Evolution of Matrix Cracking Damage in FRP Crossply Laminates. 2nd Report. Measurement of Energy-Release Rate.

Abstract

In part I, the energy-release rates (ERRs) of the whole laminate and of the 90°and 0°layers were theoretically obtained. Part II discusses an experimental determination of the ERRs. Real-time measurements of cracking stress and positions of all cracks are conducted via making use of GFRP crossply laminates in which the transverse matrix cracks are visible to the naked eye. Then the ERR can be calculated using the theoretical results obtained in part I and the experimental data of cracking stress and positions of cracks. It is found that the ERR of the whole laminate is not constant but increases with increasing crack density ; therefore, the fundamental assumption made by Nairn is not appropriate. It is also found that the ERR of the 90°layer is constant during damage evolution, which will serve as a material parameter yielding an evolution law of the cracking damage in part III. The characteristics of the energy-release rate of the 0°layer are also discussed.