Characterization of the Microstructure of Thermoplastic Composites
Abstract: Thermoplastic composites (TPCs) are gaining worldwide recognition as viable replacements for traditional materials in a wide variety of applications such as automotive, aerospace, and defense. This is due to their superior strength-to-weight ratios compared to light-weight metallic alloys. Consequently, thermoplastic composites are increasingly being used to make not only small parts such as brackets for airplanes but also large, safety-critical structures such as landing gears and fuselage panels. Unlike thermoset composites which require curing time for polymerization, thermoplastic composites do not require the curing step after consolidation. In the manufacture of thermoplastic components, the polymer is simply heated, formed into shape, consolidated and cooled.
Despite this ease of manufacture, a variety of discontinuities and defects such as fiber misorientation and wrinkling, ply misalignment, porosity and voids, delamination between fibers and matrix, can occur. Accurate characterization of these microstructural defects is of critical importance to achieving the desired properties for optimal performance. While nondestructive testing techniques can be used for the macro-inspection of the parts, they do not offer adequate insight into processing-microstructure-property-performance relationships needed for property-performance optimization. Such information is best obtained using metallographic techniques. This presentation discusses metallographic sample preparation and optical microscopy examination techniques used to obtain qualitative information such as fiber distribution and orientation, occurrence of porosity or voids, delamination, etc. that can be leveraged for optimal manufacture of thermoplastic composite parts.