Impact Response Of Sandwich Panels Research Articles

Low-velocity impact response of sandwich panels with layered-gradient metal foam cores

The low-velocity impact response of square sandwich panels (SPs) with three-layer metal foam core was examined via analytical and numerical approaches. Taking into account the core arrangements, the analytical model is formulated by employing an innovative yield criterion, to predict the impact force and deflection responses. The accuracy of the analytical predictions was confirmed through finite element (FE) results, and the influences of the core distribution, impact position, as well as core thickness on the impact behaviour of SPs were discussed. It is shown that the graded core SP exerts slightly inferior impact resistance than the uniform core SP. The closer the impact position is to the clamped boundary, the smaller the deflection of the bottom face-sheet and the greater the impact force. As the thickness of the core increases, the proportion of energy absorption attributed to the core also increases. Eventually, the analytical formula was used to generate a design chart for the lightweight configuration, providing geometric optimization pathways.

Comparisons on the Local Impact Response of Sandwich Panels with In-Plane and Out-Of-Plane Honeycomb Cores

The influence of in-plane and out-of-plane element array effects of honeycomb on the impact characteristics of sandwich panels was studied under different local impact speeds. The numerical model is calibrated by air cannon impact experiment and used to conduct the investigations. It is demonstrated that the sandwich panel with in-plane honeycomb core (SPIH) exhibits a response mode with larger local indentation and smaller overall deflection, and also shows superior energy absorption as compared to the sandwich panel with out-of-plane honeycomb core (SPOH). When facing more severe impact conditions, SPIH shows better anti-penetration capability. When the impact radius is 20 mm and the impact velocity is 83 m/s, the SHOP is penetrated while the SHIP is not. When the impact radius is 20 mm and the impact velocity is 100 m/s, the total absorbed energy of SHIP is 59.79% higher than that of SPOH, and the impact residual velocity is 32.67% lower. Furthermore, the impact mitigation performances of SPIH with different density gradient cores are investigated by comparing their deformation modes and energy absorption characteristics. The results indicate that different gradient schemes enable sandwich panels to perform multiple functions. The positive gradient design in the cell stretching direction is beneficial to reduce the overall deflection and improve the energy absorption effect.

Numerical analysis of low-speed impact response of sandwich panels with bio-inspired diagonal-enhanced square honeycomb core

The diagonal-enhanced square grid configuration inspired by glass sponge has great potential in mechanics, with geometries serving as honeycomb cores for sandwich panels, which can improve the structure’s energy absorption capabilities. Modeling the hexagonal honeycomb core (HHC) sandwich panels, a finite element numerical model for low-speed impact of sandwich panels with high accuracy is proposed, and low-speed impact response of bio-inspired diagonal-enhanced square honeycomb core (BSHC) sandwich panels is studied. The impact response of BSHC sandwich panels, Hexagonal honeycomb core (HHC) sandwich panels and ordinary square honeycomb core (OSHC) sandwich panels were studied with the same relative densities and the same face-sheets. BSHC can lead to significantly enhanced the peak loads and stiffness of the sandwich panels. BSHC sandwich panels not only have excellent energy absorption performance, but also outperform HHC sandwich panels in terms of resistance to impact deformation. BSHC can transfer dynamic loads from the front face-sheet to the back face-sheet efficiently without stress concentration in the core itself. A theoretical analysis of the energy absorption capacity of the BSHCs and HHC were performed to illustrate the energy absorption mechanism. In addition, the peak load and contact energy of BSHC sandwich panels and HHC sandwich panels were theoretically predicted under low-speed impact.

Experimental study of the low-velocity impact behavior of hybrid sandwich panel with S-shaped foldcore

Designed and prepared glass fiber S-shaped foldcore by the hot pressing method and bonded with 2A12 aluminum alloy panels to make a foldcore sandwich panel. Also, polyurethane foam is used to fill partially foldcore sandwich panels. All specimens were subjected to low-velocity impact tests with different impact energies and different impact positions. The impact response of the foldcore sandwich panel under low-velocity impact and the influence of foam filling on the impact response of the sandwich panel is studied. The experimental results have shown that the impact position has a significant impact on the damage mechanism of the sandwich panel, besides, the filling foam has different effects on the impact response of different positions of the foldcore sandwich panel. The penetration energy of the sandwich panel at node impact is higher than that of the base impact. The filling of foam increases the penetration energy of the foldcore sandwich panel and also reduces the difference in impact performance at different positions of the sandwich panel.

A review of the recent trends on core structures and impact response of sandwich panels

It is a challenging task to advance the excellent strength and structural performance of sandwich structures, while continuing to reduce the weight and cost parameters. Thousands of researchers have studied and developed the core structural innovation with periodical achievements. This review paper concentrates on the core structural trends and impact response of sandwich panels, which highlights the novel design concepts and impact failure modes. Three kinds of core structures have been classified, which are foam-core, two- and three-dimensional periodic cores. It is shown that the core structure of sandwich panels plays a vital role in structural performance and applications. Three common types of loading conditions have been considered, i.e. compression, projectile impact and three-point bending. Examples of novel core structures are further studied and summarised under corresponding impact loadings. Recent applications of sandwich structures are briefly concentrated on aerospace, automotive, marine and civil engineering areas. Furthermore, future research and development prospect of sandwich structures are suggested and predicted.

Analytical modeling of carbon nanotubes effects and their distribution patterns on the low velocity impact response of sandwich panels

In this paper, the effects of carbon nanotubes and their distribution patterns on low velocity impact response in sandwich panels are investigated. At first, the effects of carbon nanotubes and their distribution patterns on mechanical properties of sandwich panels will be obtained; then, for modeling the impact dynamics, the three-degree freedom mass-spring model has been used in which the effects of transverse flexibility of core are considered. To obtain the mechanical properties of sandwich panels, the effective properties of carbon nanotubes are calculated utilizing a composite cylinder micromechanics technique as a first step; then, these effective properties are used in the Mori–Tanaka methods to obtain elastic moduli of face sheets consisting of aligned or randomly oriented straight carbon nanotubes. After examining the validity of the present solution, the consequences of distribution patterns of carbon nanotubes, volume fraction of carbon nanotubes and initial velocity of the impactor are studied in detail.

Numerical study of low-speed impact response of sandwich panel with tube filled honeycomb core

Sandwich panel with Honeycomb Filled with Circular Tubes (HFCT) as core is numerically investigated by using ABAQUS/Explicit in this study. To calibrate the numerical model, the panels equipped with conventional hexagon honeycomb cores are modeled. Good agreement between numerical and experimental results is achieved. The sandwich panels with HFCT are compared with the sandwich panels with Honeycomb and Multi-tube cores of identical mass subjected to vertical and oblique impacts. The maximum displacement of face-sheets, plastic energy absorption, boundary reaction forces and impact load time history are calculated to assess the impact resistant capacity. The panel with HFCT core has smaller rear face-sheet displacement and higher energy absorption capacity as compared to the panels with the Multi-tube and Honeycomb core. Under oblique impact, both HFCT and Multi-tube panels have superior impact resistant capacity than the Honeycomb panel. In addition, the impact resistances of four types of multi-arc tube filled Honeycomb (HFMT) are also analysed. Their performances under vertical and oblique impacts are compared with those of HFCT.

Impact response of sandwich panels with polyurethane and polystyrene core and composite facesheets

An experimental study on the impact response of foam core sandwich panels subjected to low velocity impact is performed. Panels with glass fiber laminated facesheets and polystyrene and polyurethane foam core with density of 32 kg/m3, respectively 100 kg/m3, were tested in impact on an INSTRON Ceast 9340 drop tower at different impact energies. The composite facesheets were made of epoxy resin, glass fiber roving of 500 g/m2 and short glass fibers of 3 mm in 5 different combinations. The effect of foam core and facesheet type on the resulting impact damage and contact force is analyzed. It was noted that higher impact energies introduce matrix damages and the partial fracture of the fibers which significantly change the force-displacement histories, particularly after the maximum impact force is reached. Also, the use of polyurethane foam core increased the impact damage indentation in size and depth compared to the panels with polystyrene core. Panels having facesheets only with short glass fibers show a very poor resistance compared to the ones with roving and are completely perforated even for the smallest impact energy.

Compression and low velocity impact response of sandwich panels with polyester pin-reinforced foam filled honeycomb core

Hybridization of face, core and their combination is of great interest to develop high performance composite sandwich panels. In this regards, hybrid core of ‘polyester pin-reinforced foam filled h...

Effects of aluminum foam filling on the low-velocity impact response of sandwich panels with corrugated cores

In this study, a closed-cell aluminum foam was filled into the interspaces of a sandwich panel with corrugated cores to form a composite structure. The novel structure is expected to have enhanced foam-filled cores with high specific strength and energy absorption capacity. An out-of-plane compressive load under low-velocity impact was experimentally and numerically carried out on both the empty and foam-filled sandwich panels as well as on the aluminum foam. It is found that the empty corrugated sandwich panel has poor energy absorption capacity due to the core member buckling compared to that of the aluminum foam. However, by the filling of the aluminum foam, the impact load resistance of the corrugated panel was increased dramatically. The loading-time response of the foam-filled panel performs a plateau region like the aluminum foam, which has been proved to be an excellent energy absorption material. Numerical results demonstrated that the aluminum foam filling can decrease the corrugated core member defects sensitivity and increase its stability dramatically. The plastic energy dissipation of the core member for the foam-filled panel is much higher than that of the empty one due to the reduced buckling wavelength caused by the aluminum foam filling.

Study of low-velocity impact response of sandwich panels with shear-thickening gel cores

The low-velocity impact response of sandwich panels with shear-thickening gel cores was studied. The impact tests indicated that the sandwich panels with shear-thickening gel cores showed excellent properties of energy dissipation and stress distribution. In comparison to the similar sandwich panels with chloroprene rubber cores and ethylene-propylene-diene monomer cores, the shear-thickening gel cores led to the obviously smaller contact forces and the larger energy absorptions. Numerical modelling with finite element analysis was used to investigate the stress distribution of the sandwich panels with shear-thickening gel cores and the results agreed well with the experimental results. Because of the unique mechanical property of the shear-thickening gel, the concentrated stress on the front facesheets were distributed to larger areas on the back facesheets and the peak stresses were reduced greatly.

FEM ANALYSES OF LOW VELOCITY IMPACT BEHAVIOUR OF SANDWICH PANELS WITH EPS FOAM CORE

This study presents a numerical investigation on low velocity impact response of sandwich panels with EPS foam core. The face-sheets and foam core are made of aluminum 6061-T6 and expanded polystyrene foam (EPS). The effect of foam core density was investigated on the impact energy absorption of the panel. The dynamic response of the panels was predicted using the finite element analysis package ABAQUS/Explicit. The material and geometrical nonlinearities were considered and the foam material was modeled as a crushable foam material. The cohesive response of the adhesive interface was modeled using the cohesive zone model. The temporal variations of contact force, kinetic energy histories and central permanent deflections were compared for different foam core densities and impact energies. The peak contact force levels and central permanent deflections are increased with increasing the impact energies. As the foam core density is increased, the capability of energy absorbing is increased.

High velocity impact response of carbon nanotubes-reinforced composite sandwich panels

Effect of adding carboxyl-modified multi-walled carbon nanotubes (COOH-MWCNTs) on the high velocity impact of sandwich panels with plywood core and two different facesheets, E-glass/epoxy and E-glass/ nylon 6, was investigated in this study. Facesheets were prepared with and without COOH-MWCNTs. Three different weight percentages of 0.3, 0.5, and 1 wt% of COOH-MWCNTs were used to reinforce epoxy and nylon 6 polymers. The sandwich panels’ estimated ballistic limit ( Vbl) and impact energy absorbed ( Eab) were determined by subjecting them to impact velocities in their ballistic limit range and above by conical nose projectile. It was found that the sandwich panels containing E-glass/ epoxy facesheets exhibited more energy absorption than those containing E-glass/nylon 6 facesheets. Moreover, the high velocity impact response of sandwich panels improved with the increase of COOH-MWCNT content. Besides, the damage area for different types of materials studied is presented, and it is observed that at a given impact velocity, the damage size on the rear facesheet of target around the point of impact decreases on addition of COOH-MWCNTs.

Impact response of polyurethane and polystyrene sandwich panels

Sandwich panels with aluminum faces and polyurethane or polystyrene core were tested in impact on an Instron Ceast 9340 impact tower at speeds from 0.77 to 4.5 m/s. The faces were made from Al 6082-T6 sheet with a thickness of 1.5 mm and the thickness of the polyurethane panel (Necuron 100 core of density 100 kg/m3) and of the polystyrene panel (commercial extruded polystyrene core of density 30 kg/m3) were 15 mm, respectively 22 mm. Specimens of 140x140 mm were impacted with a mass of 13.15 kg and the variations of the impact force were monitored during the initial impact at a data acquisition frequency of 200 kHz. The important events took place in less than 15 ms. Particularities of the impact response of the sandwich panels were observed and discussed. The influence of the speed of impact was analyzed for both types of panels. The force variation during impact has a different evolution as influenced by the core behavior. There are noticed differences in the size and shape of the produced penetration of the skins after low-velocity impact.

Matrix crack interacting with a delamination in an impacted sandwich composite beam

Delamination interacting with matrix cracking is a characteristic failure mechanism that is observed in the damage evolution of laminated composites subjected to low velocity impact. This failure mode can be studied in isolation by investigating the low velocity impact response of sandwich panels that have thin face sheets bonded to a core. In these panels, failure is seen to initiate in the core (akin to the matrix) by cracking, leading to delamination between the core and the face sheet. Experimental and modeling results for the flexural response and failure mechanisms of sandwich composite beams under three point bend loading, both for quasi-static and impact loading are presented. Digital image correlation (DIC) technique is used to obtain the surface strain field during the response event as well as capturing the onset of failure. A 2D, plane strain finite element (FE) model using the Smeared Crack Approach (SCA) has been developed to predict the response, and to capture the interactive failure seen in the experiments. The FE model accurately captures the response seen in the experiments as well as the mode of failure and the progression.

Experimental study of the medium velocity impact response of sandwich panels with different cores

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 120J. 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.

The low velocity impact response of sandwich panels with lattice core reinforcement

This study presents the experimental and simulation results for the low velocity impact response of sandwich panels reinforced with a lattice core structure. Two different core material and architecture combinations are investigated; a UV-cured photopolymer lattice, produced from a network of self-propagating waveguides, and an aluminum alloy lattice cast from an initial polymer template. For each of these sandwich panel configurations, impact tests were performed with a drop-weight hemispherical impactor under four different energy levels. The applied impact force, impactor velocity and residual damage in the sandwich panel were all measured and used for comparison against finite element simulations of the impact tests. These simulations employed a homogenized continuum constitutive model, designed to replicate the deformation response of the lattice core without requiring explicit representation of the geometric features of the lattice. For both sandwich panel designs at all impact energy levels, excellent correlation was observed between the experimental measurements and impact simulations. Additionally, each sandwich design was shown to be effective at absorbing the kinetic energy of the impactor with minimal damage to the back (non-impacted) face of the panel. Implementation of these lattice core sandwich panels and extension of the homogenized constitutive model to other sandwich applications are also discussed.

Numerical assessment of the impact behavior of honeycomb sandwich structures

Composite sandwich structures are widely used in the high-performance applications where weight reduction is one of the most attractive design parameters. However, structural sandwich components have low resistance to out-of-plane impact due to the thin outer composite skins and the highly deformable cores. The present paper deals with a finite element study on the impact response of sandwich panels, obtained combining phenolic resin-based glass fiber reinforced plastics as skins and phenolic resin-impregnated aramid paper honeycomb structure (Nomex) as core. The numerical analysis has been performed using the LSDYNA software enabling to account for the main sandwich failure modes occurring during impact. The honeycomb core structure and composite skins have been modeled by means of solid and shell elements respectively. The properties of the finite element model have been calibrated on a series of experimental outcomes in order to achieve numerical parameters for both composite facesheet and orthotropic honeycomb material models. The major concerns are related to damage mechanisms, influence of strain-rate effects and energy absorbing capability. The model is validated using the results from experimental impact tests performed on different initial impact conditions. Good agreement was obtained between numerical and experimental results in terms of impact damage and force–displacement trend.

The perforation resistance of sandwich structures subjected to low velocity projectile impact loading

AbstractThis article presents the findings of a study to investigate the impact perforation resistance of sandwich structures. The dynamic response of sandwich panels based on PVC foam cores has been evaluated by determining the energy to perforate the panels. The impact response of the sandwich structures was predicted using the finite element analysis package Abaqus/Explicit. The validated FE models were also used to investigate the effect of oblique loading and to study the impact response of sandwich panels subjected to a pressure differential equivalent to flying at an altitude of 10,000m.Low velocity impact testing has shown that the energy to perforate the sandwich panels is dependent on the properties of the core. It has been shown that increasing the density of the crosslinked PVC foams by a factor of two yielded a 600% increase in the perforation resistance of the sandwich structures. At higher densities, the crosslinked foam sandwich structures offered a superior perforation resistance to the linear PVC structures. The numerical analysis accurately predicted the perforation energies of the sandwich panels, as well as the prevailing failure mechanisms following impact. Finally, it has been shown that sandwich panels impacted at high altitude offer a similar perforation resistance to those tested at sea level.

Scaling effects in the low velocity impact response of sandwich structures

Scaling effects in the impact behaviour of foam-based sandwich structures have been investigated using an instrumented drop-weight impact tower. Four scaled sizes of sandwich panel, manufactured by bonding a woven carbon fibre reinforced epoxy composite to a PMI (polymethacrylimide) foam core, were investigated. Low velocity impact tests on the sandwich structures resulted in a localised mode of fracture in all scale sizes at all energies. The resulting load–displacement traces were normalised by their appropriate scaling factors to highlight potential size effects in the impact response of the structures. Additional indentation tests were conducted at quasi-static and dynamic rates of loading to investigate scaling effects in the contact response of the sandwich panels.Size effects were observed in the load–displacement traces of the smaller samples following indentation tests at both quasi-static and dynamic rates of loading, most likely due to the relative size of the radius of the impactor and the weave dimensions of the composite skins. However, for all scale sizes, both the level and type of damage were similar in polished cross-sections removed from the indented panels. Under low velocity impact loading, for a given scaled impact condition, the energy absorbed by the sandwich panels was similar across all four scale sizes, suggesting that the impact response of these sandwich structures obeys a simple scaling law. An examination of the cross-sections of the impact-damaged sandwich structures also suggested that damage was similar in all of the samples for a given scaled impact energy. This evidence suggests that, providing microstructural effects do not play a significant role, simple scaling laws can be used to predict the low velocity impact response of sandwich panels of this type.