The final paper for my two term sophomore scholars research done with the Mechanical engineering department at Union College.

1. Bamboo: A Sustainable Alternative To Existing Downhill Ski Core
Materials
Sarah Subik
Union College
Mechanical Engineering Department
Professor Joel Lefever
June 19, 2019

2. Subik 1
Abstract:
The product evolution of downhill skis is over 5000 years long; however, the most recent
era in the ski industry has focused on material engineering to fine tune desired high performance
characteristics such as flexibility and control. ​The materials in downhill skis are sports grade
materials carefully selected for their characteristics of strength and flexibility. ​One current
research area in the industry is finding an alternative material to the traditional wood or
composite cores which are expensive and unsustainable. A comparison was done between
bamboo and traditionally used maple hardwood to analyze whether bamboo possesses properties
able to compete with existing material options. Material properties in connection to performance
and environmental impact were established for testing. Test results gathered from two prototypes
suggest that bamboo demonstrates superior strength and bending properties to maple hardwood.
Bamboo can offer a cheaper and more sustainable ski that would lower the upfront cost of skiing
to consumers, creating a larger market and allowing more people to enjoy the sport.
Introduction:
The ski industry is an environment where styles change by the season and customers pay
thousands to get the cutting edge advantage touted by each new design built with high grade
materials. The skis used today are very different from the snowshoe-like design made of animal
bones that were used 5000 years ago and the cave paintings that exist of them in China around
8000 BC [1]. Rudimentary cross country style skis were used during the middle ages around
Norway for transportation by hunters and farmers. Designs were later used during the
1700-1800s in Scandinavian and Russian military movements until the mid 1800s where ski

3. Subik 2
designs were adapted for recreational use in downhill skiing with a style typical of skis today.
Metals were added to the edges of skis in the 1920’s for greater control at high speeds and sharp
turns, making the sport safer and more appealing to individuals. In 1950, the first commercial
aluminum core ski became available offering a stronger material with more precise material
properties for ski construction. Later, in 1960, the first fiberglass ski was marketed, replacing the
majority of both aluminum and wood in ski construction due to its lightweight properties [1]. A
trend in ski engineering is making the material as light as possible while still retaining the
necessary mechanical properties for performance.
In skis, as with most high performance sports, the major goal is to create a design that
will be able to handle large amounts of energy sustained throughout dynamic motions and high
impacts. For downhill skis this stability is obtained by using a material that will dampen the
vibrations that occur at high speeds. However, it is also important for the skier to be able to ‘feel’
the terrain and have a ski that will be responsive, requiring a specific balance in material
damping properties. This balance between ​feeling and eliminating vibrations, is based on the
energy dissipation properties of the material. Energy dissipation is the ability of a material to
store and redistribute energy​. ​Most recently, for the last decade skis with ceramic piezoelectrics
called “smart skis” have been tested. An increase in vibrations results in less contact with the
snow and therefore less control. A ceramic piezoelectric can be built into the toe piece, the
source of vibrations, and generate an electric charge from motion and then dissipate it through a
circuit [2].
The second major material challenge is possessing a high flexibility axially in
comparison to a stiff cross section as a result of a higher torsional stiffness. This unique property

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combination allows the ski to handle loads at multiple points of intersection on it’s base while
having strength when forced up on edges in turns. The bending properties of the ski are
important for handling these impacts, as it is flexed with a central load, stress will accumulate in
the top and bottom layers. More specifically, the top layer must handle compression while the
bottom layer must handle the opposite reaction due to tension. The thickness and stiffness of
materials has an impact on their ability to bend requiring precise ratios in ski design.
Additionally, due to the cost of skis and the rugged nature of the sport, downhill skis are
expected to have a ‘life’ or be able to perform for multiple seasons, depending on how often they
are used. Downhill skis are exposed to not only a harsh outdoor environment but also impact
through performance and accidents. The life of a ski is affected by the fatigue of materials after
multiple seasons of high impact, making materials with high durability and yield strength
necessary for longevity. Furthermore, getting into specific needs of skis only lengthens the
design and material requirements. Women’s skis must be lighter, shorter, and softer in order to
reduce the energy needed to bend them. Similarly children's skis are made on a smaller scale
with extreme flex for forgiveness and easy maneuverability [2].
The extensive and demanding list of design requirements in downhill skis is satisfied
through layering processes in an attempt to achieve each desired property. In this layering
process the core material is placed in the center and surrounded with other materials to
complement its properties, such as the use of a rubber layer to absorb vibration in metal skis. The
core’s flexibility, strength, weight, and availability are all carefully considered when selecting
the material. Unfortunately, these demanding properties are best achieved by high grade
composite materials or numerous layers of material resulting in skis being expensive and often

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over engineered for beginners. The cost makes them inaccessible to consumers who may just be
getting into skiing or do not go often enough to justify the price. Bamboo is a relatively new core
option with the potential to fix this exact problem due to the abundance and unique properties as
a grass. Improvements to equipment, particularly those necessary for safety and performance,
have had major effects on the sport’s expansion by convincing people skiing is a more affordable
and safe past time than in the past.​ Bamboo as a material in skis would create a ski with good
properties at a price more approachable for new skiers or skiiers needing other options.
Literature Review
The use of composites in downhill skis introduced materials that were lighter and
stronger such as carbon fiber, kevlar which performs well under tension, titanium for dampening,
and foam for added flexibility. Wood is historically and currently used in skis because the
cellular structure of wood offers low density with strong properties at a lower costs than
composites. Woods commonly chosen for downhill skis include ash, beech, poplar, and maple;
of these, the most desirable is maple.
Maple hardwood is harvested from the sugar maple tree, which can take one hundred
years to fully mature, resulting in a dense wood but also lower availability. This length of
growing time in conjunction with the long time necessary to season the wood make maple
expensive in comparison to other options. For its high cost and low availability maple offers
unique properties in comparison to many other woods. Maple hardwood is stronger, stiffer,
harder and denser than most species of wood. Additionally, maple offers good dampening
properties and a decent balance in flexibility. Although, maple is a dense wood it is easy to work

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with [4]. Maple not only offers good strength and hardness but it has high resistance to abrasion
and wear while still allowing good steam bending properties [5]. ​Unfortunately, compared to
some composites, it has poor torsional strength due to the fibrous nature of wood and absorbs
moisture because it is sensitive to humidity. By contrast, bamboo is a strong grass that offers
many interesting properties, including an incredible growth rate.
One of Bamboo’s most unique property in comparison to maple is that it has a lower
embodied energy than existing options due to lower handling costs and fast growing rates
(13-30m in 2-4 months) [8]. For this reason, it is considered a sustainable material. Additionally,
it is biodegradable and can grow in diverse climates making it readily available. This availability
makes it a cheaper material. However, it also results in inconsistent characteristics depending on
the diverse conditions it may have grown in. Beyond mechanical properties the grass offers a
smooth and clean looking aesthetic when it can be left exposed on the ski but many companies
prefer not to engineer the ski out of 100% bamboo. Instead they currently incorporate other
materials such as Titanium to better performance levels, making the cost similar non bamboo
skis. This is a result of bamboo being a relatively new material emerging into ski manufacturing,
it gets neglected because of little research done on its strength in relation to force capacity and
moisture [8]. Although bamboo is a good material option, it can be difficult to sell as the existing
designs are not well backed with field research and many people are hesitant to invest in bamboo
skis until they are well reviewed. There is also the factor of durability in relation to species and
age, there are over 1000 species of bamboo to choose from each with different properties to
offer, the majority with little existing research [8]. Bamboo will mature in three to four years. If
cured and left untreated, the material will last ten to fifteen years on average offering a long

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lifetime [6]. Companies who have tried to make sustainable skis with 100% bamboo are typically
smaller companies who show interest in this sustainable area of the downhill ski market.
However, as they are smaller setups they can not make as much profit, keeping the price of
bamboo skis still high.
Methods
Two skis were made to facilitate a numerical comparison of properties. A simple three
layer prototype design was created to give a straightforward comparison between the two
materials (Figure 1). With the bamboo and maple acting as cores, a layer of acrylic was used as a
replacement for the typically used ultra high molecular weight polyethylene base layer.
Figure 1: Diagram to scale showing the simple three layer design used for comparison between
maple and bamboo core materials.
The cores were constructed from solid maple (Home Depot) and pre-glued strips of
bamboo (9”x12” bamboo cutting board, Mainstays). Both the bamboo and acrylic were cut using
a waterjet. The cutting board was cut into three sections and jointed using a simple block joint.
Optimizing the dimensions of the cutting board, the skis were made to be 60.96cm length with a
width of 7.62cm. The maple was planed down to match the thickness of the bamboo, 0.93cm.
This dimension is typical of the core thickness in downhill skis.The assembly was assembled
using a vacuum bagging process after a layer of fiberglass was applied as a top layer (Figure 2).

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Figure 2: Pictures depicting the layering process (left) in preparation for the
application of fiberglass and then vacuum bagging process to seal the assembly
(right).
The assemblies were cured for twenty-four hours and then trimmed along the edges to
remove excess epoxy. Next, they were put into a displacement controlled load frame (MTS
Exceed E43) and setup for a three point bending test to simulate the load of a skier in the middle
of the ski (Figure 3). The deflection of the crosshead was recorded in the computer until breaking
and then transferred to Excel for analysis.
Figure 3: The setup used to test the bending of the ski. Load was applied along a rod in the
middle of the ski and the ends were placed equidistant on supports.

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Results
The data showed that although the maple hardwood and bamboo prototypes had similar
material stiffnesses in the elastic region they had different properties at fracture. Bamboo’s
flexibility surpassed maple. It withstood higher deflection in addition to increased durability as it
supported a larger load. Figure 4 illustrates the material stiffnesses of both materials plotted
using the data gathered in the three point bending test. Note the irregularity in the slope before
0.005m and 200 N. Additionally, the maple plot has a maximum load of 1245 N while bamboo
had a maximum load of 1540 N.
Figure 4: A plot of the applied load against the deflection of the crosshead on bamboo and
maple cores when tested to breaking.

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During the test of the maple, the fracture first occurred in the acrylic layer. Under further
load being applied, a crack began to appear in the wood and continue at an angle until it broke
along the grain (Figure 5A). The maximum deflection in maple was 2.60 cm (Figure 4) from its
original position in the load frame (Figure 6).
(a) (b)
Figure 5: Specimens shown after breaking in the load frame (a) maple and (b) bamboo.

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Figure 6: The maple sample in the load frame, shown at the position it fractured.
The three point bending test of the bamboo revealed the material had a higher maximum
deflection of 3.60 cm in the load frame (Figure 4). In comparison, the acrylic in the bamboo ski
did not snap at all even after the core fractured (Figure 7). When the bamboo fractured it cracked
in a straight line directly under the load in the frame before breaking transversely (Figure 5B).
Figure 7: The bamboo sample bent to fracture in a three point bending test.

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Upon close examination it can be seen that the acrylic separated along the length of the
ski (Figure 8). Debonding caused the acrylic to separate and slide off the ends of the specimen as
it is bent in the middle. Although the same epoxy was used for both materials the maple did not
debond like the bamboo sample.
Figure 8: A close up image of the delamination that occurred along the base of the bamboo.
The average stiffness was calculated using regression analysis through the linear section
of each trial’s graph. Bamboo had a higher average stiffness and a beam stiffness only 1.00
kN/m​2​
away from maple (see Table 1).The beam stiffness (EI) was calculated using equation 2
(see Appendix A) to quantify each members resistance to bending deformation. The beam
stiffness takes into account the length of the specimen, the applied load, and the deflection of the
crosshead (Appendix A).

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Beam Width
(m)
Average
Stiffness
(kN/m)
Standard
Deviation
(kN/m)
Beam
Stiffness - EI
(kNm​2​
)
Standard
Deviation of
EI (kNm​2​
)
Maple 0.0755 67.2 2.14 62.9 2.01
Bamboo 0.0769 62.7 3.14 58.8 2.95
Table 1: Calculated stiffness for four trials of maple and two trials of bamboo
with the standard deviation between trials calculated.
Discussion
The results indicate that bamboo has similar properties to maple and that it is a potential
material alternative. The similarity in the slopes of Figure 1 prove that maple and bamboo have
similar stiffness. The irregularity in Figure 1 is likely due to a shift of load caused by a
movement of the bar applying the load. Bamboo having a higher maximum load shows that it is
stronger and more durable than maple as it can sustain a higher load.
Another interesting finding is that the acrylic base layer snapped (Figure 5) before the
maple did, while it never snapped on the bamboo sample (Figure 7). This is due to the
delamination process that occured between the bamboo and the acrylic layer. As a result of the
acrylic layer separating from the bamboo, the acrylic was able to slide at the ends giving it the
ability to bend in the middle. The acrylic on the maple had a better bond with the epoxy that
allowed more tension to be transferred to the acrylic from the maple which caused the acrylic
snap. The maple cracked at an angle while the bamboo snapped transversely (Figure 5). This
angle of the fracture is due to the direction of the grains indicating that bamboo has straighter
grains than maple resulting in only axial stress.
Bamboo having higher deflection by 1 cm (Figure 4), indicates that it could offer superior
properties to the maple for downhill skis. Bamboo is able to bend further because it has a higher

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strength. In the beam stiffness data bamboo has a higher value showing that it has a better
resistance to deformation. These two characteristics demonstrate that bamboo may offer superior
bending properties than maple.
Desirable characteristics in the ideal downhill ski is for it to be strong, light, flexible
axially, stiff torsionally, highly durable, with a top layer that can handle compression and a
bottom layer that can handle tension. The testing reveals that bamboo could offer improvements
to the characteristics maple offers in the areas of strength, flexibility, and bending.
Future Directions
Future steps for the project would focus on more testing and updated designs. Testing
should be continued in order to test other valuable performance properties such as torsion and
energy dissipation. Additionally, incorporating research found on triangular honeycomb core
structures show that 10% more energy absorption could result based on published research on the
mechanical properties of bamboo [4]. The design would be a bamboo lattice with the honeycomb
shape with air in between, making it more lightweight with better energy dissipation.
Other alterations would include a potential foam layer in addition to a thinner bamboo
layer, increasing the bending strength of the prototype. Altering the assembly process would
include a different epoxy or bonding process to address the delamination issue with the bamboo
sample, resulting in a more direct comparison. Another helpful addition could be roughening the
surface of the bamboo before applying the epoxy to increase the surface area. When constructing
the ski a finger joint could be done for the bamboo to better distribute the load. To create a more

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accurate depiction of commercial skis, adding a waist to the middle ski after the construction
process could be done to match commercial ratios.
The downhill ski industry in general continues to uncover new sustainable considerations
for ski design and construction that would be interesting to incorporate with bamboo. Another
alternative material replacing composites is volcanic basalt fibers. With deposits around the
world, there is a high availability. As a result of being naturally formed it has experienced years
of venting and does not release greenhouse gasses or any toxins when reacting with air or water
during mining. The igneous rock can be quarried, crushed, and melted for several hours at 1500
degrees celsius before it is extruded, stretched, and wound the same as glass fibers. Volcanic
basalt has been incorporated by multiple snowboard and ski companies with many designs
available for sale[10]. This new and innovative material would offer increased options for top
and core layer materials. A ski design with both bamboo and volcanic basalt incorporated could
become one of the most sustainable skis sold. Testing similar to that done for bamboo would be
necessary to check how effective volcanic basalt is as a layer in downhill skis.
Perfluorochemicals (PFC) present in ski wax have been attracting attention in the last
decade due to their toxic makeup building up in the bloodstream of exposed organisms. Wax
could be a good next aspect to take into consideration as it is applied by hand to the bottom of
every ski to reduce friction during contact with the snow. Unfortunately, faster speeds come at
the cost of higher concentrations of fluorine. A soy alternative can be bought on the market but it
cannot outperform the PFC alternative causing many to continue using wax containing PFC,
indicating a need for research to be done in this area [11]. PFC levels could be decreased and
supplemented with a chemical of similar structure. The effects of a switch could be tested based

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on resistance due to friction. Research could investigate the effectiveness of soy wax relative to
PFC for reducing friction, for example by determining the angle of slip on an inclined plane.
The manufacturing process of skis holds room for improvement as single shell production
offers a faster manufacturing process with less material waste. The process consists of a
fiberglass or plastic shell with a stronger inner material resulting in a lighter and cheaper ski.
Although a better alternative to the torsion box or laminated ski manufacturing, it offers
performance acceptable for recreational but not high performance skiing. The retooling of
factories is an expensive road block preventing it from being incorporated for recreational skis
[12]. Another potential future research direction is to investigate materials that may produce a
more sustainable outer shell, or which might reduce the total amount of material in the ski.
Incorporating a shell of sufficient stiffness can reduce the amount of material necessary in the
inner layers.
Conclusion
The comparison done between bamboo and traditionally used maple hardwood cores
indicates that bamboo possesses properties able to compete with the performance of maple skis.
As bamboo demonstrates a higher strength, durability, beam stiffness, and axial flexibility it
demonstrates certain characteristics superior to maple. With greater accessibility and faster
growing rates it offers a potentially cheaper and more sustainable ski. A combination of these
characteristics make bamboo an alternative ski material that could lower the upfront cost of
skiing to consumers. The use of bamboo in downhill skis could create a new area of the downhill
ski market, allowing more people to enjoy the sport.

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Appendix A: Equations for Analysis
Material stiffness = [N/m] eq. 1y
p
Beam stiffness (EI) = [Nm​2​
] eq. 2pL
3
48y
P = Applied load from load frame [N]
y = Deflection, measure of crosshead moving down [m]
L = Length between supports [m]

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