Compression Failure in Reduced Adhesion Fiber Laminates

Abstract

The compressive strength of fiber composites is of key interest in many strength critical composite structures, due to the generally lower failure values relative to tension dominated stress states. The general understanding of the factors that control compression failure is quite rudimentary, and as a consequence strength controlled design of practical structures loaded in compression can not be accomplished on a rational basis at present. In recent work it has been shown that the compressive strength of the principal load carrying axial plies is markedly affected by the adjacent plies in the laminate. A micro-mechanics model for compression failure of laminates has been formulated that attempts to explain the observed behavior. In the present work a further verification of the model is presented by means of a comparison with experiments performed on laminates with specially treated fiber-matrix interphases. In addition to control specimens using fibers with standard surface treatment, tests were carried out on laminates in which the fibers were treated with a release agent to reduce fiber-matrix adhesion. The specimens with reduced fiber adhesion showed a loss of strength of up to 75 percent, indicating the effects of loss of matrix support. The results show that the model explains a number of important features of the experiments, and thus gives insight into compression failure of laminates.