An experimental investigation of the optimum joining and repair of structural composites

Because of their high stiffness-to-weight and high strength-to-weight ratios, composite materials are rapidly gaining acceptance in today's aerospace industry. As the technology associated with the utilization of composite materials matures, it is transferred to many other industries such as the automotive industry. The primary problems that need to be addressed in composite structural design are a thorough understanding of the characteristics of composites, as well as the repairability of such materials.; The composite materials under investigation are being developed for the automotive industry, therefore repair techniques must be established to facilitate the expanding use of structural composite components. The current repair techniques involve: (1) determining the damage mode, (2) selecting the joining technique and geometry, (3) choosing an adhesive that is compatible with the matrix material, (4) applying reinforcement patches to both sides of the damaged zone, and (5) assessing the strength of the repaired composites.; Three different types of composite panels are analyzed. They consist of a chopped glass fiber in a polyester matrix, a continuous glass mat in a vinylester matrix, and a cross-woven fabric chemically bonded to randomly oriented glass fibers in a vinylester matrix. These three samples exemplify most of the composite materials utilized by the automotive industry.; Artificial damage modes performed in the laboratory are used to simulate real composite damage. Various repair parameters are explored to repair these artificial damage modes. Results show that by careful selection of geometrical bond line configuration, scarf angle, filler, and reinforcing patch material, 100% of the composite material's strength can be restored. Three-point bending is utilized to assess the restored strengths of the composites. Further results show that the bond line geometry between two separated specimen parts plays a critical role in the joining efficiency and repair strength of composite materials.; Based on this research, the fundamental techniques for composite joining and repair are achieved and the development of an optimal design for superior joining efficiency and repair strength becomes possible.