Analysis of Crack Growth Data with Application to Trip Steel.

摘要

A procedure is advocated to replace the common practice of establishing a rate of crack growth law directly from increments of growth or from slopes of smooth curves drawn through crack length vs number of loading cycles data. In the advocated procedure, a postulated rate equation such as, for example, the power law da/dN approx (K)m, is integrated for the specimen geometry used and values of the integral corresponding to experimental crack lengths are plotted against cycles of loading to reach these lengths. Thus, where, and if, the rate equation is valid the plot will consist of one or more straight line segments for each of which constant parameters may be obtained, or confirmed if theoretical. Intersections of straight line segments will correspond to crack rate of growth discontinuities unobservable by the usual method. Using Trip Steel data supplied by Syracuse University as an example, it was found that all growth discontinuously at various amounts of growth law. This conclusion is not invalidated by a gradual decrease in loading during testing, or by the differences in analytical expressions for K found by different investigators.