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The detrimental effect of autofrettage on externally cracked modern tank gun barrels

Defence Technology（防务技术） 2019年第2期15卷 146-153页

作者： M.Perl T.Saley pearlstone center for aeronautical engineering studies Department of Mechanical Engineering Ben-Gurion University of the Negev

Overstraining gun tubes has a twofold advantage. First, it enables the increase of the Safe Maximum Pressure(SMP) in the tube, resulting in a higher muzzle velocity which extends the gun's range and its projectile kinetic energy. Second, it reduces the tube's susceptibility to internal cracking which prolongs its fatigue life. Unfortunately, autofrettage also bears an inherent detrimental effect as it considerably increases the tensile hoop stress at the outer portion of the barrel's wall, which enhances external cracking of the tube by increasing the prevailing Stress Intensity Factor(SIF). In order to quantify this disadvantageous effect, 3-D Mode I SIFs distributions along the front of a single external radial semielliptical crack initiating from the outer surface of an autofrettaged modern gun barrel, overstrained by either the Swage or the Hydraulic autofrettage processes, are evaluated. The analysis is performed by the finite element(FE) method, using singular elements along the crack front. Innovative residual stress fields(RSFs), incorporating the Bauschinger effect for both types of autofrettage are applied to the ***'s [1] RSF is also applied to the tube for comparison reasons. All three RSFs are incorporated in the FE analysis, using equivalent temperature fields, Values for K_(IA)-the SIF resulting from the tensile residual stresses induced by autofrettage are evaluated for: a typical barrel of radii ratio R_o/R_i = 2, crack depth to wall-thickness ratios(a/t = 0.005-0.1),crack ellipticities(a/c = 0.2-1.0),and five levels of Swage,Hydraulic and Hill's autofrettage(e = 40%,60%,70%,80%,and 100%). In total,375 different 3-D cases are analyzed. The analysis demonstrates undoubtedly the detrimental effect of all types of autofrettage in increasing the prevailing effective stress intensity factor of external cracks, resulting in crack initiation enhancement and crack growth rate acceleration which considerably shortens the total fatigue life of the bar

关键词： Gun barrel Swage and hydraulic autofrettage External crack 3-D Finite element

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Accelerating CFD–DEM simulation of processes with wide particle size distributions

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Particuology 2014年第1期12卷 113-121页

作者： Tamir Brosh Haim Kalman Avi Levy pearlstone Centre for aeronautical engineering studies Department of Mechanical Engineering Ben-Gurion University of the Negev School of Mechanical and Systems engineering Stephenson Building Claremont Road Newcastle University

Sizereduction systems have been extensively used in industry for many years. Nevertheless, reliable engi neering tools to be used to predict the comminution of particles are scarce. Computational fluid dynamics （CFD）discrete element model （DEM） numerical simulation may be used to predict such a complex phe nomenon and therefore establish a proper design and optimization model for comminution systems, They may also be used to predict attrition in systems where particle attrition is significant. Therefore, empirical comminution functions （which are applicable for any attrition/comminution process）, such as： strength distribution, selection, equivalence, breakage, and fatigue, have been integrated into the three dimensional CFDDEM simulation tool. The main drawback of such a design tool is the long computational time required owing to the large number of particles and the minute timestep required to maintain a steady solution while simulating the flow of particulate materials with very fine particles. The present study developed several methods to accelerate CFDDEM simulations： reducing the num ber of operations carried out at the singleparticle level, constructing a DEM grid detached from the CFD grid enabling a no binary search, generating a subgrid within the DEM grid to enable a no binary search for fine particles, and increasing the computational timestep and eliminating the finest particles in the simulation while still tracking their contribution to the process. The total speedup of the simulation process without the elimination of the finest particles was a factor of about 17. The elimination of the finest particles gave additional speedup of a factor of at least 18. Therefore, the simulation of a grinding process can run at least 300 times faster than the conventional method in which a standard no binary search is employed and the smallest particles are tracked.

关键词： Computational fluid dynamicsDiscrete element modelSearch algorithmIncreased time-step

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In-hand manipulation of a circular dynamic object by soft fingertips without angle measurement

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Science China(Information Sciences) 2021年第5期64卷 193-208页

作者： R.GARCIA-RODRIGUEZ V.PARRA-VEGA aeronautical engineering Program and Postgraduate Program in Aerospacial engineering Universidad Politecnica Metropolitana de Hidalgo Robotics and Advanced Manufacturing Department Research Center for Advanced Studies (CINVESTAV)

A multi-fingered robotic hand with curved fingertips enables contact re-positioning without reattaching at the expense of fingertip rolling. This rolling stands for a characteristic that facilitates dexterous manipulation but results in an algebraically complex dynamic model subject to such constraints. The hemispherical shape of fingertips allows a dexterous manipulation when controlling the tangent forces, which are essential to rotate object. However, the measurement of the object angle in practice requires tactile-optical sensing. In this paper, considering robotic fingers with curved soft tips, we propose a feedback control that ensures optimal dynamical grasping of a circular rigid object. It is shown that the collaboration of the contact forces, to get a minimum pose of internal forces, and the tangential forces, to induce the conditions for assuring the grasp closure, is necessary to get a skillful manipulation. In this case, the orientation control of a circular object to the desired angle while avoiding direct measurement of the object angle is presented. Stability conditions of the system are presented in the sense of stability-in-the-manifold. Finally, representative simulations are shown and discussed.

关键词： optimal grasping manipulation soft-fingertips circular object stability-in-the-manifold

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Synthesis of WS_(2)and MoS_(2)Fullerene-Like Nanoparticles from Solid Precursors

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Nano Research 2009年第5期2卷 416-424页

作者： Inna Wiesel Hamutal Arbel Ana Albu-Yaron Ronit Popovitz-Biro Jeffrey MGordon Daniel Feuermann Reshef Tenne Department of Materials and Interfaces Weizmann Institute of ScienceRehovot 76100Israel Electron Microscopy Unit Weizmann Institute of ScienceRehovot 76100Israel Department of Solar Energy and Environmental Physics Jacob Blaustein Institutes for Desert ResearchBen-Gurion University of the NegevBeer Sheva Campus 84990Israel The pearlstone center for aeronautical engineering studies Department of Mechanical EngineeringBen-Gurion University of the NegevBeer Sheva 84105Israel

Inorganic fullerene-like WS_(2)and MoS_(2)nanoparticles have been synthesized using exclusively solid precursors,by reaction of the corresponding metal oxide nanopowder,sulfur and a hydrogen-releasing agent(NaBH4 or LiAlH4),achieved either by conventional furnace heating up to~900℃or by photothermal ablation at far higher temperatures driven by highly concentrated white *** contrast to the established syntheses that require toxic and hazardous gases,working solely with solid precursors permits relatively safer reactor conditions conducive to industrial scale-up.

关键词： Nanoparticles fullerene-like synthesis WS_(2) MoS_(2)

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Special issue on conveying and handling of particulate solids–Challenges of discrete element simulation, application and calibration

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Particuology 2014年第1期12卷 1-1页

作者： Avi Levy Aibing Yu pearlstone Centre for aeronautical engineering studies Department of Mechanical EngineeringBen-Gurion University of the Negev School of Materials Science and engineering University of New South Wales

A series of international Conveying and Handling of Particulate Solids （CHOPS） conferences was initiated in Herzliya, Israel in 1995 and has since proceeded with six successive conferences held in Jerusalem （1997）, the Dead Sea （2000）, Budapest （2003）, Sorrento （2006）, Brisbane （2009） and Friedrichshafen （2012）. The conference series covers processes involvin particulate solids, for example,

关键词： DEM Special issue on conveying and handling of particulate solids application and calibration

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Hierarchical Dragonfly Wing： Microstructure-Biomechanical Behavior Relations

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Journal of Bionic engineering 2012年第2期9卷 185-191页

作者： Yinglong Chen Xishu Wang Huaihui Ren Hang Yin Su Jia Department of engineering Mechanics AML School of Aerospace Tsinghua University Beijing 100084 P. R. China Beijing aeronautical engineering Technology center Beijing 100076 P. R. China

The dragonfly wing, which consists of veins and membrane, is of biological hierarchical material. We observed the cross-sections of longitudinal veins and membrane using Environmental Scanning Electron Microscopy （ESEM）. Based on the experiments and previous studies, we described the longitudinal vein and the membrane in terms of two hierarchical levels of organization of composite materials at the micro- and nano-scales. The longitudinal vein of dragonfly wing has a complex sandwich structure with two chitinous shells and a protein layer, and it is considered as the first hierarchical level of the vein. Moreover, the chitinous shells are concentric multilayered structures. Clusters of nano-fibrils grow along the circumferential orientation embedded into the protein layer. It is considered as the second level of the hierarchy. Similarly, the upper and lower epidermises of membrane constitute the first hierarchical level of organization in micro scale. Similar to the vein shell, the membrane epidermises were found to be a paralleled multilayered structure, defined as the second hierarchical level of the membrane. Combining with the mechanical behavior analysis of the dragonfly wing, we concluded that the growth orientation of the hierarchical structure of the longitudinal vein and membrane is relevant to its biomechanical behavior.

关键词： dragonfly wing longitudinal vein membrane hierarchical structure biomechanical behavior

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Learning Scalable Task Assignment with Imperative-Priori Conflict Resolution in Multi-UAV Adversarial Swarm Defense Problem

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Journal of Systems Science & Complexity 2024年第1期37卷 369-388页

作者： ZHAO Zhixin CHEN Jie XIN Bin LI Li JIAO Keming ZHENG Yifan School of Electronics and Information engineering Tongji UniversityShanghai 201804China Shanghai Institute of Intelligent Science and Technology Tongji UniversityShanghai 201804China School of Automation Beijing Institute of TechnologyBeijing 100081China National Key Laboratory of Autonomous Intelligent Unmanned Systems Beijing 100081China Shanghai Institute of Intelligent Science and Technology Tongji UniversityShanghai 201804China.

The multi-UAV adversary swarm defense(MUASD)problem is to defend a static base against an adversary UAV swarm by a defensive UAV *** the problem into task assignment and low-level interception strategies is a widely used ***-based approaches for task assignment are a promising *** studies on learning-based methods generally assume decentralized decision-making architecture,which is not beneficial for conflict *** contrast,centralized decision-making architecture is beneficial for conflict resolution while it is often detrimental to *** achieve scalability and conflict resolution simultaneously,inspired by a self-attention-based task assignment method for sensor target coverage problem,a scalable centralized assignment method based on self-attention mechanism together with a defender-attacker pairwise observation preprocessing(DAP-SelfAtt)is ***,an imperative-priori conflict resolution(IPCR)mechanism is proposed to achieve conflict-free ***,the IPCR mechanism is parallelized to enable efficient *** validate the algorithm,a variant of proximal policy optimization algorithm(PPO)is employed for training in scenarios of various *** experimental results show that the proposed algorithm not only achieves conflict-free task assignment but also maintains scalability,and significantly improve the success rate of defense.

关键词： Conflict resolution reinforcement learning scalability task assignment.

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ELECTROCHEMICAL POLYMERIZATION OF 5-CYANOINDOLE IN MIXED ELECTROLYTES OF BORON TRIFLUORIDE DIETHYL ETHERATE AND DIETHYL ETHER

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Chinese Journal of Polymer Science 2006年第1期24卷 47-52页

作者： Jing-kun Xu Wei-qiang Zhou Jian Hou Shou-zhi Pu Jing-wu Wang Liu-shui Yan Jiangxi Key Laboratory of Organic Chemistry Jiangxi Science and Technology Normal University Nanchang 330013 China Department of Chemistry Nanchang University Nanchang 330047 China Department of Environmental and Chemical engineering Nanchang Institute of Aeronautical Technology Nanchang 330034 China

High quality poly（5-cyanoindole）（P5CI） films were electrosynthesized by direct anodic oxidation of 5-cyanoindole on stainless steel sheet in the mixed electrolytes of boron trifluoride diethyl etherate （BFEE） and diethyl ether （EE）（by volume 1：1）＋ 0,05 mol L^-1 Bu4NBF4. The film formed can be peeled off the electrode into freestanding films, The addition of EE into BFEE can improve the solubility of monomer. P5CI films obtained from this medium showed excellent electrochemical behavior with conductivity of 10^-2 S cm^-1, Structural studies showed that the polymerization of 5-cyanoindole occurred at the 2,3 position. As-formed P5CI films were thoroughly soluble in strong polar organic solvent dimethyl sulfoxide （DMSO） while partly soluble in tetrahydrofuran （THF） or acetone. Fluorescence spectral studies indicated that P5CI was a good blue-ight emitter.

关键词： Electrochemical polymerization Conducting polymers Polyindole Poly(5-cyanoindole) Boron trifluoride diethyl etherate.

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Electrical and mechanical performance of graphene sheets exposed to oxidative environments

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Nano Research 2013年第7期6卷 485-495页

作者： Mario Lanza Yan Wang Teng Gao Albin Bayerl Marc Porti Montserrat Nafria Yangbo Zhou Guangyin Jing Yanfeng Zhang Zhongfan Liu Dapeng Yu Huiling Duan State Key Laboratory for Turbulence and Complex System Department of Mechanics and Aerospace Engineering CAPT College of Engineering Peking University Beijing 100871 China Beijing aeronautical Science and Technology Research Institute Beijing 10221 I China center for Nanochemistry (CNC) Beijing National Laboratory for Molecular Sciences State Key Laboratory for Structural Chemistry of Unstable and Stable Species College of Chemistry and Molecular Engineering Academy for Advanced Interdisciplinary Studies Peking University Beijing 100871 China Electronic engineering Department Universitat Autonoma de Barcelona Cerdanyola del Valles 08193 Spain Department of Physics State Key Laboratory for Mesoscopic Physics Peking University Beijing 100871 China Physics Department Northwest University Xi'an 710069 China

Graphene coatings have been shown to protect the underlying material from oxidation when exposed to different media. However, the passivating properties of graphene in air at room temperature, which corresponds to the operating conditions of many electronic devices, still remain undear. In this work, we analyze the oxidation kinetics of graphene/Cu samples in air at room temperature for long periods of time （from I day to 113 days） using scanning electron microscopy, conductive atomic force microscopy and Auger electron microscop3~ and we compare the results with those obtained for similar samples treated in H202. We observe that unlike the graphene sheets exposed to H202, in which the accumulation of oxygen at the graphene domain boundaries evolves in a very controlled and progressive way, the local oxidation of graphene in air happens in a disordered manner. In both cases the oxide hillocks formed at the graphene domain boundaries can propagate to the domains until reaching a limiting width and height. Our results demonstrate that the local oxidation of the underlying material along the domain boundaries can dramatically decrease the roughness, conductivity, mechanical resistance and frictional characteristics of the graphene sheet, which reduces the performance of the whole device.

关键词： graphene local oxidation domain boundary passivating layer

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Progress of continuously rotating detonation engines

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Chinese Journal of Aeronautics 2016年第1期29卷 15-29页

作者： Zhou Rui Wu Dan Wang Jianping center for Combustion and Propulsion College of Engineering Peking University center for Applied Physics and Technology Peking University State Key Laboratory for Turbulence & Complex Systems Peking University

Continuously rotating detonation engine （CRDE） is a focus for concern in the field of aerospace propulsion. It has several advantages, including one-initiation, high thermal efficiency and simple structure. Due to these characteristics, it is expected to bring revolutionary advance- ments to aviation and aerospace propulsion systems and now has drawn much attention throughout the world. In this paper, an overview of the development of CRDE is given from several aspects： basic concepts, applications, experimental studies, numerical simulations, and so on. Representative results and outstanding contributions are summarized and the unresolved issues for further engi- neerin~ applications of CRDE are 13rovided.

关键词： Aerospace Continuously rotatingdetonation CRDE Detonation engine Propulsion system

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