Laminate tailoring of composite tubular structures to improve crashworthiness design at off-axis loading

This paper presents experimental and numerical investigation on the parameters effecting energy absorption capability of composite tubular structures at oblique loading to improve crashworthiness performance. Various inclined angles of 5˚, 10˚, 20˚ and 30˚ were selected for the study of off-axis loading. The results indicate that by increasing the lateral inclination angle the mean crushing force and also energy absorption capability of all tested sections decreased. From design perspective, it is necessary to investigate the parameters effecting this phenomenon. The off-axis loading effect that causes significant reduction in energy absorption was investigated and the effected parameters were improved to increase energy absorption capability. To establish this study, 10˚ off-axis loading was chosen to illustrate the obtained improvement in energy absorption capability. Five cases were studied with combinations of ply-orientation and flat trimming with 45˚ chamfer. This method was applied to the integrated 10˚ off-axis loading and the final results showed significant improvement in energy absorption capability of composite absorbers. Finite element model (FEM) was developed to simulate the crushing process of axial and off-axis composite section in LS-DYNA and the results were in good agreement with the experimental data

Lightweight design to improve crushing behaviour of multi-stitched composite tubular structures under impact loading

This paper presents experimental and numerical studies on the effect of multi-stitching pattern on the energy absorption capability of composite tubular structures under impact loading. A new multi-stitching pattern was developed to study the increase of specific energy absorption capabilities in GFRP and CFRP crash absorbers. The stitching pattern on both specimens showed a significant increase in energy absorption capability under impact loading. According to our results, the specific energy absorption of GFRP and CFRP composite tubes are 17% and 18% higher than non-stitched specimens respectively. A multi-shell finite element model was constructed to predict the axial crushing behaviour and energy absorption capability of composite structures under impact loading. The method is based on an energy-based contact card modelling technique in the stitched and non-stitched area, and the initiation of main central crack growth occurs when the critical separation (PARAM function) is attained, and this represents the functionality of the stitched area during an impact event. The developed numerical approach is efficient in terms of accuracy and simplicity in comparison with the existing methods for multi-layered composites structures

Effect of variable core stiffness on the impact response of curved sandwich plates

An extensive analytical model to determine behaviour of curved sandwich plates with variable stiffness cores and face-sheets under low velocity impact with foam core is presented in this paper. A developed method is introduced to determine effective dynamic stiffness of the face-sheets and core with variable stiffness. A modified spring-mass-dashpot model was used to obtain the contact force function related to effective dynamic stiffness and effective dynamic frequency to determine the contact force histories by impact of a hemispherical-nose impactor. A parametric study was also performed to understand the effects of several factors such as impactor velocity, face-sheet thickness, core thickness (constant and variable stiffness), layup orientation and curvature on the contact force histories of curved sandwich plates. Different geometries of curved sandwich plates are analysed to study their performance under impact loading. Numerical analysis was performed in LS-DYNA to further validate with the developed analytical models

Improvement of specific energy absorption of composite tubular absorbers using various stitching pattern designs

In this paper, various patterns of multi-stitched locations were studied experimentally and numerically to improve the specific energy absorption (SEA) in composite tubular absorbers. In this regard, stitching patterns with a horizontal distance of 3 mm, 6 mm, 9 mm and 18 mm in straight and zig-zag designs were investigated to justify their effect on mean crushing force and energy absorption capability. A multi-shell configuration finite element model is also developed based on energy-based contact definitions, which considers the delamination in Mode-I and stitching pattern design to accurately predict the energy absorption capability and axial crushing behaviour of composite crash absorbers, At stitched locations, the critical normal surface separation was utilised concerning experimental data to improve delamination resistance. The multi-stitching rows of 10–15-20–25-30–35 mm with 3 mm horizontal and 2.5 mm vertical distances between each stitched point can increase the specific energy absorption up to 32% in comparison with non-stitched specimens. The developed numerical model for multi-layered composites absorbers in comparison with the existing methods is efficient in terms of accuracy with less than 5% error in comparison with experimental data

Finite element modelling approach for progressive crushing of composite tubular absorbers in LS-DYNA: review and findings

Robust finite element models are utilised for their ability to predict simple to complex mechanical behaviour under certain conditions at a very low cost compared to experimental studies, as this reduces the need for physical prototypes while allowing for the optimisation of components. In this paper, various parameters in finite element techniques were reviewed to simulate the crushing behaviour of glass/epoxy tubes with different material models, mesh sizes, failure trigger mechanisms, element formulation, contact definitions, single and various numbers of shells and delamination modelling. Six different modelling approaches, namely, a single-layer approach and a multi-layer approach, were employed with 2, 3, 4, 6, and 12 shells. In experimental studies, 12 plies were used to fabricate a 3 mm wall thickness GFRP specimen, and the numerical results were compared with experimental data. This was achieved by carefully calibrating the values of certain parameters used in defining the above parameters to predict the behaviour and energy absorption response of the finite element model against initial failure peak load (stiffness) and the mean crushing force. In each case, the results were compared with each other, including experimental and computational costs. The decision was made from an engineering point of view, which means compromising accuracy for computational efficiency. The aim is to develop an FEM that can predict energy absorption capability with a higher level of accuracy, around 5% error, than the experimental studies

Manufacturing of 3D printed laminated carbon fibre reinforced nylon composites: impact mechanics

This paper presents the manufacturing development of laminated Carbon Fibre Reinforced Thermoplastics Polymer (CFRTP) specimens, which show significant improvement of mechanical properties in comparison with existing thermoplastic composites. There is a need to improve structural performance of thermoplastic composites by using a fully integrated chopped and continuous carbon fibre bundle into a thermoplastic resin matrix in a laminated shape with various stacking sequences. The developed manufacturing technique is capable to print components with various fibre orientations, which is spotted as the novelty of this research. The CFRTP specimens were tested under quasi-static tensile and low-velocity impact loading to proof the improvement of mechanical performance in both static and dynamic applications. Our results indicate a significant improvement in impact resistance and energy absorption capability of CFRTP composites in comparison with existing thermoplastic composites

Z-pinning techniques to improve energy absorption capabilities of CFRP tubular structures

This paper investigates the use of z-pinning reinforcement in CFRP tubular structures under axial impact, to find the optimum design to increase the specific energy absorption (SEA). Through-the-thickness reinforcement is known as a technique to improve integrity and fracture resistance in composite materials and structures. Manufacturing and testing of unpinned tubular structures are conducted to create a base model to validate numerical results. A finite element model of the tube under dynamic impact is developed using LS-DYNA software, conducting parametric studies, mesh sensitivity analysis and trigger modelling research. The proposed z-pinning modelling techniques are researched, and an energy-based contact model is proposed to model pinned areas. Five different designs of reinforced tubes are designed and analysed, to find the optimum z-pinned pattern in terms of SEA. The novelties of this research indicate that z-pinning can improve the SEA and reduce the initial collapse load during crushing. Our results indicate that the vertical banded design shows the highest SEA and least initial collapse load values in comparison with the unpinned specimen, which indicates an improvement in the crashworthiness parameters of z-pinned composite tubes

Analytical development on impact behaviour of composite sandwich laminates by differentiated loading regimes

Given the widespread usage of composite components in critical structures within the aerospace and automotive industries, it is deemed as an essential task to determine the effect of normal operation phenomena on its performance in impact. In particular, the present study aims for providing the developed analytical modelling techniques which are needed for describing the low velocity impact dynamic response of sandwich laminated structures. Alongside the analytical models, experimentally validated high-fidelity numerical models are used to check both the validity of the assumptions made as well as the accuracy of the analytical results in the different considered scenarios. An extensive analysis of the sandwich laminate impact performance has been studied, eventually resulting in a much improved, herein developed analytical formulation which is capable of accounting for the differentiated loading, unloading and reloading indentation regimes as well as for the lower facesheet local deflections. These considerations, which are normally neglected in equivalent studies, allow a precise capture of the energy absorption mechanisms

Transverse impact response analysis of graphene panels: Impact limits

Explicit numerical studies were conducted to determine the transverse impact response of graphene panels. Although the mechanical properties of graphene are well documented in both quasi-static and dynamic conditions via nanoand microscopic studies, the impact behaviour of the material at the macroscale has not yet been studied and would provide interesting and crucial insight in to the performance of the material on a more widely recognizable scale. Firstly, a numerical impact model was validated against an analytical impact model based on continuum mechanics which showed good correlation between contact-force histories. The performance of graphene panels subjected to impact was compared to the performance of panels composed of aerospace-grade aluminium and carbon fiber reinforced polymer (CFRP) composite. The graphene panel was found to exhibit lower specific energy than aluminium and CFRP at the low-energy range due to its inherently superior stiffness and intrinsic strength. On the other hand, the ballistic limit of 3 mm thick graphene panels was found to be 3375 m/s, resulting in an impact resistance 100 times greater than for aluminium or CFRP, making graphene the most suitable material for high-velocity impact protection