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High-Velocity Projectile Impact Behaviour of Friction Stir Welded AA7075 Thick Plates

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Defence Technology（防务技术） 2023年第11期29卷 153-163页

作者： r.Praveen S.r.Koteswara rao G.Selvakumar r.Damodaram Department of robotics and Automation Karpaga Vinayaga College of Engineering and TechnologyChengalpattu603308TamilNaduIndia Department of Mechanical Engineering Sri Sivasubramaniya Nadar College of EngineeringChennai603110TamilNaduIndia

In this study, high velocity impact behaviour of friction stir welded AA7075-T651 25 mm thick plates were investigated using a 7.62 mm × 51 mm lead core and 7.62 mm × 39 mm steel core projectiles. Prior to ballistic trails, mechanical and metallurgical properties of friction stir welded AA 7075-T651 25 mm thick plates were studied. Microstructural and hardness studies revealed that friction stir welds constituted three distinct regions namely Weld Nugget(WN), Thermo-Mechanically Affected Zone(TMAZ) and Heat Affected Zone(HAZ). Base Material(BM) and all three weld regions were ballistically tested as per military standard NIJ.0108.01 using lead and steel core bullets at maximum permissible velocities of 830 ± 20 and 700 ± 30 m/s, respectively. It has been found that base material(AA7075-T651)and all three weld regions of 25 mm thick plates were able to resist perforation by both types of projectiles used. However depth of penetration has been found to increase from BM to WN, HAZ and TMAZ for both types of projectiles. In all cases steel core projectiles caused higher depth of penetration compared to those caused by lead core projectiles. TMAZs of the friction stir welds were found to be the weakest zone. The fracture that occurred in the base material was spall fragmentation indicating brittle failure, whereas all zones of friction stir welded AA7075-T651 targets with a front petalling, indicating ductile failure. The post-ballistic tested samples showed no significant change in the microstructure of the BM and WN. On the other hand, TMAZ and HAZ showed severe grain deformation in the direction of projectile penetration, and the formation of adiabatic shear bands(ASB). This work showed that 25 mm thick friction stir welded AA7075-T651 joints responded well to ballistic impact loads, making them a good choice for light combat vehicles.

关键词： Aluminum alloy Thick plate Friction stir welding Ballistic performance Depth of penetration

STUDY OF THrEE-DIMENSIONAL SEPArATION OF BOUNDArY LAYEr OVEr BLUNT BODIES

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Journal of Hydrodynamics 2009年第1期21卷 100-107页

作者： ATMANI r. BrIMA A. ASKOVIC r. Laboratoire de mécanique des fluides Université de ValenciennesAulnoy lez Valenciennes 59326 France Département de Mécanique Université de BiskraBiskra 07000 Algérie

In the case of three-dimensional flows, the separation can be defined in more than one way. Discussions about three-dimensional boundary layer separation in the literature have found a rational extension of the zero skin friction. Attempts have been made to establish the identity of “separation lines”. Among definitions, these may be found：（1） envelopes of limiting streamlines, （2） lines dividing flow which has come from different regions, （3） lines of singularities （problems of topology）, （4） lines on which some component of the skin friction vanishes. Each of these is valid under certain conditions, but none is universally valid. In the present work, we use the definition （4）, i.e. at low incidence of a blunt body the separation line is identified as the zero of the meridian skin friction component （Wang 1975）. So the separation line on a flattened spheroid （6：3：1） at 6° of incidence is calculated, as well as experimentally determined by using the electrochemical method, which allows to follow the evolution of the parietal velocity gradient.

关键词： three-dimensional flows separation boundary layers blunt bodies

Fully developed forced convection through semi-elliptic ducts

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Applied Mathematics and Mechanics(English Edition) 2016年第1期37卷 37-44页

作者： r.ALASSAr Department of Mathematics and Statistics King Fahd University of Petroleum and Minerals

An exact solution of the problem of fully developed forced convection through semi-elliptic ducts is obtained under constant axial heat flux and peripherally uniform temperature. The solution is validated by comparing... 详细信息

关键词： convection semi-elliptic duct

Magnetocaloric and magnetic properties of La_2NiMnO_6 double perovskite

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Chinese Physics B 2016年第8期25卷 373-378页

作者： Masrour r Jabar A Laboratory of Materials Processes Environment and Quality Cady Ayyed University National School of Applied Sciences

The magnetic effect and the magnetocaloric effect in La_2NiMnO_6（LNMO） double perovskite are studied using the Monte Carlo *** magnetizations,specific heat values,and magnetic entropies are obtained for different exchange interactions and external magnetic *** adiabatic temperature is *** transition temperature is *** relative cooling power is established with a fixed value of exchange *** to the master curve behaviors for the temperature dependence of △S_m^（max） predicted for different maximum fields,in this work it is confirmed that the paramagnetic-ferromagnetic phase transition observed for our sample is of a second *** near room-temperature interaction and the superexchange interaction between Ni and Mn are shown to be due to the ferromagnetism of LNMO.

关键词： oxides magnetocaloric Monte Carlo simulation specific heat magnetic properties

Value enhancement of olivine process dust through air classification

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International Journal of Minerals,Metallurgy and Materials 2012年第3期19卷 185-191页

作者： r.A.Kleiv Department of Geology and Mineral resources Engineering Norwegian University of Science and TechnologySem Slandsvei 1N-7491 TrondheimNorway

As a result of the production of dry olivine sand products at A/S Olivin＇s production plant at Aheim in western Norway, an annual quantity of some 20000-30000 t of process dust is produced. The bulk of this material is currently being sold as a slag conditioner at a rela- tively low price; hence, alternative uses of the process dust are now being sought. Information regarding the chemical composition of the material as a function of particle size facilitates product modifications through exclusion or mixing of individual size fractions. This paper demonstrates how such information can be obtained from air classification experiments when these are combined with chemical analysis of the produced size fractions. The classification and subsequent analysis of the olivine process dust revealed that the finer size fractions had high loss on ignition （LOI） values and were relatively low in MgO when compared with the bulk analysis. removal of the finer fractions re- sulted in a remaining coarse product of significantly higher quality. The coarse material could be used as a raw material for further processing; it could be recycled or it could constitute a new product in itself.

关键词： olivine air classification dust product development

Development and characterization of stainless steel fiber-based copper-free brake liner formulation:A positive solution for steel fiber replacement

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Friction 2020年第2期8卷 396-420页

作者： Vijay r D.Lenin SINGArAVELU r.JAYAGANTHAN Department of Production Engineering National Institute of TechnologyTiruchirappalli 620015Tamil NaduIndia Department of Engineering Design Indian Institute of Technology MadrasChennai 600036Tamil NaduIndia

This study deals with the development of drum brake liner for a multi-utility vehicle possessing a hydraulic brake system by varying 7 weight%of steel fiber and stainless steel fiber each,in friction composite *** developed friction composites were tested for physical,chemical,corrosion,mechanical,thermal properties,and tribological characteristics,under near-actual conditions using an inertia dynamometer as per industrial *** element analysis software(ANSYS)analysis was performed to show the thermal stress distribution of the developed friction composites at the maximum temperature rise due to heat generated during brake stops,and an extensive evaluation method was used to rank the *** study concludes that the brake factor of the stainless steel fiber-based friction composite produces stable performance in all conditions with a lower liner temperature rise of 340°C and lower thermal stress at 4.255294 ***,the steel fiber-based composites produced high performance at the beginning but deteriorated after a certain period due to higher levels of corrosion and a high temperature rise of 361°C resulting in a negative fade(-0.84%)and more thermal stress(5.619102 MPa).The primary plateau,secondary plateau,back transfer of drum wear debris,and the distribution of constituents on the worn surface of the developed composites in a resin matrix were identified and studied using a scanning electron microscope(SEM)equipped with energy-dispersive spectroscopy.

关键词： stainless steel fiber steel fiber brake liner friction composite

Effect of spheroidization of cementite in ductile cast iron

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International Journal of Minerals,Metallurgy and Materials 2021年第3期28卷 404-411页

作者： Basavaraj Pavankumar r.Sondar Subray r.Hegde Department of Metallurgical and Materials Engineering National Institute of Technology Karnataka(NITK)Surathkal 575025India

The research aims to provide an alternative to austempering treatment of ductile cast iron with a simple and cost-effective heat-treatment *** goal was accomplished by applying a simple one-step spheroidization heat treatment to the as-cast ductile iron,which would normally possess a coarse pearlitic microstructure to a significant *** experiments involving isothermal holding below the lower critical temperature(A1)were conducted followed by standard mechanical testing and microstructural characterization for an experimental ductile *** improving the spheroidization holding time at a given temperature,the work shows that the ductility and toughness of an as-cast ductile iron can be improved by 90%and 40%,respectively,at the cost of reducing the tensile strength by 8%.Controlled discretization of the continuous cementite network in pearlitic matrix of the ductile iron is deemed responsible for the improved *** work also shows that prolonged holding time during spheroidization heat treatment leads to degradation of mechanical properties due to the inhomogenous microstructure formation caused by heterogeneous decomposition and cementite clustering in the *** main outcome of this work is the demonstration of ductile cast iron’s necking behavior due to spheroidization heat treatment.

关键词： spheroidization cementite ductile iron toughness heat treatment

Future Trends in Computer Graphics： How Much is Enough？

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Journal of Computer Science & Technology 2003年第5期18卷 531-537页

作者： A.r.Forrest SchoolofComputingSciences UniversityofEastAngliaNorwichU.K.

Over the forty-year history of interactive computer graphics, there have beencontinuous advances, but at some stage this progression must terminate with images beingsufficiently realistic for all practical purposes. How much detail do we really need? Polygon countsover a few million imply that on average each polygon paints less than a single pixel, making useof polygon shading hardware wasteful. We consider the problem of determining how much realism isrequired for a variety of applications. We discuss how current trends in computer graphics hardware,and in particular of graphics cards targeted at the computer games industry, will help or hinderachievement of these requirements. With images now being so convincingly realistic in many cases,critical faculties are often suspended and the images are accepted as correct and truthful althoughthey may well be incorrect and sometimes misleading or untruthful. Display resolution has remainedlargely constant in spatial terms for the last twenty years and in terms of the number of pixels hasincreased by less than an order of magnitude. If the long-promised breakthroughs in displaytechnology are finally realised, how should we use the increased resolution?

关键词： computer graphics displays graphics hardware human vision point-basedmodelling

Dirac r-matrix calculations of photoionization cross sections of Ni Ⅻ and atomic structure data of Ni 

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Chinese Physics B 2017年第2期26卷 127-140页

作者： r T Nazirt M A Bari M Bilal S Sardar M H Nasim M Salahuddin Department of Physics and Applied Mathematics Pakistan Institute of Engineering and Applied Sciences Islamabad 45650 Pakista

We performed r-matrix calculations for photoionization cross sections of the two ground state configuration 3s^23p^5（~2P_（3/2,1/2）~o） levels and 12 excited states of Ni Ⅻ using relativistic Dirac Atomic r-matrix Codes（DArC） across the photon energy range between the ionizations thresholds of the corresponding states and well above the thresholds of the last level of the Ni XIII target ion. Generally, a good agreement is obtained between our results and the earlier theoretical photoionization cross sections. Moreover, we have used two independent fully relativistic GrASP and FAC codes to calculate fine-structure energy levels, wavelengths, oscillator strengths, transitions rates among the lowest 48 levels belonging to the configuration（3s^23p^4, 3s3p^5, 3p^6, 3s^23p^33d） in Ni XIII. Additionally, radiative lifetimes of all the excited states of Ni XIII are presented. Our results of the atomic structure of Ni XIII show good agreement with other theoretical and experimental results available in the literature. A good agreement is found between our calculated lifetimes and the experimental *** present results are useful for plasma diagnostic of fusion and astrophysical plasmas.

关键词： photoionization cross sections energy levels wavelengths lifetimes