Visual Testing (VT) Practice Exam

Which type of fatigue is characterized by a sudden failure without prior signs?

1. Mechanical fatigue

2. Thermal fatigue

3. Stress corrosion cracking

4. Overloading fatigue

The correct answer is: Mechanical fatigue

The correct response is mechanical fatigue. This type of fatigue occurs when materials are subjected to repeated cycles of stress and strain over time, leading to the development of micro-cracks that can accumulate and ultimately result in failure. Importantly, mechanical fatigue failure can occur suddenly and unexpectedly, often without any visible warning signs or prior indications of issue. This characteristic makes it especially critical in engineering applications where the reliability of materials under cyclic stress is essential. Other types of fatigue, such as thermal fatigue, stress corrosion cracking, and overloading fatigue, often present different behaviors and failure mechanisms. Thermal fatigue, for example, results from temperature fluctuations that cause expansion and contraction in materials, which usually exhibit signs of distress over time. Stress corrosion cracking happens due to the interaction of stress and a corrosive environment, which also tends to show signs before catastrophic failure. Overloading fatigue is associated with exceeding the material’s strength limits but generally leads to failure after a clear load application or stress event. Hence, mechanical fatigue is specifically noted for its abrupt nature of failure, making it distinct in the context of this question.