Failure mechanisms and serviceable life

Because of the fact that all materials are more or less inhomogenous, cracking always is initiated at places which are special weak spots, or at places of stress concentrations. Thus, the various cracking processes are discussed with regard to their classification according to these weak spots. At the moment, the possibility to improve the lifetime by means of suppression of the cracking is not at all exhausted. The cracking takes place relatively early as to the entire lifetime, and the lifetime is determined above all by propagation of microcracks. Therefore, possible universal correlations which determine the growth of microcracks are considered. Then, the integration of the microcrack propagation is discussed as a natural basis for a prediction of lifetime. (orig.)