ASSESSING THE DEVELOPMENT OF FATIGUE CRACKS: FROM GRIFFITH FUNDAMENTALS TO THE LATEST APPLICATIONS IN FRACTURE MECHANICS

Engineering analysis of fatigue crack growth depend oil different loading conditions, wherever those conditions have been studied, in laboratory or real-world practice. Such analyses call be done on basis of different parameters: the stress intensity factor range, Delta K, introduced in linear elastic fracture mechanics; the J -integral range, Delta J, employed in elastic-plastic material characterization; the square-root area parameter of Murakami, effective in the presence of small defects and non-metallic inclusions. An alternative presentation of fatigue data has been proposed that uses the crack growth rate against a newly introduced parameter, namely an energy fatigue-function Delta W based at different conditions on different parameters, Delta K or Delta J or the square-root area parameter of Murakami. This alternative presentation shows fatigue data as forming an almost straight line, which may be termed the "natural fatigue tendency" of a material, and specified more precisely at a given stress range. Also the present study introduces a physical interpretation of the line presentation of fatigue data and some illustrations of the "natural fatigue tendency" for different materials under different conditions.