Mechanical behaviour of rigid polyurethane foam under combined cutting and compression loads

Rigid polyurethane foam (RPUF) is a porous material with good energy absorption characteristics, but it may suffer from the destructive effects of impact and cutting when used as a protective structure. Herein, the mechanical response characteristics of RPUF under combined cutting and compression loads is analysed. A cutting tool with a certain width is used to apply a load to the polyurethane foam under quasi-static conditions. The force and displacement are measured, and the influence of the geometric parameters of the cutting tool and the density of RPUF on the force are analysed. In addition, a theoretical model of the total force on RPUF under the combined action of cutting and compressive loads is established. Based on this model, the proportion of component force in the total force is calculated and the influence of size effect on the deformation mechanism of RPUF is analysed. Experimental results indicate that when the density of the RPUF is high, the amplitude of the increase in the total force improved after the increased cutting depth and tear length. Theoretical analysis results indicate that the proportion of crushing force increases with the increase of the foam's pore size, whereas the proportion of tearing force and friction decreases with the increase of the foam's pore size. When the width of the cutting tool is 0.5–20 times the pore size, the proportion of the crushing force decreased from 86.01% to 34.19%, and the proportion of tearing force is 0%–60.25%.