Bore-expanding test for thermosetting carbon-fiber-reinforced plastic sheets

Press forming technology for carbon-fiber-reinforced plastic (CFRP) sheets consisting of thermosetting resin and continuous fibers is required to manufacture lightweight structures. It is considered that the formability of CFRP sheets is less than that of metallic sheets. Formability tests for metallic sheets can also be applied to compare the formability of CFRP sheets. There are four types of formability for metallic sheets; bendability, deep drawability, stretchability, and stretch flangeability. Bending and stretching tests for CFRP sheets under a suitable forming temperature and means of assisting the deformation of the sheets have been developed. The stretch flangeability of CFRP sheets should be low because cracks in the resin around the edge tend to develop under smaller strain. In this study, the bore-expanding ratio was obtained in a bore-expanding test to determine the stretch flangeability of laminated CFRP structures.