Fiber reinforced composites (FRCs) consist of two or more components: a matrix and a reinforcement. The matrix is usually a polymer, metal, or ceramic that binds the reinforcement together and shields it from environmental damage. The reinforcement is typically a fiber — carbon, glass, or aramid — that gives the composite its strength and stiffness.
Manufacturing FRCs breaks down into four main steps: fiber preparation, matrix preparation, fiber impregnation, and composite consolidation.
Fiber preparation
This step involves selecting the fiber type, form, and orientation used in the composite. Fiber type shapes the composite’s mechanical and thermal properties — tensile strength, modulus, coefficient of thermal expansion. Fiber form can be continuous or discontinuous, depending on the composite’s desired shape and size. Fiber orientation can be unidirectional, bidirectional, or multidirectional, depending on loading conditions and design requirements.
Matrix preparation
This step involves selecting the matrix type and form used in the composite. Matrix type affects chemical and physical properties — corrosion resistance, density, melting point. Matrix form can be liquid or solid, depending on the processing method and curing conditions. Liquid matrices are usually thermosetting polymers requiring heat or chemical agents to cure and harden; solid matrices are usually thermoplastic polymers or metals requiring heat and pressure to melt and flow.
Fiber impregnation
This step combines the fibers and matrix into a preform or a prepreg. A preform is a semi-finished product with the final composite’s shape and dimensions but not yet cured or consolidated. A prepreg is a pre-impregnated fiber that’s partially cured or stabilized and can be stored for later use. Methods for impregnating fibers with matrices include hand lay-up, spray lay-up, filament winding, pultrusion, resin transfer molding, vacuum infusion, autoclave molding, compression molding, injection molding, and stamp forming.
Composite consolidation
This final step applies heat and pressure to the preform or prepreg, curing and bonding the fibers and matrix into a solid composite. Curing involves chemical reactions that cross-link the matrix’s molecules into a rigid network; bonding involves physical interactions that adhere fibers and matrix together. This consolidation process shapes the composite’s quality and performance — void content, resin distribution, fiber volume fraction, interfacial strength, and residual stress.