抄録
The flexural fracture behavior of unidirectional CFRP laminates (X) using pitch based carbon fibers XN40, which was recently developed as high grade fiber, was investigated by three point bending test over wide ranges of temperature and strain rate. At the same time, similar experiments were carried out for two types of CFRP, M and P, in which PAN based carbon fibers M40 and pitch based carbon fibers P55S are used, respectively. By comparing the results of three types of CFRP laminates, characteristics of CFRP(X) were clarified as mentioned below;
(1) The flexural strength of CFRP(X) as well as the others remarkably changes with temperature and strain rate. The master curves of flexural strength can be constructed for those CFRPs by using the reciprocation law between time and temperature. The time-temperature shift factors of flexural strength in respective CFRP are in quantitatively good agreement with each other.
(2) The region of reduced time is clearly divided into three parts by the mechanism of fracture for CFRP(X), that is, the micro-buckling of fibers as the initiation of fracture in the region of long reduced time, the compressive fracture of fibers in the region of medium reduced time and the tensile fracture of fibers in the region of short reduced time. In the region of long reduced time, the flexural strength of CFRP(X) is in good agreement with those of CFRP(M) and CFRP(P), which remarkably changes with reduced time. However, in the region of medium reduced time, the flexural strength of CFRP(X) shows characteristic behavior which is different from the others. The flexural strength of CFRP(X) remarkably changes with reduced time, although those of the others slightly change.
