Analytical, Numerical and Experimental Analysis of the Creep Behaviour of Polyethylene Polymers

Polyethylene (PE) is a semi-crystalline polymer that has been used for decades in many different applications. Two commonly used forms of PE are high-density polyethylene (HDPE) and ultra-high molecular weight polyethylene (UHMWPE). Since the material is used in various industrial applications, ranging from prosthetic joints to rotational moulded tanks, the need to understand its mechanical behaviour under different loading scenarios is of high importance. Creep is a particularly important mechanical property for polymers due to their relaxation characteristics associated with prolonged loading of the polymers' chains. As such, understanding the creep behaviour of PE products is very important for its long-term performance. In the present investigation, experimental testing, analytical analysis and numerical modelling using the finite element (FE) method have been conducted on HDPE and UHMWPE samples subjected to tensile load, step-loaded creep, short-term creep, and long-term creep. Boltzmann superposition principle was utilised to predict the long-term creep behaviour using short-term creep test results. The adopted stress relaxation models, using Maxwell elements, successfully captured the experimental viscoelastic and viscoplastic response of PE. A parametric investigation was conducted using ABAQUS FE software to obtain the optimum Prony series components that can accurately simulate the creep behaviour under constant and stepped-loading scenarios. The results showed great agreement between the experimental, analytical and numerical methods. The developed FE models can be used to predict the serviceability of PE products after prolonged exposure to constant loading cases.