Question

When a component is subjected to varying (sinusoidal) load, which statements are correct: A. Mean stress is zero for fluctuating stress
B. Minimum stress is zero for repeated stress
C. Mean stress is zero for reversed stress
D. Amplitude stress is the average of minimum and maximum stress

• A. A and B only
• B. B and C only
• C. C and D only
• D. B, C and D only

Hint:

Mean = average, Amplitude = half the range — key fatigue formulas.

Answer 1

The Correct Option is B

Concept: For fluctuating stresses: \[ \sigma_m = \frac{\sigma_{max} + \sigma_{min}}{2}, \quad \sigma_a = \frac{\sigma_{max} - \sigma_{min}}{2} \]

Step 1: Statement A (Fluctuating stress).
Fluctuating stress means:
• \(\sigma_{max} \neq -\sigma_{min}\)
• Mean stress generally not zero Hence A is incorrect.

Step 2: Statement B (Repeated stress).
Repeated stress varies between: \[ 0 \text{ and } \sigma_{max} \] Thus: \[ \sigma_{min} = 0 \] Hence B is correct.

Step 3: Statement C (Reversed stress).
Reversed stress varies symmetrically: \[ \sigma_{min} = -\sigma_{max} \] Thus: \[ \sigma_m = 0 \] Hence C is correct.

Step 4: Statement D (Amplitude).
Amplitude is: \[ \sigma_a = \frac{\sigma_{max} - \sigma_{min}}{2} \] NOT average.
Hence D is incorrect.

Step 5: Final conclusion.
Correct statements: B and C. \[ \boxed{\text{Answer: B and C only}} \]