Analytical investigation of self-heating phenomenon of polymers considering frequency, liquid ageing and molecular-chain motion

The article explores the critical self-heating phenomenon in polymers subjected to cyclic loading, a key concern for industries aiming to reduce structural weight and enhance sustainability. It introduces a novel predictive model that considers the frequency of loading, liquid ageing, and molecular-chain motion, providing a more accurate estimation of temperature rise in thermoplastics. The study highlights the importance of understanding the mechanical behavior of short fibre-reinforced thermoplastics, especially in high-temperature and humid environments. The proposed 1D model, validated through experimental data, offers insights into the fatigue behavior of materials like PA6.6, widely used in automotive applications. The research delves into the thermodynamic framework, incorporating the Helmholtz free energy and Clausius–Duhem inequality to model the viscoelastic dissipation and molecular-chain damage. It also discusses the influence of water absorption on the mechanical properties and the self-heating phenomenon, providing a detailed analysis of the microstructural changes induced by liquid ageing. The article concludes with a comparative study of the internal damage evolution and suggests future improvements, such as considering diffusion and desorption gradients, to refine the predictive capabilities of the model.