Fatigue assessment of metallic materials beyond strain measurement

The comprehensive characterization of microstructural changes caused by cyclic loading is of major importance for the understanding of basic fatigue mechanisms and for an optimized fatigue life calculation of metallic materials. Different mechanical parameters have been considered relevant to describe fatigue processes and to characterize damage accumulation. Among those plastic strain is dominating especially for metallic materials. However measuring this parameter can easily become a challenge because the proportions of plastic strain are usually small when compared to the governing elastic strains. Besides conventional extensometers additional measurement techniques have been introduced over the past years. Even magnetic and ultrasonic sensing which are very much associated with physical parameters being used in nondestructive testing has been moreover considered recently for the determination of fatigue relevant parameters resulting from constant and variable amplitude loading.Based on these measures obtained in load increase as well as constant amplitude tests a realisable fatigue life calculation according to the PHYBAL method can be performed leading to a significant reduction with respect to the time required for testing and consequently costs. The database provided by PHYBAL can be used for a variety of applications, e.g. the design and lifetime assessment of new as well as aged components and based on this, it offers a huge potential with respect to nondestructive testing.