MMC-Characteristics of Composite Materials

The constituents of a composite are generally arranged so that one or more discontinuous phases are embedded in a continuous phase. The discontinuous phase is termed the reinforcement and the continuous phase is the matrix. In general the reinforcements are much stronger and stiffer than the matrix. The physical and mechanical properties of composites are dependent on the properties, geometry and concentration of these constituents. Increasing the volume content of reinforcements can increase the strength and stiffness of a composite to a point. If the volume content of reinforcements is too high there will not be enough matrix to keep them separate and they can be entangled. Similarly, the geometry of individual reinforcements and its arrangement within the matrix can affect the performance of a composite. There are many factors to be considered when working with composite materials. The type of reinforcement and matrix, the geometrical arrangement and volume fraction of each constituent, the anticipated mechanical loads, the operating environment for the composite, etc., must all be taken into

account.

Analysis of composites subjected to various mechanical and thermal conditions is the main thrust of this work. The constitutive relationship between stress and strain is established for homogeneous isotropic materials as Hooke's law. A composite material is analyzed in a similar manner by establishing a constitutive relationship between stress and strain. Isotropic, homogeneous materials (steel, aluminum, etc.) are assumed to be uniform throughout and have the same elastic properties in all the directions. Assuming a unit width and thickness for the specimen, the transverse in-plane and out-of-plane displacements are the same for these materials. Unlike these conventional engineering materials, a composite material is generally non-homogeneous and does not behave as an isotropic material. Most composites behave as anisotropic. There is typically a coupling of extension and shear deformation under conditions of uniaxial tension. There are varying degrees of anisotropic material behavior and the actual deformation resulting from applied loads depends on the nature of material.