The mechanical properties of extruded shapes may differ from the values published by resin producers. The difference is most pronounced for reinforced grades as fiber orientation is highly influenced by processing.
Published resin data is always generated from injection molded test specimens processed under ideal conditions and is suitable for comparing different resin grades. In practice the actual properties of molded parts are influenced by gating, part geometry and material flow within the mold cavity. They rarely approach the values published within resin datasheets.
MCAM’s mechanical property values are generated using specimens machined from extruded, compression molded, cast or injection molded shapes.
The size and shape being processed influence fiber orientation as well as crystallinity, all of which may impact the mechanical properties. Additionally machining operations influence the surface finish of test specimens vs the surface finish imparted from a highly polished mold cavity when resins are tested. For example hand polished tensile specimens test higher than rough machined specimens. In the case of some cured materials like Duratron® PAI, the lack of cured surfaces on machined specimens may influence strength and stiffness values.
In summary the properties of most reinforced plastics should be thought of as being anisotropic meaning there may be directionality in certain properties including strength, stiffness and coefficient of linear thermal expansion. Most of the figures given for the mechanical properties are average values of tests run on dry test specimens machined out of rods 40-50 mm (1.5 - 2") when available, else out of plate 10-20mm (0.4 - 0.8"). Samples are taken in the direction of extrusion. The values presented are not intended to be used for specification minimums. They are provided for material comparison purposes and engineering/design estimates.
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