Question Bank: Properties

Question 1

What is meant by the yield strength of a material?

Answer 1

The maximum stress a material can take before it begins to deform permanently. Also, resistance to plastic deformation.

Question 2

What is meant by the ductility of a material?

Answer 2

The amount of plastic strain prior to failure.

Question 3

What is meant by the tensile strength of a material?

Answer 3

The maximum stress a material can take before it fractures or fails.

Question 4

What is meant by the resilience of a material?

Answer 4

The elastic strain energy absorbed prior to yielding.

Question 5

What is meant by the modulus of a material?

Answer 5

The resistance to elastic deformation: the proportionality constant between stress and strain in the elastic regime.

Question 6

What is meant by the tensile toughness of a material?

Answer 6

The total energy absorbed per unit volume by a material prior to failure when deformed by a gradually applied load.

Question 7

Sketch an engineering stress-strain curve and a true stress-strain curve for a typical engineering metal.

Answer 7

• Same elastic region - True stress doesn’t decrease - True stress is higher

Question 8

What equation gives the plastic strain of a material?

Answer 8

e_p = e - (σ/E)

Question 9

Why can ductility measured by reducation in area differ from the ductility measured as a change in length?

Answer 9

Ductility measured as a change in length is sensitive to the initial length of the sample. The ductility measured by reduction in area is only sensitive to the degree of necking and is independent of sample length.

Question 10

How might you estimate the relative toughness of two materials from tensile tests?

Answer 10

Determine the relative areas under the curves

Question 11

How does a charpy impact tester evaluate the toughness of a material?

Answer 11

It determines how much of the kinetic energy of a swinging hammer is absorbed by a sample when it is struck

Question 12

State the disadvantages of the Charpy/Izod testing procedure.

Answer 12

• Sensitive to sample preparation
• Sensitive to machine used for testing
• Sensitive to temperature
• Sample hard to observe
• Physics of failure is unclear

Question 13

State the advantages of the Charpy/Izod testing procedures.

Answer 13

• Straightforward to prepare samples
• Little need for post-test analysis (simple readings)
• Easy to test at high/low temperature
• Huge databases of historical measurements
• Many engineers and technicians are familiar with the method