陶瓷/金属复合靶板受可变形弹体撞击的理论分析模型

针对弹体撞击陶瓷/金属复合靶板的问题,将弹体的变形、陶瓷面板的碎裂和金属背板的变形结合起来,建立了新的可变形弹体垂直撞击陶瓷/金属靶板的理论分析模型．模型中计入了弹体刚性区长度和运动速度、塑性变形区长度、横截面积和运动速度的变化以及弹体对靶板的侵入速度和深度;对陶瓷面板考虑了陶瓷锥体积和抗压强度的变化;对金属背板的变形,根据其塑性变形功、外力功及其动能守恒原理,得到金属背板的运动方程．最后对具体算例进行了分析,得到了各物理量随时间的变化,给出了一些有价值的规律．结果表明,模型能较好地描述撞击过程中的有关规律;与实验结果和数值模拟结果进行对比,吻合较好,说明了模型的有效性．     

反应装甲与陶瓷复合装甲集成技术研究探讨

为了得到抗弹性能较好的装甲,将反应装甲与陶瓷复合装甲集成。由长杆弹侵彻复合装甲的理论和撞击反应装甲时的动量定理,得出计算模型。据此模型进行了侵彻深度的数值计算,并证明相同面密度的集成装甲的抗弹性能明显优于陶瓷复合装甲。根据此计算模型对集成装甲进行优化设计,以得到较轻和抗弹性能较好的装甲。     

603、675装甲钢动态性能测试及本构关系建立

利用一维Hopkinson压杆实验设备，对603、675两种装甲钢的动态压缩力学性能进行了较为系统的测试，在此基础上建立了2种装甲钢的Bodner-Partom本构方程，经程序计算与实际试验结果对比，表明本构方程能够较好地反映材料在动载荷条件下的力学行为．     

Stability of hard plates on soft substrates and application to the design of bioinspired segmented armor

Flexible natural armors from fish, alligators or armadillo are attracting an increasing amount of attention from their unique and attractive combinations of hardness, flexibility and light weight. In particular, the extreme contrast of stiffness between hard plates and surrounding soft tissues give rise to unusual and attractive mechanisms, which now serve as model for the design of bio-inspired armors. Despite a growing interest in bio-inspired flexible protection, there is little guidelines as to the choice of materials, optimum thickness, size, shape and arrangement for the protective plates. In this work, we focus on a failure mode we recently observed on natural and bio-inspired scaled armors: the unstable tilting of individual scales subjected to off-centered point forces. We first present a series of experiments on this system, followed by a model based on contact mechanics and friction. We condense the result into a single stability diagram which capture the key parameters that govern the onset of plate tilting from a localized force. We found that the stability of individual plates is governed by the location of the point force on the plate, by the friction at the surface of the plate, by the size of the plate and by the stiffness of the substrate. We finally discuss how some of these parameters can be optimized at the design stage to produce bio-inspired protective systems with desired combination of surface hardness, stability and flexural compliance.     

橡胶复合靶板抗射流侵彻的理论和实验研究

根据射流侵彻橡胶复合靶板后射流变形情况,将橡胶复合靶板抗射流侵彻过程分为4个阶段。基 于应力波传播理论和开尔文-亥姆霍兹不稳定性对橡胶复合靶板抗射流侵彻过程进行了理论分析,得到射流 失稳时射流的速度区间及橡胶复合靶板对射流的干扰频率,并分析了射流侵彻橡胶复合靶板后的剩余侵彻 能力。分析了橡胶夹层厚度变化和橡胶复合靶板倾角对橡胶复合靶板抗射流干扰的影响,得到最佳橡胶夹层 厚度和倾角,并通过实验对理论结果进行了验证。结果表明,开尔文-亥姆霍兹不稳定性能很好地分析橡胶复 合靶板对射流的干扰作用。橡胶复合靶板在倾角为60、橡胶夹层厚度为3~3.5mm 时具有最佳防护性能。     

动能杆斜撞击靶板后效破片描述研究

针对动能杆式弹大倾角斜撞击靶板产生的靶后破片,建立了其初始破片云数学描述模型,并在此基础上对斜撞击靶后破片特征分布进行了建模。仿真结果与工程试验结果的比较表明,该模型具有较高的可信度。     

Deformation of an elastic helix in contact with a rigid cylinder

Summary The deformation of a short helix in contact with a rigid cylinder is investigated. Deformations occur due to bending, torsion and longitudinal elasticity of the helix. Shear deformation is neglected. Some of the equations describing the problem have been given already in Love's Treatise on the Mathematical Theory of Elasticity, in terms of curvature changes. Nevertheless, the equations for small deformations have to be reformulated in terms of displacements and rotations, because contact constraints cannot be expressed in terms of curvature. Friction is neglected, thus the problem is symmetric, and it is sufficient to determine its solution for one half of the helix.Without friction between the cylinder and the helix, the contact problem arises only for a helix longer than one length of twist. For a shorter helix, the global equilibrium conditions cannot be satisfied for nonvanishing contact forces. For the minimum length, there are two noncontact zones, and the helix is in contact with the cylinder only at three points: at the ends and in the middle. For a slightly longer helix, four contact points and three noncontact regions are found. The dependence of the noncontact zones and the contact forces, which are of practical interest, can be calculated as a function of the length of the helix and its geometrical parameters. The case of a very long helix with more than four contact points remains unsolved.     

基于剪切增稠液体防护装甲的研究

综述了剪切增稠液体(Shear Thickening Fluid,即STF)的基本性质、组成成分、流变机理,影响STF流变性能的诸多因素以及对STF流变性能的研究方法,介绍了STF中聚乙二醇(PEG)/纳米SiO2颗粒体系和SiO2的制备方法,对PEG/SiO2的增稠机理进行了讲解。在对STF研究的基础上,阐述了STF-织物组成的液体防护装甲的优异防护性能、防弹和防刺(防锥、防刀)机理,讲述了STF-Kevlar构成的液体防护装甲及防刺机理,介绍了动态防刺测试和准静态防刺测试,最后对液体防护装甲未来研究方面进行了展望。     

Hydrolytic stability of polybenzobisoxazole and polyterephthalamide body armor

Previous work conducted at the National Institute of Standards and Technology (NIST) to investigate the field failures of soft body armor containing the material poly(p -phenylene-2,6-benzobisoxazole), or PBO, revealed that this material was susceptible to hydrolysis, and a mechanism of this hydrolysis was proposed. In this work, viscometric estimations of the molar mass of environmentally conditioned PBO are used to support a previously proposed mechanism of PBO hydrolysis. Results with PBO were compared with poly(p-phenylene terephthalamide), or PPTA, which has been used in body armor applications for more than 30 years. Losses in tensile strength were found to correspond to a reduction in molar mass for PBO. This indicates that chain scission due to complete hydrolysis is occurring in this material. Similar trends were observed for PPTA, but the relationship between molar mass reduction and losses in tensile strength was not as evident for this material. Confocal microscopy, mechanical properties measurements, and molecular spectroscopy are used to further investigate the degradation of both PBO and PPTA.     

Effect of moisture on copolymer fibers based on 5-amino-2-(p-aminophenyl)-benzimidazole

In recent years, there has been concern in the soft body armor community that copolymer fibers based on 5-amino-2-(p-aminophenyl)-benzimidazole can release hydrochloric acid, which is present in these fibers as a by-product of the manufacturing process. The presence of acids could potentially be detrimental to other fibers that might come in contact with these materials. In an effort to examine this issue, a study was designed to investigate the release of acid in different environments from these fibers. During the first phase of the study, fibers were exposed to water and pH decreases were observed. While immersed in deionized water, two of the fiber samples studied released a sufficient amount of acid to drop the pH of the solution from approximately pH 6.0 to approximately pH 3.0 in less than 10 d at room temperature. Further ion-selective electrode studies of chloride ion released from these fibers indicated that hydrochloric acid may not be the species responsible for this pH reduction. In a second phase of the investigation, fibers were exposed to water vapor in an elevated temperature environment (conditions were 65 °C, 80% RH). While the pH reduction released by the water vapor exposure was substantially less than observed in the submersion phase, a reduction in the yarn tensile strength of some of the fibers was observed during this phase of the study. In a third phase, fibers were exposed in a dry oven (less than 5% RH) at 65 °C. Almost no pH reduction or strength reduction was observed. Molecular spectroscopy was also performed to better understand the effect of elevated temperature and moisture environments on these fibers.