Defect and damage analysis of advanced discontinuous carbon/epoxy composite materials

Recent composite technology research and development efforts have focused on discontinuous carbon fiber/epoxy molding systems derived from chopped aerospace-grade unidirectional tape prepreg. This study analyzes in detail the meso-structure of this class of materials, which exhibit point-to-point variations associated with the random chip distribution, by means of destructive and non-destructive inspections, in the attempt to identify characteristic traits that can yield insight in its quality and performance. Results show that several types of defects can be encountered within the molded panel, such as macro-voids, fiber kinking and swirling, or resin-rich areas. However, it is found that failure may or may not occur in proximity of these hot spots, independently from their size and location, even for specimens containing the circular hole. Therefore it appears that for this class of materials conventional ultrasonic inspection and defect classification may not be suitable as criteria for part acceptance or rejection.