【作者】 宋延泽；

【导师】 赵隆茂；

【作者基本信息】 太原理工大学 ， 固体力学， 2009， 博士

【摘要】 超轻多孔金属作为理想吸能材料,因其轻质、具有较高的吸能特性等优点,近年来被逐步应用于航空航天飞行器、高速轨道车辆、汽车、舰船等领域和重要建筑物的吸能缓冲、减震装置上。其主要使用形式之一是由高空隙率多孔金属为芯层构成夹芯结构。典型的夹芯结构由上下两层复合材料或金属面板和多孔芯层(格栅、金属泡沫和点阵材料等)组成。面板提供给结构较高的抗弯曲和拉伸强度,而多孔芯层材料所特有的细观结构可以在几乎恒应力条件下产生大的塑性变形,从而在变形过程中耗散大量的能量。此类结构主要应用于结构—功能性(如能量吸收、隔热隔音、电磁屏蔽等)要求的场合。这种结构在强动载荷作用下的良好性能引起了学术界和工程界的极大关注,已成为当前学术界研究的焦点。但是,该领域的研究仍处于起步阶段,许多工作还很不完善。因此,有必要对撞击载荷下多孔金属夹芯板的动力响应作进一步系统深入的研究。本文应用泡沫金属子弹撞击加载的方式研究了固支夹芯方板和等质量实体方板的动力响应。从实验研究、理论分析和数值模拟方面开展了系统的工作。取得如下重要成果:实验研究发现,泡沫铝子弹撞击下,夹芯板的变形主要集中在子弹作用的中心区域。前面板主要表现为子弹作用区域的压入变形,其失效模式分为压入失效和侵彻失效。芯层的变形在中心区域可分为压缩失效和剪切失效,在与中心区域较近的周边区域有较小的压缩,而在接近固支边的区域则几乎没有压缩变形。后面板的变形为非弹性大变形,中心点挠度最大,部分试件在中心点周围伴有花瓣形的变形,周边挠度最小,整体变形为穹形。通过与准静态加载实验结果的比较发现,动态加载下板的主要塑性变形发生在泡沫子弹撞击区域,而且变形是连续的。而准静态压缩下在压头的周边和固支边,板的倾角不同,这些位置存在明显的静态塑性铰。参数研究(包括冲量、面板厚度、芯层厚度及芯层密度对结构变形/失效的影响)表明,与等质量的实体板相比,多孔金属夹芯板具有优越的抗撞击性能,同时在本文研究的两种不同芯层等质量的夹芯板中蜂窝铝夹芯板又优于泡沫铝夹芯板。可见,在结构设计中适当采用蜂窝夹芯结构可以达到较好的抗撞击效果。结果还表明,结构响应对子弹冲量和芯层密度比较敏感,后面板中心点的永久变形与泡沫子弹冲量或芯层密度近似成线性关系。基于Fleck等关于爆炸载荷下固支夹芯梁和固支夹芯圆板的动力响应的理论分析,以及关于中心撞击加载下固支夹芯梁的动力响应分析,本文将泡沫子弹撞击下多孔金属夹芯板的变形过程分为三个阶段,分别是前面板获得冲量阶段、芯层压缩阶段和夹芯结构的整体动力响应阶段。建立了泡沫金属子弹撞击下多孔金属夹芯方板的刚塑性分析模型,得到了响应时间和后面板的最大挠度,分析结果与实验结果基本一致。在此基础上研究了子弹加载半径、芯层密度及芯层厚度对固支夹芯板最终挠度的影响。结果表明,增加芯层密度能够提高结构的抗撞击能力;芯层厚度与板的半边长的比值(C/L)大约为0.12时,结构后面板的最终挠度最小,表现出较好的承载能力。应用有限元程序LS-DYNA.V970在HP-J6750工作站上模拟了泡沫铝子弹撞击下多孔金属夹芯板的动力响应的全过程。数值结果与实验数据的对比充分验证了本文建立的有限元模型的可靠性。通过泡沫子弹加载和压力加载的对比表明,多孔金属夹芯板与等质量的实体板表现出的不同抗撞击性能主要由结构本身的性质决定。夹芯板变形过程中,前面板和多孔芯层吸收了大部分能量。研究表明,增加相同质量的前提下,增加芯层厚度比增加面板厚度能获得更好的抗撞击效果。冲量一定的条件下,蜂窝铝夹芯板的抗撞击能力优于等质量的泡沫铝夹芯板。更多还原

【Abstract】 Ultra-light cellular metal as an ideal material of absorbing energy has many advantages such as light quality, highly efficient energy absorption, and so on. They have been gradually applied to many fields, for example, aerospace aircrafts, high-speed rail vehicles, automotives, ships, etc. And cellular metallic materials are also used to energy-absorbing buffer and damping device of the buildings. One of the main using of cellular metallic materials is the sandwich structure with core of high-porosity porous metal. A typical sandwich structure is composed of two layers of thin composite material plate or metal plate and thick metallic foam core which includes grid, metal foam and lattice truss core. Face-sheets provide high bending resistance and tensile strength to structures. At the same time, cellular materials can have a larger plastic deformation under almost constant stress conditions. And then in the process of deformation a lot of energy is dissipated. These structures are mainly applied to occasions at which the structure-functional property is required, for instance, energy absorption, sound absorption, electromagnetic shielding, etc. A great deal of concern is taken on good properties of these structures to strong dynamic loading in the academic and in engineering field. As has become research focus of academia. But investigation on dynamic response of the sandwich structure is in its infancy. Much work is still imperfect. Therefore, it is necessary to further investigate dynamic response of the metallic sandwich plate to impact loading.Dynamic responses of clamped cellular sandwich plates and solid plates of the same weight are studied in the paper. Experimental investigation, theoretical analysis and numerical simulation are applied to finish work systematically. Some significant conclusions are drawn.Experimental results show that deformations of sandwich plates are mainly concentrated in the central region to projectile impacting. Deformation mode of the front face is mainly indenting in the region of impacting. Failure mode includes indenting and penetration failure. Failure mode of core includes compression and shearing in central region. Near this region less compression is observed. No deformation is found close to the clamped edges. Deformation mode of the back face is non-elastic large deformation. Maximum deflection is observed on central point of the plate and minimum is on the edges. Deformation of the flower pattern is observed around central point of the back face. Mode of the overall deformation is arched shape. It is found that main plastic deformation is concentrated in the region of projectile impacting subject to dynamic loading and is continuous. However, static plastic hinge lies in surrounding of indenter and in clamped edges due to different angle of plate to quasi-static loading, obviously.Parameters studied include impulse of projectiles, thickness of face-sheet, thickness of core and density of core. It is found that the cellular metallic plate can sustain larger impacting impulses than a solid plate of the same mass. And a sandwich plate with aluminum honeycomb core has a superior shock resistance relative to the sandwich plate with aluminum foam core. Thereby, the best performance of the structures can be provided by applying the sandwich plate with aluminum foam core in structures. Experimental results reveal that the response of the structure is sensitive to impulse of the projectile and density of core. Permanent deflection of the central point of the back face is proportion to impulse or density.An analytical model is developed to investigate dynamic responses of clamped sandwich plates and solid plates of the same weight subject to impulse loading over a central loading patch. Reliability of the model is supported by the experimental results. The analytical formulae are employed to determine optimal geometries of the sandwich plates that maximize the shock resistance of the plates for a given mass. It is found that increasing density of core can provide the better performance. Results also reveal that deflection of the back face of the sandwich plate is the smallest when the ratio of thickness of core to half side length of the plate is or so 0.12.Dynamic responses of foam projectile impacting cellular metallic sandwich plates are simulated using finite element code LS-DYNA.V970 on the HP-J6750 workstation. Numerical results are in good agreement with the experimental measurements. Comparison between direct loading by the foam projectiles and pressure loading shows that difference of shock resistance performed by sandwich plates and solid plates of the same mass is mainly determined by the property of the structure itself. In the deformation process of the sandwich plate energy absorbed by the front face and core are more than energy by the back face. It is also found that capacity of shock resistance provided by increasing thickness of core is better than by increasing thickness of face-sheet of the same weight. The sandwich plate with aluminum honeycomb core has a superior shock resistance relative to the sandwich plate with aluminum foam core of the same mass to a certain impulse.更多还原