In a composite material the constituents are arranged generally with the reinforcement phase embedded in the matrix phase. Due to a composite being essentially a mixture between the reinforcement phase and the matrix there is no intermolecular bonding between the two, however, as in the case of fibrous composites, the most mechanically efficient structure is a criss-crossed fibrous lattice suspended in a material matrix. In the case of particulate composites however, the reinforcement phase acts essentially to strengthen the matrix material adding support.
Types of Composites
Composite materials are usually classified according to the type of their reinforcement phase. The two main types of composites are fibrous composites and particulate composites, which may again be divided further.
In fibrous composites the fibres acting as the reinforcement, may be either continuous or chopped, and suspended in a material matrix.
In composites in which the reinforcement phase is composed of either chopped or discontinuous fibres, the composite may have an either random or biased orientation. They may be used to make single layer composites or lamina.
In particulate composites particles are suspended in a matrix, an example of which is concrete.
These particles may be of any shape or size and may have any configuration throughout the matrix.
There are a further two subclasses to particulates, being flake and filled/skeletal.
In flake composites particles, the reinforcement phase, with large ratios of platform area to thickness are suspended in a matrix material.
In filled/skeletal composites there is a skeletal matrix filled with a second reinforcement material.
Mechanical Properties of Composites
The mechanical properties rely mostly on the ratio of the reinforcement phase to matrix material and for fibrous composites for example is strongest in the direction of the fibers. Perpendicular, or transverse, to the fibers, the matrix properties dominate because load must be transferred by the matrix to every fiber diameter. Due to a weight distribution through the material, even though one direction may dominate, it is necessary to stack layers of fibres in multiple directions, creating a laminate. The fibrous composites that have their fibres orientated in the primary load direction and enough fibres orientated to support secondary loads and to give support to the structure are the most efficient mechanically.
The high elastic modulus and strength in Table 1.1, again do not provide an insight into the mechanical properties of the composite when the fibres are suspended into a matrix. The properties of the matrix also contribute to the strength and stiffness of the material system. Since the matrix is generally much weaker and less stiff than the fiber, the composite material will not have as great a tensile strength and modulus as the fibres themselves. In addition, the properties cited in the table above refer only to...