MICROVOID GROWTH IN METALS DURING PLASTIC-DEFORMATION

Plastic deformation in metals is accompanied by internal damage, the development of the damage being mainly by nucleation, growth and coalescence of microvoids. Finally, the damage leads to ductile fracture. As reported in this paper, it is found from the results of microscopic tests that the model of microvoid growth in actual metals may be described by the Rice-Tracey model, which is a model of the void growth for idealized metals originally, but in which the coefficient C for actual metals is not equal to 0.283 generally and is a material coefficient. The coefficient C for plain steel 20 was found to be 0.2, from the results of tensile and compression tests. It has been proposed in previous works that failure occurs when a critical value of (R/R0), i.e., (R/R0)c, is reached, regardless of the value of the stress triaxiality ratio. (R is the current radius of a void; R0 is the original radius of the void.) Taking into account the critical value (R/R0)c and assuming that the one-dimensional strain at the damage threshold epsilon(D) = 0, the availability of the ductile fracture criterion derived from the concept of damage mechanics by the authors, is further substantiated by the results of the microscopic tests.