An investigation into high flow compression molding for recycling thermoplastic discontinuous long fiber composites is presented. High flow recycled panels and conventional low flow baseline panels were produced with a large rectangular (2:1 aspect ratio) mold. Flow was induced in the recycled panels by stacking cut sections of conventionally produced baseline panels in the center of the mold cavity, representing 25% initial coverage. High flow compression molded panels were found to exhibit significantly higher than baseline tensile strength (+50%) and modulus (+31%) when tested in the direction parallel to flow. When tested in the direction perpendicular to flow, the opposite effect was found, with reductions in tensile strength (−42%) and modulus (−37%). However, when the average results of both directions are compared to baseline, no significant difference was found between the recycled and baseline panels. This severe anisotropic redistribution of mechanical properties suggests chip orientation is affected by flow. Additionally, micrographic analysis revealed that high flow molding induces intra-ply chip shearing and a reduction in resin rich regions within panels. Baseline panels also exhibited in-plane anisotropy, despite initial random distribution of chips and no or near no flow induced during molding. In this case, mechanical properties favored the direction perpendicular to that of the recycled panels.
Elastic properties in critical areas of 3 D shells made from discontinuous long fibre (DLF) composites are difficult to determine via traditional methods, due to the heterogeneity of the material and the geometry of the part. In this paper, a method is proposed to predict the local modulus of DLF composites based on a micrograph of the polished edge of a specimen. The position and orientation of each fibre are extracted from the micrograph and used in conjunction with classical lamination theory to predict the elastic modulus. Fibre discontinuity is accounted for by including a correction factor based on the Cox formula for averaged elastic constants. Model predictions successfully matched the experimental tests results. In a previous study, material flow during compression moulding of recycled DLF panels led to anisotropic behaviour, which was hypothesized to be caused by chip alignment in the flow direction. By using the proposed method, chip alignment due to flow was confirmed and the anisotropy in the elastic modulus was accurately predicted.
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