designing damage tolerant structure, the interaction of fibres and matrix is very important. The defects in a composite material rely strongly on the physical and thermal characteristics such as viscosity, melting point and curing temperature of matrix. Additional functions of a matrix are as follows [1]:
To retain the fibres in place in the structure
Help distribute or transfer load
Shield the filaments, both in structure and before fabrication
Control the electrical and chemical properties
Transfer inter laminar shear
Polymers, metals and ceramics are all normally used as matrix material in continuous fibre composites. Polymeric matrix is divided into thermoplastic and thermosets. The thermoplastics soften upon heating and can be reshaped with heat and pressure. Thermoplastic polymers used for composite manufacturing include polypropylene, polyvinyl chloride, nylon, poly urethane, poly-ether-ether-ketone (PEEK), polyphenylene sulphide (PPS), and polysulfone. The thermoplastic composites offer the potential for higher toughness and high-volume, low-cost processing. They have a suitable temperature range upwards of 2250C (4370F) [8].
In the case of thermoset polymers, they become cross linked during fabrication and do not soften upon reheating. The most commonly used thermoset polymer material is polyester, epoxides, and polyamides. Polyesters are widely used with glass fibres. They are inexpensive, are lightweight, have a useful temperature range up to 1000C (2120F) and are somewhat resistant to environmental exposures. Epoxies are more expensive but have better moisture resistance and lower shrinkage on curing. Difficulties with the use of polymer matrix materials are the limited use temperature range, vulnerability to environmental degradation due to moisture, radiation, and atomic oxygen, low transverse strength, and high residual stresses due to the large mismatch in coefficients of thermal expansion between fibre and matrix [8].
2.2复合材料的制造-2.2 Manufacturing of Composites
There are a variety of fabrication methods for composite materials. The selection of a manufacturing process depends on the constituent material in the composite, with the matrix material being the main key constituent [17]. The main fabrication methods for the composite materials are explained below briefly.
2.2.1 Ordinary Hand Lay-Up
In hand lay-up techniques, a smooth flat surface such as a sheet of thick plate glass or a metal panel is coated with parting agent. The parting agents are such materials as release wax or Teflon based aerosol spray. After the application of the release agent, an optional gel coat is applied. The gel coat is a specially formulated resin that is entitled to give high resistance to moisture, good impact and weathering properties and in most cases, the colour to the surface of the finished composite. After the application of the gel coat, the first layer of catalysed resin is applied by brush, spray or simply by flooding on a small pool which is pressed thinner and wider by squeegee. A layer of cloth or mat is placed over the resin, and the resin is absorbed by the fibres. A second layer of resin and a second layer of reinforcement are applied in the same way. The procedure is repeated with alternate layers of resin and fibre until the desired thickness is
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