Question

True or False

1. For a fatigue failure, a part always fails above the ultimate strength of the material.

2. For a ductile material, the tensile yield strength and the compressive yield strength are not equal

3. Mode I of crack propagation occurs due to compressive stress

4. Distortion energy theory is used to predict failure for brittle materials

5. Temperature does not affect the endurance limit of a material

6. For a fatigue failure, a part always fails above the ultimate strength of the material

7. For a given stress cycle, the higher stress level causes longer cracks

8. Maximum shear stress theory is more conservative than the distortion energy theory

9. Fatigue failure is sudden and usually does not provide any warning

10. The elastic limit of a material can be changed by applying cyclic stress

11. For some materials, the compression strengths and the tensile strengths are not equal.

Answer 1

1. False.
In fatigue failure, part always fails below the ultimate strength of the material.

2. False.
For ductile materials, the tensile yield strength and the compressive yield strength are nearly equal.

3.False.
Mode I of crack propagation occurs due to tensile stress normal to the opening of crack.

4.False.
Distortion energy theory is used to predict failure for ductile materials.

5.False.
Temperature affects the endurance limit of a material and temperature stress concentration factor due to temperature change should be included in calculation.

6.False.
Same as 1.

7.True.
The higher stress level causes longer cracks due to increase in slipping.

8.True.
In the design of parts made of ductile materials maximum shear stress theory is more conservative than the distortion energy theory . Whereas distortion energy theory is more economical.

9.True.
There is no yielding in fatigue failure so no warning and sudden failure.

10.True.
Cyclic stress causes strain hardening which increases yield limit in each cycle.

11. True.
This is majorly true for brittle materials. The compression strength of brittle materials is much higher than tensile strength.

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