Failure of material is called fatigue when it fails

Explanation:

Failure of Material Due to Fatigue

• Fatigue is the failure of a material under repeated or cyclic stress. It occurs when a material is subjected to fluctuating loads that are below its ultimate tensile strength and sometimes even below its yield strength. Over time, these repeated stresses cause the material to weaken and eventually fail, even though the applied stress levels are well below the material's maximum capacity.
• Fatigue failure is a phenomenon that occurs when a material is subjected to cyclic loading over an extended period. The stresses causing fatigue failure are typically lower than the yield strength of the material. When a material experiences fluctuating stresses below its yield point repeatedly, microscopic cracks begin to form at points of high stress concentration, such as surface defects, sharp corners, or material imperfections.
• These microscopic cracks grow over time due to the repeated application of stress. Eventually, the cracks propagate to a critical size, leading to sudden and catastrophic failure of the material. This type of failure is unique because it does not require the stress to reach the yield point or the ultimate tensile strength of the material.

Key characteristics of fatigue failure:

• It occurs below the yield strength of the material.
• It is caused by repeated or cyclic loading over time.
• The failure is sudden and does not exhibit significant plastic deformation before it occurs.
• Fatigue cracks typically initiate at stress concentrators, such as surface irregularities or material defects.

Fatigue failure is commonly observed in components subjected to varying loads, such as rotating shafts, bridges, aircraft wings, and mechanical springs. To predict and prevent fatigue failure, engineers use the S-N curve (Stress vs. Number of Cycles curve) and design components with factors of safety to ensure that operating stresses remain well below the fatigue limit of the material.

Additional Information:

Fatigue failure is influenced by several factors, including:

• Stress amplitude: The magnitude of the cyclic stress applied to the material.
• Mean stress: The average stress level around which the cyclic stress varies.
• Surface finish: Rough surfaces can act as stress concentrators and promote crack initiation.
• Environmental factors: Corrosive environments can accelerate fatigue failure through stress corrosion cracking.
• Material properties: Materials with higher toughness and resistance to crack propagation have better fatigue performance.