API 571 Certification (Corrosion & Materials) Practice Test

What is a primary factor contributing to mechanical fatigue in materials?

1. High temperatures

2. Cyclic loading

3. Corrosive environments

4. Radiation exposure

The correct answer is: Cyclic loading

Mechanical fatigue is primarily caused by cyclic loading, which refers to the repeated application and removal of stress on materials over time. When a material is subjected to such repetitive loadings, it can lead to the development of micro-cracks and eventual failure, even if the loads applied are below the material's yield strength. This phenomenon occurs because the repeated stress can induce changes in the material's microstructure, leading to an accumulation of damage over time. Cyclic loading is significant because it can affect all types of materials, including metals and polymers. The nature of the loading, such as its frequency and amplitude, alongside the material's inherent properties, heavily influences the fatigue life of a component. Factors such as geometry, surface finish, and any pre-existing flaws also play crucial roles in how a material will respond to cyclic loading conditions. While high temperatures, corrosive environments, and radiation exposure can indeed impact the integrity and longevity of materials, they do not directly contribute to mechanical fatigue in the same way that cyclic loading does. For instance, high temperatures may lead to creep or softening but do not necessarily induce the repetitive stress conditions characteristic of mechanical fatigue.