What is Metal Fatigue? Causes, Stages, and Prevention
What is Metal Fatigue?
Metal fatigue can cause sudden catastrophic failure, leading to severe consequences. Imagine an aircraft fan blade failure causing damage or even death! For instance, metal fatigue contributed to the Southwest Airlines Flight 1380 incident on 17 April 2018, resulting in damage and loss of life.
This phenomenon occurs when metals experience repeated stress, leading to cracks and eventual failure. While sudden failure may result from excessive tensile load, shear load, or impact load, fatigue metal failures typically develop over time, unnoticed until an unexpected breakdown occurs.
Causes of Metal Fatigue
A sudden failure might be visibly witnessed during an extreme event where the stress exceeds the ultimate tensile strength and yield tensile strength of the material. However, fatigue metal failure typically stems from cyclic stress that accumulates gradually.
Understanding what is fatigue in metals involves recognising that these stresses can often be lower than the material's ultimate tensile strength.
The Stages of Metal Fatigue Failure
We can identify three key stages in a metal fatigue failure:
1. Crack Initiation As the material undergoes load cycle stress, micro-cracks begin to form at points of high stress concentration. due to cyclic loading. These cracks are often microscopic and are not visible to the naked eye and signify the initial failure phase. This is referred to as crack initiation. The stress required to cause these micro-cracks can be less than the ultimate tensile strength and yield tensile strength of the metal.
2. Crack Propagation When the cyclic loading continues, these initial cracks begin to expand and propagate throughout the material’s weakest paths, often branching out and following paths of least resistance in the material’s structure. This stage is known as crack propagation.
3. Sudden Fracture The final stage happens when the remaining cross-section of the material is no longer sufficient to withstand the applied load, leading to sudden and acute failure. This can be unexpected, especially if the initiation and propagation stages were undetected. This is referred to as sudden fracture.
Fatigue Testing and Prevention
Preventing metal fatigue involves understanding a material's fatigue strength. Engineers measure this through testing, where samples undergo repeated stress cycles at varying levels to determine their breaking points. These tests yield data that inform the design of more robust components.
Additionally, modern software design analysis enables engineers to predict potential weak points in structures, reducing the risk of fatigue metal failures. Proper material selection and engineering considerations further minimise risks.
Real-World Applications
Industries such as aerospace, automotive, and construction routinely perform fatigue metal testing. By identifying and mitigating weak points, they prevent failures that could lead to equipment damage or safety risks.
Understanding what is fatigue in metals and the stages of its development is critical for preventing unexpected failures. With proper testing, advanced engineering techniques, and vigilance, catastrophic outcomes from metal fatigue can be significantly reduced.
