Effect of Fiber Type on the Thermomechanical Performance of High-Density Polyethylene (HDPE) Composites with Continuous Reinforcement

The thermal, thermomechanical, and viscoelastic properties of continuous unidirectional (UD) glass fiber/high-density polyethylene (GF/HDPE) and ultra-high molecular weight polyethylene/high-density polyethylene (UHMWPE/HDPE) tapes were systematically characterized to support their use in extreme environments. Unlike prior studies focusing on short-fiber composites or limited thermal conditions, this work examines continuous fiber architectures under five operational environments derived from Army Regulation 70-38, reflecting realistic defense-relevant extremes. Differential scanning calorimetry (DSC) identified melting transitions,127.8 ± 0.2 °C for GF/HDPE and 128.3 ± 0.2 °C for UHMWPE/HDPE, that guided the selection of test conditions for thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA). TMA revealed anisotropic thermal expansion consistent with fiber orientation, while DMA, via temperature ramp, frequency sweep, and stress relaxation, quantified the temperature- and time-dependent viscoelastic behavior. The frequency-dependent storage modulus highlighted multiple resonant modes, and stress relaxation data fitted with high accuracy (R² > 0.99) to viscoelastic models, offering parameters for predictive modeling. By integrating thermal and viscoelastic characterization across realistic operational profiles, this study provides a foundational dataset for the application of continuous fiber thermoplastic tapes in structural components exposed to harsh thermal and mechanical conditions.