A numerical study on the influence of strain rate in finite-discrete element simulation of the perforation behaviour of woven composites

Predicting the perforation limit of composite laminates is an important design aspect and is a complex task due to the multi-mode failure mechanism and complex material constitutive behaviour required. This requires high-fidelity numerical models for a better understanding of the physics of the perforation event. This work presents a numerical study on the perforation behaviour of a satin-weave S2-glass/epoxy composite subjected to low-velocity impact. A novel strain-rate-dependent finite-discrete element model (FDEM) is presented and validated by comparison with experimental data for impacts at several energies higher and lower than their perforation limit. The strain rate sensitivity was included in the model by developing a novel user-defined material model, which had a rate-dependent bilinear traction separation cohesive behaviour, implemented using a VUSDFLD subroutine in Abaqus/Explicit. The capability of the model in predicting the perforation limit of the composite was investigated by developing rate-sensitive and insensitive models. The results showed that taking the strain rate into account leads to more accurate predictions of the perforation limit and damage morphology of the laminate subjected to impacts at different energies. The experimental penetration threshold of 89 J was estimated as 79 J by the strain-rate-sensitive models, which was more accurate compared to 52 J predicted by the strain-rate-insensitive model. Additionally, the coupling between interlaminar and intralaminar failure modes in the models led to a more accurate prediction of the delamination area when considering the rate sensitivity

Experimental and numerical study of the influence of pre-existing impact damage on the low-velocity impact response of CFRP panels

This paper presents an experimental and numerical investigation on the influence of preexisting impact damage on the low-velocity impact response of Carbon Fiber Reinforced Polymer (CFRP). A continuum damage mechanics-based material model was developed by defining a userdefined material model in Abaqus/Explicit. The model employed the action plane strength of Puck for the damage initiation criterion together with a strain-based progressive damage model. Initial finite element simulations at the single-element level demonstrated the validity and capability of the damage model. More complex models were used to simulate tensile specimens, coupon specimens, and skin panels subjected to low-velocity impacts, being validated against experimental data at each stage. The effect of non-central impact location showed higher impact peak forces and bigger damage areas for impacts closer to panel boundaries. The presence of pre-existing damage close to the impact region leading to interfering delamination areas produced severe changes in the mechanical response, lowering the impact resistance on the panel for the second impact, while for noninterfering impacts, the results of the second impact were similar to the impact of a pristine specimen

Repeated impact behaviour of inter-ply hybrid aramid/S2-glass epoxy laminates

This paper presents an experimental study on the repeated low-velocity impact behaviour of inter-ply hybrid composites of aramid/S2-glass/epoxy. The impacts were performed using a drop-tower apparatus following ASTM D7136 Standard. Two energies (19 and 37 J) were chosen for the study with up to twenty and five repeated impacts, respectively. A double exponential empirical model is proposed to describe the degradation due to the repeated impacts, considering the hybridization ratio. The impact response and progressive damage are presented and discussed for different laminates: single-fibre, and asymmetric or symmetric hybrids. The results show that hybridization may lead to the mitigation of repeated impact degradation. For asymmetric hybrids, impact on S2-glass showed a combination of higher impact stiffness and lower degradation rate, outperforming single-fibre laminates

Experimental and numerical studies on the repeated low-velocity impact response and damage accumulation in woven S2-glass fibre/epoxy composites

In this paper, the repeated low-velocity impact response of woven S2-glass/epoxy composites is studied. The impacts were performed with energies from 18.4 to 59.2 J using a drop-tower apparatus, and a post-mortem analysis after each impact was employed to assess the impact response. A damage index was used to describe the changes in impact response due to repeated impacts. Finite element simulations considering both interlaminar and intralaminar failure modes were performed. The results showed that the impact force and bending stiffness decreased with the number of impacts, while impact duration and maximum central displacement increased. The shape of the damaged area was also affected. The numerical results showed that interlaminar damage initiated at most interfaces during the first impact, followed by in-plane propagation in the next impacts. Also, intralaminar damage initiated at the backside of the laminate, and then in-plane and through-thickness propagations followed until penetration occurred

Experimental study on the low-velocity impact response of inter-ply S2-glass/aramid woven fabric hybrid laminates

This paper presents an experimental evaluation of the effect of hybridization and stacking sequence on the low-velocity impact response of aramid/S2-glass/epoxy hybrid laminates. Plain-weave Kevlar ®29 and satin S2-glass fabrics were used and the laminates were manufactured by vacuum infusion moulding. Eight laminate configurations were studied, including two single-fibre samples (pure aramid or pure S2-glass) and six interply hybrids. Low-velocity impact tests were performed with three different impact energies (19 J, 37 J, 72 J) and significant variations in impact behaviour were observed among the laminates. Response Surface Methodology (RSM) was employed to investigate the effect of hybridization on impact performance, focusing on greater absorbed energy and smaller back face deformation. Hybridization led to significant changes in failure morphology and the combination of aramid and S2-glass laminates enhanced the impact performance, especially for up to 49.5 J impact energy, while the pure S2-glass laminate performed better for higher impact energies