Abstract
Consolidation of thermoplastic prepregs was measured with an integrally- heated parallel platen apparatus attached to a servo-hydraulic mechanical testing machine. The apparatus was designed as a small-scale, well-instrumented press The lamination or consolidation process was viewed as a superposition of three distinctly occurring events identified as void volume reduction, fiber spreading, and autohesion. Consolidation was measured in relation to the original prepreg thickness and was reported as compressive or consolidation strain as a function of temperature. The derivative of the consolidation strain, the consolidation strain rate, was found to be qualitatively descriptive of vis coelastic phenomena occurring in the prepreg stack during consolidation. The apparatus was sensitive enough to identify glass and melt transitions of the polymer matrix, and to provide a measure of the net consolidation for a given processing cycle. The strain and the strain rate data were compared to thermoanalytical prepreg data obtained by Differential Scanning Calorimetry (DSC), and Dynamic Mechanical Analysis (DMA). Three different thermoplastic matrix composite systems were examined with this apparatus: Poly (etheretherketone) (PEEK), Poly(etherimide) (PEI), and Poly(ethylene terephthalate) (PET). Each of these materials exhibited a distinct consolidation profile. Collectively, the results generated by these diverse systems established the usefulness of this consolidation thermal analysis as a processing screening tool for thermoplastic-based composites.