Fracture evolution in thick composites under compression

Abstract This study reports the evolution of fracture in thick woven fabric composites under static compression loading. The materials examined were carbon/epoxy composites laminated with up to 180 plies of the woven prepreg. A pressure rolling setup was designed and employed in the present materials in order to compact the laminate and to remove air possibly trapped in between plies. To apply the compressive load, an end‐supported, end‐loaded fixture was used. The growth of cracks was monitored and recorded in real‐time by picture and video cameras. The continuous monitoring of the failure progression provides detailed information about the onset and growth of cracks in various specimens under different support conditions. The modulus, strength, and the loss of stiffness in the post‐failure portion have been examined. The loading curves have several sudden drops and regains in the post‐failure portion. The causes of the sudden load drop can be identified by correlating with the corresponding fracture image. The influence of the support in the fixture has been examined. Two major modes of failure are fiber kink‐band and longitudinal splitting. The branching and coalescence of cracks of these two modes of failure have been observed and examined. Thickness effects exist in the present composites. The processing–property relationships are discussed. How these modes evolve with the applied strain in specimens of different thicknesses and how they affect the load‐carrying capability of the material are examined. POLYM. COMPOS., 28:425–436, 2007. © 2007 Society of Plastics Engineers