Mechanical response of 45 angle-ply CFRP plates under low-velocity impact and quasi-static indentation: Influence of the multidirectional strain state

This work studies the relation of the strain fields, final failure patterns and the apparent flexural modulus in CFRP laminates subjected to quasi-static indentation (QSI) with the in-plane mutiaxial loading state produced. QSI tests could be utilised for evaluating the degradation process in composites under low-velocity impacts (LVI) whenever analogous damage initiation and propagation are expected. Then, the research is focused on the LVI and QSI response of [+/- 45](4S) squared-plates simply-supported in a circular steel window. Similar levels of internal energy are found in the most notable events during the loading process, what supports the comparable final failure patterns observed. Nevertheless angle-ply laminates under LVI present non-negligible higher levels of apparent rigidity, opening the possibility of a certain efferct of the strain rate on the impact response. Besides, [0 90](4S) configurations are taken into consideration for reviewing the effect on the results of the stacking sequence out of the simply-supported region. A strong influence on the internal energy is found, being 41.7% higher in angle-ply than in cross-ply laminates. The analytical estimation of the multiaxial apparent linear response of the laminate combined with the measured strains are utilised for the qualitative description of the experimental final failure modes. The deformation fields in QSI testing are acquired by Digital Image Correlation techniques and strain gauges, completing the analysis with the results of a finite element approach. The variation of the apparent flexural modulus with the in-plane loading direction leads to non-simetrical strain fields and lower out-of-plane displacements in the stiffer direction.