A phenomenological study of the mechanical properties of long-fiber filledinjection-molded thermoplastic composites

Tensile and flexural tests on specimens cut from rectangular injection-mold ed plaques show that long-fiber filled thermoplastic composites are complex , nonhomogeneous, anisotropic material systems. Like all fiber-filled mater ials, they exhibit through-thickness nonhomogeneity as indicated by differe nces between tensile and flexural properties. The in-plane orientation of f ibers in through-thiekness layers causes the material to have in-plane anis otropic properties. However, these long-fiber filled materials exhibit an u nexpectedly large level of in-plane nonhomogeneity. Also, the effective mec hanical properties of these materials are strongly thickness dependent. The thinnest plaques exhibit the largest differences between the flow and cros s-flow tensile properties. These differences decrease with increasing thick ness. A methodology for part design with this class of materials is discuss ed.