Three-point bending behavior of aluminum foam sandwich with steel panel

Static three-point bending tests of aluminum foam sandwiches with glued steel panel were performed. The deformation and failure of sandwich structure with different thicknesses of panel and foam core were investigated. The results indicate that the maximum bending load increases with the thickness of both steel panel and foam core. The failure of sandwich can be ascribed to the crush and shear damage of foam core and the delamination of glued interface at a large bending load, The crack on the foam wall developed in the melting foam procedure is the major factor for the failure of foam core. The sandwich structure with thick foam core and thin steel panel has the optimal specific bending strength. The maximum bending load of that with 8 mm panel and 50 mm foam core is 66.06 kN.

A plastic indentation model for sandwich beams with metallic foam cores

Light weight high performance sandwich composite structures have been used extensively in various load bearing applications.Experiments have shown that the indentation significantly reduces the load bearing capacity of sandwiched beams.In this paper,the indentation behavior of foam core sandwich beams without considering the globally axial and flexural deformation was analyzed using the principle of virtual velocities.A concisely theoretical solution of loading capacity and denting profile was presented.The denting load was found to be proportional to the square root of the denting depth.A finite element model was established to verify the prediction of the model.The load-indentation curves and the profiles of the dented zone predicted by theoretical model and numerical simulation are in good agreement.

Preparation of Aluminum Foam Sandwich by Rolling-bonding/Powder Metallurgy Foaming Technology

Aluminum foam sandwich was prepared by rolling-bonding/powder metallurgical foaming technology, and the effects of rolling on bond strength of face sheet/powders and powder density were studied. Moreover, the foaming agent, TiH2, was heat treated and a certain amount of Mg was added into powder in an attempt to understand how the stability and uniformity of foam was improved. The experimental results show that the foaming precursors with ideal quality were obtained by rolling-bonding process. When rolling reduction is 67%, the consistency of powders reach to 99.87%. Throughout consideration of the bonding of face sheet/ core layer powders and deformation characteristic of powders, the optimum rolling reduction is 60%-70%. Cracks and drainage during foaming were inhibited by heat treatment of foaming agent TiH2 and the addition of a certain amount of Mg. The optimum heat treatment way of TiH2 is that heat preserving 1 hour at 450 ℃; the amount of adding Mg is 1wt%.

Study on the Interface Bonding and Bending Fatigue Properties of Aluminum Alloy Foam Sandwich

Foam materials have many attractive properties because of their low-weight and cell structure. By sandwiches with an aluminum-foam core, it is possible to obtain higher structural stiffness and rigidity, maintain stability against buckling and additionally make use of the high energy dissipation capability of the bare foams. The most obvious and straightforward one is adhesive bonding of pre-fabricated aluminum foams and metal face sheets. A new manufacture processing is proposed for preparation of aluminum alloy foam sandwich, ie., Al-plate/mixed element powder/ Al-plate are sandwich rolled together by a large reduction in pass, which is then foamed in heating furnace to manufacture end-use product. Aluminum alloy foam sandwich is obtained in this experiment. The experimental results showed that the process of rolling interface belongs to mechanical bonding, whose mechanism is film theory. While interface bonding belong to metallurgy bonding in the process of foaming, Al atom interdiffused in the interface, and no new phase was generated in the foaming process of aluminum face sheet/powders precursor. Bending fatigue test results showed that the bonding force of the foamed sandwich interface is very high, in fatigue test fracture occurred in the whole foam aluminum sandwich panels and Al/foam core interface was not laminated.

Low-Velocity Impact Response of Stitched Multi-layer Foam Sandwich Composites

Low-velocity impact damage known as“imperceptible”damage usually destroys the structural integrity of the material and seriously affects the service life of the materials.To improve the low-velocity impact resistance of foam sandwich composites,an innovative concept of a stitched multi-layer sandwich structure by organically combining the discrete splitting of foam layer with full thickness stitching was proposed,and its low-velocity impact resistance obtained through drop-hammer impact tests was explored.The results showed that the multi-layer foam sandwich structure acted as a stress disperser and reduced the irreversible impact damage.The depth and area of low-velocity impact damage of multi-layer foam sandwich composites gradually decreased with increasing the number of the layers.The stitched structure would improve the integrity of the foam sandwich composites and inhibit the propagation of cracks.The maximum impact load of the stitched foam sandwich composite increased by approximately 5% compared with that of the non-stitched material.In addition,the low-velocity impact damage depth,damage area and absorbed energy of the stitched three-layer foam sandwich composite were reduced by 37.7%,34.6% and 20.7%,respectively,compared with those of the non-stitched single-layer sandwich material.

PMI Foam Cored Sandwich Components Produced by Means of Different Manufacturing Methods

The paper introduced the structural applications with PMI (Polymethacrylimide) foams in sandwich components for rotor craft, launching vehicle and civil aircraft and discuss some typically used manufacturing methods, such as e.g. in-mould pressing, autoclave curing and resin infusion. The advantages of foam-cored sandwich design versus honeycomb-cored design will be discussed, focussing on manufacturing costs.

Experiment on Mode Ⅰ/Ⅱ Mixed Interfacial Fracture Characterization of Foam Core Sandwich Materials at Elevated Temperatures

Foam-cored sandwich materials have been widely used in the civil engineering due to their advantages such as lightweight,high strength,and excellent anti-corrosion ability. However,the interfacial bonding strength of foamcored sandwich materials is weakened at elevated temperatures. In practice,the effect of high temperature cannot be ignored,because the composites and foams are sensitive to the change of temperature in the environment. In this study,a series of single-leg bending beams were tested at different temperatures to evaluate the influences of high temperatures on Mode Ⅰ/Ⅱ mixed interfacial fracture of foam core sandwich materials. The temperature was from29 ℃ to 90 ℃,covered the glass transition temperature of composites and foam core,respectively. The Mode Ⅰ/Ⅱ mixed interfacial crack prorogation and its corresponding interfacial strain energy release rate were summarized.

Effect of Core Thickness and Core Density on Low Velocity Impact Behavior of Sandwich Panels with PU Foam Core

Composite sandwich structures are highly proven materials that provide high strength to weight ratio. However research works are still being carried out in the area of impact characteristics of sandwich composites. This paper provides a better understanding on the effect of core density and core thickness of sandwich panels subject to low velocity drop test. Specific energy absorption capacity of sandwich panels is obtained and factors affecting the same are explored with facings made of woven glass fiber laminates and polyurethane foam core with three different densities of 70 Kg/m3, 100 Kg/m3, 200 Kg/m3.

电动飞机蒙皮结构的冲击损伤试验与优化设计

飞机蒙皮结构常受到冰雹、维修碰撞等低能冲击,机身结构易出现损伤,引发飞机性能减退。为了提高蒙皮结构的抗冲击性能,结合Hashin失效准则建立了一种复合材料泡沫夹层结构低速冲击有限元等效模型,并利用超声C扫描对冲击后的复合材料泡沫夹层进行无损检测,试验结果表明,与无损检测结果相比较,模拟结果的误差低于10%,证明了该冲击等效模型的合理性。最后利用该有限元等效模型对某型电动飞机机身复合材料泡沫夹层蒙皮结构进行优化设计,以提高抗冲击能力、减小吸收的破坏能量、降低结构损伤程度为目标,在相同铺层数量下,得到了最优的复合材料泡沫夹层结构铺层设计方案。

泡沫填充负泊松比蜂窝夹层结构的抗爆性能数值模拟

为研究爆炸荷载作用下泡沫填充负泊松比蜂窝夹层结构(Foam-filled Auxetic Honeycomb Sandwich Structure,FAHSS)的动态响应及其对混凝土板的防护性能,利用有限元软件,考虑应变率对材料动态本构特性的影响,建立FAHSS在爆炸荷载下的有限元数值模型。通过已有负泊松比蜂窝夹层结构(Auxetic Honeycomb Sandwich Structure,AHSS)的爆炸试验对数值模型进行验证,基于验证模型分析爆炸荷载作用下FAHSS的损伤破坏规律、能量吸收特性及其对混凝土板的应力分布影响,并与AHSS和FSS(Foam Sandwich Structure)进行对比。在此基础上综合考虑聚氨酯泡沫材料密度、爆炸比例距离及填充材料等因素对FAHSS抗爆性能的影响。研究结果表明:FAHSS中的泡沫填充降低了负泊松比蜂窝夹层结构的破坏程度;随着聚氨酯泡沫材料密度的增加,FAHSS中的泡沫材料吸收能量增加;随着比例距离的增加,FAHSS的破坏程度逐渐降低,破坏形态也由局部破坏转变为整体破坏。

泡沫铝夹芯板重复击穿塑性响应及失效破坏

文中基于泡沫铝夹芯板的重复冲击实验,研究了冲头形状对夹芯板塑性响应及失效破坏的影响,并分析了其变形累积和能量耗散特性.结果表明:冲头直径与夹芯板边长比α直接影响夹芯板的变形模式,进而影响夹芯板的失效破坏模式.当α为0.2时,夹芯板主要产生局部凹陷,芯层通过局部压缩耗散能量,正面板首先发生破坏;当α达到0.4时,夹芯板主要产生整体弯曲和拉伸,芯层通过整体压缩耗散能量,背面板首先发生破坏.α越大,碰撞力峰值越大,碰撞时间越短,夹芯板的抗击穿次数越大.冲击能量越大,夹芯板在重复冲击下的能量恢复系数越小.

多胞子弹冲击泡沫夹芯梁的动力学响应分析

为了研究均匀/梯度多胞子弹冲击泡沫夹芯梁的耦合响应过程和多胞子弹对夹芯梁的加载效果,对该冲击过程开展了理论分析、数值模拟和试验研究:通过将泡沫夹芯梁等效为单梁以简化分析,基于多胞子弹的冲击波模型和泡沫夹芯梁的等效单梁响应模型,构建了多胞子弹冲击泡沫夹芯梁的耦合分析模型,给出了冲击过程中各响应阶段的控制方程,并结合龙格-库塔方法对方程进行了数值求解;基于三维Voronoi技术,开展了均匀/梯度多胞子弹冲击泡沫夹芯梁的细观有限元模拟;在多胞子弹的冲击测试平台上进行了试验研究,结合高速摄影技术获取了多胞子弹和泡沫夹芯梁的速度响应。结果表明:耦合分析模型可以准确地预测多胞子弹和泡沫夹芯梁的速度历程曲线以及多胞子弹产生的冲击压强;在初始动量相同但密度分布或初速度不同的多胞子弹冲击下,同一构型的泡沫夹芯梁展现出不同的力学响应,这说明多胞子弹的加载不能简单地等效为脉冲加载,多胞子弹与夹芯梁之间的耦合效应不可忽略;相较于均匀多胞子弹,梯度多胞子弹的冲击压力波形更加尖锐,在其衰减过程中展现出更强的非线性特征。

爆炸加载下蜂窝夹芯板和泡沫夹芯板变形行为实验研究

多孔夹芯结构因优异的比强度、比刚度而广泛应用于爆炸冲击防护领域,然而目前与爆炸相关的研究主要集中在小当量爆炸加载下夹芯结构的失效机制,实际大当量加载场景下的吸能特征研究较为少见。为更好指导工程应用,设计了三种夹芯材料(泡沫铝、边长3 mm及边长10 mm的蜂窝铝)在不同夹芯构型(单层夹芯、两层夹芯)及不同面板/夹层板/背板厚度下的十种夹芯结构,并对上述夹芯结构开展了0.5 kg TNT和1 kg TNT当量爆炸加载实验,分析了不同当量下夹芯结构的整体变形特征,探讨了夹芯材料、夹芯构型等因素对吸能防护的影响。实验结果表明:爆炸加载下,泡沫夹芯结构及蜂窝夹芯结构均可通过芯体材料的大幅压缩变形吸收转换能量,但整体而言蜂窝结构的变形均匀化更好;芯体吸能效率的发挥一方面与自身的比压缩强度相关,另一方面也与表层面/背板的强度及刚度相关,在实际应用时需优化匹配芯体的压缩强度与面/背板的强度及刚度,保证芯体材料可获得最大程度的压缩,发挥其吸能优势;实验中发现双层夹芯结构在吸能防护性能上优于等面密度的单层夹芯结构,即在等面密度的情形下,通过对内部芯体的合理结构优化是提升结构整体吸能防护效果的有效途径。该研究可以为实际应用中的防护结构设计提供更多参考数据。

复合材料夹芯结构低速冲击性能研究

复合材料夹芯结构为电子设备与外层蒙皮提供了一体化设计的思路,可以大幅降低飞行器的结构重量。通过低速冲击试验和ABAQUS仿真研究了5 J和10 J冲击能量下某飞行器复合材料机翼蒙皮典型夹芯区域在低速冲击下的性能。随着冲击能量的增加,复合材料泡沫夹芯结构的能量吸收率由5 J的72.0%提升至10 J的76.0%。由仿真结果可知,当冲击能量达到10 J时,出现了纤维损伤,且损伤沿表层铺层角度扩展,基体压缩损伤主要出现在冲击正面,基体拉伸损伤主要出现在冲击背面,损伤随冲击能量的增加而变大。当冲击能量达到10 J时,上面板与泡沫芯体粘接处也产生了较大的损伤。

PET泡沫三明治结构准静态弯曲和疲劳性能试验研究

在材料尺度下,借助试验手段获得了聚对苯二甲酸乙二醇酯(PET)泡沫三明治结构各组分材料(PET泡沫芯层、铝合金面板以及胶粘剂)的力学性能,以及PET泡沫的玻璃化转变温度和微观拓扑形态。在结构尺度下,在不同温度下进行了三点弯曲准静态试验,探究了温度对弯曲性能的影响,揭示了温度对变形响应过程的影响机理;同时,开展了常温下的三点弯曲疲劳试验,分析了载荷水平和加载频率对失效模式、疲劳寿命和刚度退化等指标的影响;在此基础上,开展了计及温度效应的三点弯曲疲劳试验,探究了环境温度对PET泡沫三明治结构疲劳性能的影响。结果表明,温度效应会显著影响PET泡沫三明治结构在准静态和疲劳弯曲载荷作用下的变形和破坏机理。

铝面板泡沫夹芯结构材料脱粘缺陷的超声脉冲多次反射法检测

针对铝面板泡沫夹芯结构材料脱粘缺陷的检测问题,开展了超声脉冲多次反射法检测技术研究。分析了超声脉冲多次反射法的检测原理,制作了人工模拟缺陷试样,进行了自动检测C扫描成像,通过灰度点数量统计方法分析和优化了缺陷识别的结果。研究结果表明,超声脉冲多次反射法能有效检出铝面板泡沫夹芯结构材料中的脱粘缺陷,为材料研制和质量评估提供依据。

孔柱锥度对纤维柱增强夹芯结构压缩性能的影响

纤维柱增强泡沫夹芯材料孔柱在加工过程中会产生一定的锥度,为研究孔柱锥度对夹芯结构压缩性能的影响,设计并制备了15组不同锥度孔柱的纤维柱增强复合材料。对制备的夹芯结构进行准静态压缩试验并结合数值模拟,研究了孔柱锥度与芯材厚度对夹芯结构压缩强度、模量、比强度以及失效形式的影响。结果表明:芯材厚度为25 mm、30 mm、35 mm的夹芯结构,孔柱锥度由0°提升至16°后,压缩强度分别提升了14.7%、22%、24.8%,压缩模量分别提升了25.9%、31.6%、37.7%,比强度分别提升了4%、9.95%、10.24%;孔柱锥度较小和无锥度孔柱的夹芯结构失效形式为纤维柱的屈曲、断裂,且屈曲、断裂位置随着孔柱锥度的增大逐渐向孔径较小的一端偏移;当孔柱锥度提升至16°时,夹芯结构中部分纤维柱孔径较小的一端与面板发生脱黏,导致纤维柱未能起到良好的支撑效果,影响材料的力学性能。

高速磁浮列车泡沫三明治板在冲击载荷下的吸能特性与参数优化

建立模拟高速磁浮列车泡沫三明治裙板冲击的有限元模型,基于搭建的钢球冲击试验装置验证模型的有效性,研究冲击速度、前后金属面板厚度和支撑间距对泡沫三明治板吸能量和冲击载荷的影响。采用响应面法建立泡沫三明治板内能和初始峰值载荷的代理模型,基于遗传算法提出冲击速度、前后面板厚度和支撑间距等参数的优化方法。研究结果表明:在低速(8 m/s)冲击下,泡沫三明治板具有更好的吸能效率,吸能效率能达到90%以上;随着冲击速度增加,吸能效率显著下降;增加冲击间距不仅能延长冲击作用时间,也能显著降低冲击载荷峰值力,降幅达到13.59%;针对高速磁浮列车泡沫三明治板的吸能设计要求,通过调整前、后金属面板的厚度可有效改善其吸能效果。内能和峰值力的预测值与其真实值之间的最大相对误差分别为4.14%和0.96%,满足高速磁浮列车泡沫三明治板吸能特性预测的精度要求。

芯材双向开槽工艺对PET泡沫三明治结构弯曲性能的影响

借助实验结合仿真分析的研究方法,深入探究了芯材表面双向开槽对PET泡沫三明治结构弯曲性能的影响,采用熵权法-优劣解距离法对16种开槽工况进行了详细分析。结果表明,在三点弯曲实验中,PET泡沫芯材的压缩应变主要集中在中间压头附近,永久塑性变形出现在铝合金面板和胶层处,未在各组分材料中发现明显的失效行为。随着芯材开槽体积的增大,结构的刚度、峰值载荷和总能量吸收均增大,结构的比吸能减小;开槽深度、宽度、间距会对这些性能指标产生显著影响;胶粘剂在连接芯材和面板的同时,增强了结构的抗弯曲性能。最后,基于熵权法-优劣解距离法,确定了芯材表面最优的开槽方案。

基于增强内积矩阵的PMI泡沫夹层结构损伤检测

聚甲基丙烯酰亚胺(polymethacrylimide,PMI)泡沫夹层复合材料结构因其独特的力学性能而广泛应用于航空航天领域,如何快速、准确、低成本地检测面板与芯材的脱粘损伤对结构安全使用具有重大意义,然而传统的基于超声波的无损检测技术由于PMI泡沫的吸声特性难以有效地检测到此类结构的脱粘损伤,该文探索基于振动响应测试的方法在PMI泡沫夹层结构损伤检测中的可行性及有效性。以振动时域响应相关性分析建立的结构损伤特征——内积矩阵(inner product matrix,IPM)为基础,通过将不同激励点下计算得到的IPM进行堆叠,提出了增强内积矩阵(enhanced inner product matrix,EIPM)的概念,并以EIPM为卷积神经网络(convolutional neural network,CNN)的输入、PMI泡沫夹层结构的损伤状态为输出,建立了基于EIPM及CNN的结构损伤检测方法。PMI泡沫夹层悬臂梁结构的脱粘损伤检测仿真算例及实验验证结果表明,所提方法在3个及以上测点时的平均识别准确率均在99%以上,且与基于IPM的方法相比,EIPM方法具有更好的收敛速度和稳定性。