Initiation and growth criteria for transverse matrix cracks in composite laminates

Cecchin and Monti [Cecchin E, Monti A. Experimental techniques for analysis of matrix crack evolution in composite laminates. Masters thesis, Department of Solid Mechanics, Royal Institute of Technology (KTH), Stockholm, Sweden, 1998.] have presented experimental results using off-axis loaded tensile specimens that made it possible to introduce transverse matrix cracks which started from one edge of a specimen and arrested before reaching the other edge. Matrix crack positions and lengths were registered as functions of the applied load through optical images which were captured at regular external load intervals. In the present paper, the experimental data from Cecchin and Monti are analysed. Since several transverse matrix cracks appeared in each specimen and crack growth can be observed at different load levels, a single macroscopic specimen generates lots of data for crack initiation and propagation. Glass/epoxy cross-ply laminates with two different transverse ply thicknesses are investigated. The results strongly indicate that the energy release rate is a relevant measure for prediction of crack growth whereas the local strain controls matrix crack initiation.