Abstract
By using reaction injection molding of rigid polyurethane including a blowing agent in its raw materials, an integral-skin foam (referred as RIM molding) consisting of high density skin and low density foamed core layers can be obtained in one injection processing. By considering this RIM molding as a sandwich structure, the relation between the layer construction and flexural fatigue properties of RIM molding was investigated. It was found that the fracture modes in the fatigue test were classified as: (1) the tensile fracture-type and (2) the shear fracture-type, depending upon the layer construction. Moreover, a remarkable difference in the degree of decrease in flexural strength due to fatigue between two fracture modes was observed. That is, the fatigue strength at 107 cycles in the tensile fracture mode was about 20% of the static strength, while the one in the shear fracture mode was about 30% of that.
The results obtained here can provide an important guide to determine the optimum layer construction concerning flexural fatigue properties in the structural design of moldings, when RIM moldings are applied to thermal-insulated housing.
