碳纤维复合材料-泡沫铝夹芯板的冲击响应

采用泡沫金属子弹撞击加载的方式研究了T700碳纤维复合材料面层-泡沫铝芯体的夹芯结构动力响应。利用激光测速装置、高速摄像仪和位移传感器记录了泡沫子弹的撞击速度、子弹撞击夹芯板全过程和夹芯板后面板中心点的位移时程曲线。研究了加载冲量和芯层相对密度对夹芯板冲击响应的影响,得到了碳纤维复合材料-泡沫铝夹芯板的变形与失效模式。同时,采用ABAQUS有限元软件进行数值模拟,研究了复合材料面板铺层方式、面层厚度、芯层厚度和相对密度以及泡沫铝子弹的长度、速度和相对密度等参数对夹芯板冲击响应的影响。     

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。     

泡沫金属子弹撞击载荷下多孔金属夹芯板的动态响应

应用泡沫金属子弹撞击加载的方式研究了固支多孔金属夹芯板的塑性动力响应。讨论了多孔金属夹芯板在冲击载荷作用下的破坏模式。结果表明夹芯板的破坏主要表现在前面板的压痕与侵彻失效,芯层压缩和芯层剪切破坏。基于实验研究,应用LS-DYNA 3D非线性动力学有限元分析软件对夹芯板动力响应进行了有限元分析。数值研究结果与实验结果吻合较好。考察了加载冲量、面板厚度、芯层厚度及相对密度对多孔金属夹芯板抗撞击性能的影响。夹芯板的结构响应对其结构配置比较敏感,增加面板厚度或芯层厚度能够明显地减小后面板的挠度,提高夹芯板的抗撞击能力。研究结果对多孔金属夹芯板的优化设计具有一定得参考价值。     

钢板夹泡沫铝组合板抗爆性能研究

鉴于泡沫铝材料优异的吸能特性和夹层结构在强度、刚度上的优势,提出了分层结构为钢板-泡沫铝芯层-钢板的抗爆组合板。对厚度为10 cm、7 cm和5 cm的组合板进行了5组不同装药量的爆炸试验,考察了各板在不同装药量爆炸条件下的变形及破坏情况,并对变形破坏过程进行了理论分析。研究表明:组合板承受爆炸冲击荷载时,通过局部压缩变形和整体弯曲变形吸收能量。钢板相同时,适当增大泡沫铝芯层厚度,增强面板与芯层间连接,可提高该组合板的抗爆性能,防止组合板发生剥离,减小其承受爆炸冲击荷载时产生的变形。     

开孔泡沫铝-环氧树脂复合夹芯板局压性能试验研究

对一种开孔泡沫铝-环氧树脂复合夹芯板进行了准静态局部压缩试验,研究了其破坏形态和典型荷载-位移曲线,并与传统蒙皮夹芯板进行了对比,分析了不同复合层厚度、不同压头类型和不同边界条件对局压刚度、极限承载力及吸能量等主要性能参数的影响。结果表明开孔泡沫铝/环氧树脂复合夹芯板在局部压力作用下表现了较好的整体性、稳定性和吸能性能,其典型荷载-位移曲线经历四个阶段:弹性阶段、局部损伤阶段、整体损伤阶段和冲切破坏阶段。泡沫铝-环氧树脂复合层能显著提高夹芯板力学性能,且随厚度增加有增强趋势,球柱形压头作用下的破坏形态和力学性能与圆柱形压头和方形压头有明显区别,简支边界条件下力学性能比固支时明显降低。与传统夹芯板相比,这种夹芯板的刚度、强度、吸能量和整体性都有较大提高。     

碳纤维铝蜂窝夹芯复合结构隔声性能研究

铝蜂窝夹芯复合结构在航空工业、高速列车及汽车车体中得到越来越多的应用,其隔声性能对车内及机舱噪声有重要影响。建立了碳纤维铝蜂窝夹芯复合结构有限单元模型,用有限单元法计算了结构在声载荷激励下的响应,并计算分析了复合结构的隔声性能,分析了碳纤维复合面板厚度、面板层数、铺设角度、铝蜂窝芯层的厚度、铝蜂窝壁厚对隔声性能的影响。研究结果表明,面板采用碳纤维复合结构时,在小于1 000 Hz的低频段,相同面板厚度的铝蜂窝复合结构隔声性能比全铝合金材料的铝蜂窝夹芯复合结构有所降低,而且在高频段会出现隔声量更低的隔声低谷;相较于铝合金面板,复合结构的面板采用碳纤维复合材料时,能够实现整体结构轻量化也提高复合结构的隔声性能;各层之间按相对90°铺设时复合结构隔声性能最好;随着面板厚度的增加复合结构隔声性能增加,面板层总厚度不变的情况下,单层面板或者过多的层数都会使复合结构隔声性能降低。     

梯度铝泡沫夹层结构抗爆性能仿真与优化

采用动力显式有限元方法,以面比吸能和背板最大变形量为评价指标,研究了铝合金面板—梯度铝泡沫芯体—装甲钢背板夹层结构的抗爆性能。分析了芯体密度梯度排布对结构抗爆性能的影响,并与均匀密度铝泡沫夹层板进行了对比。同时,基于径向基函数建立了夹层结构抗爆性能预测响应面模型,在此基础上对夹层结构进行了多目标优化设计。结果表明,铝泡沫芯体相对密度排布顺序对夹层结构抗爆性影响明显;具有最佳芯体密度梯度排布的铝泡沫夹层结构的抗爆性能明显优于等质量的均匀密度铝泡沫夹层结构;多目标优化可进一步提高梯度铝泡沫夹层结构的综合抗爆性能。     

泡沫铝衰减冲击波峰值压力的理论及数值分析

为比较系统地了解表面粘贴泡沫铝及其夹芯层对结构上作用冲击波峰值压力的衰减性能与影响因素,运用理论及数值模拟方法分析了泡沫铝及其夹芯层衰减冲击波峰值压力的性能。并讨论了影响泡沫铝及其夹芯层衰减冲击波峰值压力的几个主要因素。研究结果显示,在达到压实应变之前,表面粘贴泡沫铝及其夹芯层能有效地衰减冲击波的峰值压力。达到压实应变后,泡沫铝及其夹芯层对冲击波峰值压力的衰减性能下降。孔洞形式、相对密度对泡沫铝衰减冲击波峰值压力具有明显地影响,面板材料对泡沫铝夹芯层衰减冲击波峰值压力的性能也有一定的影响。要取得较好地衰减冲击波峰值压力的性能需综合考虑以上因素进行优化设计,否则可能出现粘贴的泡沫铝或其夹芯层达不到衰减结构上冲击波峰值压力的目的。     

泡沫铝衰减冲击波压力的理论分析

由于泡沫铝具有良好的缓冲与吸收撞击或爆炸能量性能,常被粘贴在主结构可能遭受撞击面或迎爆面,用于降低撞击或爆炸冲击波对主结构的破坏作用。目前关于泡沫铝缓冲层衰减主结构上冲击波压力的理论计算没有得到很好的解决。为考查泡沫铝相对密度、孔洞形式及厚度对其衰减主结构上冲击波压力的影响,运用一维冲击波理论,考虑冲击波在压缩泡沫铝材料过程中的能量损耗,提出一种简化计算泡沫铝缓冲层衰减结构物上冲击波压力的方法。运用该方法分析了结构物上包覆一层泡沫铝缓冲层对飞片撞击结构所产生冲击波压力的衰减情况。并通过实例给出计算泡沫铝缓冲层衰减飞片冲击结构上冲击波压力的计算步骤及其影响因素。     

缝纫泡沫夹芯复合材料板的稳定性分析

整体屈曲是缝纫复合材料夹芯板的一种重要失效模式。考虑到缝纫夹芯复合材料板一般较厚且面板与芯层厚度相差较大, 缝纫工艺对夹芯板刚度影响较大的特点, 基于高阶剪切理论, 编制了缝纫泡沫夹芯复合材料板稳定性分析的有限元程序。利用该程序对多个算例进行了计算, 所得临界屈曲应力与文献及试验结果吻合很好。同时, 讨论了不同边界条件下缝纫泡沫夹芯复合材料板稳定性随缝纫参数(包括针距、 行距和缝纫针半径)以及结构参数(包括面板铺层角、 芯层厚度和缝纫夹芯板边长)的变化规律。      

Response of thin-skinned sandwich panels to contact loading with flat-ended cylindrical punches: Experiments,numerical simulations and neutron diffraction measurements

The response of aluminium foam-cored sandwich panels to localised contact loading was investigated experimentally and numerically using flat-ended cylindrical punch of four varying sizes. ALPORAS and ALULIGHT closed-cell foams of 15 mm thickness with 0.3 mm thick aluminium face sheets (of 236 MPa yield strength) were used to manufacture the sandwich panels. Face sheet fracturing at the perimeter of the indenter, in addition to foam cells collapse beneath the indenter and tearing of the cell walls at the perimeter of the indenter were the major failure mechanisms of the sandwich panels, irrespective of the strength and density of the underlying foam core. The authors employed a 3D model in ABAQUS/Explicit to evaluate the indentation event, the skin failure of the face sheets and carry out a sensitivity study of the panel's response. Using the foam model of Deshpande and Fleck combined with the forming limit diagram (FLD) of the aluminium face sheet, good quantitative and qualitative correlations between experiments and simulations were achieved. The higher plastic compliance of the ALPORAS led to increased bending of the sheet metal and delayed the onset of sheet necking and failure. ALULIGHT-cored panels exhibited higher load bearing and energy absorption capacity, compared with ALPORAS cores, due to their higher foam and cell densities and higher yield strength of the cell walls. Additionally, they exhibited greater propensity for strain hardening as evidenced by mechanical testing and the neutron diffraction measurements, which demonstrated the development of macroscopically measurable stresses at higher strains. At these conditions the ALULIGHT response upon compaction becomes akin to the response of bulk material with measurable elastic modulus and evident Poisson effect.     

Localized indentation of sandwich panels with metallic foam core: Analytical models for two types of indenters

Sandwich structures with metallic foam core are sensitive to local indentation because of the low strength of the core and low bending stiffness of the thin face sheets. In this paper, local indentation response of sandwich panels with metallic foam core under a flat/spherical indenter was analyzed. The composite sandwich is modeled as an infinite, isotropic, plastic membrane on a rigid-plastic foundation. For simplicity, a quadratic polynomial displacement field was employed to describe the deformation of the upper face sheet. By using the principle of minimum work, explicit solutions for the indentation force and the sizes of the deformation regions were derived. The analytical results were verified by those from simulation by using the ABAQUS code, and they are in close agreement. Distribution of radial tensile strain of the upper face sheet and the ratio of energy dissipation of foam core to that of the upper face sheet were analyzed.     

Indentation study of Z-pin reinforced polymer foam core sandwich structures

Z-pin reinforced foam core sandwich panels with composite face sheets, supported on a rigid base and subjected to quasi-static indentation using spherical indenter was studied in this paper. The effects of configurations of Z-pin, including inclination angle and pinning density, on the load–indentation response were studied, and the resulting damage modes were investigated. The effect of inclination angle of pin on the load–indentation behavior is not notable compared with those of Z-pinning density and Z-pin configuration. The collapse of Z-pinned foam core is due to the buckling of pin, and the pin buckling is significantly dependent on the location of indenter. An approximate solution was developed based on the principle of minimum potential energy to simulate the indentation damage response of Z-pin reinforced foam core sandwich. The analytical predictions compare well with the experimental results.     

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.     

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.     

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.     

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.     

Mechanical behavior of sandwich panels with hollow Al–Si tubes core construction

A new type of lightweight sandwich panels consisting of vertically aligned hollow Al–Si alloy tubes as core construction and carbon fiber composite face sheets was designed. The hollow Al–Si alloy tubes were fabricated using precision casting and were bonded to the face sheets using an epoxy adhesive. The out-of-plane compression (i.e. core crushing), in-plane compression, and three-point bending response of the panels were tested until failure. The hollow Ai–Si alloy tubes core configuration show superior specific strength under crushing compared to common metallic and stochastic foam cores. Under in-plane compression and three-point bending, the buckling of face sheets and debonding of hollow cores from the face sheets were observed. Simple analytical relationships based on the concepts of mechanics of materials were provided for the compression tests, which estimate the sandwich panels’ strength with high fidelity. For three-point bending, detailed finite element analysis was used to model the response and initial failure of the sandwich panels.     

Precise bending stress analysis of corrugated-core,honeycomb-core and X-core sandwich panels

A semi-analytical method for bending analysis of corrugated-core, honeycomb-core and X-core sandwich panels is presented. The real displacement of sandwich panels is divided into the global displacement field and local displacement field. The discrete geometric nature of the core is taken into account by treating the core sheets as beams and the sandwich panel as composite structure of plates and beams with proper displacement compatibility. In the global displacement field, the governing equations of these sandwich panels are derived using energy variation principle and solved by employing Fourier series and the Galerkin approach. In the local displacement field, the face sheets under external loads are taken as a multi-span thin plate and the local bending response are then computed. Then the real bending responses are obtained by superposing these bending responses calculated in the two displacement fields and the structural stress fluctuation can be captured. Results from the proposed method agree well with available results in the literature and those from detailed finite element analysis. Furthermore, the mechanical properties of the three kinds of sandwich panels have been compared.