Breaking Boundaries: Pioneering Residual Stress Characterization in Polymer Composites through the Contour Method

Digital twin technology is transforming composite manufacturing by enabling optimized product design and total stress analysis to enhance structural integrity. Despite these advancements, accurately validating residual stresses in numerical models remains a major challenge. Residual stresses arise during the curing process due to the mismatch in thermal expansion and chemical shrinkage between the fibre and matrix materials. These internal stresses can critically affect structural performance—as seen in the failure of NASA’s X-33 program, which was linked to unaccounted residual stresses. While analytical models can predict such stresses, they are computationally intensive and depend heavily on cure- and temperature-dependent physio-chemo-rheological properties. Furthermore, the experimental characterization of bulk residual stress in polymer composites remains unresolved, with no standardized method currently available.

In this study, various experimental and numerical methods of characterising residual stress in polymer composites are reviewed and compared with each other. Traditional destructive approaches, such as hole drilling and ring core suffer from limitations in resolution. Similarly, non-destructive methods like photoelasticity, Raman spectroscopy, fiber optic sensors, and diffraction-based methods possess their own drawbacks. The contour method, widely used in metallic structures, has yet to prove effective in the context of polymer composites. This research underscores the necessity for more robust and precise techniques to assess and mitigate residual stresses in these materials. Here we present a novel approach for evaluating two-dimensional through-thickness residual stress in carbon fiber-reinforced polymer composites. This evaluation is conducted using the contour, slitting method, a numerical model, and an analytical-based classical laminate theory. Importantly, this research marks the pioneering application of the contour method in polymer composites and assesses the stress profile using both analytical and numerical methods.

Keywords: Residual Stress, Carbon Fibre Polymer Composites, Simulation, Contour Method