Abstract
Mechanical properties and damage onset stress in 24 or 25-ply unidirectional CFRP laminates that contain different thicknesses and gap lengths of fiber discontinuity are investigated by tensile testing and analytical model. Same damage behavior, as with previously reported, that interlaminar delamination between fiber continuous and discontinuous plies follows after crack initiation at the edge of the discontinuous fibers is observed even if thinner and longer gap of the fiber discontinuities are introduced. It has been shown that the laminates with long gap fiber discontinuity show higher stress of crack onset than that with short gap, and the crack onset stress decreases with the number of the discontinuous plies. A similar trend can be seen for the onset stress of the interlaminar delamination though no delamination has been observed in the short and long gap 1-ply and long gap 2-ply discontinuous laminates. The crack onset stress is evaluated by representing the energy release rate with crack initiation by using stress change in shear-lag model. Due to the fact that the relation between the number of discontinuous plies and crack onset stress can be predicted for both short and long gaps of fiber discontinuity by assuming a certain value of critical energy release rate, it is shown that the crack onset behavior is not affected by thickness and gap length of the fiber discontinuity. Another analytical model with an assumed critical energy release rate has successfully predicted the delamination onset stress regardless of sizes of fiber discontinuities by applying the exact thicknesses of continuous and discontinuous plies. By comparing the predicted delamination onset stress and fracture stress of the laminates, it is concluded that two and more fiber discontinuous plies can affect the overall damage behavior of the laminates.
