Red Seal Ironworker (Structural/Ornamental) Practice Exam

What does the term "fatigue" refer to in metal structures?

1. The increase of strength in metals over time

2. A type of corrosion in metal structures

3. The weakening of a material caused by repeatedly applied loads

4. The process of welding different metals together

The correct answer is: The weakening of a material caused by repeatedly applied loads

The term "fatigue" in metal structures specifically refers to the weakening of a material caused by repeatedly applied loads. This phenomenon occurs when a structure is subjected to cyclic stresses, which can lead to the development of microscopic cracks that grow over time with each load cycle. Eventually, these cracks can propagate and result in sudden failure, even if the applied stress is below the material's strength threshold. Fatigue is a critical consideration in structural engineering, as many structures experience varying loads during their service life, such as those from wind, traffic, or seismic activity. Understanding fatigue is essential for ensuring safety and reliability in construction, as designs must account for potential fatigue failure through appropriate material selection, design techniques, and regular inspections. The other options relate to different aspects of material science but do not accurately define "fatigue." For example, the increase of strength in metals over time refers to processes such as work hardening or aging, while corrosion involves the deterioration of metals due to chemical reactions. The process of welding different metals together describes a method of joining materials rather than a condition of material performance under load.