A Study of Elasto-Plastic Fracture Toughness of R-RIM Materials by CTOD

Abstract

The method to determine the stable crack initiation point of R-RIM polyurethane by three point bending test is proposed and the value of crack tip opening displacement at this point is studied by using the relation between the rotational factor and the crack tip displacement with a concept of fracture mechanics. The critical crack tip opening displacement can be confirmed by continuous observation of the crack blunting and the following stable crack growth processes. It is found that critical value for specimen with the fiber weight content of ten percent is larger than that of zero percent, and the critical value for specimen with void content of sixteen percent is larger than those of three and ten percent. The results can be explained by an increase of the deformation in resin part due to the fiber reinforcement at the crack tip and the ductile deformation in resin part between the notch and the voids.