Fuzzy logic methods in fatigue and creep

Fatigue and creep laboratory data for metals normally exhibit scatter, whic h implies an element of uncertainty or vagueness in the results. Such data are usually treated by empirical correlations or by mathematical models wit h some theoretical basis. Confidence limits are sometimes given based upon an assumed probability distribution. On a fine scale, fracture mechanics st udies consider the mechanism of crack growth, assuming a uniformly smooth c ontinuum. The treatments aim to provide design working stresses and also th e reliability basis for the formulation of inspection and maintenance sched ules. Further uncertainty in the interpretation of laboratory test data in terms of in-service material characteristics arises from a few other source s, even if the material types are nominally the same. Fuzzy logic is a natural means of expressing vague categories of informatio n by means of fuzzy sets and also provides the means of performing logic op erations on them. In this work, consideration is given to the application t o some aspects of fatigue and creep. Some examples, including fuzzy boundar ies between safe and unsafe states, are given to illustrate the methodology , the conclusions are also initially in the form of fuzzy sets. Compared wi th other methodologies, richer meaning is found in the results.