V型折叠式夹层板横向压皱吸能特性研究

金属夹层板具有优越的力学性能,良好的吸能特性可用于船舶耐撞、抗爆防护结构设计。以V型折叠式夹芯结构为研究对象,通过试验分析夹芯层结构变形模式、压皱力历程曲线等,得到了夹芯层结构横向压皱力学性能,采用有限元软件Abaqus对其在横向受压时的力学行为进行数值仿真分析,分析结构压皱动态渐进屈曲过程、变形模式、吸能效率、平均压皱强度等。对比分析表明,V型夹芯层结构在横向压皱载荷下发生屈曲、褶皱变形模式,变形模式决定了压皱力学行为及其性能,其中单元变形模式I的吸能效率较高。采用合理的模型化技术得到的有限元计算结果与试验结果两者吻合较好,验证了有限元数值仿真的计算精度。     

Crushing energy absorption of GFRP sandwich panels and corresponding monolithic laminates

Steady quasi-static compression of GFRP monolithic laminates and sandwich panels made of a randomly oriented continuous filament mat/polyester were undertaken. The effects of facing/laminate thickness, trigger collapse system and aspect ratio on their failure mechanisms, hence their energy absorption capability were examined. A numerical model, using a non-linear finite element explicit code, LS-DYNA, was used for pre-analysis of the effect of aspect ratio. A collapse trigger configuration was also studied numerically. The experimental data showed that high values of energy absorbed per unit mass were a predominant feature of the thickest monolithic laminates and sandwich panels with the thickest facings. The monolithic laminates showed higher specific energy than their sandwich panel counterparts. It seems that this difference was due to instability of the sandwich specimens.     

In-plane compression of sandwich panels with debonds

The post failure behaviour of sandwich panels loaded in in-plane compression is studied by considering the structural response of such panels with symmetrically located edge debonds. A parametric finite element model is used to determine the influence of different material and geometrical properties on the failure progression, i.e. after initiation of damage. The investigated failure modes are buckling of the debonded face sheets, debond propagation and face sheet failure. The postbuckling failure mode is mainly determined by the fracture toughness of the core and the bending stiffness and strength of the face sheets. The presented approach and results can be used to determine how sandwich panels should be constituted, or not, to promote damage progression favourable for efficient energy absorption during in-plane crushing. The prolonged damage propagation is very complex as it is strongly non-linear and depends on a combination of stiffness, strength and geometry of the constituent materials.     

Failure initiation and propagation characteristics of honeycomb sandwich composites

The energy absorbed during the failure of a variety of structural shapes is influenced by material, geometry and the failure mode. Failure initiation and propagation of the honeycomb sandwich under loading involves not only non-linear behavior of the constituent materials, but also complex interactions between various failure mechanisms. Therefore, there is a need for an improved understanding of the material characteristics and energy absorption modes to facilitate the design of sandwich performance. In the present study, failure initiation and propagation characteristics of sandwich beams and panels subjected to quasi-static and impact loadings were investigated. Experimental studies involved a series of penetration and perforation tests on 2D beam and 3D panel configurations using a truncated cone impactor with impact velocities up to 10 m/s. Preliminary tests were also performed on the sandwich beams subjected to the three-point bending. Load-carrying, energy-absorbing characteristics and failure mechanisms under quasi-static and impact loading were determined. Dominant deformation modes involved upper skin compression failure in the vicinity of the indenter, core crushing and lower skin tensile failure.     

Compression and impact testing of two-layer composite pyramidal-core sandwich panels

Quasi-static uniform compression tests and low-velocity concentrated impact tests were conducted to reveal the failure mechanisms and energy absorption capacity of two-layer carbon fiber composite sandwich panels with pyramidal truss cores. Three different volume-fraction cores (i.e., with different relative densities) were fabricated: 1.25%, 1.81%, and 2.27%. Two-layer sandwich panels with identical volume-fraction cores (either 1.25% or 2.27%), and also stepwise graded panels consisting of one light and one heavy core, were investigated under uniform quasi-static compression. Under quasi-static compression, load peaks were identified with complete failure of individual truss layers due to strut buckling or strut crushing, and specific energy absorption was estimated for different core configurations. In the impact test, the damage resulting from low-velocity concentrated impact was investigated. Our results show that compared with glass fiber woven textile truss cores, two-layer carbon fiber composite pyramidal truss cores have comparable specific energy absorptions, and thus could be used in the development of novel light-weight multifunctional structures.     

The mechanical behaviour of corrugated-core sandwich panels

A series of experimental investigations and numerical analyses is presented into the compression response, and subsequent failure modes in corrugated-core sandwich panels based on an aluminium alloy, a glass fibre reinforced plastic (GFRP) and a carbon fibre reinforced plastic (CFRP). The corrugated-cores were fabricated using a hot press moulding technique and then bonded to face sheets based on the same material, to produce a range of lightweight sandwich panels. The role of the number of unit cells and the thickness of the cell walls in determining the overall deformation and local collapse behaviour of the panels is investigated. The experiments also provide an insight into the post-failure response of the sandwich panels. The results are compared with the numerical predictions offered by a finite element analysis (FEA) as well as those associated with an analytical model. Buckling of the cell walls has been found to be initial failure mode in these corrugated systems. Continued loading resulted in fracture of the cell walls, localised delamination as well as debonding between the skins and the core. The predictions of the FEA generally show reasonably good agreement with the experimental measurements. Finally, the specific compressive properties of the corrugated structures have been compared to those of other core materials where evidence suggests that these systems compare favourably with their more conventional counterparts.     

Three-point bending of sandwich beams with aluminum foam-filled corrugated cores

Sandwich panels having metallic corrugated cores had distinctly different attributes from those having metal foam cores, the former with high specific stiffness/strength and the latter with superior specific energy absorption capacity. To explore the attribute diversity, all-metallic hybrid-cored sandwich constructions with aluminum foam blocks inserted into the interstices of steel corrugated plates were fabricated and tested under three-point bending. Analytical predictions of the bending stiffness, initial failure load, peak load, and failure modes were obtained and compared with those measured. Good agreement between analysis and experiment was achieved. Failure maps were also constructed to reveal the mechanisms of initial failure. Foam insertions altered not only the failure mode of the corrugated sandwich but also increased dramatically its bending resistance. All-metallic sandwich constructions with foam-filled corrugated cores hold great potential as novel lightweight structural materials for a wide range of structural and crushing/impulsive loading applications.     

Advanced composite sandwich structure design for energy absorption applications: Blast protection and crashworthiness

This paper describes an experimental investigation on the response of composite sandwich structures with tubular inserts to quasi-static compression. The performance parameters, namely the peak load, absorbed crash energy, specific energy absorption; average crushing load and crush force efficiency were evaluated. The composite sandwich specimens were fabricated from glass fiber, polystyrene foam and epoxy resin. The primary mode of failure observed was progressive crushing with the composites exhibiting high energy absorption capabilities and high crushes force efficiency. The mechanism of progressive crushing of the sandwich structures and its relation to the energy absorption capabilities was deliberated. Furthermore, a statistical analysis was performed to investigate the effects of the design variables and also to determine if there were interactions between these variables. Such information is vital in the design of polymer composite sandwich structures as energy absorbers.     

High Velocity Impact Response of Composite Lattice Core Sandwich Structures

In this research, carbon fiber reinforced polymer (CFRP) composite sandwich structures with pyramidal lattice core subjected to high velocity impact ranging from 180 to 2,000 m/s have been investigated by experimental and numerical methods. Experiments using a two-stage light gas gun are conducted to investigate the impact process and to validate the finite element (FE) model. The energy absorption efficiency (EAE) in carbon fiber composite sandwich panels is compared with that of 304 stainless-steel and aluminum alloy lattice core sandwich structures. In a specific impact energy range, energy absorption efficiency in carbon fiber composite sandwich panels is higher than that of 304 stainless-steel sandwich panels and aluminum alloy sandwich panels owing to the big density of metal materials. Therefore, in addition to the multi-functional applications, carbon fiber composite sandwich panels have a potential advantage to substitute the metal sandwich panels as high velocity impact resistance structures under a specific impact energy range.     

Composite sandwich structures with nested inserts for energy absorption application

Polymer composite sandwich structures are promising candidate structures for reducing vehicle mass, thereby improving the fuel economics. Nonetheless, to fully explore this material as the primary structure and energy absorber in vehicles, it is important to understand the energy absorption capability of this material. Hence, in the present work, comprehensive experimental investigation on the response of composite sandwich structures to quasi-static compression has been carried out. The crashworthiness parameters, namely the peak force, absorbed crash energy, specific absorbed energy, average crushing force and crush force efficiency of various types of composite sandwich structures were investigated in a series of edgewise axial compression tests. The tested composite sandwich specimens were fabricated from glass and carbon fiber with epoxy resin. Four distinct modes of failure were observed and recorded. The primary mode of failure observed was progressive crushing with high energy absorption capability. The optimized design in this study had a specific energy absorption capability of 47.1 kJ/kg with a good crush force efficiency of 0.77, higher than conventional metals.     

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.     

Behavior and Failure Modes of Sandwich T-Joint Using Cohesive Zone Material Model and Contact Elements

One of the significant concerns of sandwich panels is their joints. T-joint is one the most common joint in sandwich structures. This paper deals with the numerical study of triangle T-joint under static loading. The results of numerical solution obtained by ANSYS modeling are verified with the results of experimental tests obtained in the literature. In general, the results obtained for anticipated failure load by numerical solution with the results of experimental test is in good agreement. Contact elements and cohesive zone material model are used to model the adhesive layer, hence debonding and fracture of adhesive is observed by the numerical modeling. Also, by using a written macro code in the ANSYS software, the ability of damage is explained for the core of sandwich panels; thus both the modes in fracture of T-joints (core shear failure in base panel and debonding of adhesive) are modeled. Core materials consist of Divinycell H100, H160, H250, and HCP70 are used for modeling sandwich panels, so that the function of joint is studied under different conditions of the sandwich core material. Nine different geometrical models are created by changing the base angle of the core triangle. The absorbed energy associated with different segments of the T-joint are used to investigate the effect of joint geometry and core material on the load transfer and failure mode of the T-joint.     

Experimental,Theoretical and Numerical Investigation of the Flexural Behaviour of the Composite Sandwich Panels with PVC Foam Core

This study presents the main results of an experimental, theoretical and numerical investigation on the flexural behaviour and failure mode of composite sandwich panels primarily developed for marine applications. The face sheets of the sandwich panels are made up of glass fibre reinforced polymer (GFRP), while polyvinylchloride (PVC) foam was used as core material. Four-point bending test was carried out to investigate the flexural behaviour of the sandwich panel under quasi static load. The finite element (FE) analysis taking into account the cohesive nature of the skin-core interaction as well as the geometry and materials nonlinearity was performed, while a classical beam theory was used to estimate the flexural response. Although the FE results accurately represented the initial and post yield flexural response, the theoretical one restricted to the initial response of the sandwich panel due to the linearity assumptions. Core shear failure associate with skin-core debonding close to the loading points was the dominant failure mode observed experimentally and validated numerically and theoretically.     

The bending and failure of sandwich structures with auxetic gradient cellular cores

We describe the bending and failure behaviour of polymorphic honeycomb topologies consisting of gradient variations of the horizontal rib length and cell internal across the surface of the cellular structures. The novel cores were used to manufacture sandwich beams subjected to three-point bending tests. Full-scale nonlinear Finite Element models were also developed to simulate the flexural and failure behaviour of the sandwich structures. Good agreement was observed between the experimental and FE model results. And the validated numerical model was then used to perform a parametric analysis on the influence of the gradient core geometry over the mechanical performance of the structures. It was found that the aspect ratio and the extent of gradient (i.e. the horizontal rib length growth rate or the internal angle increment) have a significant influence on the flexural properties of the sandwich panels with angle gradient cores.     

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.     

Compression-after-Impact Strength of Sandwich Panels with Core Crushing Damage

Compression-after-impact (CAI) strength of foam-cored sandwich panels with composite face sheets is investigated experimentally. The low-velocity impact by a semi-spherical (blunt) projectile is considered, producing a damage mainly in a form of core crushing accompanied by a permanent indentation (residual dent) in the face sheet. Instrumentation of the panels by strain gauges and digital speckle photography analysis are used to study the effect of damage on failure mechanisms in the panel. Residual dent growth inwards toward the mid-plane of a sandwich panel followed by a complete separation of the face sheet is identified as the failure mode. CAI strength of sandwich panels is shown to decrease with increasing impact damage size. Destructive sectioning of sandwich panels is used to characterise damage parameters and morphology for implementation in a finite element model. The finite element model that accounts for relevant details of impact damage morphology is developed and proposed for failure analysis and CAI strength predictions of damaged panels demonstrating a good correlation with experimental results.     

LOW VELOCITY PERFORATION BEHAVIOUR OF POLYMER COMPOSITE SANDWICH PANELS

The paper describes low-velocity impact tests on square panels made from two polymer composite sandwich constructions, namely woven glass vinyl ester skins with Coremat core and woven glass epoxy pre-preg skins with honeycomb core. The impact velocity was up to 8 m s^-1 with an impact mass of up to 30 kg giving a maximum impact energy of 882 J. This maximum energy gives full perforation of the panels. The panels were 0.5 m by 0.5 m with clamped but free to pull in boundary conditions. The impactor geometry considered was a 50 mm diameter hemisphere. Results are expressed in the form of energy and failure mode plots and it is shown that the energy absorbing capabilities of the panels increase with the velocity of impact. The increase in energy absorption is attributed to an increase in the core crush stress and skin failure stress at high strain rates. Some discussion is given on the influence of the energy absorbing capabilities of constituent materials on the overall energy absorption behaviour of the panel. Suggestions have also been made for increasing panel perforation energy.     

Geometry effect on the behaviour of single and glue-laminated glass fibre reinforced polymer composite sandwich beams loaded in four-point bending

The research investigated the behaviour of single and glue laminated glass fibre reinforced polymer (GFRP) composite sandwich beams considering different spans and beam cross sections. The composite sandwich beams with different thicknesses (1, 2, 3, 4, and 5 sandwich layers) have been tested in four-point static flexural test with different shear span to depth ratio (a/d). The a/d ratios showed a direct effect on the flexural and shear behaviour. The capacity of the beam decreased with increasing a/d. Various failure modes were observed including core crushing, core shear, and top skin compression failure. The failure mode map developed based on the experimental finding and analytical prediction indicated that the failure mode is affected by the a/d with the number of glue laminated panels.     

Mechanical behaviors of carbon fiber composite sandwich columns with three dimensional honeycomb cores under in-plane compression

Mechanical properties and failure modes of carbon fiber composite egg and pyramidal honeycombs cores under in plane compression were studied in the present paper. An interlocking method was developed for both kinds of three-dimensional honeycombs. Euler or core shear macro-buckling, face wrinkling, face inter-cell buckling, core member crushing and face sheet crushing were considered and theoretical relationships for predicting the failure load associated with each mode were presented. Failure mechanism maps were constructed to predict the failure of these composite sandwich panels subjected to in-plane compression. The response of the sandwich panels under axial compression was measured up to failure. The measured peak loads obtained in the experiments showed a good agreement with the analytical predictions. The finite element method was used to investigate the Euler buckling of sandwich beams made with two different honeycomb cores and the comparisons between two kinds of honeycomb cores were conducted.     

Bending response of sandwich panels with discontinuous wire-woven metal cores

The effects of a gap between discontinuous WBK (Wire-woven Bulk Kagome) cores on the bending properties of mild steel sandwich panels were elaborated. Analytic solutions were derived, and the experimental and numerical results of the bending response of sandwich panels with continuous and discontinuous WBK cores were presented. The analytic solutions of sandwich panels with continuous or discontinuous WBK cores under bending load provided good estimations of the failure mode, peak load, and bending stiffness in comparison with the experimental results. The strength and stiffness of sandwich panels with discontinuous WBK cores under bending load often substantially deteriorated depending on the gap width between the cores and on the detailed geometry near the gap. The analytic solutions successfully explained how the deterioration of the bending strength or stiffness could be minimized, when two separate sandwich panels or cores are to be joined.