Influence of Temperature Profile on Crack Evolution in Constrained Thermoset Matrix Curing

ABSTRACT This study investigates the crack evolution in the epoxy matrix under constrained curing conditions. Epoxy resin was cured in a glass tube to simulate the strong constrained conditions encountered in composite manufacturing. A novel in situ imaging monitoring system was developed to identify the cracking process under three different two‐step temperature profiles. The tests revealed, for the first time, a dynamic ‘cracking‐closure‐cracking’ phenomenon during curing, with crack initiation consistently occurring at the first dwell stage with a critical cure degree of 70%. Quantitative analysis demonstrated the process‐dependent nature of cure‐induced cracking. A coupled thermal‐chemical–mechanical model was established to elucidate the relationship between free shrinkage and cure cracking. The results showed that thermal expansion during the second heating stage can effectively compensate for the chemical shrinkage and then reduce cracks by over 80%. Based on the findings, an optimized curing strategy featuring “low‐temperature dwelling and high Δ T heating” was proposed for the industrial two‐step curing profile to limit curing‐induced cracking. This work provides both fundamental insights and practical solutions for mitigating cracks in constrained thermoset composites.