爆炸载荷作用下铝蜂窝夹芯板动力响应研究

采用自行设计的冲击摆实验系统对铝蜂窝夹芯板在爆炸载荷作用下的动力响应进行了系统实验研究,给出了面板和铝蜂窝不同区域的不同变形模态,得到了不同炸药当量对铝蜂窝夹芯板动态响应的影响规律,证实了铝蜂窝夹芯板产生较大塑性变形时,比一般的结构具有更好的能量吸收特性.并利用LS-DYNA对其动力响应进行了数值仿真,考察了炸药起爆、接触界面及上表面接触力对夹芯板变形影响的全过程,得到了板中心的最终变形和芯层的变形模式,与实验结果吻合较好.     

爆炸载荷下分层梯度泡沫铝夹芯板的失效模式与抗冲击性能

采用弹道冲击摆系统开展了爆炸载荷下分层梯度泡沫铝夹芯板的变形/失效模式和抗冲击性能实验研究，并配合激光位移传感器得到试件后面板中心点的挠度-时程响应曲线。研究了炸药当量和芯层组合方式对夹芯板试件变形/失效模式和抗冲击性能的影响。实验结果表明，泡沫铝夹芯板的变形/失效模式主要表现为面板的非弹性大变形，芯层压缩变形、芯层拉伸断裂以及芯层剪切失效。在研究爆炸冲量范围内，非梯度芯层夹芯板的抗冲击性能明显优越于所有分层梯度芯层夹芯板。对于分层梯度夹芯板试件，爆炸冲量较小时芯层组合形式对分层梯度芯层夹芯板的抗冲击性能的影响不大，而爆炸冲量较大时，最大相对密度芯层靠近前面板组合形式的分层梯度夹芯板试件抗冲击性能较好。研究结果可为泡沫金属夹芯结构的优化设计提供参考。     

梯度蜂窝夹芯板在爆炸荷载作用下的动力响应

利用弹道冲击摆锤系统对分层梯度蜂窝夹芯板在爆炸荷载下的动力响应进行了实验研究,分析了梯度蜂窝夹芯板在爆炸荷载作用下的变形失效模式,并与传统非梯度蜂窝夹芯板的抗爆性能做了对比。通过一维应力波理论,分析了应力波在梯度芯层中的传播规律。应力波透射系数在梯度试件中比非梯度芯层中小,而且相对密度递减的芯层组合有最小的应力波透射系数。综合考虑结构变形失效模式,后面板挠度,芯层压缩量以及应力波传播特点得到:分层梯度蜂窝夹芯板的抗爆性能明显优于传统的非梯度夹芯板,在所研究的荷载范围内,芯层相对密度从大到小排列试件的抗爆性能相对较好。     

夹芯板结构局部压入力学响应研究

利用材料试验机(MTS)实验研究了复合材料面板、闭孔泡沫铝芯层夹芯板结构在准静态压入时的变形和破坏特征。实验结果表明,夹芯板的破坏主要集中在压头作用的局部区域内;同时,根据最小势能原理建立了泡沫铝夹芯板在半球形压头作用下的压入力学响应理论预测模型。通过引入无量纲参数分析了夹芯板压入载荷-位移响应,并在不同面板厚度、芯层厚度和芯层相对密度情况下,对夹芯板压入响应理论解的有效性和适用性进行了讨论。     

多层梯度点阵夹芯结构抗爆性能研究

基于CONWEP对多层梯度点阵夹芯板在爆炸载荷下的动态响应进行了模拟研究。在相同爆炸载荷下,对四种梯度点阵模型的后面板中心挠度峰值进行了对比分析,讨论了各模型每层芯子的总变形能随相对密度比的变化规律,并对多层点阵夹芯板各层的变形情况进行了比较。分析结果表明:对于三层金字塔点阵夹芯结构,强弱相间的点阵夹芯板充分利用了前两层芯子的变形吸能,从而对第三层芯子和后面板起到了很好的保护作用;且在350g TNT炸药和200mm爆距的爆炸载荷下,相对密度比为0.5的强弱相间点阵夹芯板的后面板中心挠度峰值最小,抗爆冲击性能最优。     

孔结构金属复合夹芯板抗爆炸冲击响应及吸能特性研究

采用有限元方法研究爆炸载荷下四边固支孔结构金属复合夹芯板的动力响应及吸能特性，给出了孔结构金属复合夹芯板的动力响应过程，得到夹芯板的变形模式，比较了孔结构金属复合夹芯板与非孔结构金属复合夹芯板的抗爆炸冲击性能，同时讨论了孔大小、间距、排布方式和面板质量分布等因素对孔结构金属复合夹芯板抗爆炸冲击性能的影响。研究结果表明，迎爆面外面板的孔设计使爆炸冲击波穿过孔洞直接作用在芯材上，增强了芯材的压缩，从而提高了夹芯板的能量吸收能力。同等面密度情况下，内外面板厚度比大于1的孔结构金属复合夹芯板变形挠度小于内外面板厚度比小于1的孔结构金属复合夹芯板。进一步研究发现，通过合理设计内外面板的质量分布，可以使孔结构金属复合夹芯板的抗爆炸冲击性能最优。     

孔结构金属复合夹芯板抗爆炸冲击响应及吸能特性研究

采用有限元方法研究爆炸载荷下四边固支孔结构金属复合夹芯板的动力响应及吸能特性,给出了孔结构金属复合夹芯板的动力响应过程,得到夹芯板的变形模式,比较了孔结构金属复合夹芯板与非孔结构金属复合夹芯板的抗爆炸冲击性能,同时讨论了孔大小、间距、排布方式和面板质量分布等因素对孔结构金属复合夹芯板抗爆炸冲击性能的影响。研究结果表明,迎爆面外面板的孔设计使爆炸冲击波穿过孔洞直接作用在芯材上,增强了芯材的压缩,从而提高了夹芯板的能量吸收能力。同等面密度情况下,内外面板厚度比大于1的孔结构金属复合夹芯板变形挠度小于内外面板厚度比小于1的孔结构金属复合夹芯板。进一步研究发现,通过合理设计内外面板的质量分布,可以使孔结构金属复合夹芯板的抗爆炸冲击性能最优。     

金属蜂窝夹芯板等效弹性模量的实验测试

总结了以往所用的金属蜂窝夹芯板的等效弹性模量的计算方法。在此基础上提出了金属蜂窝夹芯板的等效弹性模量的实验测试方案。通过三点弯曲线载荷两端简支板的挠度测试，得到金属蜂窝夹芯板的等效弹性模量，并与非金属复合材料如玻璃钢材料的等效弹性模量方法进行比较，说明金属蜂窝板的等效弹性模量计算与非金属蜂窝板之间存在较大的差异。证明金属蜂窝夹芯板的等效弹性模量实验测试方案是有效可行的。     

电炮加载下芳纶蜂窝夹芯板的动力响应

研究了方形钛-芳纶蜂窝夹芯板在电炮驱动的高速聚酯飞片撞击加载下的动力响应,给出了面板和蜂窝芯层在不同冲击速度下的变形及失效模式。采用VISAR(velocity interferometer system for any reflector)测速技术测量了后面板中心点的速度时程,分析了芳纶蜂窝夹芯板的动态响应过程,讨论了冲击速度对夹芯板动力响应和抗冲击能力的影响。研究结果表明,低波阻抗的芳纶蜂窝破碎行为阻断了应力波向后面板的传播途径,破碎的蜂窝和塑形大变形的前面板吸收了高速冲击的大部分能量,充分发挥了钛合金的高强度和芳纶蜂窝的缓冲吸能特性,提高了夹芯板整体的防护能力。     

金属蜂窝夹层结构抗水下爆炸特性

金属蜂窝夹层结构是一种新型的舰船防护结构,在舰船防护领域具有广阔的应用前景,但目前缺乏对其在实际水下爆炸载荷作用下动态响应的研究。为研究金属蜂窝夹层结构在水下爆炸载荷作用下的动态响应及防护性能,设计并制备了背板加筋蜂窝夹层结构样件以及相应的浮箱,在大型露天水池中进行了水下实爆 实验;通过声固耦合算法对结构响应进行模拟,实验结果与模拟结果吻合良好,随后分析了蜂窝夹层板的变形过程及能量吸收特性,量化了载荷参数（冲击因子）及结构参数（前后面板厚度比和芯体相对密度）对结构动态响应的影响;最后,以蜂窝夹层板的面密度和后面板中心点最大变形的无量纲量为目标函数,使用NSGA-Ⅱ遗传算法对结构进行了多目标优化,得到对应的Pareto前沿。结果表明,随着冲击因子的增大,蜂窝夹层板整体变形显著增大,蜂窝芯体始终是主要的吸能构件,但其吸能占比逐渐降低;随着前后面板厚度比或芯体相对密度的增加,蜂窝夹层结构的最大变形呈现先降低后升高的趋势,同时呈现不同的变形模式,芯体相对密度对结构变形的影响更为显著;对蜂窝夹层结构开展多目标优化可有效降低结构的面密度及最大变形,优化结果可为蜂窝夹层结构的设计选型提供参考。     

EXPERIMENTAL AND NUMERICAL STUDIES OF THE ANTI-PENETRATION PERFORMANCE OF SANDWICH PANELS WITH ALUMINUM FOAM CORES

Effects of face-sheet thickness and core thickness of sandwich panels, and shape of projectiles on the penetration resistance of sandwich panels were discussed, while typical penetration failure modes were presented. It was shown that the anti-penetration performance of sandwich panels was enhanced with the increase of face-sheet or core thickness; The penetration resistance of sandwich panels was shown to be strongest to blunt-shaped projectile impacts,weaker to hemispherical-nose-shaped projectile impacts, and weakest to conical-shaped projectile impacts. The corresponding numerical simulation was carried out using the finite element code LS-DYNA V970. Numerical results showed that the penetration time decreased with the increase of projectile impact velocity.     

Sandwich Panel Cores for Blast Applications: Materials and Graded Density

Sandwich composites are of interest in marine applications due to their high strength-to-weight ratio and tailorable mechanical properties, but their resistance to air blast loading is not well understood. Full-scale 100 kg TNT equivalent air blast testing at a 15 m stand-off distance was performed on glass-fibre reinforced polymer (GFRP) sandwich panels with polyvinyl chloride (PVC); polymethacrylimid (PMI); and styrene acrylonitrile (SAN) foam cores, all possessing the same thickness and density. Further testing was performed to assess the blast resistance of a sandwich panel containing a stepwise graded density SAN foam core, increasing in density away from the blast facing side. Finally a sandwich panel containing compliant polypropylene (PP) fibres within the GFRP front face-sheet, was subjected to blast loading with the intention of preventing front face-sheet cracking during blast. Measurements of the sandwich panel responses were made using high-speed digital image correlation (DIC), and post-blast damage was assessed by sectioning the sandwich panels and mapping the damage observed. It was concluded that all cores are effective in improving blast tolerance and that the SAN core was the most blast tolerant out of the three foam polymer types, with the DIC results showing a lower deflection measured during blast, and post-blast visual inspections showing less damage suffered. By grading the density of the core it was found that through thickness crack propagation was mitigated, as well as damage in the higher density foam layers, thus resulting in a smoother back face-sheet deflection profile. By incorporating compliant PP fibres into the front face-sheet, cracking was prevented in the GFRP, despite damage being present in the core and the interfaces between the core and face-sheets.     

Interaction effects of multiple damage mechanisms in composite sandwich beams subject to time dependent loading

Theoretical models are formulated to explain evolution and interaction of the damage mechanisms for multiple delamination of the face-sheet and core crushing in composite sandwich beams subjected to dynamically applied out-of-plane loading and continuously supported by rigid planes. The models are based on simplified one-dimensional formulations and describe the impacted face of the sandwich as a set of Timoshenko beams joined by cohesive interfaces and resting on a nonlinear Winkler foundation, which approximates the response of the core; the dimensionless formulation highlights the material/structure groups that control the mechanical response. The characteristic features of the problem and transitions in damage progression are explored on varying geometrical parameters and material properties and magnitude and duration of the applied load. For quasi-static loading and low velocity impact, core/face-sheet interactions generate energy barriers to the propagation of delaminations; the efficacy of the barriers in controlling damage in the face-sheets depends on the relative stiffnesses of face-sheet and core and on the foundation yielding strength. For dynamic loading conditions, significant dynamic effects arise in certain regimes and cause substantial changes in behavior: shielding of the crack tip stress fields provided by the foundation is reduced, especially after the load is removed when important delamination openings occur; core plasticity generally opposes this behavior and limits damage in the face-sheet.     

High order behavior of sandwich plates with free edges––edge effects

The edge effects of a sandwich plate with a “soft” core and free edges, i.e. the plate is supported only at the lower face-sheet, and the upper face-sheet and the core are free of stresses at their edges, using the high order approach (HSAPT), are presented. The two-dimensional analysis consists of a mathematical formulation that uses the classical thin plate theory for the face-sheets and a three-dimensional elasticity theory for the core. The governing equations and the required boundary conditions are derived explicitly through variational principals, yielding a system of eight partial differential equations. The non-homogeneous differential equations system is numerically solved using a modification of the extended Kantorovich method (MEKM). The model presented enables a two-dimensional solution of the stress and displacement fields when subjected to a general scheme of loads. It is applicable to any type of boundary conditions that can be applied separately on each face-sheet and on the core. A numerical study is presented, and it examines the behavior and the two-dimensional stress field of a sandwich plate with free edges, at the upper face-sheet and core, subjected to thermal and uniformly distributed loads, for various boundary conditions at the lower face-sheet. For completeness, the MEKM solution of the two-dimensional high order model is verified through comparison with a three-dimensional Finite Element model revealing good correlation. Furthermore, the problems involved in the construction of an appropriate three-dimensional FE model of a full scale sandwich plate that require large computer resources are discussed.The numerical study yields that the peeling (normal) stresses, which reach their maximum values at the edges of the sandwich plate, using a one-dimensional analysis, varies also in the transverse direction from a maximum value in the middle of the edge, descending towards the corners. Moreover, the nature of variation along the boundaries strongly depends on the type of loading and the transverse boundary conditions. The substantial variation of the stress field in the transverse direction clearly shows the necessity of a two-dimensional analysis and the inefficiencies of the one-dimensional model.     

Imperfection sensitivity of axially compressed stringer reinforced cylindrical sandwich panels

This paper presents some numerical results of the effects of several nondimensional parameters on the buckling and initial post buckling behaviors of shallow sandwich panels under axial compression. Results are presented that show these effects due to transverse shearing resistance of the core material, different face-sheet thicknesses, and different core thicknesses. Further effects on the buckling and initial postbuckling behaviors of sandwich panels are presented due to the torsional resistance of longitudinal edge stiffeners.The results show that the range of flatness parameter, δ/d, for which sandwich panels remain imperfection-insensitive increases with increases in transverse shearing resistance of the core material and with larger core thicknesses. These results also indicate that this range of δ/d is smallest when the face-sheet thicknesses are equal. Finally, as in the case of homogeneous panels, torsional resistance of the longitudinal edge stiffeners has the effect of making the sandwich panel less imperfection-sensitive.     

撞击载荷下泡沫铝夹芯梁的塑性动力响应

应用泡沫金属子弹撞击加载的方式研究了固支泡沫铝夹芯梁和等质量实体梁的塑性动力响应。 采用激光测速装置和位移传感器测量了泡沫子弹的撞击速度和后面板中心点的位移-时间曲线,研究了加载 冲量、面板厚度和芯层厚度对夹芯梁抗冲击性能的影响。给出了泡沫铝夹芯梁的变形与失效模式,实验结果 表明结构响应对夹芯结构配置比较敏感,后面板中心点的残余变形与加载冲量、面板厚度呈线性关系。与等 质量实体梁的比较表明,泡沫铝夹芯梁具有更好的抗冲击能力。实验结果对多孔金属夹芯结构的优化设计具 有一定的参考价值。     

Progressive fracture analysis of planar lattices and shape-morphing Kagome-structure

Lattice solids are being contemplated for use in prospective lightweight structural applications. Hence, the understanding of their mechanical behavior is essential. In this work, the tensile behavior of the triangular (T), hexagonal (H) and Kagome (K) planar lattices containing notches is explored using FE-based progressive failure analysis. As an elastic-brittle material is assumed for the struts, they fail in rupture. The effects of notch-length and relative density are examined. Computations show a dramatic decrease of both stiffness and strength of the lattices with increasing the notch-length. For the relative density, the opposite effect is ascertained. Fracture patterns are found to depend only on the topology of the lattices. T- and K-lattice show a similar and much stronger behavior than the H-lattice.Using the same numerical method, the bending behavior of the shape-morphing Kagome-structure (KS) is simulated in regard of the different materials used in the members of the structure. Failure analysis of the KS involves progression of yielding and initiation of buckling in the face-sheet and struts. It was found that the bending rigidity of the KS is governed by the stiffness of the material of the face-sheet while the material of the core determines whether yielding or buckling will initiate first.     

嵌锁式CFRP方形蜂窝夹芯梁低速冲击响应及失效机理

采用嵌锁组装工艺制备了碳纤维/树脂基复合材料方形蜂窝夹芯梁，实验研究了低速冲击载荷下简支和固支夹芯梁的动态响应及失效机理，获得了不同冲击速度下夹芯梁的失效模式，分析了其损伤演化过程和失效机理，探讨了冲击速度、边界条件、面板质量分布以及槽口方向等因素对夹芯梁破坏模式及承载能力的影响。研究结果表明，芯材长肋板槽口方向对夹芯梁的失效模式有较大影响，槽口向上的芯材跨中部分产生了挤压变形，而槽口向下的芯材跨中部分槽口在拉伸作用下出现了沿槽口开裂失效，继而引起面板脱粘和肋板断裂；同等质量下，较厚的上面板设计可以提高夹芯梁的抗冲击能力，冲击速度越大，夹芯梁的峰值载荷和承载能力越高；固支边界使得夹芯梁的后失效行为呈现出明显的强化效应，在夹芯梁跨中部分发生初始失效后出现了后继的固支端芯材和面板断裂失效模式。     

Higher-order dynamic response of composite sandwich panels with flexible core under simultaneous low-velocity impacts of multiple small masses

Small mass impactors, such as runway debris and hailstones may result in a wave controlled local response, which is essentially independent of boundary conditions. The higher-order impact model of sandwich beams presented by Mijia and Pizhong [Mijia, Y., Pizhong, Q., 2005. Higher-order impact modeling of sandwich structures with flexible core. International Journal of Solids and Structures 42 (10), 5460–5490] is developed and enhanced to impact analysis of sandwich panels with transversely flexible cores. Therefore, an improved fully dynamic higher-order impact theory is developed to analyze the low-velocity impact dynamic of a system which consists of a composite sandwich panel with transversely flexible core and multiple small impactors with small masses. Impacts are assumed to occur normally and simultaneously over the top face-sheet with arbitrary different masses and initial velocities of impactors. The contact forces between the panel and the impactors are treated as the internal forces of the system. First shear deformation theory (FSDT) is used for the face-sheets while three-dimensional elasticity is used for the soft core. The fully dynamic effects of the core layer and the face-sheets are considered in this study. Contact area can be varied with contact duration. The results in multiple mass impacts over sandwich panels that are hitherto not reported in the literature are presented based on proposed improved higher-order sandwich plate theory (IHSAPT). Finally, for the case study of the single mass impact, the numerical results of the analysis have been compared either with the available experimental results or with some theoretical results. As no literature could be found on the impact of multiple impactors over sandwich panels, the present formulation is validated indirectly by comparing the response of two cases of double small masses and single small mass impacts. Also, in order to demonstrate the applicability of the validation, the analytical relation of minimum distance between two impactors is derived based on Olsson’s wave control principle in this paper.