Measurement of cohesive laws for interlaminar failure of CFRP

For carbon fibre reinforced composites, two different delamination processes are identified; one at the crack-tip with a sub millimetre sized process zone and one with a large-scale process zone associated with fibre bridging. In the present paper we focus on the crack-tip process that is important when studying initiation of cracks and when crack growth has to be avoided. Methods to measure the cohesive laws associated with the fracture processes are developed for loading in mode I and II using the DCB- and ENF-specimens. An evaluation method involving finite element simulations and an optimization procedure is proposed and verified. Experiments performed on a CFRP are evaluated using the proposed method. For loading in mode I, the fracture energy and cohesive strength are in the order of 300 J/m2 and 75 MPa, respectively. The corresponding values for mode II loading are 1200 J/m2 and 80 MPa.