SOLUTE-ENHANCED BACK STRESSES AND THEIR ROLE IN A SIMPLIFIED PHENOMENOLOGICAL CONSTITUTIVE MODEL FOR THE NONELASTIC DEFORMATION OF METALS AND ALLOYS

A new unified phenomenological constitutive model has been developed that is capable of simulating complex deformation phenomena in a way that minimizes the complexity of the equations and the number of material constants. The new model is an extension of the MATMOD approach, but simplicity has been emphasized because determination of the constants for materials of interest is one of the most problematic aspects of advanced phenomenological models.; The new model, MATMOD-BSSOL, was developed from the results of experiments designed to clarify the nature of flow stress plateaus in solute strengthened alloys, analyses of the accepted fundamentals of nonelastic deformation, and phenomenological trends in a variety of published data. The major improvement present in MATMOD-BSSOL is the simple method of simulating solute strengthening through solute-enhanced back stresses. This method of simulating solute strengthening is consistent with the experimentally observed behavior and most aspects of recent theories and physical models. In addition, it provides a physically reasonable link between the low temperature and high temperature behavior of alloys. The remaining improvements present in MATMOD-BSSOL, which are not associated with solute strengthening, simplify the equations without compromising their physical basis.; MATMOD-BSSOL contains 40% fewer material constants than previous versions of MATMOD that have similar modeling capabilities. The procedures for evaluating the constants directly from mechanical test data or for estimating their values based on those of similar alloys are demonstrated for pure aluminum and three Al-Mg binary alloys.; The results of MATMOD-BSSOL calculations are compared with a variety of mechanical test data for pure aluminum and the three Al-Mg alloys. Particularly significant are the simulations of peaks and plateaus in the stress-temperature curve, which are consistent with the data over a wide range of temperature and strain. The steady state creep data are also simulated accurately over a wide range of temperature-compensated strain rate, including power-law breakdown and the transition from Class I and Class II behavior. Finally, a variety of independent predictions are presented. The MATMOD-BSSOL predictions are generally consistent with the data.