Characterization of multi-physics aging effects on the thermomechanical viscoelastic response of ultra high molecular weight polyethylene fiber reinforced composites

Abstract

Ultra High Molecular Weight Polyethylene (UHMWPE) fiber reinforced composites have a high strength-to-weight ratio and are gaining attention as a material of choice for specialized applications subjected to extreme environmental conditions. Users value the water-repellent, lightweight, and flexible nature of the material for applications where weight is crucial. Marine, aerospace, and alternative energy sectors are exploring UHMWPE fiber reinforced composites for specialized applications in demanding environments where strength, flexibility, and weight efficiency are important design criteria. The viscoelastic and hydrophobic nature of UHMWPE makes it an attractive replacement for Kevlar® in ballistics protection shields and other industrial applications, providing similar performance while achieving upwards of 40% reduction in weight. However, the durability of UHMWPE composites under real-world aging conditions remains insufficiently examined. This research investigates how the viscoelastic properties of UHMWPE fiber reinforced composites, created through various manufacturing techniques, are altered after exposure to harsh conditions including immersion in water, temperature variations, humidity, and UV exposure. Additionally, the composites were irradiated with: X-rays, gamma-rays, and neutrons. After exposure to adverse environments, the thermomechanical viscoelastic response was characterized through Dynamic Mechanical Analysis (DMA). Surface morphology was evaluated using a field emission scanning electron microscope. DMA revealed an increase in the storage modulus with aging; however, elevated temperature creep tests showed that UV and hygrothermal aging had a higher creep compliance and decreased the ability of the composite to recover strain after unloading. Both single layer and pressed UHMWPE panels showed an increase in weight after submersion in water. Distilled water resulted in a faster rate of hydrolysis in the matrix than did salt water. The UV, gamma-ray, and neutron environments caused the composites to become brittle and yellow through chain scission and crosslinking, whereas the X-ray radiation exposure did not cause a measurable effect. Analysis on the surface of these composites after aging suggested the matrix protects these fibers from damage in harsh environments. Synthetic rubber matrix materials aged at a faster rate than the polyurethane rubber matrix materials. Increasing the strain rate showed an increase in moduli response during tensile DMA. These results quantify the limitations and strengths of this material for future models to accurately predict the lifespan and expand the application of this performance material in extreme environments to ensure safety for applications ranging from extreme sports to aerospace.