Prediction of crushing morphology of GRP composite sandwich panels under edgewise compression

This paper describes the use of finite element analysis (FEA) for the simulation of the crushing response of glass reinforced plastic (GRP) composite sandwich panels aimed to absorb collision energy. FEA was employed to predict the failure mode associated with the geometry of a triggering mechanism that was introduced in the foam-cored sandwich panels, and for analyses of the influence of the specimens’ aspect ratio on the specific energy absorption of these panels. The formulated numerical models were found to be effective in reproducing the failure mode and crush zone morphology experimentally observed. The numerical results predicted a trigger geometry that marks the transition from catastrophic buckling failure to progressive crushing and showed that there is not an apparent trend between the aspect ratio of the panels and their specific energy absorption.     

Compressive and shear buckling analysis of metal matrix composite sandwich panels under different thermal environments

Combined inplane compressive and shear buckling analysis was conducted on flat rectangular sandwich panels using the Rayleigh-Ritz minium energy method with a consideration of transverse shear effect of the sandwich core. The sandwich panels were fabricated with titanium honeycomb core and laminated metal matrix composite face sheets. The results show that slightly slender (along the unidirectional compressive loading axis) rectangular sandwich panels have the most desirable stiffness-to-weight ratios for aerospace structural applications; the degradation of buckling strength sandwich panels with rising temperature is faster in shear than in compression; and the fiber orientation of the face sheets for optimum combined-load buckling strength of sandwich panels is a strong function of both loading condition and panel aspect ratio. Under the same specific weight and panel aspect ratio, a sandwich panel with metal matrix composite face sheets has a much higher buckling strength than one having monolithic face sheets.     

Experimental, numerical, and analytical results for buckling and post-buckling of orthotropic rectangular sandwich panels

Rectangular orthotropic sandwich fiber reinforced plastic (FRP) panels were tested for buckling in uniaxial compression. The panels, with either balsa or linear PVC foam cores, were tested in two sizes: 183 cm×92 cm (72 in.×36 in.) and 122 cm×92 cm (48 in.×36 in.) for aspect ratios of 2.0 and 1.3, respectively. The sandwich panels were fabricated using the vacuum-assisted resin transfer molding (VARTM) technique. The two short edges of the sandwich panels were clamped, while the two long edges were simply supported. The experimental elastic buckling loads of panels with an aspect ratio of 1.3 were 400 kN (90 klb) for balsa core panels and 267 kN (60 klb) for foam core panels. For balsa and foam core panels with an aspect ratio 2.0, the experimental buckling loads were 334 kN (75 klb) and 240 kN (54 klb), respectively. Experimental buckling results for balsa core panels of both sizes differed by 5–8% from numerical and analytical results. Differences in experimental and predicted buckling loads for foam core panels ranged between 15% and 23%. Post-buckling collapse of balsa and foam core panels with an aspect ratio of 1.3 were 694 kN (156 klb) and 347 kN (78 klb), respectively. For balsa and foam core panels with an aspect ratio of 2.0, post-buckling collapse occurred at 592 kN (133 klb) and 334 kN (75 klb), respectively. A numerical post-buckling analysis qualitatively followed that of the experimental results.     

Impact response of sandwich plates with a pyramidal lattice core

The ballistic performance edge clamped 304 stainless-steel sandwich panels has been measured by impacting the plates at mid-span with a spherical steel projectile whose impact velocity ranged from 250 to 1300 m s⁻¹. The sandwich plates comprised two identical face sheets and a pyramidal truss core: the diameter of the impacting spherical projectile was approximately half the 25 mm truss core cell size. The ballistic behavior has been compared with monolithic 304 stainless-steel plates of approximately equal areal mass and with high-strength aluminum alloy (6061-T6) sandwich panels of identical geometry. The ballistic performance is quantified in terms of the entry and exit projectile velocities while high-speed photography is used to investigate the dynamic deformation and failure mechanisms. The stainless-steel sandwich panels were found to have a much higher ballistic resistance than the 6061-T6 aluminum alloy panels on a per volume basis but the ballistic energy absorption of the aluminum structures was slightly higher on a per unit mass basis. The ballistic performance of the monolithic and sandwich panels is almost identical though the failure mechanics of these two types of structures are rather different. At high impact velocities, the monolithic plates fail by ductile hole enlargement. By contrast, only the proximal face sheet of the sandwich plate undergoes this type of failure. The distal face sheet fails by a petalling mode over the entire velocity range investigated here. Given the substantially higher blast resistance of sandwich plates compared to monolithic plates of equal mass, we conclude that sandwich plates display a potential to outperform monolithic plates in multi-functional applications that combine blast resistance and ballistic performance.     

Large inelastic response of unbonded metallic foam and honeycomb core sandwich panels to blast loading

Sandwich panels constructed from metallic face sheets with the core composed of an energy absorbing material, have shown potential as an effective blast resistant structure. In the present study, air-blast tests are conducted on sandwich panels composed steel face sheets with unbonded aluminium foam (Alporas, Cymat) or hexagonal honeycomb cores. Honeycomb cores with small and large aspect ratios are investigated. For all core materials, tests are conducted using two different face sheet thicknesses. The results show that face sheet thickness has a significant effect on the performance of the panels relative to an equivalent monolithic plate. The Alporas and honeycomb cores are found to give higher relative performance with a thicker face sheet. Under the majority of the loading conditions investigated, the thick core honeycomb panels show the greatest increase in blast resistance of the core materials. The Cymat core panels do not show any significant increase in performance over monolithic plates.     

表面增韧层对层板,夹芯板撞击行为的影响

本文对层板和夹芯板受硬物低速撞击的撞击力进行了计算和测量。本研究的目的是比较层板和夹芯板的耐撞击行为并确定表面增韧层对其低能量撞击行为的影响。     

表面增韧层对层板、夹芯板撞击行为的影响

本文对层板和夹芯板受硬物低速撞击的撞击力进行了计算和测量.本研究的目的是比较层板和夹芯板的耐撞击行为并确定表面增韧层对其低能量撞击行为的影响.     

水下冲击波作用的铝合金蜂窝夹层板动力学响应研究

为研究铝合金蜂窝夹层板水下爆炸冲击波载荷作用的动态响应及抗冲击性能,利用非药式水下爆炸冲击波加载装置对气背固支5A06铝合金夹层板及具有相同面密度的单层板进行水下冲击波加载试验。利用高速相机结合三维数字散斑技术(DIC)对夹层板后面板动态响应进行实时测量,获得夹层板气背面受水下冲击波作用的动态响应历程及变形毁伤模式,比较分析铝合金蜂窝夹层板抗冲击防护性能。结果表明,较相同面密度的单层板,蜂窝夹层板受水下冲击波载荷作用的芯层压缩能有效减少气背面板的塑性变形,提高夹层结构整体抗冲击性能。     

Characteristics of joining inserts for composite sandwich panels

Composite sandwich constructions are widely employed in various light weight structures, because composite sandwich panels have high specific stiffness and high specific bending strength compared to solid panels. Since sandwich panels are basically unsuited to carry localized loads, the sandwich structure should provide joining inserts to transfer the localized loads to other structures.In this work, the load transfer characteristics of the partial type insert for composite sandwich panels were investigated experimentally with respect to the insert shape. The static and dynamic pull out tests of the composite sandwich panels composed of an aluminum honeycomb core, two laminates of carbon fiber/epoxy composite and aluminum insert, were performed. From the experiments, the effect of the insert shape on the mechanical characteristics of composite sandwich panels was evaluated.     

An experimental investigation of static and fatigue behaviour of sandwich composite panels joined by fasteners

An experimental investigation has been carried out to estimate the static and fatigue behaviour of specimens made up of steel plates and sandwich composite panels joined together by either blind or mechanical lock fasteners.A preliminary study was carried out in order to analyse the drilling operation of sandwich panels to determine the best values of parameters to use for fastener installation.A first set of pull-out and shear static tests was performed in 1992, using sandwich panels composed of a nomex honeycomb core between two laminates of glass/graphite/kevlar fibres in epoxy matrix.The investigation was completed in 1998. It consisted of performing a set of pull-out and shear fatigue tests on joints with blind fasteners, and of performing a new set of static tests on identical specimens with the same loading conditions as in 1992 so as to evaluate the possible ageing effect on mechanical proprieties of sandwich panels tested.     

The impact resistance of polypropylene-based fibre–metal laminates

The high velocity impact response of a range of polypropylene-based fibre–metal laminate (FML) structures has been investigated. Initial tests were conducted on simple FML sandwich structures based on 2024-O and 2024-T3 aluminium alloy skins and a polypropylene fibre reinforced polypropylene (PP/PP) composite core. Here, it was shown that laminates based on the stronger 2024-T3 alloy offered a superior perforation resistance to those based on the 2024-O system. Tests were also conducted on multi-layered materials in which the composite plies were dispersed between more than two aluminium sheets. For a given target thickness, the multi-layered laminates offered a superior perforation resistance to the sandwich laminates. The perforation resistances of the various laminates investigated here were compared by determining the specific perforation energy (s.p.e.) of each system. Here, the sandwich FMLs based on the low density PP/PP core out-performed the multi-layer systems, offering s.p.e.’s roughly double that exhibited by a similar Kevlar-based laminate.A closer examination of the panels highlighted a number of failure mechanisms such as ductile tearing, delamination and fibre failure in the composite plies as well as permanent plastic deformation, thinning and shear fracture in the metal layers. Finally, the perforation threshold of all of the FML structures was predicted using the Reid–Wen perforation model. Here, it was found that the predictions offered by this simple model were in good agreement with the experimental data.     

Ballistic limit for oblique impact of thin sandwich panels and spaced plates

Ballistic perforations of monolithic steel sheets, two-layered sheets and lightweight sandwich panels were investigated both experimentally and numerically. The experiments were performed using a short cylindrical projectile with either a flat or hemispherical nose that struck the target plate at an angle of obliquity. A total of 170 tests were performed at angles of obliquity 0–45°. The results suggest that during perforation by a flat-nosed projectile, layered plates cause more energy loss than monolithic plates of the same material and total thickness. There was no significant difference in the measured ballistic limit speed between monolithic plates and layered plates during oblique impact perforation by a hemispherical-nosed projectile.     

钢板夹泡沫铝组合板抗爆性能数值模拟

鉴于泡沫铝材料良好的吸能特性和三明治型组合构件在强度、刚度上的优势,通过有限元分析软件ANSYS/LS-DYNA对钢板-泡沫铝-钢板三明治型组合板进行了装药量为10.0kgTNT的非接触爆炸数值模拟,考察组合板在爆炸荷载作用下的动力响应。研究表明:钢板夹泡沫铝组合板承受爆炸冲击波荷载时,响应方式主要为组合板整体弯曲变形和泡沫铝芯层局部压缩变形,芯层压缩变形是组合板吸收耗散能量的主要途径;适当地增加泡沫铝芯层厚度和面板厚度能够提高组合板的抗爆性能,同时使组合板充分发挥耗能作用。     

Dynamic response of aluminum honeycomb sandwich panels under foam projectile impact

The dynamic response of honeycomb sandwich panels under aluminum foam projectile impact was investigated. The different configurations of panels were tested, and deformation/failure modes were obtained. Corresponding numerical simulations were also presented to investigate the energy absorption and deformation mechanism of sandwich panels. Results showed that the deformation/failure modes of sandwich panels were sensitive to the impact velocity and density of aluminum foam. When the panel was impacted by the aluminum foam projectile with the back mass of nylon, the “accelerating impact” stage can be produced and may lead to further compression and damage of the sandwich structures.     

Deformation and impact energy absorption of cellular sandwich panels

The response and energy absorption capacity of cellular sandwich panels that comprises of silk-cotton wood skins and aluminum honeycomb core are studied under quasi-static and low velocity impact loading. Two types of sandwich panels were constructed. The Type-I sandwich panel contains the silk-cotton wood plates (face plates) with their grains oriented to the direction of loading axis and in the case of Type-II sandwich panel, the wood grains were oriented transverse to the loading axis. In both of the above cases, aluminum honeycomb core had its cell axis parallel to the loading direction. The macro-deformation behavior of these panels is studied under quasi-static loading and their energy absorption capacity quantified. A series of low velocity impact tests were conducted and the dynamic data are discussed. The results are then compared with those of quasi-static experiments. It is observed that the energy absorption capacity of cellular sandwich panels increases under dynamic loading when compared with the quasi-static loading conditions. The Type-I sandwich panels tested in this study are found to be the better impact energy absorbers for low velocity impact applications.     

泡沫铝夹芯板抗冲击性能分析

试验设计了3块钢板夹泡沫铝夹芯板,厚度分别为50 mm、70 mm和100 mm。对每种厚度夹芯板进行七组不同落锤高度的冲击试验,测得了上、下面板变形值,记录了夹芯板的破坏情况。应用数值模拟软件ANSYS/LS-DYNA进一步还原夹芯板冲击过程,导出了面板与芯材的吸能占比。基于假设的夹芯板理论模型,给出了平均冲击荷载、局部变形和整体变形最大值的估算公式。结果表明:当夹芯板尺寸和材料强度一定时,局部变形值与落锤高度的平方根成正比,整体变形最大值、平均冲击力均与落锤高度的平方根成线性关系。夹芯板的抗冲击性能主要依靠增大泡沫铝芯层的变形进行耗能,芯层越厚,泡沫铝吸能占比越大,局部变形越小,夹芯板受到的冲击力越大。     

Effect of a Thin Soft Core on the Impact Behaviour of CFRP Laminates

Low-velocity impact tests were carried out on sandwich plates having CFRP facings and thin rubbery core. Two types of cores, differing in the material nature and thickness, were used. For comparison, similar tests were performed on the monolithic laminate. Various impact parameters, among which indentation, first failure energy, perforation energy, absorbed energy and maximum contact force, were analyzed, to highlight the effect of the core on the material response. The influence of the core on the macroscopic behaviour of the panels was quite limited, except in the elastic phase, where the lower stiffness of the sandwich configurations resulted in a higher energy at first failure. More relevant differences were found from the study of failure modes, carried out combining ultrasonic C-scan and a limited number of microscopic observations. In particular, in correspondence of the energy for barely visible impact damage, besides considerable facing-core debonding, both the facings of the sandwich structures exhibited fibre breakage at their back side.     

The low velocity impact response of foam-based sandwich panels

This paper describes the results of a combined experimental/numerical study to investigate the perforation resistance of sandwich structures. The impact response of plain foam samples and their associated sandwich panels was characterised by determining the energy required to perforate the panels. The dynamic response of the panels was predicted using the finite element analysis package ABAQUS/Explicit. The experimental arrangement, as well as the FE model were also used to investigate, for the first time, the effect of oblique loading on sandwich structures and also to study the impact response of sandwich panels on an aqueous support.     

Response of metallic pyramidal lattice core sandwich panels to high intensity impulsive loading in air

Small scale explosive loading of sandwich panels with low relative density pyramidal lattice cores has been used to study the large scale bending and fracture response of a model sandwich panel system in which the core has little stretch resistance. The panels were made from a ductile stainless steel and the practical consequence of reducing the sandwich panel face sheet thickness to induce a recently predicted beneficial fluid-structure interaction (FSI) effect was investigated. The panel responses are compared to those of monolithic solid plates of equivalent areal density. The impulse imparted to the panels was varied from 1.5 to 7.6 kPa s by changing the standoff distance between the center of a spherical explosive charge and the front face of the panels. A decoupled finite element model has been used to computationally investigate the dynamic response of the panels. It predicts panel deformations well and is used to identify the deformation time sequence and the face sheet and core failure mechanisms. The study shows that efforts to use thin face sheets to exploit FSI benefits are constrained by dynamic fracture of the front face and that this failure mode is in part a consequence of the high strength of the inertially stabilized trusses. Even though the pyramidal lattice core offers little in-plane stretch resistance, and the FSI effect is negligible during loading by air, the sandwich panels are found to suffer slightly smaller back face deflections and transmit smaller vertical component forces to the supports compared to equivalent monolithic plates.     

Design and manufacture of all-PP sandwich panels based on co-extruded polypropylene tapes

This paper describes the creation of polypropylene sandwich panels, based on all-polypropylene (all-PP) composite laminates combined with a polypropylene based honeycomb or foam core. These all-PP composite laminates are based on high modulus polypropylene tape reinforcing a polypropylene matrix. Sandwich panels containing these all-PP composite laminate faces are compared with sandwich panels containing conventional glass fibre reinforced polypropylene laminate faces, and the mechanical properties, failure modes, and design requirements of these different materials are discussed.