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, Departme nt of Solid Mechanics, Royal Institute of Technology (KTH), Stockholm, Swed en, 1998.] have presented experimental results using off-axis loaded tensil e specimens that made it possible to introduce transverse matrix cracks whi ch started from one edge of a specimen and arrested before reaching the oth er edge. Matrix crack positions and lengths were registered as functions of the applied load through optical images which were captured at regular ext ernal load intervals. In the present paper, the experimental data from Cecc hin 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 transv erse ply thicknesses are investigated. The results strongly indicate that t he energy release rate is a relevant measure for prediction of crack growth whereas the local strain controls matrix crack initiation. (C) 2000 Elsevi er Science Ltd. All rights reserved.