Characterization of damage in non-crimp fabric glass fiber-reinforced reactive thermoplastic composites at low temperature using an in-situ digital imaging technique

An in-situ digital imaging technique was developed to characterize damage in non-crimp fabric glass fiber/reactive thermoplastic cross-ply laminates subjected to tensile loading at −50 °C. A custom algorithm was developed to automatically detect the initiation and growth of 90° tow cracks, matrix cracks, and 0° tow cracks through image stacking, shift-correction, and thresholding. The laminates exhibited four stages of deformation/damage, including linear elastic, onset/growth of 90° fiber tow cracks, onset/growth of 0° fiber tow cracks, and progressive failure of 0° fiber tows. Although at low temperature the effective laminate strength and stiffness increased by 4 % and 13 %, respectively, damage initiated sooner and propagated at a higher rate leading to a 60 % increase in crack density at saturation. The digital imaging technique proved to effectively detect local damage in the glass fiber/thermoplastic laminates, which led to a deeper understanding of their low-temperature deformation response, damage characteristics, and damage tolerance.