b-VALUE ANALYSIS OF MICROCRACK SIZE AND ACOUSTIC EMISSION SIGNAL DISTRIBUTIONS

摘要

The process of initiation and growth of microcracks occupying the most period of a metal lifetime under fatigue/static loading is considered. Both replica method for the direct observation of surface microcrack patterns and acoustic emission testing method were used to study the evolution of microcrack system and the transition to the localized fracture of material. Results include estimation of crack accumulation rate and analysis of crack size distributions at different stages of loading. A probabilistic model of damage accumulation for a constant-amplitude fatigue loading of metals has been developed to interpret the observed variety of crack-size and AE amplitude distributions. The model is based on concepts of fracture mechanics and damage accumulation in solids and uses the physically founded parameters of the fracture process and heterogeneity of a medium. It follows from modeling that the b-value, which is a slope of a cumulative crack size distribution relates to parameter describing a microcrack growth law.