Nondestructive method for determining residual stresses in polymers and composites

The object of research was a polymer material (a hot-cured epoxy compound with an anhydride hardener), in which it was necessary to determine the level of residual stresses without damaging the integrity of the product. The goal was to develop and experimentally test a new nondestructive method for determining residual stresses that would reduce the complexity of assessing the stress state in real structures and prevent their damage. The proposed method is based on locally heating a section of the structure above the glass transition temperature, which temporarily brings the material into a highly elastic state and relieves internal stresses in the specified area. A strain gauge is used as the measuring instrument, recording changes in deformation before and after heating. This approach makes it possible to determine the level of residual stresses without mechanically removing material, while the localized heating and the presence of a cooling system ensure controlled experimental conditions. Results of experimental studies on samples made of the epoxy polymer confirmed the method’s effectiveness. Strain gauge readings recorded changes in deformation corresponding to the partial release of residual stresses after localized heating. The obtained data demonstrated the reproducibility of the results and the potential of this method for evaluating residual stresses in polymer composites, including large-scale and in-service structures.

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