爆炸成型弹丸对装甲靶板的高速冲击效应研究

摘　要：爆炸成型弹丸(Explosively Formed Projectiles,简称EFP)垂直高速冲击603装甲靶板实验,呈现了靶板入口卷边花瓣状破坏、出口具有拉伸断裂特征的外翻花瓣形穿孔、入口直径明显大于出口直径等宏观的冲击现象。为了从机理上研究EFP对装甲靶板的高速冲击效应,利用ANSYS/LS-DYNA动力学仿真软件,对整个冲击过程进行了数值模拟,再现了EFP形成、开坑、稳定侵彻、尾翼侵彻和冲塞贯穿的物理过程,模拟结果与实验现象吻合较好,并从原理上分析了实验中各宏观现象产生的原因。研究结果不但认识了EFP冲击装甲靶板的机理,也可为增强装甲防护能力和优化EFP设计提供理论参考,具有重要的现实意义和较高的工程应用价值。     

On the effect of the backup plate stiffness on the brittle failure of a ceramic armor

The present investigation enquires the role of the backup plate mechanical properties in the brittle failure of a ceramic tile. It provides a full-field solution for the elastostatic problem of an infinite Kirchhoff plate containing a semi-infinite rectilinear crack (the tile) resting on a two-parameter elastic foundation (the backup plate) and subjected to general transverse loading condition. The backup plate is modeled as a weakly non-local (Pasternak type) foundation, which reduces to the familiar local (Winkler) model once the Pasternak modulus is set to zero. The same governing equations are obtained for a curved plate (shell) subjected to in-plane equi-biaxial loading. Fourier transforms and the Wiener–Hopf technique are employed. The solution is obtained for the case when the Pasternak modulus is greater than the Winkler modulus. Superposition and a two-step procedure are employed: First, an infinite uncracked plate subjected to general loading is considered; then, the bending moment and shearing force distribution acting along the crack line are adopted as the (continuous) loading condition to be fed in the solution for the cracked plate. Results are obtained as a function of the ratio of the Pasternak over the Winkler foundation stiffness times the tile flexural rigidity. It is established that the elastic foundation significantly affects the mechanical behavior of the elastic plate. In particular, the Winkler model substantially underestimates the stress state near the crack tip. Stress-intensity factors are determined, and they are employed as a guideline for increasing the composite toughness. The analytical solution presented in this paper may serve as a benchmark for a more refined numerical analysis.     

Ballistic impact performance of an armor material consisting of alumina and dual phase steel layers

Utilization of a ceramic front layer provides an improvement in the ballistic efficiency of monolithic metallic materials. In the current paper, the ballistic behavior of laminated composite having alumina front and dual phase steel backing layers was studied using 7.62 mm armor piercing (AP) projectiles under normal impact. The variables used were martensite content of the backing layer and the areal density of the composite. Experimental results showed that utilization of a 6 mm thick alumina front layer which was bonded to dual phase steel enhanced the ballistic resistance of the dual phase steel remarkably.     

陶瓷复合装甲优化设计及弹击后剩余弯曲强度

根据防护要求和防护机制,设计了一种C/C-SiC陶瓷/铝基复合泡沫复合装甲。在确保复合装甲面密度为44 kg/m²的前提下,以弹击后剩余弯曲强度为评价标准,以陶瓷板布置位置、各组成层厚度、泡沫金属中泡沫孔径尺寸为研究因素,设计了三因素三水平的正交模拟优化方案,利用有限元软件ABAQUS模拟了子弹侵彻陶瓷靶板的过程及弹击损伤后复合装甲的弯曲实验过程,预测了剩余弯曲强度,并进行了结构优化。根据数值模拟结果制备陶瓷复合装甲试样,进行实弹打靶和弯曲实验以验证复合装甲试样剩余弯曲强度。结果表明,以MIL-A-46103E Ⅲ类2A级为防护标准,剩余弯曲强度最高的陶瓷复合装甲最优化结构形式为：陶瓷板厚度12 mm、陶瓷板做防弹面板、Al基复合泡沫孔径为4 mm+10 mm的混合;对剩余弯曲强度的主次影响因素排序为：陶瓷板厚度>陶瓷板布置位置>Al基复合泡沫孔径。     

The hybrid-Trefftz finite element model and its application to plate bending

This paper presents a new hybrid element approach and applies it to plate bending. In contrast to more conventional models, the formulation is based on displacement fields which fulfil a priori the non-homogeneous Lagrange equation (Trefftz method). The interelement continuity is enforced by using a stationary principle together with an independent interelement displacement. The final unknowns are the nodal displacements and the elements may be implemented without any difficulty in finite element libraries of standard finite element programs. The formulation only calls for integration along the element boundaries which enables arbitrary polygonal or even curve-sided elements to be generated. Where relevant, known local solutions in the vicinity of a singularity or stress concentration may be used as an optional expansion basis to obtain, for example, particular singular corner elements, elements presenting circular holes, etc. Thus a high degree of accuracy may be achieved without a troublesome mesh refinement. Another important advantage of the formulation is the possibility of generating by a single element subroutine a large number of various elements (triangles, quadrilaterals, etc.), presenting an increasing degree of accuracy. The paper summarizes the results of numerical studies and shows the excellent accuracy and efficiency of the new elements. The conclusions present some ideas concerning the adaptive version of the new elements, extension to nonlinear problems and some other developments.     

Study on terminal effects of dense fragment cluster impact on armor plate. Part I: analytical model

The phenomena and the test results of dense fragment cluster impacting armor plate are briefly summarized. The test results indicate that the impulse and the rate of energy deposition on the target and the impacting duration of the fragment cluster are the most important factors, which induces the multi-fragment effects, i.e. synergistic effects, in the impacting process. Meanwhile, they are the characteristic parameters that distinguish the cumulative effects from the additive effects. The analytical methods are employed to investigate the cumulative effects and additive effects caused by the dense fragment cluster. Based on the analysis of the terminal effect of a single fragment, the extrusion-shear damage model of the target impacted by the fragment cluster is developed, and two criteria for the occurrence of the cumulative effect are given and applied to the test analysis. The dimensionless characteristic parameter of the fragment-cluster/target-plate system is also derived.     

Study on terminal effects of dense fragment cluster impact on armor plate. Part II: numerical simulations

In the paper of analytic modelling, i.e. Part I of this project, the phenomena and the test results of dense fragment cluster impacting armor plate are introduced. The analytical method is used to investigate the cumulative and additive effects. The extrusion-shear damage model of the target impacted by the fragment cluser is developed, and two criteria of the cumulative effect are proposed. This article describes numerical study of the problem in order to examine the analytical model and to study the target damage pattern. The numerical simulations of multi-fragment impact reproduce the experimental phenomena of fragment cluster penetrating into a target plate. It shows that the cumulative and additive damage phenomena can be identified by the fragment density and the fragment hit-time interval. Meanwhile, the fragment density is more sensitive than the hit-time interval to the target damage pattern.     

剪切增稠液体在防刺材料中的应用研究

制备出质量分数为22%的剪切增稠液体(STF)并对其稳态和动态流变性能进行研究,发现体系具有明显的剪切增稠现象,用"粒子簇"生成机理能较好地解释这种现象.用STF处理不同经纬密的芳纶,制备出STE-复合织物,并对其和纯芳纶织物进行准静态防刺试验.结果表明,剪切增稠液体的使用能够有效地增强芳纶织物的防刺性能,但经纬密小的...     

用多面体逼近球体及其在工业设计中的应用

球体是工业设计中常用的造型语言,但由于某些需要或限制,往往采用多面体来近似表示球体。文章提出了用多面体逼近球体效果的评判标准和改进方法,以及多面体对球体的逼近在工业设计中的应用,最后以实例加以说明。     

Generalized elastic damage theory and its application to composite plate

Based on continuum mechanics, a generalized damage theory for elastic material which can be used for anisotropic composite is presented in this paper. This theory for anisotropic elastic material has been proposed here from the stress-strain relation of the actual damaged material. Introducing a fourth order damage operator that may be formed by a symmetrical second order damage factor tensor, the constitutive equation of the damaged material has been set up. The expressions of components of both the stress tensor and the strain tensor of the damaged material and their first order invariants have been also derived. The application of this theory to the 2-dimensional composite laminate, including the technique estimating the components of the damage factor tensor and the damage variable tensor and also the practical measure technique of the damage in the whole process, have been explained in detail. Finally, the changes of the anisotropic elastic properties and the actual stress state of damaged material have been discussed and some interesting results have been obtained in this paper.     

Artificial intelligence and its impact on computer-aided design

This paper provides, for readers unfamiliar with the field, an introductory account of research which has been carried out in artificial intelligence. It attempts to distingussh between an artificial intelligence and a conventional computing approach and to assess the future influence of the former on computer-aided design.     

Back to the future with CAD: its impact on product design and development

This paper briefly examines the history of the management and organisation of the product development cycle. It looks at some of the key factors that have affected product development, and how information technology through CAD may have opened the door to a simultaneous product design process that has more in common with ‘older’ craft-based methods than those developed in the recent industrial era.     

Impact resistance of a rectangular polycarbonate armor plate subjected to single and multiple impacts

In the present work the plastic deformation of a thin rectangular polycarbonate armor plate subjected to single and multiple impacts was investigated in detail. The impacts were conducted on a horizontal and diagonal path to explore the plate vulnerability against the in-coming single and multiple projectiles striking at various locations. Single impacts revealed the overall trend in plate dent sizes and thickness reductions on the horizontal and diagonal paths. Results were compared with previous research [Shah QH, Abakr YA. Effect of distance from the support on the penetration mechanism of clamped circular polycarbonate armor plates. International Journal of Impact Engineering 2008;35:1244–50] conducted on circular armor plate for validation purposes. The single impact data scatter necessitated to conduct repeated impact tests at reduced number of locations to search for a definite answer for the possible failure process in the vicinity of the clamped edges of the plate. An accelerated plastic deformation resulting in early perforation was found to occur in the diagonal plate corner compared to the plate center impact position or close to a straight clamped edge. Multiple impact results presented can be significantly helpful in designing rectangular shape polycarbonate armor plates to enhance safety. LSDYNA was used to simulate the impact event for the plate midpoint, the horizontal edge, and the diagonal edge. The results show a close agreement with the experimental work.     

Sea-ice management and its impact on the design of offshore structures

A methodology for including ice-management in a structural reliability analysis is presented. The approach mainly focuses on how icebreakers or offshore installation disconnection capabilities may alter ice-load distributions and thereby reduce the probability of failure. To demonstrate the approach, a moored symmetrical structure in the central Barents Sea was considered. Realistic ice data from a probabilistic ice-drift simulator was used as a basis and ice loads were calculated in hourly time steps for a 1000-year period. The load calculations were based on the transformation of all developing ice conditions into a standardized equivalent ice thickness. Furthermore, empirical formulations for ice resistance on icebreaking vessels were combined with “max-to-mean ratios” from physical tank-model tests to estimate peak loads.The demonstration reveals a need for more relevant ice-load models that are valid both for managed as well as unmanaged ice. The methodology used for the calculation of ice equivalency and ice loads significantly underestimates the loads from severe ice features (compared to approaches recommended in ISO 19906). In a severe ice environment, it was found that the icebreaker's ability to reduce ice loads was insufficient to reduce the most extreme (abnormal) loads. The ability to disconnect moorings and risers and escape the site prior to abnormal ice events will ensure that the ice loads are within an acceptable range, conditional that the disconnection capabilities are sufficiently reliable. A fault-tree analysis including failure probabilities in ice-management operations and/or disconnection operations is considered useful for estimating the frequency of specified accidents.     

低速碰撞下复合材料叠层板的微裂纹演化及其对弹性模量的影响

采用双线性特性破坏模型研究了复合材料叠层板各层内部开裂裂纹的演化;通过引入弹性模量的裂纹影响系数表示,推导出裂纹影响系数与应变及应变率之间的微分关系,并得到裂纹耗散功率与裂纹影响系数变化率之间的关系。通过计算不同初始碰撞速度下复合材料叠层板的应变、应变率响应以及裂纹影响系数的演化,得到整个冲击过程中各层内任意点附近裂纹开裂情形及其对弹性模量的影响;通过检查界面各点处的裂纹影响系数是否发生改变,预测了碰撞完成之后复合材料叠层板中各层内微裂纹的分布区域位置与大小;并将该预测结果与其他破坏准则计算结果进行了比较。计算结果表明,在碰撞过程中各层内任意点处的应力值超过其屈服强度后,该点附近的弹性模量开始发生衰减,衰减大小随铁球初始碰撞速度的增大而增大。在四边夹支的边界条件下,复合材料叠层板的裂纹分布区域同样最先出现在碰撞点及边界中点位置,区域面积随初始碰撞速度的增大不断扩大