2018 Volume 59 Issue 690 Pages 129-134
In this study, the degradation of the strength of press-formed hemispheres of thermoplastic matrix composite (CFRTP) was investigated considering the residual stress in fibers generated during the forming process. CFRTP sheets reinforced with woven carbon fiber fabric were stamped into hemispheres under various conditions of die temperature and blank holding force. The strength of formed hemispheres was evaluated by the internal pressure test. Residual stress in fibers around the fracture origin was directly measured by the micro-Raman spectroscopy and then its relation with the internal pressure strength was examined. As a result, die temperature was found to have negligible effect on the fracture pressure. On the other hand, blank holding force strongly influenced the internal pressure strength. The variation in strength was well correlated with fiber residual stress, which varied little with die temperature but changed significantly with blank holding force. It was well explained that the decrease in strength could be mostly due to fiber residual stress. Fiber residual stress differed with location, resulting in a local distribution of strength in the press-formed composites.