Fracture-Toughness-and-FATIGUE-AND-Engineering-MAterials-1.pptx

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FRACTURE TOUGHNESS
AND FATIGUE AND
ENGINEERING
MATERIALS
Altar, Ronnel Romar C.
Amilano, Ma. Missy Louise M.
Aninipot, Ronnelyn

2. TOUGHNESS VS. FRACTURE TOUGHNESS
2
Toughness is a materials
ability to absorb energy
without fracturing.
Toughness = Strength and
Ductility
1. Tensile test
2. Impact test
Fracture Toughness it
measures a materials
resistance to fracture when a
crack or flaw is present.

3. WHAT IS FRACTURE TOUGHNESS?
3
Fracture toughness describes a material’s
resistance to brittle fracture when a crack is
present. It is related to its ability to deform
plastically instead of further increasing the
local stress and energy level.

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Metals hold the highest values of
fracture toughness. Cracks cannot easily
propagate in tough materials, making
metals highly resistant to cracking under
stress and gives their stress–strain
curve a large zone of plastic flow.

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How to Calculate and Solve for Fracture Toughness | Fracture
The image of fracture toughness is represented below.
To compute for fracture toughness, three essential parameters are needed,
and these parameters are Applied Load Constant (Y), Material Critical
Stress (σc) and Length of Crack on Surface (a).
The formula for calculating fracture toughness:
Kc = Yσc√(πa)
Where:
Kc = Fracture Toughness
Y = Applied Load Constant
σc = Material Critical Stress
a = Length of Crack on Surface

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Let’s solve an example;
Find the fracture toughness when the applied
load constant is 9, the material critical stress is 5
and the length of crack on surface is 2.
This implies that;
Y = Applied Load Constant = 9
σc = Material Critical Stress = 5
a = Length of Crack on Surface = 2
Kc = Yσc√(πa)
Kc = (9)(5)√(π(2))
Kc = (45)√(6.283)
Kc = (45)(2.50)
Kc = 112.7
Therefore, the fracture toughness is 112.7 J/cm².

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Calculating the Applied Load Constant when the Fracture
Toughness, the Material Critical Stress and the Length of Crack on
Surface is Given.
Y = K
c / σc √(πa)
Where:
Y = Applied Load Constant
Kc = Fracture Toughness
σc = Material Critical Stress
a = Length of Crack on Surface

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Let’s solve an example;
Find the applied load constant when the fracture toughness is 32, the
material critical stress is 12 and the length of crack on surface is 10.
This implies that;
Kc = Fracture Toughness = 32
σc = Material Critical Stress = 12
a = Length of Crack on Surface = 10
Y = K
c / σc √(πa)
Y = 32 / 12 √(π(10))
Y = 32 / 12 √31.41
Y = 32 / 67.25
Y = 0.47
Therefore, the applied load constant is 0.47.

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Calculating the Material Critical Stress when the Fracture
Toughness, the Applied Load Constant and the Length of Crack
on Surface is Given.
σc = K
c / Y √(πa)
Where:
σc = Material Critical Stress
Kc = Fracture Toughness
Y = Applied Load Constant
a = Length of Crack on Surface

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Let’s solve an example;
Find the material critical stress when the fracture toughness is
24, the applied load constant is 14 and the length of crack on surface
is 8.
This implies that;
Kc = Fracture Toughness = 24
Y = Applied Load Constant = 14
a = Length of Crack on Surface = 8
σc = K
c / Y √(πa)
σc = 24 / 14 √(π(8))
σc = 24 / 14 √25.13
σc = 24 / 70.18
σc = 0.34
Therefore, the material critical stress is 0.34.

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Calculating the Length of Crack on Surface when the
Fracture Toughness, the Applied Load Constant and
the Material Critical Stress is Given.
a = (K
c / Yσc)2 x 1 / π
Where:
a = Length of Crack on Surface
Kc = Fracture Toughness
Y = Applied Load Constant
σc = Material Critical Stress

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Let’s solve an example;
Find the length of crack on surface when the fracture toughness is 28, the
applied load constant is 8 and the material critical stress is 4.
This implies that;
Kc = Fracture Toughness = 28
Y = Applied Load Constant = 8
σc = Material Critical Stress = 4
a = (K
c / Yσc)2 x 1 / π
a = (28 / (8)(4))2 x 1 / π
a = (28 / 32)2 x 0.318
a = (0.875)2 x 0.318
a = 0.765 x 0.318
a = 0.243
Therefore, the length of crack on surface is 0.243.

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WHAT IS
FATIGUE?

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Fatigue is a failure mechanism that
involves the cracking of materials and
structural components due to cyclic (or
fluctuating) stress.

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Types of Fatigue
High-Cycle Fatigue: This occurs when materials are subjected to
stresses much lower than their yield strength, over a high number of
cycles.
Low-Cycle Fatigue: Contrarily, Low-Cycle Fatigue transpires when
materials are subjected to higher stresses, typically exceeding the
yield strength over a smaller number of cycles. This can cause
structural failure within thousands or even hundreds of cycles.
Thermal Fatigue: This is a specific type of fatigue caused by cyclic
thermal loads, usually as a result of fluctuating temperatures. This
fluctuation causes materials to expand and contract, leading to
stress build-up and eventual crack propagation.

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High-Cycle Fatigue
Failure occurs over millions
of cycles due to stresses
lower than yield strength.
Low-Cycle Fatigue
Occurs within thousands or
hundreds of cycles due to
stresses exceeding yield
strength.
Thermal Fatigue
Induced by cyclic thermal
loads causing material to
expand and contract leading
to stress build-up and cracks.

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Fatigue analysis
There are two primary things in understanding fatigue:
1. Initiate a crack
Fatigue crack initiation is normally associated with the
endurance limit of a material and the stress concentration.
2. Propagate a crack once it is formed.
Fatigue crack propagation is associated with the fracture
toughness and crack growth characteristics of a material.

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(a) (b) (c)
Load applied in y direction Load applied in x direction Load applied in z direction
The stress field near a fatigue crack tip can be
divided into three types:
Opening Mode Tearing (or anti-
plane) Mode
Sliding Mode

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4.1 IMPACT
TESTING

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Impact tests measure the ability of a
material to resist deformation in response to a
sudden load. These tests are normally conducted
according to test methods and standards
published by ASTM International.
Four commonly used types of impact tests
include: Charpy, Izod, drop-weight, and
dynamic tear tests.

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WHAT IS AN IMPACT TEST?
An impact test is a technique used to determine a
material’s ability to resist deformation when subjected to a
sudden shock or impulse load. There are several different
types of impact tests, but all entail striking a prepared test
specimen with a weight. Different materials testing standards,
such as ASTM E23, ASTM A370, and ASTM D256 govern the
exact testing procedure and test specimen requirements for
each type of impact test, and for different material groups
(e.g., metals vs. plastics).

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ASTM E23
ASTM E23 outlines standards for impact testing
using both the Charpy and Izod methods.
ASTM E23 / ISO 148-1: These standards govern impact
testing for metals.
ASTM A370
ASTM A370 is an umbrella spec used to cover
assorted mechanical testing on steel specimens. Tests
included under the specification are tensile tests, bend
tests, compression tests, impact tests and hardness
tests.
ASTM D256 / ISO 180: These standards govern impact
testing for plastics.
ASTM D256
The international standard for determination
of the impact strength of plastic and insulation
materials. The ASTM D256 standard describes
impact testing using the Izod test method for
determination of the impact strength and notched
impact strength of plastics.
ASTM A370 / ASTM E208: This standard governs
impact testing for steel materials.
Different materials testing standards

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How Does Impact Test Work?
An impact test works by striking a properly prepared and fixtures test
specimen with a weight, either from the side or from above.
• For Charpy and IZOD impact tests, a pendulum with a weighted
hammer is released from a specific height. The arc of its motion
strikes the vertically oriented test specimen on its side.
• For drop-weight impact tests and dynamic tear tests, a weight is
guided by rails and dropped directly onto a test specimen from
above. For each type of impact test, a notch is cut into the test
specimen, forcing the fracture of the specimen to occur at a
repeatable location.

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What Are the Different Types of Impact Testing?
1. Charpy
The Charpy impact test, also known as the V-notch test, is a type of impact test
where a weighted pendulum hammer is released from a specified height and strikes
the part. A Charpy impact testing apparatus, a device with a pendulum with various
locking points at specified heights and a fixture to hold the test specimen, is used to
determine Charpy impact strength.
The Charpy impact test is most commonly used for ductile materials such as metals
and thermoplastics. The test can be conducted at different temperatures and is often
used to determine the ductile-to-brittle transition temperature of a material.

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The Izod impact test is similar to the Charpy test in that a weighted pendulum
hammer strikes a test specimen containing a V-shaped notch. An Izod impact testing
apparatus — which is essentially identical to a Charpy impact testing machine — is
used to determine Izod impact strength. The primary differences between the Izod
and Charpy impact tests are the size of the test specimen, how it is restrained, and
which side is struck by the pendulum hammer.
The Izod test, governed by ASTM D256, is most commonly used for thermoplastics.
However, it can also be used for metals. Like the Charpy test, the Izod test is used to
determine a material’s toughness and its ductile-to-brittle transition temperature.

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3. Drop-Weight Impact Test
The drop-weight impact test, also known as the Pellini test, uses a weight suspended
over a simply supported horizontal test specimen and then dropped to produce the
impact. A tube or rails guide the weight during its “free-fall” onto the specimen. Unlike
Charpy and Izod tests, the height of the weight before and after it strikes the test
specimen cannot be used to determine the energy absorbed by the test specimen.
Instead, results only pass or fail since energy absorbed by the test specimen cannot
be adequately determined. Fracture is not the only criterion for failure, deformation or
the formation of a crack can also be considered a failure.

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4. Dynamic Tear Test
The dynamic tear test is similar to the drop-weight impact test. In the dynamic tear
test, a notched test specimen is simply supported on both ends. A weight is dropped
on the face opposite the notched side, and subjecting the test specimen to a bending
impact load and 3-point bending. The primary difference between drop-weight impact
testing and dynamic tear testing is that dynamic tear testing is often used for test
specimens with a thickness less than 5/8” while drop-weight impact testing is for test
specimens thicker than 5/8”.

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CONCLUSION
Overall, impact testing plays a vital role in science and industry, allowing engineers
and researchers to make informed decisions regarding material selection, design,
and safety. This article will review what impact testing is, and discuss its types,
benefits, and the standards used to perform the tests and analyze the results.

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CONCLUSION
Overall, impact testing plays a vital role in science and industry, allowing engineers
and researchers to make informed decisions regarding material selection, design,
and safety. This article will review what impact testing is, and discuss its types,
benefits, and the standards used to perform the tests and analyze the results.

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4.2
DESTRUCTIVE
TESTING

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What is destructive testing?
Destructive testing (often abbreviated as DT) is a test method
conducted to find the exact point of failure of materials,
components, or machines. During the process, the tested item
undergoes stress that eventually deforms or destroys the material.
Naturally, tested parts and materials cannot be reused in regular
operation after undergoing destructive testing procedures.

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The need for destructive testing
Materials that undergo destructive testing are damaged due to the
test procedures. Still, destructive testing has many legitimate use
cases. Oftentimes, destructive testing and using materials of
specific characteristics come as a regulatory requirement.
The reality is that machines and materials have physical and
chemical characteristics that are not suitable for all conditions. For
instance, metals that corrode easily are not suitable for use in
extremely humid environments.

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Destructive testing is conducted by specialized researchers,
scientists, and technicians. Who conducts it is
determined by the type of destructive testing to be
done. Generally, destructive testing is done by:
• Material scientists
• Metallurgical and polymer engineers
• Chemistry and electrochemical process experts
• Failure analysis experts
• Quality control analysts
• Regulatory compliance experts

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More commonly used destructive testing methods
Corrosion testing
Metals are used extensively in many industries due to their tensile strength
and versatility. However, they are also prone to corrosion. Rust on iron-
based materials, tarnish on silver, and patina on copper and copper alloys
are common examples of corrosion. This is a problem because corrosion
decreases the tensile strength and life of these metals.
Brass samples after 5 days of salt spray corrosion
test

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4.1 FATIGUE
TESTING

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Fatigue Test
A fatigue test helps determine a material’s ability to
withstand cyclic fatigue loading conditions. By design, a material
is selected to meet or exceed service loads that are anticipated in
fatigue testing applications. Cyclic fatigue tests produce repeated
loading and unloading in tension, compression, bending, torsion
or combinations of these stresses. Fatigue tests are commonly
loaded in tension – tension, compression – compression and
tension into compression and reverse.

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What is the Purpose of Fatigue Testing?
Usually the purpose of a fatigue test is to determine the
lifespan that may be expected from a material subjected to cyclic
loading, however fatigue strength and crack resistance are commonly
sought values as well. The fatigue life of a material is the total number
of cycles that a material can be subjected to under a single loading
scheme. A fatigue test is also used for the determination of the
maximum load that a sample can withstand for a specified number of
cycles. All of these characteristics are extremely important in any
industry where a material is subject to fluctuating instead of constant
forces.

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How to Perform a Fatigue Test?
To perform a fatigue test a sample is loaded into a fatigue
tester or fatigue test machine and loaded using the pre-
determined test stress, then unloaded to either zero load or an
opposite load. This cycle of loading and unloading is then
repeated until the end of the test is reached. The test may be run
to a pre-determined number of cycles or until the sample has
failed depending on the parameters of the test.