Static and Dynamic Constitutive Equations to Finite Plastic Strain for Rolled Homogeneous Armor
ARMY BALLISTIC RESEARCH LAB ABERDEEN PROVING GROUND MD
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Experimentally determined quasi-static and dynamic constitutive equations of the form sigma-sigmasuby betaepsilon-epsilonsuby12 are reported for rolled homogeneous armor steel. The quasi-static compression data are characterized by a parabolic response function, the origin of which lies at the yield point. Two deformation moduli epsilon, are required to describe the data to six percent strain, and both are predicted by a mode index and transition strain structure of a general theory of plasticity. Dynamic strain, duration of impact, and final strain distribution are measured on specimen rods subjected to axial, symmetric, constant velocity impacts over a range of 20 to 100 meteres per second. The dynamic yield stress is higher than the quasi- static, but equal to the stress at a transition strain of a one-dimensional, rate independent, finite amplitude wave propagation theory. The dynamic response function determined is also parabolic, with its origin at the dynamic yield point, and a single deformation modulus equal to the initial quasi-static value applies. This dynamic response function accurately predicts wave velocities and strain maxima to over four percent strain. Thus, it is shown that the form of the quasi-static plastic response function is preserved in dynamic loading, and that the increase in dynamic stress is in the elastic region.
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