On the Injection Molding of Long Glass Fiber Filled Thermoplastic Test Specimens

The mechanical properties of test specimens used for material characterization are in fact strongly dependent on factors such as conditions of the molding process, preparation of test specimen and test conditions. There are well-established international standards for material testing available. Even the tests adhering to these standards were seem to have issues with regard to consistency of results particularly for long glass fiber filled thermoplastic test specimens. In injection molding of long glass fiber filled thermoplastic specimen, the flow of molten polymer may influence the orientation of fibers, resulting in anisotropy. The presence of residual stresses in the molded test specimen and thermal degradation of the polymer melt may also influence the test results. Exact definition of each of the main parameter of the molding process and consistent test procedures are the basic requirements for reproducible material data. This enables the design engineers to construct appropriate material models for finite element analysis to be able to accurately predict the part performance. This paper describes the influence of the molding and test conditions on the material characterization of long glass fiber filled thermoplastics.