engleski

Some Aspects of Statistical Size Effect in Fatigue Life Prediction

Originally developed for forecasting of fracture probability on rigid materials (Weibull, Freudenthal), the method of statistical value influence, derived from laws of fracture mechanics, proved applicable for prediction of fracture probability on cyclically loaded ductile materials. But technological influences (e.g. surface, residual stresses, and constitution changes) have to be considered separately. If the inhomogenities of a multi-crystalline metal constitution, like cleavage, impurity atoms, boundary interface, external phase etc. are considered as defect with known dimensions, they can be interpreted as very small cracks in the meaning of fracture mechanics. These cracks start propagating under a fatigue load, if they have a critical length concerning the local level of stress. They will reach a size, which can be detected using technical methods. In the numerical calculation (e.g. FEM) the procedure of determining the stress function f is similar to the procedure in case of photoelasticity. In the vicinity of the notch, a large total area A0 is randomly selected, within which every element represents a partial area Ai with average stress.

fracture mechanics; multi-crystalline metal; crack; fatigue

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