**Design Against Fluctuating Load**

1. Stress concentration is defined as the localization of high stresses due to irregularities present in the component and no changes of the cross section.

A. True

B. False

.

**Answer: B**

**Explanation:** The given statement is true apart from the fact that there is no change in the cross section.

2. Stress Concentration Factor is the ratio of nominal stress obtained by elementary equations for minimum cross-section and highest value of actual stress near discontinuity.

A. True

B. False

.

**Answer: B**

**Explanation:** The stress concentration factor is just the reciprocal of that cited in the question.

3. If a flat plate with a circular hole is subjected to tensile force, then its theoretical stress concentration factor is?

A. 2

B. 3

C. 4

D. 1

.

**Answer: B**

**Explanation:** For any ellipse, K=1+2 x (semi major axis/semi minor axis).

4. For an elliptical hole on a flat plate, if width of the hole in direction of the load decrease, Stress Concentration Factor will______

A. Increase

B. Decrease

C. Remains constant

D. Can’t be determined. Varies from material to material

.

**Answer: A**

**Explanation:** K=1+2 x (semi major axis/semi minor axis. Hence K is inversely proportional to the semi minor axis.

5. In which of the following case stress concentration factor is ignored?

A. Ductile material under static load

B. Ductile material under fluctuating load

C. Brittle material under static load

D. Brittle material under fluctuating load

.

**Answer: A**

**Explanation:** In ductile materials under static load, there is plastic deformation near yielding point and hence redistribution of stresses take place. The plastic deformation is restricted to a smaller area and hence no perceptible damage take place.

6. Is it logical to use fluid analogy to understand the phenomenon of stress concentration?

A. True

B. False

.

**Answer: A**

**Explanation:** There is a similarity between velocity distribution in fluid flow in a channel and the stress distribution in an axially loaded plate. The equations for flow potential and in fluid mechanics and stress potential in solid mechanics are same.

7. Use of multiple notches in a V shaped flat plate will

A. Reduce the stress concentration

B. Increase the stress concentration

C. No effect

D. Cannot be determined

.

**Answer: A**

**Explanation:** The sharp bending of a force flow line is reduced due to multiple notches.

8. Which of the following reduces the stress concentration?

A. Use of multiple notches

B. Drilling additional holes

C. Removal of undesired material

D. Each of the mentioned

.

**Answer: D**

**Explanation:** All the mentioned options reduce the sharp bending of a force flow line.

9. A flat plate 30mm wide and “t”mm wide is subjected to a tensile force of 5kN. The plate has a circular hole of diameter 15mm with the centre coinciding with the diagonal intersection point of the rectangle. If stress concentration factor=2.16, find the thickness of the plate if maximum allowable tensile stress is 80N/mm².

A. 8mm

B. 9mm

C. 10mm

D. 12mm

.

**Answer: B**

**Explanation:** σ=P/ (w-D. x t or σ=5000/(30-15)xt ; σ(max)=K x σ or σ(max)=2.16 x σ or σ(max)=720/t; Also σ(max)=80.

10. The stress represented by sin (t) + 1 belongs to which category?

A. Fluctuating Stresses

B. Alternating stresses

C. Repeated Stresses

D. Reversed Stresses

.

**Answer: C**

**Explanation:** The minimum stress value is zero and hence is belongs to Repeated Stress category.

11. The stress represented by sin (t) + 2 belongs to which category?

A. Fluctuating Stresses

B. None of the mentioned

C. Repeated Stresses

D. Reversed Stresses

.

Answer:a

**Explanation:** The mean as well as the amplitude value is non zero hence it belongs to Fluctuation Stress Category.

12. The stress represented by sin (t) + 4 belongs to which category?

A. Alternating Stresses

B. None of the mentioned

C. Repeated Stresses

D. Reversed Stresses

.

**Answer: A**

**Explanation:** The mean as well as the amplitude value is non zero hence it belongs to Alternation Stresses category which is the other name of Fluctuation Stresses.

13. The stress represented by cos (t) belongs to which category?

A. Fluctuating Stresses

B. Alternating Stresses

C. Repeated Stresses

D. Reversed Stresses

.

**Answer: D**

**Explanation:** Half cycle is in tensile stress and other half in compressive stress, hence it belongs to Reversed Stresses Category.

14. If the mean stress value for a sinusoidal stress function is zero, then this type of stress falls in which category?

A. Fluctuating Stresses

B. Alternating Stresses

C. Repeated Stresses

D. Reversed Stresses

.

**Answer: D**

**Explanation:** If mean is to be zero, then there must be compressive as well as tensile stresses and hence belongs to reversed stresses category.

15. The phenomenon of decreased resistance of the materials to fluctuating stresses is the main characteristic of _____ failure.

A. Fracture

B. Fatigue

C. Yielding

D. None of the mentioned

.

**Answer: B**

**Explanation:** Fatigue failure of the material is the failure at low stress levels under fluctuating syresses.

16. Fatigue failure is time dependent failure.

A. True

B. False

.

**Answer: A**

**Explanation:** Fatigue failure is defined as time delayed fracture under cyclic loading.

17. There is sufficient plastic deformation prior to fatigue failure, which gives a warning well in advance.

A. True

B. False

.

**Answer: B**

**Explanation:** Fatigue cracks are not visible until they reach the surface and by that time the failure has already taken place. Material nevers enters in the plastic range