AWS Welding Inspection and Testing Certification Practice Test

What type of fatigue is typically of concern in welded structures?

1. Low-cycle fatigue

2. High-cycle fatigue

3. Thermal fatigue

4. Creep fatigue

The correct answer is: Low-cycle fatigue

In welded structures, low-cycle fatigue is typically of concern because it involves the repeated application of high loads over a small number of cycles. This type of fatigue is critical in welds, where there can be significant stress concentrations due to geometrical discontinuities, including weld joints and heat-affected zones. Welded connections often experience varying stress levels from dynamic loads, vibration, or other operational conditions, which can lead to material yielding during the first few cycles. The nature of the welding process itself can introduce residual stresses into the joint, making these areas more susceptible to low-cycle fatigue failure. High-cycle fatigue, on the other hand, pertains more to lower stress levels over many cycles, typically being less critical in the context of welded structures where stresses can exceed the yield strength during operational conditions. Thermal fatigue is related to the thermal cycling of materials, which is significant but not as prevalent as low-cycle fatigue in the context of structural integrity during load applications. Creep fatigue involves the slow deformation of materials under constant load and high temperature, which is less applicable to typical welding concerns where immediate cyclic loading is the focus. Thus, low-cycle fatigue is most relevant to welded structures, as it directly correlates with the performance and safety of the weld