Question

Fatigue failure occurs due to

• A. Single static load
• B. Repeated or fluctuating stresses
• C. High temperature
• D. Creep deformation

Hint:

Associate the word "Fatigue" with cyclic or repeated action.
Unlike static loading, fatigue involves progressive damage over thousands or millions of stress cycles, often at stress levels well below the material's yield point.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the underlying cause of fatigue failure in engineering materials.
Fatigue is a destructive structural phenomenon that leads to sudden fracture in components even when the applied stresses are lower than the yield strength of the material.

Step 2: Key Formula or Approach: This is a fundamental theoretical question about material failure modes.
Fatigue is structurally characterized by crack initiation, crack propagation, and final rapid catastrophic fracture under cyclic loading.

Step 3: Detailed Explanation:

• When a component is subjected to repeated or fluctuating stress cycles (dynamic loading), micro-cracks begin to form at localized regions of high stress concentration.

• These stress concentrations typically occur around structural discontinuities such as sharp corners, keyways, surface scratches, or internal material defects.

• With each successive cycle of loading and unloading, the micro-cracks slowly propagate through the cross-section of the material.

• As the crack grows, the effective load-bearing area of the component decreases over time.

• Eventually, the remaining cross-sectional area becomes too small to sustain the applied load, resulting in a sudden and brittle fracture.

• This process is distinct from creep (which occurs due to constant static load at elevated temperatures) and static failure (which is caused by a single high-magnitude load exceeding ultimate strength).

Step 4: Final Answer:
Fatigue failure occurs due to repeated or fluctuating stresses.