Particulate reinforced composite system

Particle reinforced composite systems can be either large particle or dispersion strengthened. If a composite is reinforced by large particles (larger than 0.1 [xm and equiaxed, which are harder and stiffer than the matrix), mechanical properties are dependent on volume fractions of both components and are enhanced by increase of particulate content. Concrete is a common large particle strengthened composite where both matrix and particulate phases are ceramic materials. 

Large particle reinforced composite systems are utilised with all three types of materials (metals, ceramics and polymers). Concrete is a common large particle strengthened composite where both matrix and particulate phases are ceramic materials. 

Unlike fibre- or whisker-reinforced composites, particulate composites have the advantage of being compatible with conventional powder processing, and in many cases can be pressurelessly sintered. As with other ceramic microstructures, a myriad of other ingenious fabrication routes have also been reported, but these are too numerous and system-specific to describe here. This section merely outlines the main points of powder processing where the production of composites in chemically compatible systems (i.e. those in which the components do not react chemically with one another) differs from that of monolithic ceramics. 

It was mentioned above that the simulation method of Termonia [67-72] can be used to calculate the stress-strain curves of many fiber-reinforced or particulate-filled composites up to fracture, including the effects of fiber-matrix adhesion. Such systems are morphologically far more complex than adhesive joints. Many matrix-filler interfaces are dispersed throughout a composite specimen, while an adhesive joint has only the two interfaces (between each of the bottom and top metal plates and the glue layer). If one considers also the fact that there will often he a distribution of filler-matrix interface strengths in a composite, it can be seen that the failure mechanism can become quite complex. It may even involve a complex superposition of adhesive failure at some filler-matrix interfaces and cohesive failure in the bulk of the matrix. 

UPE resins can be used as clear castings or in combination with particulate fillers or fibres. The resin was developed to meet the demand of lightweight materials in military application. The first functional use of UPE was in radome. Because of the obvious advantages of easy processability and low cost, it was used in a wide range of applications in civil sectors such as tanks, pipes, and electronic gears. Some of the important products based on cast UPE resins are encapsulation of electronic assembly, buttons, door handles, knives, umbrellas, industrial wood and furniture finishing. A filled resin system using limestone, silica, and china clay are used for floor tiles. The major use of UPE is as a matrix for fibre-reinforced composites. Such composites have wide applications in automobile and construction industries such as boats, water-skis and television antennae. Examples of applications of UPE resins are presented in Table 2.7. 

Even in the apparently linear range, the response to stress should be considered as viscoelastic rather than elastic. Most polymers that behave in a linear, viscoelastic manner at small strains (< 1 %) behave in a nonlinear fashion at strains of the order of 1 % or more. However, in a fibrous composite, the resin may behave quite differently than it would in bulk. Stress and strain concentrations may exceed the limiting values for linearity in localized regions. Thus the composite may exhibit nonlinearity (Ashton, 1969 Trachte and DiBenedetto, 1968), as is the case with particulate-filled polymers (Section 12.1.2). Although nonlinearity at low strains is characteristic, Halpin and Pagano (1969) have predicted constitutive relations for isotropic linear viscoelastic systems, and verified their prediction using specimens of fiber-reinforced rubbers. 

The main fields of application of particulate filled polymers is shown in Figure 2. As was mentioned earlier, the major benefit of the application of fillers and reinforcement is increased stiffness and HDT. Specific applications which must be mentioned here are garden furniture (CaC03), air-filter covers, heater boxes (talc) for cars, washing machine soap dispensers (talc), etc. Bumpers are usually made from multi-component PP systems containing a PP homo- or copolymer, an elastomer and a filler. In order to demonstrate the usual property range of particulate filled polymers. Table 1 presents the most important characteristics of several commercial grade PP composites. 

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