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fatigue strength – To characterize the failure response of nonferrous materials, and of ferrous alloys in the finite life range (See Stress-Life), the term fatigue strength at a specified life SN is used. The term fatigue strength identifies the stress level at which failure will occur at the specified life. The specification of fatigue strength without specifying the corresponding life is meaningless. A statement of this strength value must always be accompanied by a statement of the number of cycles N to which it corresponds. Can be thought of as a pseudo-endurance limit. Shot peening improves the fatigue strength of a part. See Stress-Life.
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fracture toughness – Same as stress intensity factor.
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initiation life – Encompasses the development and early growth of a small crack. Initiation may be assumed to be the portion of life spent developing an engineering size crack (approx. 0.1 inch). It is often very difficult, if not impossible, to define the transition from initiation to propagation.
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propagation life – The portion of the total life spent growing a crack to failure. May be assumed to be the remainder of fatigue life after the initiation life. It is often very difficult, if not impossible, to define the transition from initiation to propagation.
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stress intensity factor – Denoted by KI, same as the fracture toughness, may also be just abbreviated by K.
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wallowing – The gradual elongation of a hole toward a load over time, such as a bolt or pin connection. (picture). Also see cyclic loading.
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