Composite materials appear to offer substantial advantages over metals for application to structures subjected to various types of loading. Their characteristic response to time-dependent phenomena, however, is substantially different from that of metals. In the present study, the fracture machanism related to short time-dependent phenomena at room temperature of roving glass cloth FRP has been examined. The results obtained are as follows.
A close correlation was observed between the modulus of elasticity and the strength which varied depending on the dispersion of the material characteristics. Therefore the stress and the strain at the fracture point did not scatter independently but distributed along a line in the stress-strain diagram, leading to a fracture criterion called as the fracture envelope.
Creep fracture was also able to be determined by the fracture envelope similar to that obtained from the statical behavior. In both cases, the gradient of the fracture envelope increased with the ply number of laminate. The phenomenon that the specimens sometimes fracture during the stress relaxation tests can also be explained by the concept of the fracture envelope.