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The failure or fracture of a product or component as a result of a single event is known as mechanical overload. It is a common failure mode, and may be contrasted with fatigue, creep, rupture, or stress relaxation. The terms are used in forensic engineering and structural engineering when analysing product failure. Failure may occur because either the product is weaker than expected owing to a stress concentration, or the applied load is greater than expected and exceeds the normal tensile strength, shear strength or compressive strength of the product.
Examples include the many components which fail in car crashes, train crashes, and airplane crashes as a result of impact loading. The problem for the investigator is to determine which failures have been caused by the crash, and which may have caused the crash. It usually involves examining the broken parts for signs of fatigue crack growth or other damage to the part which cannot be attributed to the crash itself. For very large structural failures such as the collapse of bridges, it is necessarily a long and tedious process of sifting through the broken parts.