Evaluation of different methods for determining fatigue crack growth threshold values

Evaluation of different methods for determining fatigue crack growth threshold values. For the dimensioning of components and structures, but in particular for the definition of inspection intervals, fracture mechanical approaches play a decisive role. The basis of fracture mechanical concepts is an exact description of the material behaviour e.g. in terms of the fatigue crack growth threshold value, whose determination is standardised by the ASTM. However, not all parameters are explicitly defined. Within the scope of this paper a parameter study is presented. It has been shown that with an increasing reduction gradient of an exponential decrease of the cyclic stress intensity the threshold tends to higher values. In contrast the initial stress intensity has only a marginal effect. With a linear decrease in average the same threshold value is determined as in the case of an exponential decrease, but the scatter is considerably lower using a linear reduction procedure.