Fatigue failure in materials occurs due to:

Explanation:

Fatigue Failure:

• Fatigue failure is one of the most critical failure mechanisms observed in engineering materials and structures. It is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. This failure mechanism is particularly dangerous because it can occur well below the ultimate tensile strength or even the yield strength of the material. Fatigue failure is a leading cause of failure in mechanical components such as shafts, gears, and bridges.
• When a material undergoes repeated loading and unloading (cyclic loading), microscopic cracks may form at stress concentration points, such as sharp corners, holes, or surface imperfections. Over time, these cracks propagate and grow, eventually leading to catastrophic failure. The phenomenon is influenced by several factors, including the magnitude of cyclic stress, the number of cycles, material properties, and environmental conditions.

Additional Information

Stages of Fatigue Failure:

1. Crack Initiation: Fatigue failure begins with the initiation of a small crack at a point of high stress concentration, such as a surface defect, notch, or inclusion in the material.

2. Crack Propagation: Under cyclic loading, the initiated crack grows incrementally with each load cycle. The crack growth rate depends on the magnitude of the applied stress and the material's resistance to crack propagation.

3. Final Fracture: When the crack grows to a critical size, the remaining cross-sectional area of the material becomes insufficient to support the applied load, leading to sudden and catastrophic fracture.

Factors Influencing Fatigue Failure:

• Stress Concentrations: Features such as sharp corners, notches, and holes act as stress concentrators and significantly reduce fatigue life.
• Surface Finish: A rough surface finish can reduce fatigue resistance because it provides sites for crack initiation.
• Material Properties: Materials with higher toughness and ductility generally exhibit better fatigue resistance.
• Environment: Corrosive environments can accelerate fatigue failure through a process known as corrosion fatigue.
• Load Magnitude: Higher cyclic stress amplitudes result in faster crack growth and shorter fatigue life.