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Material Testing
Material Testing Reproducible evaluation of material properties
Material response to varying loading
conditions, including magnitude, cycling,
and mode
Dynamic Testing
Material response to constant loading
Static Testing
Static Material Testing
Strength
Deformation
Fracture
Design requirement compliance
Tensile test
Compression test
Hardness test
Evaluation of Material
Standardized Tests
Tensile Test Uniaxial
A straight line axial force is
applied to a test sample
(typically in the y axis)
Destructive Force is applied until sample fails.
Image courtesy of NSW Department of Education and Training
Hounsfield Tensometer
Tensile Test
Ensures meaningful and reproducible results.
Uses a uniform cross section.
Standard Test Sample (dog bone)
Tensile Test Procedure Dog bone is created to test specifications
Dog bone is secured in tester
Tensile Test Procedure A tension force (F) is applied to the dog bone until failure occurs.
Simultaneously the applied tension force (F) and dog bone elongation (d) are recorded.
A plot is created from the stored load
elongation data.
F
d
Tensile Test Data
F
d
Test sample A and B are 230 red brass. Test
sample A has a diameter of 0.125 in. Test
sample B has a diameter of 0.375 in.
If both samples are tested to failure, will the
applied tension force and elongation be the
same for both tests?
A
B
NO – Why?
Tensile Test Data
Load-elongation results are dependent upon
sample size.
How can test data be manipulated to
represent a material and not an individual
test sample?
Larger sample indicates larger load-elongation.
Tensile Test Data
To eliminate test results based on sample
size, calculate sample stress.
Divide load (F) by the original test sample
cross-sectional area (A0)
Stress is load per unit area.
lo
stread
ss =area
Fσ = A
Tensile Test Data
Calculate the stress in the dog bone with a
430 lb applied force.
2area = r
2area = (0.0625 in.)
2area = 0.0123in.
Fσ = A
2
430 lb
0.0123 in.
35,000 psi
Tensile Test Data
Manipulating Elongation Results
To eliminate test results based on sample
size, calculate sample strain.
Strain (e) – is the amount of stretch per unit
length.
Elongation (d) under load, divided by the
original length (L0)
amount of stretchstrain =
original length
Tensile Test Data Calculate the strain in the dog bone with an
elongation of 0.0625in.
0.0625in.ε =
1.000in. = 0.0625
amount of stretchstrain =
original length
Tensile Test – Stress-Strain Curve
Elastic Range
Initial response is linear.
Stress and strain are proportional
to one another.
Tensile Test – Stress-Strain Curve
Proportional
Limit
Proportional Limit
Stress at which material starts elongating
more than the proportion in force.
Tensile Test – Stress-Strain Curve
Proportional
Limit
Modulus of Elasticity (E)
The proportional constant (ratio of
stress and strain).
A measure of stiffness – The ability of a
material to resist stretching when loaded.
An inherent property of a given material.
σ stressE = =
ε strain
Tensile Test – Stress-Strain Curve
If the load is removed, the
test sample will return to
its original length.
The response is elastic or
recoverable.
Exaggerated stretch to
illustrate principle
Tensile Test – Stress-Strain Curve
Elastic Limit = Yield Point
Uppermost stress of elastic behavior .
Elastic limit and yield strength mean the
same thing.
Elastic limit and proportional limit are
almost identical, with the elastic limit being
slightly higher.
Tensile Test – Stress-Strain Curve
Resilience
The amount of energy per unit volume
that a material can absorb while in the
elastic range.
Area under the stress-strain curve.
Why would this be important to designers? Hint:
car bumper 1 bh2
Tensile Test – Stress-Strain Curve
Yield Point
When the elastic limit is exceeded.
A very small increase in stress
produces a much greater strain.
Most materials do not have a well-
defined yield point
Tensile Test – Stress-Strain Curve
Offset Yield Strength
Defines the stress required to
produce a tolerable amount of
permanent strain.
Common value is 0.2%
Tensile Test – Stress-Strain Curve
Plastic Deformation
Unrecoverable elongation beyond
the elastic limit.
When the load is removed, only the
elastic deformation will be recovered.
Tensile Test – Stress-Strain Curve
Yield
Point
Tensile Test – Strength Properties Stress Strain Curve
Plastic deformation represents failure.
Part dimensions will now be outside of
allowable tolerances
Plastic Deformation without necking
Elongation continues, some is permanent
Cross-section decreases along entire
sample.
Load can continue increasing.
Tensile Test – Stress-Strain Curve
Tensile Strength
Load bearing ability peaks.
Less force is now required to
continue elongating.
Weakest location begins to
decrease in area more than other
locations – Necking
Tensile Test – Stress-Strain Curve
Plastic Deformation with Necking
Sample can now be stretched with less
force.
Tensile Test – Stress-Strain Curve
Tensile Test – Stress-Strain Curve
Failure
If continued force is applied,
necking will continue until fracture
occurs.
Ductility
Amount of plasticity before fracture;
The greater the ductility, the more a
material can be deformed.
Compare the material properties of these
three metal samples.
Tensile Test – Samples
Brittleness
Material failure with little or no ductility.
Lack of ductility, not lack of strength.
Tensile Test – Stress-Strain Curve
Toughness Work per unit volume required to fracture a material.
Total area under the stress-strain curve from test
initiation to fracture (both strength and ductility).
Tensile Test – Stress-Strain Curve
Tensile Testing Examples
steel rebar tensile test
steel cylinder tensile test
welded steel
concrete cylinder
metal cable
Stress and strain relationships are similar to tension
tests – elastic and plastic behavior
Test samples must have large cross-sectional area
to resist bending and buckling
Material strengthens by stretching laterally and
increasing its cross-sectional area
Compression Test
Video examples
concrete test
composite test
soda can
concrete 2
Resistance to permanent deformation.
Resistance to scratching, wear, cutting or
drilling, and elastic rebound.
Brinell Hardness Test A tungsten carbide ball is held with a 500 lb
force for 15 sec into the material.
The resulting crater is measured and
compared.
Hardness Testing
Brinell testing video
Rockwell Test A small diamond-tipped cone is forced into
the test sample by a predetermined load
Depth of penetration is measured and
compared.
Hardness Testing
Rockwell testing video
Resources
NSW Department of Education and Training (2011). Retrieved from
http://lrrpublic.cli.det.nsw.edu.au/lrrSecure/Sites/Web/tensile_testin
g/index.htm?Signature=%287e02281c-318a-461b-a8ed-
3394db0c4fe6%29
Askeland, Donald R. (1994). The Science and Engineering of
Materials, 3rd ed. PWS Publishing: Boston.
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