Post on 05-Apr-2022
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Jiangyu Li, University of Washington
Lecture 10Mechanical Behaviors and Testing
Mechanical Behavior of Materials Chapter 4
Jiangyu LiUniversity of Washington
Mechanics of Materials Lab
Jiangyu Li, University of Washington
Loading
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MTS Machine
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Specimen
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Specimen
Material Properties:The Uniaxial Tensile Test
• Specimen is subjected to an axial tensile force, inducing auniform tensile stress in the "gage" region of the specimen
• Stress is increased until fracture occurs; strains are measuredthroughout the test
• The ASTM has developed "standard" specimenstyles/procedures for most materials
F F
"Gage Region" 40
Prof. M. E. TuttleUniversity of Washington
Jiangyu Li, University of Washington
Stress-Strain Curve
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Stress Strain Curve
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Offset Method
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Polymer
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Initial Portion
Material Property:Young's Modulus
• At stress levels below theyield stress the response iscalled "linear elastic"
• The slope of the linearregion is called "Young'smodulus" or the "modulus ofelasticity", E
• In the linear region (only):
σ = Eε (or) ε = σ/E
σ
ε
0.2% Offset Yield Strength
1
E
In Linear Region:
σ = Eε
Prof. M. E. TuttleUniversity of Washington
Material Property:Poisson's Ratio
• A uniaxial tensile stress causes both a tensile axial strain (εa)as well as a compressive transverse strain (εt)
• Poisson's ratio is defined as: ν = -(εt/εa)
εaεt
FF
44
Prof. M. E. TuttleUniversity of Washington
Load-Unload Cycles
σ
ε
Tensile Strength
0.2% Offset Yield Strength
Inelastic Strain Elastic Strain
σ
ε
Tensile Strength
0.2% Offset Yield Strength
Inelastic Strain
Elastic Strain
σ
ε
Tensile Strength
0.2% Offset Yield Strength
Elastic Strain
42
Prof. M. E. TuttleUniversity of Washington
Jiangyu Li, University of Washington
Necking and Ductility
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Necking and Ductility
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Structure Steel
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Aluminum
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Polymer
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Effect of Strain Rate
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True Strain
AP=σ
∫ ==l
l ll
ldl
0 0lnε
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True Stress and Strain
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True Stress and Strain
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Bridgman Correction
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True Stress and Strain
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Compression Test
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Compression Specimen
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Stress Strain Curve
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Assignment
• Mechanical behavior of materialsHW 4.6, 4.20