Definition
Composite Matereals (or composites for short) are engineered materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct on a macroscopic level within the finished structure.
About
Years ago the most primitive composite materials were straw and mud combined to form bricks for building construction. In modern times The most advanced examples perform routinely on (but are in no way limited to) marine and aviation in demanding environments. The most visible applications we see in the marine industry is the hull, deck and mast.
Matrix and Reinforcement
There are two categories of constituent materials: matrix and reinforcement. At least one portion of each type is required. The matrix material surrounds and supports the reinforcement materials by maintaining their relative positions. The reinforcements impart their special mechanical and physical properties to enhance the matrix properties. A synergism produces material properties unavailable from the individual constituent materials, while the wide variety of matrix and strengthening materials allows the designer of the vessel to choose an optimum combination. Engineered composite materials must be formed to shape. The matrix material can be introduced to the reinforcement before or after the reinforcement material is placed into the mold cavity or onto the mold surface. The matrix material experiences a melding event, after which the part shape is essentially set. Depending upon the nature of the matrix material, this melding event can occur in various ways such as chemical polymerization or solidification from the melted state.
Molding methods
A variety of molding methods can be used according to the end-item design requirements. The principal factors impacting the methodology are the natures of the chosen matrix and reinforcement materials. Most commercially produced composites use a polymer matrix material often called a resin solution. There are many different polymers available depending upon the starting raw ingredients. There are several broad categories, each with numerous variations. The most common are known as polyester, vynalester, epoxy, phenolic, polymide, polypropelene and others. The reinforcement materials are often fibers known as fiiberglass, carbon fiber, kevlar and others. The various methods described below have been developed to reduce the resin content of the final product, or the fibre content is increased. As a rule of thumb hand lay up results in a product containing 60% resin and 40% fibre, whereas vacuum infusion gives a final product with 40% resin and 60% fibre content. The strength of the product is greatly dependent on this ratio.
There are many different types of molding methods are available. Some of which are: Hand lay up, Vacuum bag molding, infusion, Pressure bag, RTM(Resin Transfer Molding), Autoclave, Filament winding and Compression.
Mark Ashton AMS
