Numerical modelling of the damage modes in UD thin carbon/glass hybrid laminates - Sensitivity analysis

Hybridization is one of the approaches in the HiPerDuCT programme that aims to create pseudo-ductile composites. In a recently published work [1], different combinations of unidirectional (UD) thin carbon and standard thickness glass prepreg have been tested and three different damage modes have been observed experimentally: (i) multiple cracks within the carbon ply, (ii) delamination and (iii) glass fibre failure. A new numerical approach has been proposed to take all of the possible damage modes of UD hybrids into account [2].To capture multiple discrete carbon failures over the length of the hybrid specimen, cohesive element rows have been placed periodically between carbon quadrilateral elements, and to avoid simultaneous damage initiation, a random distribution of cohesive strengths is applied. For delamination, a row of cohesive elements is placed at the carbon/glass interface. In this work, two different bilinear and tri-linear cohesive laws with the same toughness and strength are applied to the interface. The final failure load which depends on the glass fibre failure is predicted by integrating the stress distribution to calculate an equivalent stress for unit volume of the glass layers. The obtained results show that although delamination initiation and propagation is only dependent on the toughness of the interface and not the shape of the cohesive constitutive law, the glass failure depends not only on interface toughness but also its shape. Comparing the predicted final failure results of both of the cohesive laws with the experimental results, the bilinear cohesive law is found more compatible than the tri-linear one.