Characterizing the energy absorption of rigid polymeric foams under compressive direct impact loading

The use of rigid polymeric foams has been well-established to result in a significant improvement in the energy absorption and safety of the vehicles, owing to the excellent energy absorption characteristics of these materials. As an optimum energy-absorbing material system, polymeric foams need to dissipate the kinetic energy of the impact, while maintaining the impact force transferred to the protected object at a low level. Therefore, it is crucial to accurately characterize the load bearing and energy dissipation performance of foams at high strain rate loading conditions. However, there are challenges render to accurately measure the deformation response of foams due to their low mechanical impedance properties. Recently a nonparametric method was proposed and successfully implemented to enable the accurate measurement of the compressive constitutive response of rigid polymeric foams subjected to impact loading conditions. The method is based on stereovision high speed photography in conjunction with 3D digital image correlation and allows for accurate evaluation of inertia stresses developed within the specimen during deformation time. The inertia stresses are then superimposed with the boundary measured impact force to facilitate the measurement of full-field stresses in the specimen. Full-field distributions of stress, strain and strain rate are then used to extract the local constitutive response of the material at any given location along the specimen length. Accordingly, the local energy absorption curves are extracted and then averaged to give the effective energy absorption response of the examined foam. Finally, results obtained from the proposed non-parametric analysis are compared with the data obtained from the conventional test procedures.