EFFECTS OF CONSOLIDATION PROCESS ON THE TENSILE STRENGTH OF UHMWPE FILAMENTS EXTRACTED FROM COMPOSITE PANELS

Abstract

This research focuses on the investigation of damage mechanisms induced through the processing and consolidation of UHMWPE composites (HB210). The HB210 composites consist of Dyneema® fibers and thermoplastic polyurethane resin. The composite panel consisting of 72 sheets was processed following the manufacturer’s recommended temperature and pressure profile of 100°C and 2 MPa (290 psi) for 10 minutes, followed by 125°C and 20.7MPa (3ksi) for 30 minutes. Each sheet consists of 0/90/0/90 ply orientation with an average sheet thickness of 200 μm. To quantify the effects of consolidation pressure on fiber deformation and tensile strength distribution, a technique for extracting fibers from the processed panels was developed. Specimens (11 x 19 x 152 mm) were cut from the panel and immersed in tetrahydrafuran (THF) fluid for 7-20 days (dependent on the specimen thickness). The THF effectively dissolved the matrix enabling UHMWPE fibers to be extracted at different locations through the thickness. The baseline tensile strength distribution was based on testing virgin fibers from the spool and fibers extracted using the THF method from a single as-received layer of HB210. The two baselines exhibited statistically equivalent tensile strength distributions proving the THF extraction method did not affect the fiber properties and that degradation of tensile strength is a result of the consolidation process. From tensile test data, strength distributions for extracted fibers from consolidated panel were generated, and strength at 50% failure probability was evaluated. Compared to the baseline, the fibers extracted from the processed panel showed a 15% reduction in the average tensile strength. SEM microscopy of the extracted fibers from the consolidated panel exhibits different damage modes. Surface cracking and flattening damage modes were induced by the consolidation pressure (20.7 MPa) applied in the thickness direction of the panel. Additionally, axial kinking was observed along the length of the fibers. The possible mechanisms for the formation of these kinks are – viscous forces from the resin during the consolidation process, where fibers loaded in compression are observed to kink into large voids between fibers, or due to the CTE mismatch between the fibers and the resin within a layer or between the 0 and 90 layers within a sheet during the cooling stage.