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HW#3 –Ch.3- MECHANICAL PROPERTIES OF MATERIALS

Due: Friday March 6th, 2015

Questions

1. What are the three types of static stresses to which materials are subjected?

2. What is the difference between engineering stress and true stress in a tensile test?

3. Define tensile strength of a material.

4. In what case does the strength coefficient have the same value as the yield strength?

5. Tensile testing is not appropriate for hard brittle materials such as ceramics. What is the test commonly used to determine the strength properties of such materials?

6. How is the shear modulus of elasticity G related to the tensile modulus of elasticity E, on average?

7. How is shear strength S related to tensile strength TS, on average?

8. What is hardness, and how is it generally tested?

9. Define the recrystallization temperature for a metal.

Multiple Choices

1. If stress values were measured during a tensile test, which of the following would have the higher value: (a) engineering stress or (b) true stress?

2. If strain measurements were made during a tensile test, which of the following would have the higher value: (a) engineering strain, or (b) true strain?

3. Which one of the following types of stress strain relationship best describes the behavior of brittle materials such as ceramics and thermosetting plastics: (a) elastic and perfectly plastic, (b) elastic and strain hardening, (c) perfectly elastic, or (d) none of the above?

4. Which one of the following types of stress strain relationship best describes the behavior of most metals at room temperature: (a) elastic and perfectly plastic, (b) elastic and strain hardening, (c) perfectly elastic, or (d) none of the above?

5. Which one of the following types of stress strain relationship best describes the behavior of metals at temperatures above their respective recrystallization points: (a) elastic and perfectly plastic, (b) elastic and strain hardening, (c) perfectly elastic, or (d) none of the above?

Problems

Strength and Ductility in Tension

1. A test specimen in a tensile test has a gage length of 2.0 in and an area = 0.5 in2. During the test the specimen yields under a load of 32,000 lb. The corresponding gage length = 2.0083 in. This is the 0.2 percent yield point. The maximum load of 60,000 lb is reached at a gage length = 2.60 in. Determine (a) yield strength, (b) modulus of elasticity, and (c) tensile strength. (d) If fracture occurs at a gage length of 2.92 in, determine the percent elongation. (e) If the specimen necked to an area = 0.25 in2, determine the percent reduction in area.

Flow Curve

3.5 In a tensile test on a metal specimen, true strain = 0.08 at a stress = 265 MPa. When true stress = 325 MPa, true strain = 0.27. Determine the strength coefficient and the strain-hardening exponent in the flow curve equation.

3.8 A tensile test for a certain metal provides flow curve parameters: strain-hardening exponent is 0.3 and strength coefficient is 600 MPa. Determine (a) the flow stress at a true strain = 1.0 and (b) true strain at a flow stress = 600 MPa.

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