Experimental characterization and plastic modeling of polycarbonate at static and dynamic rates

Polycarbonate is widely used for impact protections, therefore it is of crucial interest to adequately characterize its elastoplastic response extended up to the effective ultimate local strains, at static and dynamic rates. The mechanical response of polycarbonate includes some peculiarities in common with other polymers, making the experimental and postprocessing procedures for its hardening derivation somehow more complex than they are for metals. The two main aspects still requiring further understanding and modeling efforts are: firstly the non-monotonic stress-strain response exhibiting a peak, a drop and the successive increase of the stress-strain curves; secondly the transition between three very different straining modes including the initial uniform straining, the successive necking-induced strain localization and the final strain propagation, where the necked region progressively extends all over the tensile specimen while the already-necked zones of the specimen slow down their evolution and nearly stop deforming further. The special deformation modes of polycarbonate induce local hydrostatic stresses evolving from negative to positive, consequently affecting the relationship between the measurable true stress and the not-measurable flow stress. Especially in dynamic tests, the above straining features also induce increasing-decreasing trends of the effective local strain rate, whose effects would require to be properly quantified by experiments and included in the modeling strategy. The present work identifies a procedure for deriving the flow curves of polycarbonate at static - dynamic rates by correcting the experimental true curves, and proposes this approach to investigate the strain rate effect on the material hardening