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Braided composite laminates allow a reinforcement architecture design method of varying ply-to-ply braided structure instead of rotating fiber orientation in traditional unidirectional laminates. The stacking sequence sensitivities of braided laminates subjected to low-velocity impact were experimentally studied. Uniform ([±45° 6 ]) and non-uniform ([±30° 2 /±45° 2 /±60° 2 ]) architectures were designed to evaluate the effect of braided structure on impact performance. In addition, non-uniform laminate was impacted on both sides to identify the role of impact side on the failure mode. Quasi-static indentation was conducted to understand the damage initiation and propagation of braided laminates. The experimental results show that braided ply with high crimp level in impact side induced the main cracks along the load-carrying yarn, causing that the laminate failed in a kink-band dominated mode. For braided ply with low crimp level, a micro-buckling damage was found in the impact side, leading to the delamination dominated failure mode. It was also found that uniform braided laminate presents inferior impact resistance with respect to lower peak load and more concentrated damage because the kink-band can propagate into the specimen along braiding yarn easily. [ABSTRACT FROM AUTHOR]

The aim of this study is to characterize and assess the effect of fabric structure on the damage resistance subjected to low velocity impact. Composite panels reinforced by layered unidirectional (LU), layered woven (LW) and 3D orthogonal woven (OW) fabric were prepared respectively and the impact tests were carried out on a low-velocity testbench. Finite element models at yarn-level were established to numerically investigate the material deformation and failure mechanism. The impact tests showed that the OW composite possessed better impact resistance with respect to impact-induced deformation and inelastic energy absorption. The roles of the z-binder have also been identified through comparison of impacted morphology and numerical results. The z-binder serves as cracking trigger due to the weak debonding with resin pocket around it and its zig-zag configuration impedes the growth of delamination by damage deflection. Therefore, the discontinuous resin damage in 3D composite allows the enhancement of impact resistance instead of delamination failure in the 2D panel. In addition, the in-plane interlacement of woven fabric causes that primary yarn breaks in the high stress region and forms a circle damage area, whereas the penetrating cracking along the fiber orientation of superficial layer is induced in the unidirectional composite. [ABSTRACT FROM AUTHOR]