What is meant by the term tensile stress when applied to materials used in vehicle manufacture and construction?
Tensile stress is the stress state caused by an applied load that tends to elongate the material in the axis of the applied load, or in other words, the stress caused by pulling the material. The strength of structures of equal cross-sectional area loaded in tension is independent of the shape of the cross section. Materials loaded in tension are susceptible to stress concentrations such as material defects or abrupt changes in geometry. However, materials exhibiting ductile behaviour (most metals for example) can tolerate some defects, while brittle materials (such as ceramics) can fail well below their ultimate material strength. Tensile stress is the stress state leading to expansion; that is, the tensile stress may be increased until the reach of tensile strength, namely the limit state of stress. Tensile stress causes stress corrosion cracking (SCC), which is the combined influence of tensile stress and a corrosive environment. The required tensile stresses may be in the form of directly applied stresses or in the form of residual stresses. One method of controlling stress corrosion is to eliminate stress, or at least reduce it below the threshold stress for SCC. Residual stresses can be relieved by stress-relief annealing, and this is widely used for carbon steels.
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