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Composite materials structures often have weaknesses at the location where the materials join, where different materials are placed in proximity or bonded. These weaknesses, flaws or defects control the ultimate strength of the materials. Coupling agents are used to bond disparate materials into one coherent composite. Usually fibers and sometimes beads are part of the composite design.
The goal of this area of research sponsored by N.S.F., Transportation Research Board of National Academy of Science and Natural Process Design, has been to develop composites with unique toughness and strength by self repair which occurs at material interfaces and at damaged areas. This is not by the usual methods of hand repair but release of repair chemicals from within the composite itself. These take the form of hollow structural fibers or beads are embedded in the matrix, or a matrix, which reacts with the environment itself. The chemicals carried in the hollow vessels are released wherever and whenever cracking or other matrix damage occurs. In the case where the matrix repairs itself, this works most effectively if supplied all through the volume. Chemicals can be designed to react and repair more than once. Superior performance over the life of the composite is achieved by the selfrepairing and regenerating nature of the interface between the materials.
Research to assess and clarify the impact of the various factors involved in self-repair in a more scientific way has been done by Professor Dry who invented the field and holds the basic patents in the area. Repair efficacy of the various applications by other researchers covers a large data field. Due to a lack of clear understanding of the impact of the various factors as well as lack of proper design of all the factors from the start there is a large need for scientific understanding in this area. This research addressed some of these issues by quantifying, relating and explaining the impact of the various factors on each other. These factors are 1) parameter choices such as delivery vessel, shape/size, coating, chemicals released, release trigger and efficacy, impact on matrix properties 2) influence of end use such as the importance of speed of release in and the importance of damping and stiffening 3) combination with various processing methods’ heat and pressure. The objective of the paper is to explain the science issues involved in creating polymer composites designed to be self-repairing.
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