500 rad/s2
with an average
velocity of 30 rad/s (Duma, 2012). Although the kinematics of football collisions is always
constant, it is important to realize that the aforementioned data will not apply universally because
the biomechanics varies between individuals.
Figure 4. Probability of sustaining brain trauma based on rotational acceleration (Duma, 2012)

Mitigation of the average impact force will correspond to a reduction in both linear and
rotational acceleration. The impulse of a force is defined as the product of the net average force
and the duration of time at which the net average force is exerted.
The change in momentum and amount of total energy exerted during a given collision is always
constant; therefore the impulse is always constant. However, the net average force can be
reduced by extending the duration of the collision. A football collision of high energy over a
short period of time yields an extremely large magnitude of net average force, which results in a
large magnitude of acceleration. The same high energy collision over a longer period of time
yields a low magnitude of net average force, which results in a lesser magnitude of acceleration,
albeit over for a longer duration and longer distance. Ultimately, an extension of collision
duration will effectively dissipate impact energy, and thus result in the mitigation of both linear
Figure 5. Relationship between the impact velocity and the change in rotational velocity
of the head (Halstead, 2012).

and rotational accelerations, which are, as stated before, correlated (S. Rowson, personal
communication, December 12, 2013). A crushable helmet, which absorbs energy by irreversible
deformation of components, would effectively extend the duration of collision, in a similar
fashion as car bumpers, but would not be capable of being used multiple times (Halstead, 2012).
The use of non linear anisotropic padding materials may also attenuate acceleration using similar
principles of impulse and impact force. A stronger and stiffer neck has been proven to reduce the
rotation of the upper vertebrae, thereby attenuating rotational acceleration (Casson, 2007).
Modern football helmets are able to attenuate linear acceleration resulting from an
impact force, but are unable to attenuate rotational acceleration. Data suggests that helmets are
able to decrease acceleration of blunt linear forces by up to 33%, and sometimes over 50%
(Jeffords, 2008). NOCSAE testing only simulates a purely linear acceleration, which means that
football helmets are only tested for their ability to prevent skull fractures, and therefore, current
helmets are able to pass the evaluation, despite inadequate protection against rotational
acceleration. A 14 kg mass is propelled onto a helmet to recreate a radial helmet to helmet
impact, but this type of collision is uncommon, and hence, NOCSAE evaluation does not
accurately simulate football collisions (Halstead, 2012). Furthermore, NOCSAE testing does not
account of the fit of the helmet or the durability of the helmet (Andersen, 2012). The flaws of
NOCSAE testing have been reflected in the limitations of the modern football helmet. Methods
of evaluation must simulate and measure both linear and rotational acceleration in order to
determine the effectiveness of the helmet.
Approximately 62% of NFL concussions involve helmet to helmet contact
(Casson, 2007). Concussions also result from helmet collisions with other body parts, collisions
with the ground, and often, even in collisions where the head is not directly impacted. 27% of

concussions are caused by impacts to the facemask (Casson, 2007). An impact to the facemask
results in a greater magnitude of torque, which causes a greater magnitude of rotational
acceleration. Because most impacts occur to the front and rear of the helmet, sagittal rotational
acceleration is most commonly experienced upon collision (S. Rowson, personal
communication, December 12, 2013). Brain trauma most often occurs during kickoffs or punt
returns, when impact forces are at greatest magnitude (Halstead, 2012). Offensive players are
more vulnerable to parenchymal brain injury than defensive players (Casson, 2007).
Quarterbacks in particular have the highest risk of concussion, followed by wide receivers and
tight ends (Casson, 2007). Defensive players are in most cases the impacting force, and offensive
players in most cases are the impacted object.
The complex kinematics and biomechanics of football collisions are only beginning to be
understood. Theoretically, with a thorough understanding, Newtonian physics is capable of
modeling the effects of impact forces on the individual neural fibers of our brain. Nevertheless,
current helmets are not adequate in the attenuation of rotational forces. Manufacturers are
actually capable of constructing a helmet that will greatly reduce rotational acceleration,
however, if current technology were to be used, such a helmet would be overly heavy or large,
and would significantly hinder athlete performance and enjoyment (S. Rowson, personal
communication, December 12, 2013). For example, increased amounts of padding and cushion
offer further protection, but also add undesirable weight to the helmet and increase the effective
radius of the system, thereby increasing the rotational inertia of the impacted player (Halstead,
2012). Furthermore, the sport of football would become impracticable with excessive amounts of
currently used energy dissipating material. An increase in the width, height, and length of a
helmet has been corresponded to better performance because of the distribution of force over a

greater area. However, once again, a larger helmet would inevitably increase weight and disrupt
the game of football (Halstead, 2012). Therefore, balancing effectiveness with practicality is the
greatest challenge for manufacturers.
Material Science
The outer shell of most football helmets is made out of polycarbonate plastic, which has a
compressive strength of just under 80mPA (DeBot, 2011). Because of its strength and durability,
this material will not degrade despite repeated collisions. In addition, polycarbonate is also
employed in the facemask. The types of foam implemented in football helmets vary per
manufacturer. Riddell, in particular, utilizes a high density vinyl nitrile foam that includes
injected air, which determines the properties of the foam (DeBot, 2011). Other companies,
including Schutt and Rawlings, apply thermoplastic urethane foam.
Metal foam is a material that can be implemented in a helmet prototype. A metallic
matrix, such as an aluminum alloy, surrounds an array of closed cells injected with high
pressured gases, therefore resulting in an 80% porosity (Banhart, n.d.). Due to the
aforementioned properties, metal foam has a very low density, sometimes over 50% lighter than
steel (Banhart, n.d.), which results in extremely lightweight and unrestrictive characteristics. The
unique crush deformation properties of metal foams effectively dissipate the energy of a
collision. Studies have also provided evidence of extended impact duration induced by the
material. Research has indicated that metal foam, which was applied to the bulkhead and rear
wall of an automobile, reduces weight by 25% while increasing stiffness by 700% (Banhart,
2001). Passengers, in an automobile equipped with metal foam, experiencing an accident at 28
mph will be affected by forces associated with that of a typical automobile accident at 5 mph

(Bray, n.d.). Moreover, in addition to its energy dissipating capabilities, metal foams offer a low
rebound energy, only 3% of the impact energy, as opposed to 15% offered by polyurethane foam
(Banhart, 2001).
Aluminum honeycomb can also be applied to the proposed helmet. Honeycomb is
manufactured using the corrugated process, where corrugated sheets of aluminum are stacked
into blocks and cured with adhesives (Honeycomb, 1999). The geometric
Figure 6. Deformation of metal foam caused by compression force (Banhart, n.d.)
Figure 7: A depiction of the Corrugated
Process (Honeycomb, 1999)

honeycomb structure accounts for the intrinsic energy dissipating crush deformation properties
exhibited by aluminum honeycomb. In addition, aluminum honeycomb also offers a low rebound
energy, thereby preventing possible injury to the impacting player. Even after compressing fully,
aluminum honeycomb will continue to deform and crush uniformly, thus making this material
ideal for energy absorbing applications. Similar to metal foams, aluminum honeycomb is
extremely light weight and unrestrictive, thereby preventing an increase in the rotational inertia
of the impacted player.
The equations, model the energy dissipating
properties of aluminum foam as well as aluminum honeycomb. The final velocity ( ) is directly
related to acceleration ( , and a reduction in acceleration will decrease the likelihood of
sustaining brain trauma. For a given collision, which includes a given impact location, impact
obliquity, and impact energy, the acceleration is dependent upon the stiffness of the crushable
material and is indirectly proportionate to the thickness of the material ( . However, a
material more effective in a low energy, low impulse collision may be less effective in a high
energy, high impulse collision. In order to dissipate the maximum amount of energy and mitigate
the maximum quantity of acceleration, the true deformation distance should be exactly equal to
Figure 8: A typical load-deflection curve (Honeycomb, 1999)

the thickness of the material. At a high energy, high impulse football collision, a higher stiffness,
which permits the material to deform only under high stress, would be desired. Both aluminum
honeycomb and aluminum foam can be engineered to incorporate properties of an optimal
stiffness. Because both materials also exhibit low density characteristics, a greater thickness
can be applied, which would effectively dissipate impact energy and mitigate subsequent
accelerations without hindering athlete performance or enjoyment by adding unnecessary weight.
Patents and Existing Designs
Sports Helmet with Impact Protection (Jacques, 2012): The helmet consists of an outer shell and
an inner padding, which is placed between the external shell and the head of the user. An
adjustment mechanism, operated by the user, allows for a better fit, which may reduce the chance
of injury. A rotational impact device, which rotates relative to the external surface of the helmet,
is disposed between the outer shell and the head, and attenuates rotational energy. The material
comprising this liner is flexible; therefore some of the rotational energy will be absorbed through
this elastic liner, with a resilience of preferably less than 30%. The outer shell and the liner are
both rigid so that shape is maintained during a collision. Upon impact, the surfaces of the outer
Figure 9: A photograph of aluminum honeycomb and aluminum foam respectively
(Honeycomb, 1999)

and inner shell move opposing each other, resulting in a significant amount of friction. Some of
the rotational energy will be dissipated by friction between these two surfaces, with a coefficient
of at least 0.2, preferably more, but less than 0.75. The inner padding of this helmet would
contain of sufficient foam to protect athletes from both linear and rotational acceleration.
Although this design incorporates innovate ideas, no data collected from testing or evaluation
was provided.
This design includes springs that connect an outer and inner layer, which are able to
move relative to each other upon impact, and attenuate both linear and rotational acceleration.
Connector springs are under high tension along the longitudinal axis, and are temporarily
deformable, which allows the two shells to move relative to each other. To absorb linear and
rotational energy, these springs can be stretched in various directions, and then reformed into
their natural position. This reduces the rotational acceleration of the head and neck during impact
by having the outer layer move relative to the head.. Connectors can vary in material and length
in the most effective force absorbing arrangement. They can also be placed at different angles,
and different widths. The tension and resilience of the springs can also be adjusted. Additional
layers or shells can be imbedded within the helmet, and in order to further attenuate rotational
forces, springs can connect these layers as well. A motion sensor can sense the momentum of an
impacting object, and then can increase the tension of the springs to provide increased protection.
Figure 10. A patented helmet (Phipps, 2013)

The magnitude and direction of the force, as well as the angle of impact, can all be determined,
and appropriately addressed by varying the tensions of the springs. During evaluation, this
helmet was compared to the Riddell Revolution and the COTS Simpson NASCAR helmet. All
helmets were tested using a Hybrid III ATD head and neck mounting system, which was
connected to a linear trolley. The apparatus was equipped with linear and angular
accelerometers. Using data crash analysis and mathematical functions, Head Injury Criteria
(HIC), Severity Index (SI), Peak Angular Acceleration, Peak Resultant Upper Neck Load, and
Peak Resultant Upper Neck Moment were all calculated. The prototype performed better than the
Riddell Revolution in the following categories: Peak Angular Acceleration caused by a frontal
impact, as well as Upper Neck Load and Upper Neck Moment in all three impact locations
(Front Impact Condition, Side Impact Condition and Rear Impact Condition). Although the data
is certainly promising, the method of evaluation does not thoroughly simulate the forces
experienced in football, and does not consider the possibility of material deterioration or the
difficulties in applying the design to football helmets.
MIPS has implemented new concepts in helmet design in an effort to prevent
concussions. A sliding plastic layer was installed between the padding and outer shell of the
helmet. In this way, upon angular impacts, the outer shell of the helmet will rotate, but the head
will remain in place. Subsequently, the upper vertebrae will not accelerate in a rotational manner,
Figure 11. A depiction of a current design (MIPS, 2013)

thereby significantly attenuating rotational acceleration. During evaluation, the helmet was
dropped onto a horizontally moving sled, which recreates the angular impacts that cause
rotational forces. Data suggested that the MIPS helmet does attenuate rotational acceleration.
Following the optimistic results, this technology has been applied in motocross, equestrian
sports, and recently in hockey.
However, the forces associated with football are much more dynamic, and therefore, this
design has not been implemented in football helmets. Furthermore, although the methods of
evaluation developed by MIPS do simulate rotational acceleration, the collisions experienced in
football games are considerably different than those created by MIPS testing. Clearly, the
challenge of applying a design to football helmets is a difficult endeavor.
Figure 12. Data of MIPS helmet: Rotational acceleration
during duration of collision (MIPS, 2013)

Research Plan
Engineering Problem
Despite improvements in football helmet design and construction, athletes continue to
experience concussions, which are being reported at a higher rate each year. Current football
helmets are able to adequately attenuate linear acceleration, but are unable to mitigate rotational
acceleration, which causes the upper vertebrae to rotate violently, thereby resulting in
parenchymal brain trauma (damage to functional parts of the brain). Although it is possible to
construct a football helmet that greatly reduces linear and rotational acceleration, if current
technology were to be used, such a helmet would significantly hinder athlete performance and
enjoyment
Engineering Goals
The goal of this project was to develop a technology, which can be implemented on a
pre-existing football helmet, that reduces the likelihood of sustaining brain trauma by effectively
attenuating linear and rotational acceleration caused by a helmet to helmet impact. Linear and
rotational acceleration are correlated, and therefore, a reduction in linear acceleration will
correspond with a reduction in rotational acceleration. While rotational acceleration is also
influenced by impact location and impact obliquity, both linear and rotational acceleration are
dependent upon impact energy. The prototypes tested for this project were designed to dissipate
impact energy by extending collision duration. An increase in collision duration will cause a
decrease in average impact force, thereby mitigating both linear and rotational acceleration. In

addition, to account for oblique impacts, which typify most football collisions, the prototypes
were designed to be deformable relative to the head (deformable in multiple directions).
Several additional criteria and objectives were determined for the prototypes. The entire
apparatus was intended not to hinder athlete performance and enjoyment. Feasibility of
construction, availability of materials, and low construction/designing cost were the other
important criteria of the design. Although durability was another criterion, a less durable,
crushable helmet can be worn during kickoff or punt returns, where risk of brain trauma is
highest. Because of the criticality and urgency of the concussion crisis, durability and aesthetics
were not determined to be extremely necessary. On the next page is a table that lists the criteria,
in order from most important to least important, that were utilized in both the decision and final
engineering matrix.
Procedure
Three prototypes, one which includes aluminum honeycomb applied to the exterior shell
of the helmet, one which includes aluminum foam applied to the exterior shell of the helmet, and
one which comprises a sheet of neoprene suspended at high tension above the exterior shell of
the helmet, were designed and tested. Three separate experiments were conducted at Natick Labs
Soldier System Center to test the prototypes. Experiment 1 individually evaluated the aluminum
honeycomb and aluminum foam prototypes, which were applied to the exterior shell of an
unmodified Advanced Combat Helmet (ACH) and dropped at 10 ft. s in a non-obli ue impact as
ell as a 0 impact. xperiment 2 individually evaluated the aluminum honeycomb and
suspended elastomer prototypes, which were applied to the exterior shell of an unmodified
Schutt DNA football helmet and dropped at 10 ft. /s in a non-oblique impact. Experiment 3

evaluated the aluminum foam prototype, which was applied to the exterior shell of an
unmodified ACH and dropped at 18 ft. /s in a non-oblique impact. Testing was conducted with a
drop tower, and acceleration was measured by a DAQ accelerometer.
Criterion
1
Mitigates rotational and linear acceleration by extending collision duration, thereby
dissipating impact energy and decreasing average impact force
 Deformable in multiple directions, relative to the head, to perform effectively in
oblique collisions
 Lightweight and compact (minimal effective radius) to prevent increase in
impact force as well as an increase in rotational inertia
2
Does not hinder athlete performance or enjoyment
 Does not append additional weight
 Does not drastically affect the radius of the system, which would increase the
rotational inertia of the upper vertebrae
 Does not restrict movement
 Does not restrict range of vision
 Does not interact adversely with other pieces of equipment
3
Feasibility
 Can be constructed without highly advanced equipment
 Can be constructed using available materials
 Can be tested with available lab equipment
 Is viable for a high school student
4
Cost
 Does not demand an overwhelming budget to construct a prototype
 An extension of the technology, which can be utilized by helmet manufacturers,
does not require an impractical budget
5
Durability
 Can withstand at least one high energy collision
 If significant damage is sustained, can be easily disposed
6
Aesthetics
 Is fairly pleasing to the eye
Table 1: Criteria were used mainly in the decision matrix, however, were also implemented in the
final engineering matrix

Methodology
Aluminum Honeycomb Prototype
Aluminum honeycomb (1.5 cm thickness, donated by Team Wendy), which was chosen
because of its energy dissipating properties, (including the ability to extend collision duration,
reduce average impact force, and mitigate resulting accelerations) and lightweight, unrestrictive
characteristics, was attached to the front crown of the helmet. An impact to the front crown,
occurring at a distance from the center of mass of the helmet, produces greater amounts of
torque, thereby inducing rotational acceleration even in a primarily linear collision. In order to
determine the dimensions of the aluminum honeycomb square, the length and width of the steel
curved hemispherical base were measured and determined to be 9x9 cm. Next, using heavy duty
scissors, 9x9 cm squares of aluminum honeycomb were cut out of the 36x21 cm sample.
Subsequently, using Velcro and industrial tape, the aluminum honeycomb squares were attached
to the front crown of the helmet. After each drop test, the aluminum honeycomb coupon was
replaced with a new square.
Aluminum Foam Prototype
The Aluminum foam sample (Closed Cell, 2 cm thickness, AA.1070 alloy, 0.25 g/cm3
average density, donated by Foamtech), which was chosen because of its energy dissipating
properties and lightweight, unrestrictive characteristics, was initially divided into 7.5 cm x 7.5
cm portions using an abrasive saw. Using Velcro and industrial tape, the aluminum foam squares
were attached to the front crown of the helmet. As stated before, an impact to the front crown,
occurring at a distance from the center of gravity of the helmet, produces greater amounts of

torque, thereby inducing rotational acceleration even in a primarily linear collision. After each
drop test, the aluminum foam coupon was replaced with a new square.
Suspended Elastomer Prototype
Four Styrofoam blocks (8 cm x 6 cm x 4 cm) and four foam blocks (8 cm x 6 cm x 2 cm)
were initially cut. Styrofoam was chosen because of its light and robust properties, and foam was
chosen because of its ability to be temporarily deformed, which allowed the elastomer to be
easily elongated under high tension. The Styrofoam and foam blocks were attached to each other
using the Loctite Plastics System adhesive. On each block, three hanging hooks (30lbs load)
were inserted with nails and further secured using Liquid Nails adhesive. Using Velcro and
industrial tape, the blocks were placed in a 17.0 cm x 30.0 cm rectangle on the front crown of the
helmet, again, because an off-center impact will produce greater magnitudes of rotational
acceleration. A sheet of neoprene (Durometer 30 Shore A, 1/16 inch thickness, tensile strength
700 PSI or 5 MPA, 1 lbs./square foot, RubberCal brand), which was chosen because of its high
elasticity and high tensile strength, was then prepared to be fastened to the hooks and suspended
at high tension. When being impacted at a high tension, by exerting a normal force in the
direction opposite to the impact, the elastomer will be able to effectively dissipate impact energy
by extending collision duration, thus decreasing average impact force and mitigating resulting
accelerations. After being cut into a 23.5 cm x 17.5 cm rectangle, four 3 cm x 1 cm perforations
were incised near the corners of the neoprene sheet. The neoprene was inserted into the hooks
through the perforations. In order to prevent the neoprene from tearing, the perforations were
coated with 8 layers of 3M filament tape, which was attached to the neoprene sheet using the
Loctite Plastics Bonding System adhesive. Because of its exceptional durability, which can be
attributed to the filament fibers that are imbedded within the tape, the filament tape was chosen

to protect the neoprene perforations. The neoprene was elongated to the maximum tension that
the author was capable of inducing, and then firmly suspended above the exterior shell of the
helmet.
Figure 2: Photographs of the suspended elastomer, aluminum foam, and aluminum honeycomb prototypes respectively.
The aluminum foam and aluminum honeycomb coupons are shown after experimentation. The suspended elastomer
prototype is placed on the Schutt football helmet, and the other two prototypes are placed on the ACH. Towards the
bottom, an aluminum honeycomb and an aluminum foam sample are shown before experimentation.

Experiments 1, 2, and 3 were conducted with a drop tower pulley apparatus. The helmet was
placed on a DOT standard head form and dropped on a steel curved hemispherical base, which
was chosen because a collision with the curved base most accurately simulated a helmet to
helmet football collision. The drop tower system was operated by pulling on one end of the
pulley, thereby raising the helmet until an impact with the stopper occurred, which caused the
helmet to transition into free fall. In all three experiments, an impact occurred at the front crown
of the helmet, which causes greater magnitudes of torque, thereby inducing greater magnitudes
of rotational acceleration. Acceleration (resultant of radial and tangential acceleration) was
measured every 0.1 millisecond by a DAQ accelerometer (single axis). The accelerometer
measured the acceleration of the first impulse. Therefore, if the helmet had rebounded after the
collision, only the first “bounce” ould have been recorded.
Figure 2: A depiction of the drop tower apparatus used for the project. The steel curved hemispherical
platform can be seen at the bottom of the image.
Figure 7: An image of the DAQ accelerometer placed within the helmet

Experiment 1 individually evaluated the aluminum honeycomb and aluminum foam
prototypes against an unmodified Advanced Combat Helmet (control). he prototypes and
control ere dropped from a height of 0. m at a final velocity of approximately 10 ft. s,
hich is a common setting for testing the A . o settings ere implemented in this
experiment an impact at a 0 obli uity and an impact at a 0 obli uity. Initially, the unmodified
ACH was tested, and five trials were conducted at both settings. Next, the aluminum honeycomb
prototype was attached to the exterior shell of the ACH, and five trials were conducted at both
settings. Lastly, the aluminum foam prototype was attached to the exterior shell of the ACH, and
four trials were conducted at each setting (due to material limitations, four, instead of five trials
were conducted).
Experiment 2 individually evaluated the aluminum honeycomb and the suspended elastomer
prototypes against an unmodified Schutt DNA Football Helmet (control). The prototypes and
control were dropped from a height of 0.474 m at a final velocity of approximately 10 ft. /s. One
setting was implemented in this experiment an impact at a 0 obli uity. Initially, the unmodified
football helmet was tested, and five trials were conducted. Next, the suspended elastomer
prototype was attached to the exterior shell of the football helmet, and five trials were conducted.
Lastly, the aluminum honeycomb prototype was attached to the exterior shell of the football
helmet, and four trials were conducted (due to material limitations, four, instead of five trials
were conducted).
Experiment 3 individually evaluated the aluminum foam prototype against an unmodified
ACH (control). The prototypes and control were dropped from a height of 1.537 m at a final
velocity of approximately 18 ft. /s, which approaches a high energy, high impulse football
collision. Initially, the control was tested, however, only one trial was conducted. The

accelerations associated with the control exceeded the limits of the DAQ accelerometer, which
was often unable to record accelerations exceeding 600g. Therefore, although multiple trials
were attempted, only one trial produced the complete range of acceleration measurements.
Lastly, the aluminum foam prototype was attached to the exterior shell of the ACH, and four
trials were conducted.
The data was transposed to an Excel document, where the collision duration, average
acceleration, and peak acceleration were determined. The RSD and STD values for each
prototype, under each Experiment and each Setting, were calculated and logged in an Excel
table. After data collection was completed, 21 unpaired, unequal variances, two tailed t tests
were conducted (12 for Experiment 1, 6 for Experiment 2, and 3 for Experiment 3). Each t test
compared the collision duration, average acceleration, and peak acceleration values of the
prototypes to the control group data.

Table 1
Table 2
Prototype Collision Duration (ms) Average Acceleration (g) Peak Acceleration (g)
Unmodified Schutt Football Helmet 20.82 26.30 61.79
Suspended Elastomer 20.14 28.35 66.12
Aluminum Honeycomb 21.10 23.23 55.47
Table 3
Unmodified ACH 20.82 295.63 733.58
Aluminum Foam 10.33 70.13 196.19
Table 4
Prototype
Collision Duration
(% increase)
Average Acceleration
(% decrease)
Peak Acceleration
(% decrease)
Experiment 1 Aluminum Honeycomb 19.49 22.99 17.10
Aluminum Foam 19.02 22.12 28.25
Experiment 2 Suspended Elastomer -3.37 -7.79 -6.55
Experiment 3 Aluminum Foam 77.73 76.28 73.26
Tables 1, 2 and 3 contain the condensed data from Experiments 1, 2, and 3, respectively. Each
value represents the average measurement of all trials/drops. Table 4 contains the percentage
increases or decreases for each prototype in comparison to the control group. Before calculating
the percentage values, the data of all trials/drops was averaged, and under Experiment 1, the data
of both settings was averaged as well. A positive value indicates that the prototype performed
more effectively than the control and a negative value indicates that the prototype performed less
effectively than the control.
Setting 1 Unmodified ACH 11.24 41.34 90.72
Aluminum Foam 13.18 32.81 67.22
Setting 2 Unmodified ACH 10.32 46.55 104.25
Aluminum Foam 12.48 35.64 72.60

Figure 1
Figure 2
8
9
10
11
12
13
14
15
No Obliquity
Time(ms)
Setting
Collision Duration (Exp. 1)
Unmodified
ACH
Aluminum
Honeycomb
Aluminum
Foam
Obliquity 30°
15
20
25
30
35
40
45
50
No Obliquity
Acceleration(g)
Setting
Average Acceleration After Impact (Exp. 1)
Unmodified
ACH
Aluminum
Honeycomb
Aluminum
Foam
Obliquity 30°

Figure 3
Figures 1, 2, and 3 display bar charts for Experiment 1 that compare collision duration, average
acceleration, and peak acceleration, respectively, of the Aluminum Honeycomb and Aluminum
Foam prototypes along with the control group (Unmodified ACH).
20
30
40
50
60
70
80
90
100
110
120
No Obliquity
Acceleration(g)
Setting
Peak Acceleration After Impact (Exp. 1)
Unmodified
ACH
Aluminum
Honeycomb
Aluminum
Foam
Obliquity 30°

0
20
40
60
80
100
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Acceleration(g)
Time (ms)
Acceleration vs. Time Exp. (1 Setting 2)
Aluminum
Foam
Aluminum
Honeycomb
Unmodified
ACH
0
10
20
30
40
50
60
70
80
90
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Acceleration(g)
Time (ms)
Acceleration vs. Time (Exp. 1 Setting 1)
Aluminum
Foam
Aluminum
Honeycomb
Unmodified
ACH
Figure 4
Figure 5
Figures 4 and 5 display line graphs of Acceleration vs. Time for Experiment 1, Settings 1 and 2
respectively. For both plots, the selected data was from the trial with values that most closely
resembled the average data values.

Figure 6
Figure 7
15
25
35
45
55
65
75
Collision Duration (ms) Average Acceleration (g) Peak Acceleration (g)
Experiment 2 Data Comparison
Unmodified
Football Helmet
Suspended
Elastomer
Aluminum
Honeycomb
0
10
20
30
40
50
60
70
0 2 4 6 8 10 12 14 16 18 20
Acceleration(g)
Time (ms)
Acceleration vs. Time (Exp. 2)
Unmodified
Football Helmet
Suspended
Elastomer
Aluminum
Honeycomb

Figures 6 and 7 display data from Experiment 2. Figure 6 illustrates a bar chart that compares the
collected data values of the suspended elastomer and aluminum honeycomb prototypes in
addition to the control group (Unmodified Football Helmet). Figure 7 illustrates a line graph of
acceleration vs. time, where, for each plot, the selected data was from the trial with values that
most closely resembled the average data values.
Figure 8
Figure 9
0
2
4
6
8
10
12
Unmodified ACH Aluminum Foam
Time(ms)
Prototype
Collision Duration (Exp. 3)
0
100
200
300
400
500
600
700
800
Average Acceleration (g) Peak Acceleration (g)
Acceleration(g)
Average and Peak Acceleration (Exp. 3)
Unmodified
ACH
Aluminum
Foam

Figure 10
Figures 8, 9, and 10 display data from Experiment 3. Figure 8 displays a bar chart that compares
the collision duration of aluminum foam and the control group (Unmodified ACH). Figure 9
displays a bar chart that compares the average and peak acceleration of the aluminum foam
prototype to the average and peak acceleration of the control group. Figure 10 illustrates an
acceleration vs. time line graph, where, for each plot, the selected data was from the trial with
values that most closely resembled the average data values. In Figures 8 and 9, STDEV bars are
unavailable for the control group because the accelerometer was able to record exact acceleration
values for only one trial. The impact with the control group produced extremely high
acceleration values that exceeded the capabilities of the accelerometer. However, the
accelerometer verified that the acceleration easily surpassed 600g.
0
100
200
300
400
500
600
700
0 1 2 3 4 5 6 7 8 9 10
Acceleration(g)
Time (ms)
Acceleration vs. Time (Exp. 3)
Unmodified
ACH
Aluminum
Foam

Table 5
P Values: Comparing Prototypes to Control
Prototype
Collision
Duration
Average
Acceleration
Peak
Acceleration
Exp. 1 Setting 1 Aluminum Honeycomb 0.0035 0.0013 0.0064
Aluminum Foam 0.0091 0.0017 0.0022
Exp. 1 Setting 2 Aluminum Honeycomb 0.0004 0.0008 0.0460
Aluminum Foam 0.1325 0.0336 0.0013
Exp. 2 Suspended Elastomer 0.3648 0.0849 0.1866
Exp. 3 Aluminum Foam n/a n/a n/a
Table 5 contains the P values of the t tests conducted for the data. The P values compare the
respective prototype to the control group in each respective Experiment and Setting.
Engineering Matrix
MitigatesPeakAcceleration
ExtendsCollisionDurationandMitigates
AverageAcceleration
LowWeight
LowEffectiveRadius(Thickness/Distance
fromHelmetSurface)
EaseofApplicationorConstruction
(IncludingCostandAvailabilityof
Materials)
SufficientDurability
Total
Percentage
Max Score 10.0 8.0 5.0 4.0 4.0 3.0 34.0 100%
Aluminum Honeycomb 5.5 4.6 4.4 3.2 4.0 0.5 22.3 65.6%
Aluminum Foam 9.3 7.2 4.2 2.8 3.0 1.0 27.5 80.9%
Suspended Elastomer 3.5 2.6 2.3 1.1 1.0 2.5 13.0 38.1%
Shown above is the engineering matrix. The process for determining the scores, including the
formation of a data matrix, is presented in the appendix. The conducted Experiments suggest that
the Aluminum foam prototype most effectively meets the engineering goals of the project.

Discussion
The figures and tables of Experiment 1 and 2 reveal increased collision duration as well
as a reduction in average and peak acceleration for the aluminum honeycomb and aluminum
foam prototypes. Consequently, the data from both experiments suggests that the aluminum
honeycomb and aluminum foam prototypes are capable of extending collision duration, reducing
average impact force, and mitigating both linear as well as rotational acceleration. If the
aforementioned materials were to be implemented on the exterior shell of a football helmet, the
likelihood of sustaining brain trauma caused by rotational and linear accelerations may be
reduced. The bar charts and tables of Experiment 2 suggest that the suspended elastomer
prototype does not perform as effectively as the other two prototypes, and in some cases, is less
effective than an unmodified football helmet. In comparison to the control, the suspended
elastomer design yielded a decrease in collision duration and an increase in average as well as
peak acceleration. Therefore, as indicated by Experiment 2, the suspended elastomer prototype is
not capable of attenuating linear and rotational accelerations.
As indicated by the data from Experiment 1, under both settings, the aluminum
honeycomb prototype most effectively increased collision duration and therefore most
effectively mitigated average acceleration in a low energy, low impulse impact. The data of all
prototypes and the control group revealed a direct relationship between collision duration and
average acceleration, as was expected. In addition, Experiment 1 suggested that the aluminum
foam prototype most effectively attenuated peak acceleration, especially in an oblique impact, as
shown in Table 4. Peak acceleration is more dependent upon the material properties, including
the geometric structure and deformation tendencies, of the prototype instead of collision
duration. Therefore, aluminum foam exhibits the most favorable physical properties for the

reduction of peak acceleration. Furthermore, while the performance of the aluminum honeycomb
prototype as well as the performance of the control group deteriorated in an oblique impact, the
aluminum foam prototype remained equally effective under both settings. The exceptional
performance of aluminum foam in an oblique impact occurs as a result of the versatile
deformation properties. Aluminum foam is capable of deforming in many directions in all three
dimensions, and can deform relative to the head, thus mitigating rotational accelerations caused
by an oblique impact. As indicated by figures 4 and 5, under both settings, the peak acceleration
of the aluminum honeycomb prototype occurred after the greatest time interval, which is
reflective of its potentiality in extending the collision duration and thereby decreasing the
average acceleration, of a low energy, low impulse impact. However, the aluminum foam
prototype yielded the most minimal slope in an oblique and non-oblique impact. Experiment 3,
which will be analyzed later in this section, provides additional data that reflects the capabilities
of aluminum foam in mitigating the peak acceleration of a variety of impacts.
The results of Experiment 2, particularly those of the suspended elastomer were not
favorable. Most likely, the neoprene, which was at a minimal tension, was simply not stiff
enough to increase collision duration and dissipate impact energy. While the suspended
elastomer prototype was incapable of extending collision duration and attenuating peak
acceleration, it was especially ineffective in mitigating average acceleration, as indicated by
Table 4. Surprisingly, despite the theoretical direct proportionality between collision duration
and average acceleration, the suspended elastomer produced an approximately 3% decrease in
collision duration and an 8% increase in average acceleration. Theoretically, the percentage
changes in collision duration and average acceleration are directly proportional, and there should
not be a considerable discrepancy between the variations displayed in Table 4. The aluminum

honeycomb prototype did not meet the engineering criteria effectively in Experiment 2. In
particular, Table 4 reveals only a 1% increase in collision duration. Once again, the discrepancies
between collision duration and average acceleration reappear, but nevertheless, the aluminum
honeycomb prototype was unable to extend collision duration and mitigate average and peak
acceleration to the effectiveness suggested by Experiment 1. The football helmet, which was
used as the control in Experiment 2, was intrinsically superior to the ACH, which was used as
the control in Experiment 1. Therefore, perhaps the use of a more effective control explains the
inferior performance of the aluminum honeycomb prototype in Experiment 2. Even so,
Experiment 2 verified the potential of aluminum honeycomb in extending collision duration and
attenuating both average and peak acceleration.
The data and results of Experiment 3 were indicative of the effectiveness of aluminum
foam in a high energy, high impulse collision. As indicated in Table 4, the aluminum foam
prototype extended collision duration and reduced both average and peak acceleration by greater
than 70%. In fact, the DAQ accelerometer was often unable to measure the extremely high
accelerations induced by the unmodified ACH (control group). Figure 10 illustrates a minimal
slope of the aluminum foam when compared to the slope of the unmodified ACH. This is
reflective of a much greater quantity of dissipated energy and extended collision duration.
Clearly, the aluminum foam prototype would most effectively attenuate both linear and
rotational acceleration in a high energy, high impulse football collision.
Under Experiment 1, as was expected, an oblique impact (Setting 2) induced the greatest
magnitudes of acceleration, which included rotational acceleration. However, an oblique impact
also produced more inconsistent data, which revealed a much greater %RSD (presented in
Appendix). Despite its effectiveness in Setting 2, the aluminum foam data exhibited the greatest

variance under an oblique impact. Nevertheless, the data for all prototypes and controls tested in
Experiment 1 suggested a direct relationship between the variances in collision duration and
average acceleration. Because a linear relationship exists between collision duration and average
acceleration, the %RSD of those measurements should be directly correspondent. This
phenomenon was confirmed by the data. No meaningful statistical trends were found for peak
acceleration, which is not directly dependent on collision duration and average acceleration
(peak acceleration is dependent on collision duration, but not directly proportionate). In
comparison to the aluminum foam and control group data, the aluminum honeycomb prototype
yielded the most consistent data.
Generally, the data of Experiments 2 and 3 was relatively consistent, with much
lower %RSD values than those of Experiment 1. Inconsistencies in the data were more prevalent
in the peak acceleration measurements, especially those of the aluminum honeycomb prototype.
The unmodified football helmet (control group) produced distinctively unvarying data. No other
meaningful statistical trends were observed.
21 t tests were conducted, which compared collision duration, average acceleration, and
peak acceleration values of the prototypes to those of the control in each respective Experiment
and Setting. In Experiment 1, because the effectiveness of the prototypes was significantly
superior, significant P values were observed. Nevertheless, the inconsistent data of Setting 2 is
reflected in Table 5, especially for the aluminum foam prototype. In Experiment 2, although the
data was relatively consistent, because the performance of the prototypes did not significantly
differ from the performance of the control, insignificant P values were observed. T tests were not
conducted for Experiment 3 because the control group included only one trial. However, because

of the exceptionally superior performance of the aluminum foam in comparison to the control
group, if a t test were to be conducted, a significant P value would be observed.
Under Experiment 1, except for an exceptionally high STDEV and %RSD values of the
aluminum foam under Setting 2, no anomalies were revealed in the formatted data. Some
individual drops/trials produced anomalous data, which contributed to the generally high STDEV
and %RSD, especially in Experiment 1.
A previous study applied aluminum honeycomb on a bicycle helmet, which was tested
with a drop tower and a biofidelic neck (Botlang, 2013). Although the methodology was slightly
different in this experiment, the results of the experiment described in this paper as well as the
previously conducted experiment were similar; the data suggested that aluminum honeycomb
significantly mitigated linear and rotational acceleration, especially in low energy, low impulse
impacts. Designs similar to the aluminum foam and the suspended elastomer prototypes have not
been previously tested.

Conclusions
The research suggested that two out of the three prototypes, the aluminum honeycomb
and the aluminum foam, are capable of attenuating linear and rotational acceleration by
dissipating impact energy through an increase in collision duration. If aluminum honeycomb or
aluminum foam were to be applied to the exterior shell of a preexisting football helmet, the
likelihood of sustaining brain trauma may be reduced. As indicated by the data, the suspended
elastomer design was less effective in mitigating average and peak accelerations. Therefore, this
prototype would most likely be unable to attenuate linear and rotational accelerations
experienced during a football collision, and thus would most probably be unable to reduce the
likelihood of sustaining brain trauma.
Experiments 1 and 2 suggest that, in a low energy collision, the aluminum honeycomb
prototype most effectively extends collision duration and mitigates average acceleration.
However, in the same low impulse impact, aluminum foam most effectively mitigated peak
acceleration. Peak acceleration causes the maximum amount of parenchymal brain trauma, and
hence, a greater importance lies in attenuating peak acceleration as opposed to average
acceleration. In Experiment 1, the aluminum foam prototype performed most superiorly in an
oblique impact. Most football impacts are oblique instead of purely linear. Therefore, even in a
low energy, low impulse collision, aluminum foam is the most effective prototype. Because of its
stiff nature and versatile deformation properties, in a high energy, high impulse collision,
aluminum foam is unquestionably the most ideal prototype. Although the aluminum honeycomb
prototype was not tested in a high energy, high impulse setting, its lack of stiffness would have
prevented it from dissipating significant amounts of energy and mitigating substantial amounts of
acceleration. Even at a low energy, low impulse impact, the aluminum honeycomb was fully

deformed, or fully crushed. Nevertheless, as indicated by the engineering matrix, aluminum
honeycomb is significantly lighter than the other two prototypes. Therefore, a greater thickness
( of aluminum honeycomb can be applied to dissipate greater quantities of energy and further
extend collision duration. However, a greater thickness ( would increase the effective radius
of the system, thereby increasing the rotational inertia of the impacted player. Because the
suspended elastomer prototype was unable to perform adequately in a low energy, low impulse
impact, it can be extrapolated that the prototype would be unable to function in a high energy,
high impulse impact.
Because of its versatile deformation characteristics and exceptional performance in high
energy, high impulse impacts, aluminum foam, when applied to the exterior shell of a football
helmet, has the potential to most effectively reduce the likelihood of sustaining brain trauma.
Aluminum foam has the potential to be more efficient than traditional foams, such as
polyurethane, because of its lightweight and unrestrictive properties. A helmet that is capable of
preventing brain trauma by adequately attenuating both linear and rotational acceleration can be
designed and manufactured using current technology. However, such a helmet would have an
excessive weight and an extremely large effective radius. Athlete performance and enjoyment
would be entirely compromised. Overall, football would become unfeasible in such a helmet.
Unlike typical foams, aluminum foam is extremely light weight and exhibits a minimal density.
Furthermore, a much lesser radius of aluminum foam is capable of dissipating more energy than
a much greater radius of traditional foam. Therefore, the implementation of aluminum foam on a
football helmet will be able to attenuate linear and rotational accelerations without sacrificing
athlete performance and enjoyment. Ultimately, aluminum foam technology has the potential to
protect athletes without disrupting the game of football.

Assumptions
Regarding the materials and technologies used in this project, it was assumed that the
aluminum honeycomb samples did not differ in the intrinsic properties of the material,
particularly in stiffness (which comprises compressive strength, tensile strength, hardness, and
porosity), density, and deformation tendencies. The same assumption was made for the
aluminum foam samples. In addition, it was assumed that the DAQ accelerometer provided
relatively accurate acceleration measurements.
Although it is impossible to thoroughly simulate football collisions in a laboratory
setting, it was assumed that some aspects of the methodology resembled a helmet to helmet
collision. The methodology used in this project, which imitates NOCSAE forms of testing, only
simulates a collision involving the crowns of two helmets, with only a few variations. However,
such a collision is rare and uncommon in football.
Limitations
Despite collecting data in a state of the art facility, various limitations were associated
with this project. Aluminum honeycomb and aluminum foam are both in their primitive stages of
commercialization. Obtaining such materials is often impossible, and although both materials
were kindly donated for this project, the amount of samples was limited. This imposed a
restriction on the number of conductible drops/trials. Regarding the elastomer design, the
construction facilities ere restricted to the author’s basement. If advanced e uipment ere to be
used, an increased amount of tension could have been instilled in the neoprene, which would
increase the effectiveness of the prototype.

The lab equipment used in this project imposed a variety of limitations. The DAQ
accelerometer was unable to consistently measure accelerations exceeding 500g. Furthermore,
both the ACH and the Schutt Football Helmet could not be dropped repeatedly at velocities
exceeding 14 ft/s. Such limitations were most prevalent during Experiment 3, where the DAQ
often failed to measure accelerations for the unmodified ACH, which experienced significant
deterioration. As stated before, the task of accurately recreating a football collision is impossible
in a laboratory setting. Due to time constraints, this project was limited to the drop tower, which
is incapable of simulating the complexities of a football collision. Furthermore, this project was
limited to the DOT standard head form, which is incapable of imitating the biomechanics of the
upper vertebrae. Although the author attempted to induce rotational accelerations by altering the
impact location and impact obliquity, only minimal magnitudes of rotational acceleration were
produced through the limited methodology. Although advanced equipment, which more
accurately simulates the forces and accelerations associated with football collisions, has been
developed, such technology is only available in certain locations, such as the Virginia Institute of
Technology.
Sources of Error
After each impact with the steel curved hemispherical base, both the ACH and Schutt
football helmet experienced permanent material deformation, including outer shell deterioration,
pad compression, and foam corrosion. This causes an increase in average and especially peak
acceleration. ventually, the deformation reaches a “plateau point”, here the rate of
deformation is minimal after a certain number of drops. This phenomenon was revealed in the
data of the unmodified ACH tested in Experiment 1 (the uncondensed data is shown in the
appendix). The first drop, in which the ACH was relatively unused, a peak acceleration of 77.26g

was measured. Over the course of three drops, the peak acceleration progressively increased, and
the fifth drop yielded a peak acceleration of 98.89g. After the unmodified ACH was tested, the
data became increasingly consistent, indicating that the plateau point had been reached. For a
future experiment, before starting data collection, the helmet should be dropped until the
deformation progression reaches the plateau point. In an ideal experiment, an unused helmet
would be dropped for each trial.
Regarding the testing procedure, every drop/trial inevitably occurred at a different
location on the helmet. A different impact location will not substantially affect linear
acceleration, however, rotational acceleration, which is dependent upon impact energy, impact
obliquity, and impact location, will be significantly altered if the impact location changes for
each drop/trial. For example, an impact occurring at a distance from the center of gravity of the
helmet will produce a greater magnitude of torque, which generates greater magnitudes of
rotational acceleration. Subsequently, this source of error causes a high variance in acceleration
measurements. Inconsistencies in impact location were prevalent while testing the suspended
elastomer prototype. Although the suspended elastomer prototype did not produce inconsistent
data, the elastomer may have contorted the helmet to a slightly different position, leading to a
less favorable impact location. This phenomenon may provide additional insight into the lack of
effectiveness of the suspended elastomer prototype. In addition, after each drop/trial, the
elastomer unavoidably decreased in tension, therefore, not only producing variances in the data,
but also contributing to the lack of effectiveness of the prototype.
Although multiple sources of unavoidable human error were present throughout this
project, the most significant source of error occurred while utilizing the drop tower pulley. The
force at which the helmet is raised (through a pulley) naturally varies per each drop because of

human error. An increased applied force would increase the momentum of the helmet before
bumping the stopper. This would cause the helmet to advance to a greater height before
proceeding into free fall, which would ultimately increase the final velocity before impacting the
base. An increased velocity would increase both average and peak acceleration. Therefore, if the
helmet is “pulled harder” and raised at a faster rate, then all three measurements (collision
duration, average acceleration, peak acceleration) can be skewed.
Applications and Future Experiments
A future experiment can be conducted to determine the ideal stiffness and width of the
aluminum honeycomb and aluminum foam prototypes. For the purposes of this experiment, a
more stiff form of aluminum honeycomb and a less stiff form of aluminum foam would have
produced the optimal results. However, for high energy, high impulse football collisions, a
highly stiff form of aluminum foam would most effectively prevent the likelihood of sustaining
brain trauma. A future experiment can also test a combination of aluminum honeycomb and
aluminum foam, and perhaps combinations with other materials such as polyurethane foam. In
addition, further research can develop a technology that is capable of preventing the complete
deformation of the aluminum honeycomb or aluminum foam after impact, which would make the
material reusable.
Future research can be conducted to improve upon the suspended elastomer prototype.
More effective building materials can be determined, which would subsequently serve to
increase the tension/stiffness of the elastomer. Various forms of elastomers, in addition to
neoprene, can be tested to determine the most effective properties. Ultimately, a high tension
suspended elastomer with versatile elastic properties, including the ability to stretch in multiple

directions, might be able to mitigate linear and rotational acceleration, and thus decrease the
likelihood of sustaining brain trauma. An elastomer at extremely high tension will have an
intrinsic tendency to revert to its natural position, hich can cause a “rebound” affect capable of
delivering injury to the striking player. To address this potential issue, Velcro can be layered
beneath the elastomer and above the exterior shell of the helmet, which would provide time for
the striking player to disengage before being affected by the “rebound” of the elastomer.
As mentioned before, rotational acceleration was induced to the greatest possible
magnitude by altering impact location and impact obliquity. However, the drop tower
methodology produced mostly linear accelerations. Linear and rotational acceleration are directly
related, and therefore, a decrease in linear acceleration corresponds to a decrease in rotational
acceleration. Nevertheless, future experiments can greatly benefit from more accurate recreations
of football collisions. Experiments 1, 2 and 3 can be modified by conducting more tests under an
oblique impact, which induce greater amounts of rotational acceleration and more closely
resemble football collisions. To accurately simulate the kinesiology of a football collision, a
biofidelic neck, which imitates the biomechanics of the upper vertebrae, can be utilized.
Figure 1: An illustration of a biofidelic neck known as the FOCUS head form (Natick
Labs)

The use of a pneumatic linear actuator would simulate a football collision in the most
comprehensive manner. As stated before, rotational acceleration is dependent upon impact
location, impact energy, and impact obliquity. A pneumatic linear actuator is capable of
controlling and varying all three aforementioned variables, and therefore, is able to recreate a
variety of helmet to helmet impacts.
Preferably, future experiments would test all three prototypes at the same settings and
against the same controls. Because of time constraints and limitations associated with the
materials, the project could not test all three prototypes in one experiment and against the same
control.
All three prototypes are in the most primitive stages of development, and must be
significantly modified for realistic application in football helmets. The aluminum foam and
aluminum honeycomb prototypes would be especially applicable during punt returns and
kickoffs, where impact energies are highest. A method to proficiently attach the aluminum
honeycomb or foam to the entire surface of the helmet would need to be initially determined.
After deformation, an efficient disposable procedure would also need to be developed.
Furthermore, because both the aluminum foam and honeycomb are significantly abrasive, a
material would need to be implemented to prevent the infliction of lacerations and wounds. If
Figure 2: A depiction of a pneumatic linear actuator apparatus (Duma, 2012)

further engineered to be applicable to the entire surface area of the helmet, the suspended
elastomer design can potentially be utilized for extended periods of time. However, in order for
the elastomer to be suspended over the entire helmet, multiple design changes would be
necessary. Lastly, only offensive players, who are under most circumstances the impacted
players, would be required to wear the improved helmet. Defensive players, who are typically
the impacting players, do not experience as many concussions as offensive players.
Future research can extend to fields beyond helmet design. The material science and
technologies exhibited by all three prototypes can be investigated for use in sports equipment or
military combat gear, specifically to increase protection. The field of transportation can benefit
from energy dissipating, impact mitigating technology in car bumpers, highway railings, railroad
railings, and aviation design. Aluminum foam and aluminum honeycomb offer many unique
properties for applications beyond the scope of this project.
In order to further attenuate rotational accelerations, future helmet prototypes could
introduce slip planes or other rotating components (S. Rowson, personal communication,
December 12, 2013). Such a system would effectively extend collision duration while the helmet
and the upper vertebrae rotate on impact, thereby mitigating large quantities rotational
acceleration. Furthermore, a rotatable or motile outer shell would be particularly effective in
oblique collisions, which typify most football collisions. A combination of aluminum foam and
rotatable exterior shell technology will perhaps most successfully reduce the likelihood of
sustaining brain trauma. Nevertheless, the construction and assembly of a freely moving outer
shell would be a significant challenge. During the beginning stages of this project, prototypes
with a rotatable outer shell were brainstormed. Such concepts included the implementation of
various joints, rotatable spheres, sliding liners, springs, and magnets. However, it was eventually

determined that engineering a complex and intricate design would be unfeasible for the given
limitations associated with the project. Even helmet manufacturers that have access to advanced
construction equipment would be faced with similar challenges.
In the future, a more comprehensive understanding of the forces and accelerations
associated with a football collision would have to be established. Furthermore, more research
must be conducted on the neurological consequences of single and multiple impacts.
Subsequently, a comprehensive method for testing helmets that more accurately simulates
football collisions must be developed, perhaps through the use of pneumatic linear actuators and
biofidelic necks. Finally, through the implementation of unique materials, such as aluminum
honeycomb and aluminum foam, or through the application of distinctive technologies, such as a
suspended elastomer, a revolution in football helmet design might be necessary in order to
preserve America’s game.

Literature Cited
Andersen, A.T., Bahr, R., Greenwald, R., Kleiven, S., McCrory, P., McIntosh, A.S., Turner, M.,
Varese, M. (2012, November). Sports helmets now and in the future. British Journal of
Sports Medicine, 45, 1258-1265. doi:10.1136/bjsports-2011-090509
Apuzzo, M. L.J., Aryan, H. E., Berry, C., Ozgur, B.M., and Levy, M.L. (2004, September).
Birth and evolution of the football helmet. Neurosurgery, 55(3), 656-662. doi:
10.1227/01.NEU.0000134599.01917.AA
Banhart, J. (n.d.). Metal Foams II: Properties and Applications. Retrieved November 28, 2013
from http://materialsknowledge.org/docs/Banhart-talk2.pdf
Barth, J.T., Broshek, D.K., Freeman, J.R., and Varney, R. N. (2001). Acceleration-deceleration
sport-related concussion: The gravity of it all. NCBI, 36(3): 253–256. Retrieved from
http://www.serialsolutions.com
Beckwith, J.G., Brolinson, G. P., Chu, J.J., Crisco, Joseph. J., Duhaime. A., Duma. S.M.,
Greenwald, R. M., Maerlender, A.C., McAllister, and T.W., Rowson S. (2012, January).
Rotational head kinematics in football impacts: An injury risk function for concussion.
Annals of Biomedical Engineering, 40(1), 1-13. Retrieved from http://link.springer.com
Bottlang, M., Dau, N., Deck, C., Feist, F., Hansen, K., Madey, S.M., Willinger, R., Angular
Impact Mitigation system for bicycle helmets to reduce head acceleration and risk of
traumatic brain injury. Elsevier. 59 (2013) 109– 117. Retrieved from
http://www.biomedsearch.com/nih/Angular-Impact-Mitigation-system-
bicycle/23770518.html
Casson, I. R., Pellman, E. J., and Viano D. C. (2007). Concussion in Professional Football:
Biomechanics of the Struck Player-Part 14. Neurosurgery, 61(2), 313-328.

DeBot, B., De La Rosa, K., Kenimer, B., Ludlow, B., van Gemeren, E., Weinberg, P.
(2011, May). Riddel Revolution IQ Football Helmet. Retrieved November 27, 2013 from
http://www.engineering.dartmouth.edu/courses/11spring/engs008/halftime/riddell-
revolution-football-helmet.html
Jacques D., Jean-Francois L., Marie-Claude G., and Denis C. (2012). U.S. Patent No.
US20130025032A1. Washington D.C.: U.S. Patent and Trademark Office
Duma, S.M., and Rowson, S. (2013, May). Brain injury prediction: Assessing the
combined probability of concussion using linear and rotational head acceleration.
Annals of Biomedical Engineering, 41(5), 873-882. Retrieved from
http://link.springer.com
Foster, T. (2012, December, 18th
) The helmet that can save football Popular Science
Halstead, D., and Viano, D.C., (2012, January). Change in size and impact performance of
football helmets from the 1970s to 2010. Annals of Biomedical Engineering, 40(1), 175-
184. Retrieved from http://link.springer.com
Jeffords, B., Lauryssen, C., Lewis, Lawrence, M., Naunheim, R., Richter, C., and
Standeven, J. (2008, June). Do Football Helmets Reduce Acceleration of Impact in
Blunt Head Injuries? Academic Emergency Medicine, 8(6), 604-609.
doi/10.1111/j.1553-2712.2001.tb00171.x
Lincoln, A. E., Caswell, S. V., Almquist, J. L., Dunn, R. E., Norris, J. B., and Hinton, R. Y.
(2011). Trends in Concussion Incidence in High School Sports. The American Journal of
Sports Medicine, 20 (10), 1-6. doi: 10.1177/0363546510392326.
Phipps, C.P., Phipps, C.E., (2013). US20130185837 A1. Washington D.C.: U.S. Patent and
Trademark Office.

Post, Andrew, Oeur, Anna, Hoshizaki, Thomas Blaine., (2012). An examination of American
football helmets using brain deformation metrics associated with concussion. Materials
& Design, 45 2013-03, pp.653-662.
How It Works. (2013). Retrieved November 28, 2013 from http://mipshelmet.com/how-it-works
Honeycomb Attributes and Properties: A Comprehensive Guide to Standard Hexcel Honeycomb
Materials, Configurations, and Mechanical Properties. (1999). Retrieved December 10,
2013 from http://www.hexcel.com/Resources/DataSheets/Brochure-Data-
Sheets/Honeycomb_Attributes_and_Properties.pdf
Acknowledgements
The author would like to thank the entire Mass Academy staff for providing guidance
throughout the course of the project. In particular, the author wishes to thank Mr. David Ludt, his
STEM advisor, as well as Mrs. Maria Borowski and Dr. Judith Sumner, who both provided
assistance in writing this paper. The author would like to thank the entire Natick Lab staff for
providing the opportunity to conduct experiments and collect data using the government
facilities. In particular, the author wishes to thank Mrs. Joanna Graham for introducing the
author to Natick Labs, Mr. Donald Lee for supervising the experiments and obtaining materials,
and Mr. Jason Parker for providing help conducting the experiments and providing insight into
data analysis. The author would also like to thank Dr. Jagan Srinivasan, who helped the author
during the early stages of the project. Lastly, the author would like to thank his parents for
providing financial aid, transportation, and assistance throughout the course of the project.

Appendix
Engineering Matrix
Data Table Matrix
MitigatesPeakAcceleration(%)
ExtendsCollisionDurationand
MitigatesAverageAcceleration(%)
LowWeight(g)
LowEffectiveRadius(cm)
(Thickness/DistancefromHelmet
Surface)
EaseofApplicationorConstruction
(Scaleof0-4)(IncludingCostand
AvailabilityofMaterials)
SufficientDurability(Scaleof0-3)
Max 100.0 100.0 0.0 0.0 4.0 3.0
Aluminum Honeycomb 13.7 17.3 12.2 1.5 4.0 0.5
Aluminum Foam 50.8 49.2 35.7 2.0 3.0 1.0
Suspended Elastomer -6.6 -7.8 225.2 4.0 1.0 2.5
Minimum (Worst) -50.0 -50.0 300.0 5.0 0.0 0.0
Shown above is the data table matrix, which was created in order to develop the engineering
matrix. The values in the table were determined as follows (Criterion 1 is furthest to the left;
Criterion 6 is furthest to the right).
 Criterion 1: Because collision duration and average acceleration are directly
proportionate, the two quantities were grouped under one criterion. However, the values
in the matrix are the percentage decreases or increases in average acceleration yielded by
the prototypes (in relationship with the control group). As stated before, a positive value
indicates that the prototype performed more effectively than the control, while a negative
value indicates that the prototype performed less effectively than the control. If a
prototype was tested in more than one experiment, the average of the percentage
decreases is provided in the table. For example, the aluminum honeycomb prototype was

tested in Experiments 1 and 2, each providing data for the percentage decrease in average
acceleration. The average of the two decreases is shown in the table.
 Criterion 2: Same procedure was used as in Criterion 1, except that the percentage
decrease or increase in peak acceleration is provided.
 Criterion 3: A balance was used to measure the mass of each prototype.
 Criterion 4: The thickness, or radius from the surface of the helmet, was measured for
each prototype with a ruler.
 Criterion 5: The ease of application and construction in addition to the cost and
availability of the materials for each prototype was determined by the author.
 Criterion 6: Durability was determined by the author, based on the amount of permanent
deformation sustained by the prototype after each drop. A test or a series of
measurements was not taken.
he best and orst possible data, hich is presented as ‘maximum’ and ‘minimum’ on the table,
was subsequently determined by the author. Using this information, expected scores were then
selected by the author.
Max Score 10 8 5 4 4 3
Criterion 1 Estimated 2 Estimated 3 Estimated 4 Estimated 5) Estimated 6) Estimated
Aluminum Honeycomb 13.7 6.7 17.33 5.5 12.2 4.6 1.5 3.5 4.0 4.0 0.5 0.5
Aluminum Foam 50.8 8.9 49.2 6.8 35.7 4.0 2.0 2.5 3.0 3.0 1.0 1.0
Suspended Elastomer -6.6 2.7 -7.79 2.1 225.2 2.3 4.0 1.2 1.0 1.0 2.5 3.0
The non-shaded cells contain the data values that were presented in the data table matrix. For
each criterion, a linear function, which models the prototype score based on the data values, was
determined by finding a best fit linear model on Excel. The functions graph ‘Score vs. Data
Value’ and each point represents the data value and estimated score of a prototype. A linear

model was not found for criteria 5 and 6 because no measured data values or measurements are
available. The author determined the scores based on observation.
After determining the best fit linear model, the final engineering matrix scores were calculated
using the linear functions, here ‘x’ represents the respective data value.
y = 0.1022x + 4.1292
R² = 0.8923
0
2
4
6
8
10
-20.0 0.0 20.0 40.0 60.0
Score
Data Value
Criterion 1
y = 0.0806x + 3.2211
R² = 0.9006
0
2
4
6
8
-20 0 20 40 60
Score
Data Value
Criterion 2
y = -0.0101x + 4.5524
R² = 0.9767
0
1
2
3
4
5
0.0 50.0 100.0 150.0 200.0 250.0
AxisTitle
Data Value
Criterion 3
y = -0.8429x + 4.5071
R² = 0.9347
0
1
2
3
4
0.0 1.0 2.0 3.0 4.0 5.0
Score
Data Value
Criterion 4

Uncondensed Data Tables
Control-Exp. 1, Setting 1
Height
(m)
Final Velocity
(ft/s)
Collision Duration
(ms)
Average Acceleration (g) of
Impact
Peak Acceleration (g) of
Impact
Drop 1 0.474 10.02 10.70 40.65 77.26
Drop 2 0.474 10.02 11.10 40.37 87.52
Drop 3 0.474 10.02 12.50 37.79 93.06
Drop 4 0.474 10.02 10.40 45.67 96.87
Drop 5 0.474 10.02 11.50 42.24 98.89
Average: 11.24 41.34 90.72
STD: 0.817 2.90 8.68
%RSD 7.27 7.01 9.57
Aluminum Honeycomb-Exp. 1, Setting 1
Height
(m)
Final Velocity
(ft/s)
Collision Duration
(ms)
Impact
Impact
Drop 1 0.474 10.02 14.20 32.64 74.18
Drop 2 0.474 10.02 12.30 35.19 72.84
Drop 3 0.474 10.02 14.20 31.25 70.65
Drop 4 0.474 10.02 12.70 33.77 75.30
Drop 5 0.474 10.02 13.90 31.30 66.54
Average: 13.46 32.83 71.90
STD: 0.896 1.68 3.46
%RSD 6.66 5.13 4.81
Aluminum Foam-Exp. 1, Setting 1
Height
(m)
Final Velocity
(ft/s)
Collision Duration
(ms)
Impact
Impact
Drop 1 0.474 10.02 12.00 34.21 66.75
Drop 2 0.474 10.02 13.80 32.43 70.09
Drop 3 0.474 10.02 13.40 32.88 67.62
Drop 4 0.474 10.02 13.50 31.71 64.41
Average: 13.18 32.81 67.22
STD: 0.802 1.05 2.35
%RSD 6.08 3.21 3.49

Control-Exp. 1, Setting 2
Height
(m)
Final Velocity
(ft/s)
Collision Duration
(ms)
Impact
Impact
Drop 1 0.474 10.02 10.80 44.55 104.89
Drop 2 0.474 10.02 10.90 42.54 86.44
Drop 3 0.474 10.02 11.00 44.36 108.10
Drop 4 0.474 10.02 9.30 51.61 109.83
Drop 5 0.474 10.02 9.60 49.68 111.98
Average: 10.32 46.55 104.25
STD: 0.804 3.88 10.29
%RSD 7.79 8.34 9.87
Aluminum Honeycomb-Exp. 1, Setting 2
Height
(m)
Final Velocity
(ft/s)
Collision Duration
(ms)
Impact
Impact
Drop 1 0.474 10.02 12.00 37.98 92.88
Drop 2 0.474 10.02 13.40 35.45 93.95
Drop 3 0.474 10.02 13.40 32.42 84.26
Drop 4 0.474 10.02 14.30 31.95 77.05
Drop 5 0.474 10.02 13.50 36.51 100.49
Average: 13.32 34.86 89.73
STD: 0.829 2.61 9.14
%RSD 6.22 7.48 10.19
Aluminum Foam-Exp. 1, Setting 2
Height
(m)
Final Velocity
(ft/s)
Collision Duration
(ms)
Impact
Impact
Drop 1 0.474 10.02 14.20 31.21 67.38
Drop 2 0.474 10.02 9.30 45.52 84.79
Drop 3 0.474 10.02 13.30 33.54 70.11
Drop 4 0.474 10.02 13.10 32.28 68.11
Average: 12.48 35.64 72.60
STD: 2.170 6.66 8.21
%RSD 17.40 18.68 11.31

Control-Exp. 2
Height (m)
Final Velocity
(ft/s)
Collision Duration
(ms)
Average Acceleration (g)
of Impact
Peak Acceleration (g)
of Impact
Drop 1 0.474 10.02 21.10 26.60 61.94
Drop 2 0.474 10.02 20.60 25.47 58.77
Drop 3 0.474 10.02 22.80 24.74 60.77
Drop 4 0.474 10.02 19.80 28.08 66.28
Drop 5 0.474 10.02 19.80 26.58 61.18
Average: 20.82 26.30 61.79
STD: 1.238 1.27 2.77
%RSD 5.94 4.84 4.48
Elastomer-Exp. 2
Height (m)
Final Velocity
(ft/s)
Collision Duration
(ms)
of Impact
of Impact
Drop 1 0.474 10.02 19.00 30.57 70.76
Drop 2 0.474 10.02 20.00 29.56 71.42
Drop 3 0.474 10.02 20.70 28.06 68.78
Drop 4 0.474 10.02 21.50 25.52 60.89
Drop 5 0.474 10.02 19.50 28.06 58.76
Average: 20.14 28.35 66.12
STD: 0.986 1.91 5.88
%RSD 4.90 6.73 8.89
Aluminum Honeycomb-Exp. 2
Height (m)
Final Velocity
(ft/s)
Collision Duration
(ms)
of Impact
of Impact
Drop 1 0.474 10.02 21.40 21.31 47.42
Drop 2 0.474 10.02 21.60 22.80 68.32
Drop 3 0.474 10.02 20.30 25.07 55.13
Drop 4 0.474 10.02 21.10 23.76 51.01
Average: 21.10 23.23 55.47
STD: 0.572 1.58 9.12
%RSD 2.71 6.82 16.45

Control-Exp.3
Height (m)
Final Velocity
(ft/s)
Collision
Duration (s)
Collision
Duration (ms)
Average Acceleration
(g) of Impact
Peak Acceleration
(g) of Impact
Drop 1 1.537 18.01 0.0023 2.30 295.63 733.58
Drop 2 Beyond capabilities of accelerometer - could not record beyond 600 g. Max accel. exceeded 600 g
Aluminum Foam-Exp.3
Height (m)
Final Velocity
(ft/s)
Collision Duration
(ms)
of Impact
of Impact
Drop 1 1.537 18.01 10.80 62.96 162.42
Drop 2 1.537 18.01 10.30 72.74 224.54
Drop 3 1.537 18.01 10.60 67.24 195.11
Drop 4 1.537 18.01 9.60 77.60 202.68
Average: 10.33 70.13 196.19
STD: 0.525 6.39 25.74
%RSD 5.09 9.11 13.12

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