Analytical prediction of flow stress on aluminum alloy/self-reinforced polypropylene laminated sheet material considering temperature-dependent material constants

A flow stress model is developed prior to a material formability evaluation using analytical analysis. However, some existing models do not consider the effects of temperature on the flow stress, while others utilize a complicated process to predict the temperaturedependent behavior. Previously, the modified Hollomon and modified Ludwik models were proposed as flow stress models that incorporate the effects of temperature, but that involve relatively simple processes. However, in those models, the material constants are formulated as temperature-dependent linear equations only. In this study, material constant equations (the yield stress, strength coefficient, and work hardening exponent) based on the modified Ludwik model are obtained for a laminated sheet composed of an aluminum alloy and self-reinforced polypropylene (SRPP); these expressions are then examined in detail using nonlinear regression analysis. Newly modified models are created, in which the material constants are modeled using combinations of quadratic and exponential temperature-dependent equations. Then, the previous and newly modified models are evaluated by comparing their average maximum absolute errors and R-squared errors against experimental data. Hence, the best-fitted flow stress models are determined. Models comprising a combination of quadratic equations, or a combination of exponential (yield stress) and quadratic equations, yield the greatest accuracy.