INTERNAL FRICTION AND MODULUS DEFECT ASSOCIATED WITH THE MICROCRACKS IN MATERIALS

Inthis paper, theinvestigation of applying internalfriction ( ultrasonic attenuation) andmodulus defect(ultrasonic velocity change) tostudy the variation of dislocation density andlooplength withcycle numberintheearly fatiguestageisreviewed. On this basis,thecon ceptof characterization of fatigue microcrackformation and propagation assessed bythe mea surementofinternalfriction and dynamicalelastic modulusissuggested. Theanalyticalex pressionoftheinternalfriction and modulus defect associated with microcracksiscalculated underthe assumptionthatthe mechanicalenergy dissipation iscaused by the mutualfriction betweentheoppositefacesofthe microcrack.