These amplified stresses cause microscopic cracks to form and propagate, eventually leading to fracture. The defects act as stress risers, causing stress concentrations to develop at local regions. However, the cyclic action serves to weaken the material, causing it to eventually fail.įatigue occurs because most known materials contain defects, in one form or another, at the microscopic level. This load is usually substantially below the yield stress of the material. Material Fatigueįatigue occurs when a metal is subjected to repetitive loading. To better understand the endurance limit, it is first worthwhile to understand fatigue in metals. The former is a stress limit for infinite load cycles, while the latter describes the maximum stress for a specific number of load cycles.Įndurance limit may also be known as fatigue limit.Ĭorrosionpedia Explains Endurance Limit (Se) For example, rigid, elastic, low damping materials, like some thermoplastics or thermosetting plastics, have a very low or non-existent endurance limit.Įndurance limit should not be confused with fatigue strength. Not all materials have an endurance limit. However, if the bolt experiences a cyclic loading that is below its endurance limit, it can be expected to endure an infinite amount of vibration without developing cracks or experiencing fatigue failure. This action is very similar to bending a paper clip back and forth until it breaks. Eventually this loading can lead to fatigue in the bolt, where the material eventually weakens and the bolt fractures. As the machinery vibrates, the bolts experience repeated back and forth load cycles. In other words, when a material is subjected to a stress that is lower than its endurance limit, it should theoretically be able to withstand an indefinite amount of load cycles.įor example, bolts that are used to hold down machinery are often vulnerable to fatigue. The endurance limit (Se) of a material is defined as the stress below which a material can endure an infinite number of repeated load cycles without exhibiting failure.
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