As Reinforced Reaction Injection Molding (R-RIM) Polyurethane has an excellent impact-proof properties, this material has been used for components in motorcars, and so the studies on fracture characteristics under impact loadings are needed. The aim of this work was to clarify the effects of void, fiber content and impact velocity on the dynamic fracture toughness. The dynamic fracture toughness values decreased with an increase in void content, and took a minimum value at 5% of fiber weight content and increased again with fiber content for impact velocity from 1.4 to 5.1m/s. It was found that the values increased with an increase of impact velocity and the stable crack extension appeared during impact. Therefore, it is concluded that the dynamic fracture toughness value corrected by the stable crack extension is almost constant in this impact velocity range.
