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This paper presents an investigation on the stiffness and energy absorption capabilities of three proposed biomimetic structures based on the internal architecture of a cornstalk. 3D printing was used to manufacture specimens using a tough and impact-resistant thermoplastic material, acrylonitrile butadiene styrene (ABS). The structural stiffness, maximum stress, densification strain, and energy absorption were extracted from the compression tests performed at a strain rate of 10−3 s−1. A numerical model was developed to analyse the behaviour of the biomimetic structures under compression loading. Further, a damage examination was conducted through optical microscopy and profilometry. The results showed that the cornstalk-inspired biomimetic structure exhibited a superior specific energy absorption (SEA) capability that was three times higher than that of the other core designs as reported in the literature. [ABSTRACT FROM AUTHOR]

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]

The impact response of sandwich panels is not only dependent on the facesheet but also on the core material. This paper compares the dynamic response of sandwich panels with different core materials when subjected to medium velocity impacts. The sandwich panels were made of aluminium facesheets with five different cores, viz., low density balsa wood, high density balsa wood, cork, polypropylene honeycomb, and polystyrene foam. All the specimens were impacted by an instrumented projectile with a hemispherical steel head at three impact energies of 43, 85 and 120 J. An accelerometer attached to the projectile and a high speed camera were used to collect data and record the impact process. 3D scanning technique was used to measure the deformation of front and back faces after impact. The impact properties of the sandwich panels with the five different cores were compared in terms of contact force, energy absorption, depth of indentation, overall bending deflection, etc. Post-mortem sectioning was conducted to examine the impact induced failures such as facesheet rupture, crush of core material, and debonding between facesheet and core. Finite element modelling was also carried out to elucidate the observed experimental results and further understand the effect of core material. [ABSTRACT FROM AUTHOR]

• Steel wire mesh can provide reliable protection against windborne debris. • The impact response of steel wire mesh is dominated by transient transverse waves. • The maximum energy absorption by wire mesh occurs at the ballistic limit velocity. • Wire mesh absorbs energy mainly via the plastic deformation and breakage of wires. Considerable property damage is caused by windborne debris during extreme weather. The object of interest in this study, steel wire mesh, is an effective means of providing protection against windborne debris. However, the design and manufacture of security screens made of wire mesh typically depend on a laborious and imprecise trial-and-error process. Additionally, this anisotropic, inhomogeneous, and porous material comprising in-contact wires has rarely been examined in a comprehensive manner. Considering these issues, the current research experimentally tested the impact response of plain-weave steel wire mesh by firing a spherical projectile in a velocity regime ranging from 112 m/s to 152 m/s. The deformation and failure mechanisms of the wire mesh during the impact process were investigated via high-speed photography. The results showed that the wire mesh behaved as a membrane and failed mainly in tension over the impact velocity range of interest. Further, with a detailed finite element model consisting of interlaced warp and weft wires, additional virtual tests were carried out at a broader velocity range of 20–200 m/s. The findings indicated a linear relationship between residual velocity and impact velocity under a velocity range that exceeded the ballistic limit. The energy absorbed by the wire mesh increased with impact velocity (or impact energy) before the material reached peak absorption at the ballistic limit. Beyond this threshold, the energy absorption gradually declined to an asymptotic level. Such energy absorption was well correlated with the extent of transverse deformation in the wire mesh. Internal energy due to the deformation of wires and frictional energy associated with the interactions between sliding wires at their crossovers were two primary energy absorbing mechanisms. Moreover, the effects of impact location, clamped wire direction and projectile size were analyzed. [Display omitted] [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]

• The critical shear rate decreases with the increase in temperature. • The formation of shear bands evolving into cracks on the free surface of the STF is observed at 0 °C. • The response time for effective energy absorption is faster at lower temperatures and under higher impact velocities. • A one-dimensional model is presented to predict the response time for energy absorption. Shear thickening fluid (STF) material is a suspension with a certain amount of nano- or micro-particles dispersed into a liquid medium whose viscosity increases with the rate of shear strain. Due to its exceptional rate-dependent property, STF has been regarded as a promising energy absorption material with potential application in soft body-armour. This study examines the rheological, impact resistance and energy absorption characteristics of an STF with concentrated polymer submicron particles under various temperatures. The rheological testing was conducted using a rotational rheometer with a temperature-control hood at shear rates measured from 0.01 s−1. The studies reveal that the shear thickening behaviour of the STF is temperature-dependent and the critical shear rate for the onset of shear thickening decreases with the reduction of temperature. In particular, shear thickening behaviour of the STF at 0 °C was observed with the formation of shear bands evolving into cracks on the free surface of the STF. Low-velocity impact tests were conducted using a drop-weight tower with a temperature-control chamber. The study shows that the impact resistance of the STF increases with the decrease in temperature. In particular, the impact resistance shows an early response time when the impact resistance slowly picks up, corresponding to mechanisms of jamming-associated "solidification" and propagation of front of the "solidified" region. A simple one-dimensional model is also adopted to comprehend the response time for effective energy absorption of the STF addressing the mechanisms, and the general agreement of the predicted response time with that from the experiments demonstrates the effectiveness of the model. [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]

Porous structures fabricated through selective laser melting (SLM) are prospective candidates for high-energy-absorbing applications due to their tuneable mechanical properties. The Menger Fractal Cube (MFC) is a unique fractal cube formed through iterative removal of smaller cubes from a larger one. It is distinguished by its intricate self-similar pattern of voids and cubes repeating at diminishing scales, resulting in a lightweight and highly complex structure. Using AlSi7Mg, compression experiments and simulations investigated MFCs with three different orders. Digital image correlation was used to identify the stress concentration areas within the elastic deformation range of MFCs, and the relationship proposed in the Gibson-Ashby model was successfully implemented. The nature of the collapse, fracture mechanism, and energy absorption behaviour were investigated with the plateau and densification region deformation profiles. The highest level of specific energy absorption was recorded in third-order MFC, whereas the maximum densification displacement and energy absorption efficiency were observed in the fourth-order MFC. The test results also showed that the peak force decreased with increasing fractal order, suggesting that high-order MFCs can be employed as protective sacrificial structures that reduce force transmission to the protected structures. In brief, MFCs demonstrate outstanding energy absorption properties and hold promising potential for a wide range of structural applications that require energy-damping characteristics. • The Menger fractal cube inspired porous structures are proposed as a high performing energy absorbing structure. • The densification point of MFCs is getting higher with the increasing fractal order allowing them to absorb more energy. • The Finite Element models predict the mechanical behaviour of Menger fractal inspired porous structures. • Higher order MFCs have greater SEA values in the range of 45-50 J/g. [ABSTRACT FROM AUTHOR]

This paper presents a combined experimental and numerical study on the low-velocity impact behavior of honeycomb-core sandwich panels with different structural parameters, including facesheet thickness, core height, honeycomb cell size, and cell wall thickness. Impact tests were conducted at four different energies using a drop-weight impact facility, and the deformation and damage characteristics of the tested sandwich panels were analyzed by microscopic X-ray computed tomography. The experimental results revealed two distinct failure modes of sandwich panels: namely mode A, with localized damage in both facesheets and core, which is dominated by indentation; and mode B, which is characterized by global bending deflection of the facesheets and overall core crushing. It was found that a sandwich panel with thin facesheets and a high-density honeycomb core (e.g. with a small cell size and/or a thick cell wall) tended to fail in mode A, but core height did not influence the failure mechanism notably. Furthermore, finite element modeling was carried out to gain further understanding of the effects of these structural parameters. The perforation resistance and energy absorption capacity were significantly enhanced with increasing facesheet thickness. Whereas reducing the cell size and/or thickening the cell wall resulted in lower perforation resistance. When the total thickness of facesheets remained a constant, the impact behavior of the sandwich structure could be optimized by controlling the thickness ratio of the front to back facesheets. Finally, cost efficiency analysis was performed to achieve a rational design of the sandwich structure considering both the impact performance and cost. • Two failure modes of sandwich panels are discovered under low-velocity impact. • Failure mode depends on facesheet thickness, cell size, and cell wall thickness. • Core height does not influence the failure mechanism notably. • The density of honeycomb core shows a negative effect on perforation resistance. • A cost efficiency analysis is proposed to balance the impact performance and cost. [ABSTRACT FROM AUTHOR]