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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
Jiangyu Li, University of Washington
MTS Machine
Jiangyu Li, University of Washington
Specimen
Jiangyu Li, University of Washington
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
Jiangyu Li, University of Washington
Stress Strain Curve
Jiangyu Li, University of Washington
Offset Method
Jiangyu Li, University of Washington
Polymer
Jiangyu Li, University of Washington
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
Jiangyu Li, University of Washington
Necking and Ductility
Jiangyu Li, University of Washington
Structure Steel
Jiangyu Li, University of Washington
Aluminum
Jiangyu Li, University of Washington
Polymer
Jiangyu Li, University of Washington
Effect of Strain Rate
Jiangyu Li, University of Washington
True Strain
AP=σ
∫ ==l
l ll
ldl
0 0lnε
Jiangyu Li, University of Washington
True Stress and Strain
Jiangyu Li, University of Washington
True Stress and Strain
Jiangyu Li, University of Washington
Bridgman Correction
Jiangyu Li, University of Washington
True Stress and Strain
Jiangyu Li, University of Washington
Compression Test
Jiangyu Li, University of Washington
Compression Specimen
Jiangyu Li, University of Washington
Stress Strain Curve
Jiangyu Li, University of Washington
Assignment
• Mechanical behavior of materialsHW 4.6, 4.20
