泡沫铝合金三明治结构结合界面及剪切性能的研究

提出了一种新的泡沫铝合金三明治结构的制备工艺--直接将铝板/混合粉末/铝板通过一次大压下量复合轧制,然后在炉中直接发泡成最终产品的制备工艺.实验成功的制备出铝面板的泡沫铝合金芯的三明治板.讨论了铝面板泡沫铝夹芯板轧制过程中以及发泡过程中界面的结合情况及界面结合机理.结果表明,轧制过程中界面结合属于机械结合,结合机制为薄膜理论;发泡过程中界面结合属于冶金结合,而铝面板与粉末体结合发泡后,界面处则只发生Al原子的互扩散,没有新相生成.剪切实验结果表明,预制坯的界面剪切强度较低,能够直接在界面处剥离开或者将板剥离开一半后将板拉断;而发泡后的泡沫铝夹芯板的界面结合力很强,剪切时断裂发生在芯材中或者铝面板上.     

泡沫铝夹芯板的制备技术

泡沫金属是一类具有低密度以及新奇的物理、力学、电学、声学等特殊性能的新型材料.而泡沫铝的潜在用途之一是作为泡沫铝夹芯板的芯材使用.详细介绍了制备泡沫铝夹芯板的不同方法,如胶粘法、超声焊接法、激光协助发泡法、扩散焊接法、面板与预制材料轧制-包覆法和粉末复合轧制法等.通过比较,在国内粉末复合轧制法工艺简单,是最有希望适合高温作业和大批量生产的方法.     

泡沫铝冶金连接及其界面结构与力学性能研究

以Zn-10Al合金作为粘结合金,采用功率超声辅助的热浸镀法进行泡沫铝板的冶金连接,采用光学显微镜(OM)和扫描电镜(SEM)观察接头组织及界面结构,采用X射线能谱仪(EDS)测定界面处元素分布,对样品进行拉伸实验和摆锤冲击实验,并与无功率超声辅助样品和胶接样品比较。功率超声辅助冶金接头密实连续,Zn、Al元素相互扩散,在界面处连续分布;无功率超声辅助接头中存在大量气孔等缺陷。功率超声辅助冶金接头的拉伸性能和冲击性能均优于无功率超声辅助接头和胶接接头。在功率超声辅助下进行连接时,其空化作用和声流能较彻底地破除泡沫铝基体表面的氧化膜,同时能够促进组织均匀化、去气除杂,有利于形成良好的冶金结合和致密的冶金接头。     

粘接界面泡沫铝夹芯板的三点弯曲失效数值模拟

对粘接界面泡沫铝夹芯板三点弯曲载荷下的变形特性进行了实验和数值模拟方面的研究。基于有限元软件ABAQUS建立了泡沫铝夹芯板的三维有限元模型,应用内聚力模型对三点弯曲过程中典型的破坏模式——面板与芯层的界面脱粘给予了合理的模拟,模拟所得的结果与实验结果比较吻合。并在此基础上分析了面板和芯层厚度对夹芯板承载能力和吸收能量能力的影响。结果表明,增加芯层的厚度能够更大程度上提高泡沫铝夹芯板的承载能力和吸收能量的能力。     

泡沫铝夹心板的制备及其界面结合机理的研究

由泡沫铝芯材与金属面板构成的夹心结构具有轻质、高强度、良好的减震性等优点.现存的泡沫铝夹心板的制备方法很多,但均为先制备芯材再进行连接的方法.本研究提出一种新的工艺方法即采用粉末与面板直接轧制然后发泡的方法制备了Fe/Al/Fe泡沫铝夹心结构.研究了泡沫铝芯的发泡不均的问题,分析了发泡前和发泡后面板与泡沫铝芯的冶金结合过程,提出了扩散微观结合机理.最终面板与泡沫芯材通过扩散反应形成了牢固的冶金结合.     

加筋增强泡沫夹芯结构面内压缩与界面断裂性能试验

为解决复合材料泡沫夹芯结构面板局部屈曲与面芯脱粘的突出问题,提出了一种由筋条增强的玻璃纤维增强树脂基复合材料（GFRP）面板与泡沫芯层组合而成的新型夹芯结构。采用真空辅助树脂导入技术制备试验件,通过面内压缩与双悬臂梁试验,对比分析了加筋增强夹芯板与未加筋夹芯板的受力特性、失效模式和面芯粘结性能。面内压缩试验显示,与未加筋夹芯板相比,加筋增强夹芯板的失效模式由面板局部屈曲转化为面板压缩剪切破坏或整体屈曲,在GFRP材料使用量相同的情况下,试件长度为130 mm的加筋增强夹芯板平均失效荷载提高了40.87%,长度为190 mm试件提高了35.63%。双悬臂梁试验显示,加筋增强夹芯板的裂缝在发展过程中受到筋条与面板之间纤维丝搭接约束,改善了界面粘结性能,与未加筋夹芯板相比,其平均能量释放率提高了57.35%。     

泡沫铝芯三明治板的粉末冶金制备及其板/芯界面研究

采用粉末冶金发泡法制备了Fe/Al/Fe、Ti/Al/Ti泡沫铝芯三明治结构,研究了泡沫铝芯的膨胀规律,分析了面板与泡沫铝芯的冶金结合过程,提出了微观结合机制.试验发现,结合界面由扩散反应形成的金属间化合物以及冷却得到的凝固组织两部分组成,从而形成良好的冶金结合.     

复合材料泡沫夹芯板局部连接拉脱破坏试验与数值仿真

对复合材料泡沫夹芯板局部连接拉脱破坏进行了试验研究,分析了接头的破坏模式、失效载荷和面板对接头的影响。采用ABAQUS有限元软件进行了数值分析,通过与实验结果对比验证其模型的可靠性,预测分析内部的破坏模式以及结构参数对接头破坏的影响,研究了泡沫芯体内部的渐进破坏以及面板和泡沫芯体之间的胶层脱粘破坏。结果表明:泡沫夹芯板预埋螺栓连接结构灌封胶边缘的泡沫先产生裂纹后向中间扩展,中间区域全部开裂时两端裂纹沿着45°方向向上扩展。胶层开裂的区域呈弧形条状,分布在螺栓紧固件的两侧,在面板宽度方向,开裂的区域贯穿两侧。随着预埋件深度的增加最大破坏载荷也在增加,随着预埋件直径的增加亚临界破坏载荷和最大破坏载荷没有比较明显的变化,但最大破坏位移在减小。      

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。     

泡沫铝三明治板材的研究现状

闭孔泡沫铝是一种结构与功能一体化的多孔材料,具有轻质、高比强度和比刚度、能量吸收能力强等优点,但也存在着表层单层孔壁力学性能较差、表面粗糙度高以及耐腐蚀性差等不足.为了解决上述问题,研究人员设计并开发了泡沫铝三明治板材(AFS),其制备方法主要分为物理连接法和冶金连接法.传统物理连接法制备的AFS存在着界面结合强度低和耐候性较差等不足;粉末冶金和焊接法等冶金连接法所制备的板材实现了芯材与面板之间的冶金结合,极大地提升了板材的力学性能和服役寿命,但依然存在产品尺寸范围较小、工艺复杂、生产效率低、成本较高等不足.目前,针对AFS力学性能的研究主要集中在准静态和动态变形、失效模式、能量吸收能力等方面,研究表明其动静态力学性能主要受控于实体面板和泡沫铝芯层的性质、界面结合强度等.近年来有限元分析法逐渐得到了研究者们的青睐,但仍存在许多问题需要解决.本文结合国内外文献,概述了近年来AFS在制备技术、力学性能等方面的研究进展以及产业化应用前景,从实体面板与泡沫铝芯层的物理连接和冶金连接两个方面介绍了主要制备技术,讨论和总结了准静态和动态力学性能的主要影响因素与机理,分析了国内外应用现状并对应用前景进行了展望.     

Effect of the amount of adhesive on the bending fatigue strength of adhesively bonded aluminum honeycomb sandwich beams

The effect of the amount of adhesive for bonding face sheets and cores on the bending fatigue strength of aluminum honeycomb sandwich beams was analyzed. It was experimentally proved that the fatigue strength increases as increasing the amount of adhesive. Furthermore, the applied loading parameter is not correlated with the fatigue life data of all studied specimens with various amounts of adhesive because the global parameter has no clear physical meanings with respect to the failure mechanism. From the observations made during fatigue testing, debonding at the interface between the honeycomb core and face sheet is the main cause of fatigue failure. Finite element analyses were conducted to obtain the local stress states at the interface, and these simulated stresses were employed in fatigue life prediction parameters. Three local interfacial parameters were adopted and correlated with the experimental data for the studied specimens. The predicted failure locations using the three interfacial parameters were also examined by comparing the observation results in fatigue tests. Among the three studied interfacial parameters, the combined interfacial peeling and shear stress parameter is recommended for use in fatigue design as it provides good fatigue life correlations and predicts the correct locations of failure initiation simultaneously.     

Temperature-dependent monotonic and fatigue bending strengths of adhesively bonded aluminum honeycomb sandwich beams

The monotonic and fatigue strengths of adhesively bonded aluminum honeycomb sandwich beams subjected to four-point bending were investigated at temperatures ranging from −25 to 75 °C. Experimental results showed that the ultimate loads in the monotonic tests and fatigue strengths in the fatigue tests decrease as temperature increases, and the failure mode changes from local indentation to debonding at the skin/core interfaces. An analytical procedure based on the temperature-dependent monotonic strengths of face/core materials and simple adhesively bonded specimens were used and accurately predicted the ultimate applied loads in the monotonic tests by comparing the theoretical limit loads corresponding to several failure modes, i.e., face failure, local indentation, core shear failure, and face/core debonding modes. Furthermore, by modifying the monotonic analytical procedure and incorporating the temperature-dependent S–N curves of the face/core materials and the simple adhesively bonded specimens, the fatigue life of the sandwich beams could be predicted by comparing the estimated fatigue lives corresponding to various failure modes. Comparing the evaluated ultimate loads and fatigue lives with the observed data confirmed that the good prediction performance was obtained both in the monotonic and fatigue analyses.     

含泡沫铝芯的复合板弯曲疲劳行为的研究

应用表面位移原位分析技术对由泡沫金属铝芯和金属面板组成的三层复合板在循环弯曲载荷条件下的损伤行为进行了观察和研究。循环弯曲载荷条件下复合板失效的基本方式是表面凹陷（Indentation，ID）和泡沫铝内芯切断（Coreshear，CS）。凹陷型失效是与加载压头接触的复合板表面局部压缩密切相关，该处沿垂直方向的压缩应变最大。内芯切断型失效是泡沫铝内芯中切应变最大的区域发生的剪切破坏。在疲劳应力比R=0时，复合板凹陷型失效的疲劳极限高于内芯切断型失效的疲劳极限。     

Fatigue crack growth at the face sheet-core interface in a discontinuous ceramic-tile cored sandwich structure

The fatigue failure mechanism of a sandwich structure with discontinuous ceramic tile core is characterized. The sandwich structure in consideration comprises ceramic core tiles bonded to composite face sheet with a compliant adhesive layer. The discontinuous nature of the core results in a non-uniform stress field under in-plane loading of the sandwich. Static tensile tests performed on sandwich coupons revealed first damage as debonding at the gaps between adjacent tiles in the core. Tension–tension fatigue tests caused debonding at the gaps followed by initiation of cracks in the adhesive layer between the face sheet and core. Experimental data for crack length versus number of cycles is collected at various load levels. Crack growth rates (da/dN) are determined based on the experimental data acquired. The energy release rate available for crack propagation is computed using an analytical model and finite element analysis. Mode separation performed using the Virtual Crack Closure Technique (VCCT) revealed that crack propagation is completely dominated by shear (mode II). Fatigue crack growth behavior for the discontinuous sandwich structure is quantified by correlating the cyclic energy release rate with the rate of crack propagation. The loss of specimen stiffness with crack propagation is quantified using an analytical model.     

GFRP复合材料-轻木夹芯梁弯曲疲劳性能试验

为研究真空导入成型的玻璃纤维增强树脂基复合材料-Balsa轻木（GFRP-Balsa）夹芯梁弯曲疲劳性能,进行了普通无格构、单格构增强、双格构增强三种类型共42根试件在不同荷载等级下的四点弯曲疲劳试验,得到夹芯梁的弯曲疲劳破坏模式、疲劳寿命和损伤演化规律,分析了三种类型夹芯梁在弯曲疲劳载荷下不同的损伤机制。研究结果发现,无格构夹芯梁的失效模式统一为芯材剪切和面板脱粘,格构增强夹芯梁的失效模式随格构设置及载荷等级变化,主要有上面板屈曲或压坏、下面板拉断等;采用指数经验模型拟合夹芯梁的疲劳荷载-寿命（S-N）曲线,得到三种类型夹芯梁的寿命预测公式;夹芯梁的位移演化历经"位移瞬降-平稳演化-损伤萌生至破坏"三个阶段,相对于无格构试件,格构增强试件在疲劳失效前有较明显预兆。     

高比强高孔隙率泡沫铝合金三明治梁

研究了高比强泡沫铝合金和泡沫纯铝的单向压缩和剪切性能,对以高比强泡沫铝合金为夹芯的三明治梁失效模式的尺寸范围和承载能力进行了理论计算,结果与实验结果符合得很好.给出了泡沫铝合金三明治梁的设计方法,表明在较小的设计载荷下,三明治梁是以刚度作为设计的控制条件;在较大的设计载荷下,以相对强度为设计的控制条件.泡沫铝合金三明治梁与泡沫纯铝三明治梁的对比表明,在刚度设计控制条件下,前者的刚度是后者的1.00～1.185倍.在强度设计控制条件下,剪切破坏和压凹破坏失效模式下的泡沫铝合金三明治梁比泡沫纯铝三明治梁的极限强度分别提高57%～180%和90%～220%.     

The Effect of Load and Geometry on the Failure Modes of Sandwich Beams

Facing compressive failure, facing wrinkling and core shear failure are the most commonly encountered failure modes in sandwich beams with facings made of composite materials. The occurrence and sequence of these failure modes depends on the geometrical dimensions, the form of loading and type of support of the beam. In this paper the above three failure modes in sandwich beams with facings made of carbon/epoxy composites and cores made of aluminum honeycomb and two types of foam have been investigated. Two types of beams, the simply supported and the cantilever have been considered. Loading included concentrated, uniform and triangular. It was found that in beams with foam core facing wrinkling and core shear failure occur, whereas in beams with honeycomb core facing compressive failure and core shear crimping take place. Results were obtained for the dependence of failure mode on the geometry of the beam and the type of loading. The critical beam spans for failure mode transition from core shear to wrinkling failure were established. It was found that initiation of a particular failure mode depends on the properties of the facing and core materials, the geometrical configuration, the type of support and loading of sandwich beams.     

Development and Mechanical Behavior of FML/Aluminium Foam Sandwiches

In this study, the Fiber-Metal Laminates (FMLs) containing glass fiber reinforced polypropylene (GFPP) and aluminum (Al) sheet were consolidated with Al foam cores for preparing the sandwich panels. The aim of this article is the comparison of the flexural properties of FML/Al foam sandwich panels bonded with various surface modification approaches (silane treatment and combination of silane treatment with polypropylene (PP) based film addition). The FML/foam sandwich systems were fabricated by laminating the components in a mould at 200 °C under 1.5 MPa pressure. The energy absorbtion capacities and flexural mechanical properties of the prepared sandwich systems were evaluated by mechanical tests. Experiments were performed on samples of varying foam thicknesses (8, 20 and 30 mm). The bonding among the sandwich components were achieved by various surface modification techniques. The Al sheet/Al foam sandwiches were also consolidated by bonding the components with an epoxy adhesive to reveal the effect of GFPP on the flexural performance of the sandwich structures.     

Debonding and crack kinking in foam core sandwich beams—II. Experimental investigation

Debonding and crack kinking in sandwich beams was experimentally examined, and also analyzed using the finite element method. Double cantilever beam (DCB) and shear fracture specimens employing aluminum facings bonded to a wide range of PVC and PMI foam cores using two types of adhesives were considered. It was found that the Young modulus of the core has a profound effect on the tendency of the facing/core interfacial crack to deflect (kink) into the core in DCB testing. In shear testing, crack kinking occurred for all core materials considered. The type of adhesive strongly influences the debond fracture resistance, but not the kink resistance and kink angle. The critical load for onset of kinking increased with increased core density. Finite element analysis of the fracture specimens enabled determination of mixed mode interfacial fracture toughness for the specimens that failed by debonding. For specimens that failed by kinking, interfacial stress intensity factors at the onset of kinking were determined. Measured kink angles compared favorably with kink angles calculated based on the interfacial stress intensity factors prior to kinking.