Abstract: Rigid polyurethane foam is widely used as the energy absorption filling device. To research the mechanical response of the rigid polyurethane foam under multi-axial stress states, the triaxial compression experiments, including the multi-axial isobaric experiment and different confining pressure experiments, are performed. Experimental results show that the hydrostatic pressure versus volumetric strain curves go through the elastic stage, the plateau stage and the densification stage, and the corresponding bulk modulus of elasticity, plateau stress and energy absorption per unit volume are higher than that under the uniaxial compression. In addition, the axial deviation stress versus axial strain curves during the different confining pressure experiments experience the elastic stage and the peak back area stage, but no the apparent plateau stage and the densification stage. And the peak deviation stress decreases as the confining pressure increases generally. Moreover, the axial deviation stress of the rigid polyurethane foam shows evident randomness when the confining pressure exceeds a limit value, which can lead to losing the axial load carrying capacity. Based on the experimental data and the differential hardening model, the yield surface of the rigid polyurethane foam considering strain hardening are obtained.

Key words: cell morphology, mechanical response, multiaxial compression experiment, rigid polyurethane foam, yield surface