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This paper presents an experimental study on the impact behaviour of composite laminates made of a Dyneema ® woven fabric and four different resin matrices. Three thicknesses of each kind of resin laminate were subjected to impact by a spherical steel projectile in a velocity regime ranging from 100 to 200 m/s. The results revealed that the laminates having flexible matrices performed much better in perforation resistance and energy absorption, but had a greater extent of deformation and damage than the counterparts with rigid matrices. It was found that the matrix rigidity played a crucial role in controlling the propagation of transverse deformation, and thereby the local strain and perforation resistance of laminates. The more rigid matrix restrained the laminate's transverse deformation to a smaller area at a given time, which led to higher local strain and lower perforation resistance. Fibre failure in tension was identified as the dominant failure mechanism for the tested laminates. [ABSTRACT FROM AUTHOR]

This study explored the impact response of two bio-inspired composite laminates with linear and non-linear helicoidal fibre architectures. The helicoidal laminates, together with quasi-isotropic and cross-ply control samples, were fabricated using heterocyclic aramid fibres and tested against a spherical projectile under high impact velocities. The results revealed that helicoidal lay-ups with small rotation angles led to inferior perforation resistance and energy absorption capacity when compared to the quasi-isotropic and cross-ply counterparts. The cross-ply configuration was confirmed as the optimal fibre architecture for impact perforation. Post-impact inspections highlighted that the failure mechanisms of laminates were significantly affected by their lay-ups. The number of fractured fibres was found to reduce with the decrease of inter-ply angle. This was due to the small rotation angles promoted a wedge-in mechanism. Moreover, a smaller angle mismatch resulted in diminished overall delamination area in a laminate. Due to these two effects, therefore, helicoidal lay-up configurations with small inter-ply angles are not recommended for impact-resistant laminates reinforced by tough fibres. • High-velocity impact behaviour of bio-inspired helicoidal laminates is explored. • Helicoidal lay-ups perform worse than quasi-isotropic and cross-ply counterparts. • The decrease of inter-ply angle results in fewer fractured fibres. • The overall delamination area reduces as the inter-ply angle decreases. • Tough fibre helicoidal lay-ups are not ideal for resisting high-velocity impact. [ABSTRACT FROM AUTHOR]

Woven wire mesh is a metallic fabric outperforming traditional metal sheets in air circulation, weight saving, impact resistance, etc. In this study, the dynamic mechanical response of steel wire mesh subjected to low-velocity impact loading was investigated using both experimental and numerical methods. An instrumented drop-weight impact facility was used for experimental impact tests, with the effects of clamping wire direction, impact energy, impactor's mass and size being considered. The extents of damage to the wire mesh specimens under different loading conditions were evaluated after impact tests. Three types of contact force vs. displacement curves corresponding to the plastic deformation, wire breakage, and perforation of wire mesh were identified. Weft wires were found to be stronger and stiffer than warp wires because they could resist higher peak forces and experienced smaller maximum displacements under the same impact energies. The experimental results revealed that the peak contact force increased with impact energy until wire breakage occurred, after which the peak force remained almost unchanged. With the increase of impactor mass, wire mesh specimens experienced severer damage due to the inertia effect and strain rate effect. Impactor size had a significant influence on the dynamic response of wire mesh; a great increase in peak contact force was found when using a larger impactor tip. Moreover, a mesoscale finite element model was developed to analyse the propagation of stress and the evolution of dynamic failure in wire mesh during impact. The simulation results showed that more than 80% of the impactor's kinetic energy was absorbed through the deformation and failure of wire mesh, while the frictional energy dissipation accounted for about 10% of impact energy. • Three types of contact force vs. displacement curves of wire mesh were identified. • Weft wires could resist higher force corresponding to wire breakage than warp ones. • Wire mesh material behaved in a membrane stretching mode under low-velocity impact. • Impact-induced stress propagated in an orthotropic manner in wire mesh. • More than 80% of impact energy was absorbed as the internal energy of wire mesh. [ABSTRACT FROM AUTHOR]

This paper reports the performance of protective structure inspired by elasmoid fish scales, employing a combination of experimental and numerical techniques. The composite scale-tissue structures were fabricated using a 3D printer with a dual-material extruder. Each structure was subjected to low-velocity impact using a drop-weight tower system. Investigation of the progressive failure mechanisms relied on finite element analysis and high-speed photography. Geometrical parameters of fish scales, including scale volume fraction, scale overlapping angle, and radius of curved scales were studied for their influence on impact resistance. Further, using Taguchi's method for the design of experiments, it was determined that enhancing impact resistance was achievable through an increase in scale volume fraction (by 15.1 %) and a larger scale overlapping ratio (by 39.4 %). The outcomes suggest that using a composite scale-tissue structure can contribute to developing more effective protective structures. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract The dynamic responses of sandwich panels with homogeneous and stepwise graded aluminium foam cores subjected to impact loadings were investigated via experimentation and finite element simulation in this paper. The low-velocity impact tests were conducted using a drop-weight impact facility at four different velocities, the results of which were compared in terms of force-displacement response, energy absorption and damage status. It was found that the density gradient of graded foam cores had a marked influence on the deformation and failure behaviour of front facesheets. Moreover, different facesheet materials were experimented with a homogeneous foam core, and the results showed that the impact response of a sandwich panel was dominated by its front facesheet. The front facesheets having same materials deformed and failed in the same manner irrespective of the back facesheet materials. The results of finite element analysis indicated that the critical impact energy required to cause failure to the front facesheet increased with the density of first core layer. Besides, the impact performance of sandwich panels could be improved efficiently by increasing the front-to-back thickness ratio while the total thickness of both facesheets remained the same. Graphical abstract Unlabelled Image Highlights • The density gradient of graded foam cores markedly influenced the deformation and failure behaviour of front facesheet. • The critical impact energy required to cause failure to the front facesheet increased with the density of first core layer. • The perforation resistance of entire sandwich panels was affected slightly by the core density gradient. • The impact performance of sandwich panels was improved by increasing the thickness ratio of front to back facesheet. [ABSTRACT FROM AUTHOR]

Highlights • Increasing facesheet thickness caused smaller deformation depths but larger deformation areas. • Core height had a small effect on the ballistic limit velocity of sandwich panels. • Front facesheet failed more easily due to stress concentration with the increase of core stiffness. • The increase of front-to-back thickness ratio led to higher damage resistance. • A structural optimisation for maximising the specific energy absorption was presented. Abstract This paper presents a combined experimental and numerical study on the dynamic response and failure mechanisms of honeycomb sandwich panels subjected to high-velocity impact by a spherical steel projectile. Impact tests were performed in a velocity range from about 70 to 170 m/s to investigate the effects of facesheet thickness, core height, cell wall thickness and cell size of honeycomb on the impact behaviour of sandwich panels. These geometric parameters were found to influence the impact performance mainly by changing the deformation and failure mechanisms of both sandwich facesheets. Moreover, the ballistic limit velocity and critical perforation energy of each sandwich configuration were obtained by numerical simulation. It was found that increasing facesheet thickness and reducing honeycomb cell size were two weight-efficient ways to enhance the perforation resistance of sandwich panels when the areal density exceeded a certain value. The projectile's penetration process into the sandwich panel and the associated energy absorbing mechanisms were analysed, the results of which showed that facesheets contributed most to energy absorption. Further numerical simulation was conducted to explore the influences of core stiffness and the thickness ratio of front to back facesheet. It was found that core stiffness had a significant effect on the deformation and failure initiation of front facesheet; more specifically, the front facesheet failed more easily due to stress concentration with the increase of core stiffness. When the total thickness of front and back facesheets remained constant, increasing the front-to-back thickness ratio led to higher damage resistance but greater deformation area on the front facesheet. Finally, a discrete optimisation was conducted to generate an optimal design of sandwich structure for achieving the highest specific energy absorption without perforation under a certain impact energy. The optimised sandwich panel exhibited an increase of 23.7% in specific energy absorption compared with the initial design. [ABSTRACT FROM AUTHOR]

The present paper addresses the development of bio-inspired composite laminates based on the Fibonacci sequence for impact resistant applications. Four methods such as thickness ratio (FT), incremental angle (FI), hybrid (FY) and Fibonacci helicoidal (FH) are devised to create various sets of laminates to exploit the Fibonacci sequence into the laminate design. These methods include controlling of ply group thickness (FT), rotation fiber angle (FI), both thickness and angle (FY), and direct implementation of Fibonacci based helicoidal laminate sequence (FH). The performance of these proposed laminates is analysed by considering ballistic impact loading with six different impact velocities, out of which three are below the ballistic limit of laminates. The behaviour of these laminates under this loading is investigated using an elastic-plastic progressive damage based numerical model. The results obtained through numerical simulation are validated with experimental results and found to be well correlated. The performance of bio-inspired laminates is compared with conventional cross-ply and quasi-isotropic laminates in terms of various parameters such as residual velocity, displacement, energy absorption, peak load, number of plies damaged and delamination. These parameters are correlated by using a level-based methodology and the most versatile method to design Fibonacci based bio-inspired laminates among all methods considered is estimated for all velocities. [ABSTRACT FROM AUTHOR]