Final answer:
Welding causes residual stress due to rapid cooling, which creates tension due to uneven contraction and is a category of thermal stress, potentially impacting the structural integrity of welded materials.
Step-by-step explanation:
Welding can cause residual stress due to rapid cooling. When a material is welded, it's heated to high temperatures, and if it cools too quickly, the metal may contract unevenly, creating tension within the material. This phenomenon is a type of thermal stress, which occurs because of thermal expansion or contraction. Thermal stress can be both beneficial and detrimental, as it can be used intentionally in manufacturing processes or it can cause damage, such as cracking or warping of materials.
For instance, thermal stress is responsible for potholes when water seeps into cracks in the road and freezes, expanding and further breaking the pavement. Similarly, during welding, the localized heating and subsequent rapid cooling can lead to the development of residual stresses, which can ultimately affect the structural integrity of the welded item.