Estimation of R-curve for Mode II Interlaminar Fracture Toughness by Using CFRP Laminates with Fibre Discontinuities

Abstract

When CFRP plates of structures with complicated geometry are fabricated by using prepregs, fiber discontinuities remain in the laminates since some slits or cuts are introduced in prepregs before lamination. The CFRP laminates with fibre discontinuities show tensile failure at much lower stress due to crack originated from the discontinuities. Previous studies have shown that the stress at which crack propagation from fiber discontinuity occurs can be predicted by using mode II interlaminar fracture toughness 􀜩􀯂􀯂. The present study aims to reverse this methodology in order to estimate the R curve of mode II interlaminar fracture toughness from tensile test of CFRP laminates with fiber discontinuity. In the technique we suggest here there is no need to perform stabilized ENF tests that require a variety of controls. Tensile tests for CFRP laminates that contain fiber discontinuous dispersed at an arbitrary interval are carried out. Relations between the obtained fracture stress and the interval are converted into that between critical energy release rate (CERR) in mode II and crack extension that can be compared with R-curve obtained by ENF tests. As a result, although mismatch are found in the initial region of R-curve a.k.a. 􀜩􀯂􀯂􀮼 , CERR matched with R-curve during crack propagation, which is the region where the change of 􀜩􀯂􀯂 converges as 􀜩􀯂􀯂􀯋.