Viscoplastic Strain Rate Sensitivity Optimization for Short Glass Reinforced Components
Dynamic viscoplastic yield in short glass components depends on screw-retained fiber length and gate-driven orientation tensors under high strain rates.
Fiber Attrition
Meaning
Physical degradation of reinforcing filaments during the compounding or injection moulding process leads to a reduction in the average length of the reinforcement. High shear forces within the screw and barrel of the machine cause fiber attrition as the polymer melt moves through narrow gates and runners. This phenomenon is a primary reason why the mechanical properties of a part often fall below the values stated on the material datasheet.
Processing Shear
Friction between the screw flights and the barrel wall breaks the glass or carbon fibers as the resin melts. Lowering the screw speed or increasing the melt temperature can reduce the intensity of fiber attrition by lowering the viscosity of the carrier resin. Every transition in the flow path, such as a sharp turn or a restrictive nozzle, contributes to further breakage.
Mechanical Limitation
Reinforcement efficiency drops sharply when the length of the fibers falls below a critical threshold. Short fibers provide less surface area for stress transfer between the polymer matrix and the reinforcement, which reduces the tensile modulus and impact strength of the component. Capacity fails.
The fiber attrition also affects the way the part fails under load.
Recycle Value
Economics of using regrind material are constrained by the cumulative damage to the reinforcement. Each time a glass filled material passes through the moulding process, the fiber attrition continues, eventually turning the reinforcement into a simple filler with no measurable structural benefit. Moulders typically limit the regrind percentage to preserve the minimum fiber length required for the application.
Managing this balance ensures the cost savings do not come at the expense of part performance.