Metal Plasticity

Advances in metal forming, lifetime of turbine blades, load carrying capacity of metal structures, armor penetration, and fracture resistance of structural metals all rely on improved understanding of the plasticity of metals. Because of the inherent complexity of the plastic response of metals, development of the required understanding requires a major sustained research effort. Advances in theory, experiment, and numerical methods are required. Classical plasticity theory, although of great value in routine applications involving nearly proportional loading of metal structures, is unsatisfactory for numerous important applications involving, for example, large deformations, cyclic loading, high temperatures, localized shearing, or high strain rates. A more physically based plasticity theory is needed to address the wide class of problems faced in modern technology. Development of such a theory requires critical experiments that show the relationship between microscopic mechanisms and macroscopic plastic response as well as provide a basis for determining the validity of proposed theories. Inclusion of rate dependence, large deformations, nonproportional loading, temperature sensitivity, and the effects of grain boundaries is important in the development of a more comprehensive theory. Remarkable increases in the size and speed of computers are removing computational obstacles to the use of more realistic plasticity theories. Relaxation of computing constraints provides an exceptional opportunity for major advances on technological problems involving plasticity. Accurate, efficient computer codes are required that are suitable even for cases involving softening due to such effects as grain rotations and the expansion of voids. Capability for predicting failure due to the formation of shear bands and the coalescence of voids is a major need. Physical principles governing damage accumulation during general loading histories need to be determined and represented in computer codes.