Storage life prediction under pre-strained thermally-accelerated aging of HTPB coating using the change of crosslinking density

In order to predict the storage life of a certain type of HTPB (hydroyl-terminated polybutadiene) coating at 25 C and analyze the influence of pre-strain on the storage life, the accelerated aging tests of HTPB coating at 40 C, 50 C, 60 C, 70 C with the pre-strain of 0%, 3%, 6%, 9%, respectively were carried out. The variation regularity of the change of crosslinking density was analyzed and the aging model of HTPB coating under pre-strained thermally-accelerated aging was proposed. The storage life of HTPB coating at 25 C was estimated by using the Berthelot equation as the end point of the aging life with a 30% decrease in maximum elongation. The results showed that the change of crosslinking density of HTPB coating increased with the increase of aging temperature and aging time, and decreased with the in-crease of pre-strain. Under 0% pre-strain, the relationship between the change of crosslinking density of HTPB coating and the aging time can be described by the logarithmic model with the confidence probability greater than 99%.The stress relaxation phenomenon existed under 3%, 6% and 9% pre-strained aging. The aging model considering chemical aging and pre-strain was established with the confidence probability greater than 90%. The storage life of HTPB coating was 15.2935 years at 25 C under 0% pre-strain, which was reduced by 13.9007%, 75.6949% and 89.7859% under 3%, 6% and 9% pre-strain, respectively. The existence of pre-strain has a serious impact on the storage life of HTPB coating, therefore, the pre-strain should be avoided as much as possible during the actual storage.     

Theoretical and numerical simulation study on jet formation and penetration of different liner structures driven by electromagnetic pressure

The use of a shaped liner driven by electromagnetic force is a new means of forming jets. To study the mechanism of jet formation driven by electromagnetic force, we considered the current skin effect and the characteristics of electromagnetic loading and established a coupling model of"Electric—Magnetic—Force"and the theoretical model of jet formation under electromagnetic force. The jet formation and penetration of conical and trumpet liners have been calculated. Then, a numerical simulation of liner collapse under electromagnetic force, jet generation, and the stretching motion were performed using an ANSYS multiphysics processor. The calculated jet velocity, jet shape, and depth of penetration were consistent with the experimental results, with a relative error of less than 10％. In addition, we calculated the jet formation of different curvature trumpet liners driven by the same loading condition and ob-tained the influence rule of the curvature of the liner on jet formation. Results show that the theoretical model and the ANSYS multiphysics numerical method can effectively calculate the jet formation of liners driven by electromagnetic force, and in a certain range, the greater the curvature of the liner is, the greater the jet velocity is.     

Numerical simulation study on penetration performance of depleted Uranium (DU) alloy fragments

Due to its high strength, high density, high hardness and good penetration capabilities, Depleted ura-nium alloys have already shined in armor-piercing projectiles. There should also be a lot of room for improvement in the application of fragment killing elements. Therefore, regarding the performance of the depleted uranium alloy to penetrate the target plate, further investigation is needed to analyze its advantages and disadvantages compared to tungsten alloy. To study the difference in penetration per-formance between depleted uranium alloy and tungsten alloy fragments,firstly, a theoretical analysis of the adiabatic shear sensitivity of DU and tungsten alloys was given from the perspective of material constitutive model. Then, taking the cylindrical fragment penetration target as the research object, the penetration process and velocity characteristics of the steel target plates penetrated by DU alloy frag-ment and tungsten alloy fragment were compared and analyzed, by using finite element software ANSYS/LS-DYNA and Lagrange algorithm. Lastly, the influence of different postures when impacting target and different fragment shapes on the penetration results is carried out in the research. The results show that in the penetration process of the DU and tungsten alloy fragments, the self-sharpening properties of the DU alloy can make the fragment head sharper and the penetrating ability enhance. Under the same conditions, the penetration capability of cylindrical fragment impacting target in vertical posture is better than that in horizontal posture, and the penetration capability of the spherical fragment is slightly better than that of cylindrical fragment.     

Weapon effectiveness and the shapes of damage functions

This paper provides a review of methods of assessing a fragmentation weapon's effectiveness against a point target or an area target with keeping the focus on the necessity of using the Carleton damage function with the correct shape factor.First,cookie-cutter damage functions are redefined to preserve the shape factor of and to have the same lethal area as the corresponding Carleton damage function.Then,closed-form solutions of the effectiveness methods are obtained by using those cookie-cutter damage functions and the Carleton damage function.Finally,the closed-form solutions are applied to calculate the probability of damaging a point target and the expected fractional damage to an area target for several attack scenarios by using cookie-cutter damage functions and the Carleton damage functions with different shape factors.The comparison of the calculation results shows that using cookie-cutter damage functions or the Carleton damage function with a wrong shape factor results in quite signifi-cant differences from using the original Carleton damage function with a correct shape factor when weapon's delivery error deviations are less than or comparable to the lengths of the lethal area and the aim point is far from a target.The effectiveness methods improved in this paper will be useful for mission planning utilizing the precision-guided munitions in circumstances where the collateral damage should be reduced.     

Prediction of three-dimensional elastic behavior of filament-wound composites based on the bridging model

This work provides a method to predict the three-dimensional equivalent elastic properties of the filament-wound composites based on the multi-scale homogenization principle.In the meso-scale,a representative volume element(RVE)is defined and the bridging model is adopted to establish a theoretical predictive model for its three-dimensional equivalent elastic constants.The results obtained through this method for the previous experimental model are compared with the ones gained respec-tively by experiments and classical laminate theory to verify the reliability of this model.In addition,the effects of some winding parameters,such as winding angle,on the equivalent elastic behavior of the filament-wound composites are analyzed.The rules gained can provide a theoretical reference for the optimum design of filament-wound composites.     

ARCS动机模型在初中英语语法教学中的应用

语法学习能在一定程度上保证语言的地道性、流畅性和实用性。但就目前来看,英语学习者学习语法的积极性普遍不高,不少英语学习者抱怨英语语法项目琐碎繁杂、语法学习枯燥无聊。针对此现状,本文尝试将ARCS模型的四类动机策略整合于初中英语语法教学,以期有效激发并维持学习者的语法学习热情,提高语法教学效果。     

【专题】无人系统互操作性发展现状与关键问题

无人系统正在加速由专用化、单一化向通用化、标准化发展,多无人系统协同、无人-有人系统协同、无人系统集群等新型作战概念不断成熟。无人系统互操作性是提高无人系统联合作战能力的倍增器和推动无人系统系列化发展的重要抓手,也是适应无人系统协同化、集群化发展的必然需求。本文详细阐述了无人系统互操作性的概念内涵,从顶层规划、技术创新和能力验证三个方面分析了无人系统互操作性发展现状,提出了一种针对跨域、多域无人系统互操作的等级模型,构建了自底向上和自顶向下相结合的互操作性关键支撑技术体系,剖析了通用/开放体系架构、标准协议与模块化组件、自主能力评估验证、数据传输与数据策略等技术因素,并展望了下一步研究重点。     

太空信息支援指挥控制支持平台构建初探

针对当前太空信息支援指挥控制存在的诸如缺少统一平台进行需求综合、数据汇集和融合处理,各类数据和产品分散管理,分头为用户提供信息保障服务等现实问题,本文对太空信息支援指挥控制相关问题进行了研究,构建了太空信息支援指挥控制任务模型,并对太空信息支援指挥控制任务进行了分析。按照系统结构设计的思想,从太空信息资源提供者、太空信息资源使用者和太空信息系统管理者三个角度提出了太空信息支援指挥控制支持平台的功能需求;研究了太空信息支援指挥控制支持平台的系统组成,并按照"资源+服务+应用"的设计原则构建底层可共用基础平台,中间层提供支撑软件集成,上层面向各级各类用户系统的支持平台技术架构和相应物理架构,解决了指挥控制支持平台"建什么、怎么建"的关键问题,可为太空信息支援指挥控制支持平台设计提供理论参考。     

An interface shear damage model of chromium coating/steel substrate under thermal erosion load

The Cr-plated coating inside a gun barrel can effectively improve the barrel's erosion resistance and thus increase the service life.However,due to the cyclic thermal load caused by high-temperature gun-powder,micro-element damage tends to occur within the Cr coating/steel substrate interface,leading to a gradual deterioration in macro-mechanical properties for the material in the related region.In order to mimic this cyclic thermal load and,thereby,study the thermal erosion behavior of the Cr coating on the barrel's inner wall,a laser emitter is utilized in the current study.With the help of in-situ tensile test and finite element simulation results,a shear stress distribution law of the Cr coating/steel substrate and a change law of the interface ultimate shear strength are identified.Studies have shown that the Cr coating/steel substrate interface's ultimate shear strength has a significant weakening effect due to increasing temperature.In this study,the interfacial ultimate shear strength decreases from 2.57 GPa(no erosion)to 1.02 GPa(laser power is 160 W).The data from this experiment is employed to establish a Cr coating/steel substrate interface shear damage model.And this model is used to predict the flaking process of Cr coating by finite element method.The simulation results show that the increase of coating crack spacing and coating thickness will increase the service life of gun barrel.     

Visual SLAM in dynamic environments based on object detection

A great number of visual simultaneous localization and mapping (VSLAM) systems need to assume static features in the environment. However, moving objects can vastly impair the performance of a VSLAM system which relies on the static-world assumption. To cope with this challenging topic, a real-time and robust VSLAM system based on ORB-SLAM2 for dynamic environments was proposed. To reduce the influence of dynamic content, we incorporate the deep-learning-based object detection method in the visual odometry, then the dynamic object probability model is added to raise the efficiency of object detection deep neural network and enhance the real-time performance of our system. Experiment with both on the TUM and KITTI benchmark dataset, as well as in a real-world environment, the results clarify that our method can significantly reduce the tracking error or drift, enhance the robustness, accuracy and stability of the VSLAM system in dynamic scenes.