Abstract
Flexural properties of moldings made by RIM (Reaction Injection Molding), which are structual foams consisting of high density skin and low density core, were investigated by three-point bending tests.
Two failure modes were observed in bending tests of the moldings made by RIM, and they are classified as follows according to the density ratio of skin layer to core layer.
(1) The opposite side of the skin layer to which load was subjected was failed by tensile stress.
(2) The same side of the skin layer to which load was subjected was failed by compressive stress, causing Wrinkling buckling.
Then, the conventional composite beam theory was applied to the former failure mode and Hoff's buckling theory to the latter, and equations were derived to predict the flexural properties of the structual foams which involved buckling from the flexural properties of solid construction.
In addition, it has been shown that there exists the density distribution that maximize the flexural strength of the moldings made by RIM with the given overall density.
The results obtained here should be useful to the optimum structural design of moldings made by RIM.
