Final answer:
Weld-induced residual stresses occur due to the uneven expansion and contraction from heating and cooling during welding, caused by differences in thermal expansion coefficients. To avoid damage, engineering designs often account for these stresses, opting for materials with aligned coefficients and controlled welding procedures.
Step-by-step explanation:
Causes of Weld-Induced Residual Stresses
Weld-induced residual stresses occur due to the expansion and contraction of materials when they undergo heating and cooling during the welding process. This thermal stress is a result of the material's thermal expansion coefficients, which determine how much the material expands or contracts with temperature changes. When two different materials or two parts of the same material are welded together, they might expand and contract at different rates due to varying coefficients of thermal expansion. This mismatch can cause parts of the weld to expand more than others, leading to tensile stresses being set up in certain areas while compression occurs in others as the welded section cools.
Engineering designs often need to consider these stresses to prevent structural failure. For instance, engineers might choose materials with similar thermal expansion coefficients, design components that can freely expand and contract, or introduce features like expansion joints in structures. Moreover, controlled heating and cooling rates during welding can help mitigate the development of residual stresses.
In some cases, residual stresses can be beneficial, such as with pre-stressed concrete, where intentionally induced stresses can improve structural integrity. However, in welding, excessive residual stresses can lead to the weakening of the joint, distortion of the components, or even cracking, which undermines the strength and durability of the structure.