Experimental characterization and computational simulations of the impact behavior of injection-molded polymers

Abstract

The multiaxial impact test in polymers is analyzed. The impact response of a propylene copolymer is characterized under different test conditions. Due to the nature of the impact event and to the complex material behavior, an intricate stress state is developed rendering rather difficult the assessment of the intrinsic impact properties. Furthermore, processing determine polymer microstructure, which significantly influences the impact response. The multiaxial impact test was simulated using a finite element code. The computed force-displacement curves fall in between the computed ones with two extreme contact conditions between striker and plate. Friction plays an important role from medium strain levels until the peak force is reached, determining its intensity. The constitutive coefficients at high strain-rates were identified by an inverse method. The adopted constitutive model allows the computation of the force-deflection curve until the force peak, but not its full description. For that, a modified version was used that more correctly takes into account the strain hardening of the polymer. Finally, it is emphasized the importance of the knowledge of the heat conversion factor for realistically predicting the mechanical behavior of polymers at high strain-rates.