Low velocity impact response of autoclaved aerated concrete/CFRP sandwich plates

Autoclaved aerated concrete (AAC)-CFRP composites have proven to be structurally efficient combinations for lightweight structural components such as floor beams, lintels, walls or columns. Besides the need to possess adequate flexural properties, AAC/CFRP structures need to be evaluated for their ability to withstand localized damage. During service, the before mentioned structural members are subjected to impact loading that varies from localized object impact, blast due to explosions, or to high velocity impact of debris during tornados, hurricanes, or storms. The objective of this paper is to evaluate the response of AAC/CFRP sandwich structures to low velocity impact (LVI) and to compare the experimental results to the predicted energy absorptions values given by an energy balance model. AAC/CFRP panels are prone to heavy object impacts under relatively low velocities such as in the case of object/tool drops on floor beams or low velocity collisions against columns.     

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.     

Low-velocity flexural impact response of fiber-reinforced aerated concrete

Impact response of fiber-reinforced aerated concrete was investigated under a three-point bending configuration based on free-fall of an instrumented impact device. Two types of aerated concrete: plain autoclaved aerated concrete (AAC) and polymeric fiber-reinforced aerated concrete (FRAC) were tested. Comparisons were made in terms of stiffness, flexural strength, deformation capacity and energy absorption capacity. The effect of impact energy on the mechanical properties was investigated for various drop heights and different specimen sizes. It was observed that dynamic flexural strength under impact was more than 1.5 times higher than the static flexural strength. Both materials showed similar flexural load carrying capacity under impact, however, use of 0.5% volume fraction of polypropylene fibers resulted in more than three times higher flexural toughness. The performed instrumented impact test was found to be a good method for quantifying the impact resistance of cement-based materials such as aerated concrete masonry products.     

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.     

Prediction of impact damage on sandwich composite panels

Sandwich structures are extensively employed in the aerospace and automobile industries. The understanding of their behaviour under impact conditions is extremely important for the design and manufacturing of these engineering structures since impact problems are directly related to structural integrity and safety requirements. This paper investigates the damage behaviour of composite sandwich panels with aramid paper honeycomb (NOMEX) and polyetherimide (PEI) foam cores under transverse impacts at high velocities. A numerical model was developed using the dynamic explicit finite element (FE) structure analysis program PAM-CRASH. For both sandwich structures numerical analysis reproduces physical behaviour observed experimentally in high velocity impact tests.     

Composite and non-composite behaviors of foam-insulated concrete sandwich panels

The structural behaviors of foam-insulated concrete sandwich panels subjected to uniform pressure have been evaluated. This study showed that the interface conditions such as composite and non-composite had a significant effect on the response of foam-insulated concrete sandwich panels, indicating that the simulated shear tie resistance should indeed be incorporated in numerical analyses. Finite element models were developed to simulate the detailed shear resistance of connectors and the nonlinear behaviors of concrete, foam and rebar components. The models were then validated using data from static tests performed at the University of Missouri. The modeling approach used here was compatible with the American Concrete Institute (ACI) Code and existing design practices. The results of this study will therefore provide improved methodology for the analysis and design of foam-insulated sandwich panels under both static and blast loadings.     

泡沫填充的S型褶皱复合材料夹芯板低速冲击响应特性

为了研究泡沫填充褶皱夹芯结构低速冲击响应特性与损伤机制,采用热压法制备了玻璃纤维增强S型褶皱夹芯板,并使用聚氨酯泡沫进行了填充,通过落锤试验机对夹芯板节点与基座两个位置进行了冲击试验.研究表明,冲击位置对泡沫填充褶皱夹芯板的失效模式存在影响.当冲击位置为节点时,夹芯板芯子以凸侧面曲面壁压溃断裂失效为主,泡沫的填充起到了...     

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.     

Impact and post impact behavior of composite sandwich panels

Assessing the residual mechanical properties of a sandwich structure is an important part of any impact study and determines how the structure can withstand post impact loading. The damage tolerance of a composite sandwich structure composed of woven carbon/epoxy facesheets and a PVC foam core was investigated. Sandwich panels were impacted with a falling mass from increasing heights until damage was induced. Impact damage consisted of delamination and permanent indentation in the impacted facesheets. The Compression After Impact (CAI) strength of sandwich columns sectioned from these panels was then compared with the strength of an undamaged column. Although not visually apparent, the facesheet delamination damage was found to be quite detrimental to the load bearing capacity of the sandwich panel, underscoring the need for reliable damage detection techniques for composite sandwich structures.     

Impact response of integrated hollow core sandwich composite panels

This paper deals with an innovative integrated hollow (space) E-glass/epoxy core sandwich composite construction that possesses several multi-functional benefits in addition to the providing lightweight and bending stiffness advantages. In comparison with traditional foam and honeycomb cores, the integrated space core provides a means to route wires/rods, embed electronic assemblies, and store fuel and fire-retardant foam, among other conceivable benefits. In the current work, the low-velocity impact (LVI) response of innovative integrated sandwich core composites was investigated. Three thicknesses of integrated and functionality-embedded E-glass/epoxy sandwich cores were considered in this study—including 6, 9 and 17 mm. The low-velocity impact results indicated that the hollow and functionality-embedded integrated core suffered a localized damage state limited to a system of core members in the vicinity of the impact. The peak forces attained under static compression and LVI were in accordance with Euler's column buckling equation. Stacking of the core was an effective way of improving functionality and limiting the LVI damage in the sandwich plate. The functionality-embedded cores provided enhanced LVI resistance due to energy additional energy absorption mechanisms.     

In-plane compression response of wire-woven metal cored sandwich panels

This article presents the buckling behaviors of two types of WBK (Wire-woven Bulk Kagome) cored sandwich panels subjected to in-plane compression. Classical theories are introduced, and the experimental and numerical results are presented. The effects of several design parameters are analyzed. For both types, the peak loads were governed by macroplastic buckling. Low shear modulus and strength of the WBK core substantially influenced the buckling behaviors of the sandwich panels before and after their peaks. A small initial deflection greatly decreased the resistance against buckling of the sandwich panels with thinner cores, as confirmed by a two-stage FEA (Finite Element Analysis) and the analytic solution accounting for eccentricity.     

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.     

Modelling of aluminium foam core sandwich panels under impact perforation

Aluminium foam core sandwich panels are good energy absorbers for impact protection applications, such as light-weight structural panels, packing materials and energy absorbing devices. In this study, the high-velocity impact perforation of aluminium foam core sandwich structures was analysed. Sandwich panels with 1100 aluminium face-sheets and closed-cell A356 aluminium alloy foam core were modelled by three-dimensional finite element models. The models were validated with experimental tests by comparing numerical and experimental damage modes, output velocity, ballistic limit and absorbed energy. By this model the influence of foam core and face-sheet thicknesses on the behaviour of the sandwich panel under impact perforation was evaluated.     

Damage prediction in composite sandwich panels subjected to low-velocity impact

The paper illustrates the application of a finite element tool for simulating the structural and damage response of foam-based sandwich composites subjected to low-velocity impact. Onset and growth of typical damage modes occurring in the composite skins, such as fibre fracture, matrix cracking and delaminations, were simulated by the use of three-dimensional damage models (for intralaminar damage) and interfacial cohesive laws (for interlaminar damage). The nonlinear behaviour of the foam core was simulated by a crushable foam plasticity model. The FE results were compared with experimental data acquired by impact testing on sandwich panels consisting of carbon/epoxy facesheets bonded to a PVC foam. Good agreement was obtained between predictions and experiments in terms of force histories, force–displacement curves and dissipated energy. The proposed model was also capable of simulating correctly nature and size of impact damage, and of capturing the key features of individual delaminations at different depth locations.     

Finite element modelling of low velocity impact of composite sandwich panels

This paper outlines a finite element procedure for predicting the behaviour under low velocity impact of sandwich panels consisting of brittle composite skins supported by a ductile core. The modelling of the impact requires a dynamic analysis that can also handle non-linearities caused by large deflections, plastic deformation of the core and in-plane degradation of the composite skins. Metal honeycomb, frequently used as a core material, is anisotropic and requires a non-standard approach in the elasto-plastic part of the analysis. A suitable yield criteria based on experimental observations is proposed. Comparisons of experimental and finite element responses are shown for sandwich panels with carbon fibre skins and aluminium honeycomb cores.     

Flexural behavior of a hybrid FRP and lightweight concrete sandwich bridge deck

This paper presents a new concept for a lightweight hybrid-FRP bridge deck. The sandwich construction consists of three layers: a fiber-reinforced polymer composite (FRP) sheet with T-upstands for the tensile skin, lightweight concrete (LC) for the core and a thin layer of ultra high performance reinforced concrete (UHPFRC) as a compression skin. Mechanical tests on eight hybrid beams were performed with two types of LC and two types of FRP/LC interface: unbonded (only mechanical interlocking of LC between T-upstands) and bonded with an epoxy adhesive. The ultimate loads of the beams increased by 104% on average due to bonding. However, the beam failure mode changed from ductile to brittle. The beams using a LC of 44% higher density exhibited an 81% increase in the ultimate load. The manufacturing of the beams proved to be economic in that epoxy and concrete layers were rapidly and easily applied wet-in-wet without intermediate curing times. The experimental results showed positive results regarding the feasibility of the suggested hybrid bridge deck.     

Compressive response of notched glass-fiber epoxy/honeycomb sandwich panels

The quasi-static uniaxial compressive response of E-glass/epoxy-Nomex™ sandwich panels containing circular through-holes was studied experimentally. Specimens with four and eight-harness satin weave fabric face-sheets were tested. In both materials the principal failure mechanism consisted of linear damage zones (LDZs) emanating from the hole edge. LDZs are macroscopically similar to fiber-bridged cracks in tension, and propagated in a stable manner. Cross-sectioning indicated that the LDZ wake was characterized by fiber-kinking in all warp tows, and weft tow cracking. Strain gauges were used to measure local deformation as the LDZ propagated across the width of the specimen; a strain-softening behavior was observed in the LDZ wake.A damage zone model (DZM) was applied in order to determine its validity and mechanistic basis. This was assessed by examining its ability to predict three experimentally observed phenomena: the notched strength, local strain distribution, and LDZ growth characteristics. Two models were created in order to interrogate the DZM. The damage growth model was used to determine the ability of the DZM to predict the LDZ growth behavior and notched strength. A finite element model was implemented to predict the local strain distribution. In both cases discrete nonlinear springs acting in the wake of an equivalent crack were used to model the LDZ. This approach provided a good correlation with whichever set of measurements was used to calibrate it. Extension of the model to the other phenomena resulted in weaker correlations with the data, suggesting that further work is required to develop a true mechanism-based model.     

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.     

明胶鸟弹撞击复合材料蜂窝夹芯板试验

开展明胶鸟弹撞击复合材料蜂窝夹芯板试验,研究夹芯结构在软体高速冲击下的损伤形式,分析相关因素对结构动态响应结果的影响。通过CT扫描对复合材料蜂窝夹芯板内部进行检测可知,面板出现分层、基体开裂、纤维断裂、凹陷、向胞内屈曲等损伤形式,蜂窝芯出现芯材压溃、与面板脱粘的损伤形式;分析复合材料蜂窝夹芯板后面板的动态变形过程及撞击中心处位移-时间数据可知,复合材料蜂窝夹芯板在撞击过程中出现由全局弯曲变形主导和局部变形主导的两种变形模式;通过对比不同工况下的复合材料蜂窝夹芯板损伤程度可知,复合材料蜂窝夹芯板损伤程度随鸟弹撞击速度的增加而增大;蜂窝芯高度为10 mm的复合材料蜂窝夹芯板较蜂窝芯高度为5 mm的复合材料蜂窝夹芯板的损伤程度大;初始动能较大的球形鸟弹较圆柱形鸟弹对复合材料蜂窝夹芯板造成的冲击损伤程度更大。      

预制混凝土板、墙体系发展现状

该文在对一个含减震外挂墙板平面框架(简称减震结构)以及一个作为对比的纯框架(简称抗震结构)进行混合试验的基础上,进一步对其单跨2层试验子结构进行了拟静力试验,研究了两结构在水平地震作用下的受力过程、损伤模式及减震外挂墙板对主体结构抗震性能的影响。研究结果表明：减震结构和抗震结构的破坏机制均为梁端和柱底出现塑性铰的梁铰机制,减震外挂墙板未改变主体结构的破坏模式;减震结构中,在最大层间位移角达到1/55之前,消能器呈预期的履带式滚动变形,此后由于外挂墙板的面内转动变形,消能器水平剪切变形值增加不大,且圆弧段产生明显变形;试验过程中减震外挂墙板未出现裂缝;墙板与框架间上部线连接处裂缝宽度较小,连接钢筋应变也较小,表明连接可靠;两试件均具有较好的变形能力和耗能能力;在相同位移级别下,减震结构的刚度、极限承载力和耗能能力均更好。