This study introduces a novel predictive modelling framework for assessing the long-term behaviour of Sheet Molding Compound (SMC) composites subjected to hydrothermal ageing. The originality of this work lies in the integration of moisture diffusion, heat transfer, matrix swelling, and plasticization into a unified multi-physics model developed in COMSOL. The model accurately simulates the tensile response of SMC materials exposed to water at 25°C and 50°C, showing strong agreement with experimental data. This comprehensive approach provides new insights into the coupled ageing mechanisms and offers a reliable tool for predicting durability and guiding the design of composite components for extended service life.
