Polymer matrix composites are the most common and will be the main topic of discussion in this guide. Also known as FRP – Fiber Reinforced Polymers (or plastics), these materials use a polymer-based resin as the matrix and a variety of fibers such as glass, carbon and aramid as reinforcement. Metal matrix composites are increasingly found in the automotive industry; these materials use a metal such as aluminum as a matrix and reinforce it with fibers such as silicon carbide. There are considerable differences in published property data for metal matrix composites. This is partly because there are no industry standards for metal matrix composites, as there are for metals. Reinforcements and composites are typically made using proprietary processes and, as a result, the properties of materials having the same nominal composition can be radically different. The issue is further clouded by the fact that many reinforcements are still in development and are continually being refined. Numerous test methods are used in the industry and it is widely recognized that this is a major source of differences in reported properties. Some properties cannot be measured as in the case of monolithic metals. For example, toughness is an important but difficult to define material property. Standard fracture mechanics tests and analytical methods for metals are based on the assumption of self-similar crack extension; that is, a crack will simply stretch without changing shape. Composites, however, are non-homogeneous materials with complex internal damage patterns. As a result, the applicability of conventional fracture mechanics to metal matrix composites is controversial, particularly for fiber-reinforced... middle of paper... metal-reinforced materials which may be important in some applications. Composite materials are materials made up of two or more constituent materials with significantly different physical or chemical properties, which when combined produce a material with different characteristics than the individual components. It can be divided into several types. We are focusing on polymer matrix composites and metal matrix composites. Polymer matrix Composite is a composite material made of a polymer resin. They are not as strong or heat resistant as metal matrix and ceramic matrix composites. Besides that, metal matrix composite is a composite material with at least two constituent parts, one is a metal and the other material can be a different metal or another material. Polymer matrix composite is the most commonly used composite as it is a monolithic polymer whose process is simpler.