Meaning
Composite material composition defines the ratio of reinforcing fiber volume to the total volume of the composite structure. This ratio is expressed as the fiber volume fraction, which determines the mechanical performance and stiffness of the moulded component. Higher values increase the load-bearing capacity but make the composite more difficult to process due to reduced resin flow.
Strength Determination
Mechanical properties like tensile modulus and ultimate strength depend directly on the amount of fiber reinforcement present. A high fiber volume fraction improves structural performance but can lead to dry spots where the polymer fails to wet out the fibers completely. Incomplete wetting represents a critical limit in composite manufacturing.
Processing Limitation
Resin viscosity and infusion pressure restrict the maximum amount of fiber that can be incorporated into a tool. When the fiber volume fraction is too high, the flow resistance rises, causing incomplete cavity filling and part defects. Moulders must balance the structural requirements of the design with the flow limits of the resin.
In many automotive applications, a value between thirty and fifty percent provides the best trade-off.
Defect Prevention
Void formation and resin-rich regions occur when the flow of the polymer matrix through the fiber bed is non-uniform. Maintaining the correct fiber volume fraction ensures that the resin penetrates all gaps between fibers during the moulding process. Proper reinforcement distribution prevents mechanical failures under fatigue loads.
