Translaminar Fracture Toughness of a Composite Wing Skin Made of Stitched Warp-knit Fabric

Abstract

: A series of tests were conducted to measure the fracture toughness of carbon/epoxy composites. The composites were made from warp-knit carbon fabric and infiltrated with epoxy using a resin-film-infusion process. The fabric, which was designed by McDonnell Douglas for the skin of an all-composite subsonic transport wing, contained fibers in the 0°, ±45°, and 90° directions. Layers of fabric were stacked and stitched together with DuPont KevlarÒ yarn to form a 3-dimensional preform. Three types of test specimens were evaluated: compact tension, center notch tension, and edge notch tension. The effects of specimen size and crack length on fracture toughness were measured for each specimen type. These data provide information on the effectiveness of the test methods and on general trends in the material response. The scope of the investigation was limited by the material that was available. Introduction McDonnell Douglas will design and build an all-composite wing for a commercial trans...