金属粉末型坯动态注射成形技术的研究

提出一种金属粉末型坯动态注射成形新方法,在注射成形过程中全程引入振动力场作用,即将振动力场引入金属粉末喂料的输送、塑化、注射和保压全过程,实现动态固体输送、动态塑化混炼、动态注射和动态保压,使注射成形全过程处于周期性振动状态。通过在实验装置和样机上进行的一些相关实验研究发现,振动力场可以改变熔体在模具内的流动方式,降低充模压力。金属粉末的动态注射成形能得到比传统稳态下注射成形更优的型坯微观结构和性能,振动力场的作用对型坯品质的提高具有较明显的作用。

铟锡氧化物 (ITO) 靶材的应用和制备技术

对铟锡氧化物（ＩＴＯ）靶材的现有生产工艺方案和应用现状及前景作了综合评述．

Al-Mg-Si合金导线的生产现状及其发展前景

分析了铝合金导线的市场需求,以及国内外高强度铝合金导线的开发情况,提出了Al-Mg-Si合金导线的优势及应用领域,并对铝合金导线的制造及加工工艺进行了综述,对铝合金导线加工工艺的发展方向进行了展望。

振动力场对金属粉末注射熔体流变性能及相分离的影响

在金属粉末注射成形过程中,会出现喂料的粘结剂与金属粉末的相分离,从而影响产品密度、硬度等质量参数.为了解决这个问题,在注射成形过程中引入振动力场,将蜡基粘结剂与平均粒径为10μm的气雾化316L不锈钢粉末按各种装载量进行配比,探讨了振动频率、振幅对喂料熔体流变性能及相分离的影响.结果表明:振动力场的引入能改善金属喂料的流动性能,增加金属喂料在阿基米德螺旋模具中充模过程的流程;振幅、频率的改变能改善制品的相分离情况,频率为10Hz、振幅为0.10mm时对相分离的改善作用最为明显.

Sheet Metal Forming Simulation and Its Application in Stamping Process of Automobile Panels

The paper starts with a brief overview to the necessity of sheet metal forming simulation and the complexity of automobile panel forming, then leads to finite element analysis (FEA) which is a powerful simulation tool for analyzing complex three-dimensional sheet metal forming problems. The theory and features of the dynamic explicit finite element methods are introduced and the available various commercial finite element method codes used for sheet metal forming simulation in the world are discussed,and the civil and international status quo of automobile panel simulation as well. The front door outer panel of one certain new automobile is regarded as one example that the dynamic explicit FEM code Dynaform is used for the simulation of the front door outer panel forming process. Process defects such as ruptures are predicted. The improving methods can be given according to the simulation results. Foreground of sheet metal forming simulation is outlined.

DETERMINATION OF MATERIAL PARAMETERS FOR COMPUTER SIMULATION OF SUPERPLASTIC FORMING PROCESSES

In order to analyze and simulate the complex super-plastic forming process by computer, a method of equal height bulging for determining material parameters m and K of the superplastic alloy is presented. The formulae related to the method are deduced in this paper. The accuracy of the method is available for evaluating the examples used in simulating the superplastic sheet-metal bulging processes.

The asymptotic field of a dynamically growing crack in a viscoelastic materia

A mechanical model of a fracturing viscoelastic material was developed to investigate viscous effects in a dynamically growing crack-tip field. It was shown that in the stable creep-growing phase, elastic deformation and viscous deformation are equally dominant in the near-tip field, and stress and strain have the same singularity, namely, （σ-e）∝r^-1/（n-1）. The asymptotic solution of separating variables of stress, stain and displacement in the crack-tip field was obtained by asymptotic analysis, and the resulting numerical value of stress and strain in the crack-tip field was obtained by the shooting method and the boundary condition of a mode I crack. Through numerical calculation, it was shown that the near-tip fields are mainly governed by the creep exponent n and Mach number M. When n →∞, the asymptotic solution of a viscoelastic material can be degenerated into that of Freund＇s elastic-ideally plastic material by analyzing basic equations.

Pancreatic carcinoma coexisting with chronic pancreatitis versus tumor-forming pancreatitis:Diagnostic utility of the time-signal intensity curve from dynamic contrast-enhanced MR imaging

AIM: To evaluate the ability of the time-signal intensity curve (TIC) of the pancreas obtained from dynamic contrast-enhanced magnetic resonance imaging (MRI) for differentiation of focal pancreatic masses, especially pancreatic carcinoma coexisting with chronic pancreatitis and tumor-forming pancreatitis. METHODS: Forty-eight consecutive patients who underwent surgery for a focal pancreatic mass, including pancreatic ductal carcinoma (n = 33), tumor-forming pancreatitis (n = 8), and islet cell tumor (n = 7), were reviewed. Five pancreatic carcinomas coexisted with longstanding chronic pancreatitis. The pancreatic TICs were obtained from the pancreatic mass and the pancreatic parenchyma both proximal and distal to the mass lesion in each patient, prior to surgery, and were classified into 4 types according to the time to a peak: 25 s and 1, 2, and 3 min after the bolus injection of contrast material, namely, type-Ⅰ, Ⅱ, Ⅲ, and Ⅳ, respectively, and were then compared to the corresponding histological pancreatic conditions. RESULTS: Pancreatic carcinomas demonstrated type-Ⅲ (n = 13) or Ⅳ (n = 20) TIC. Tumor-forming pancreatitis showed type-Ⅱ (n = 5) or Ⅲ (n = 3) TIC. All islet cell tumors revealed type-Ⅰ. The type-Ⅳ TIC was only recognized in pancreatic carcinoma, and the TIC of carcinoma always depicted the slowest rise to a peak among the 3 pancreatic TICs measured in each patient, even in patients with chronic pancreatitis.CONCLUSION: Pancreatic TIC from dynamic MRI provides reliable information for distinguishing pancreatic carcinoma from other pancreatic masses, and may enable us to avoid unnecessary pancreatic surgery and delays in making a correct diagnosis of pancreatic carcinoma, especially, in patients with longstanding chronic pancreatitis.

Corner forming of AZ61A magnesium alloy tube within warm hydroforming

The comers with small radii on cross sections are crucial for forming hydroformed components with polygonal sections. In this paper, warm hydroforming experiments of AZ61A magnesium alloy tubes were cartied out to study the forming regularity of round comers by using a demonstration part with square sections. Effects of temperature on radius forming, thinning ratio distribution and microstructure were revealed and a component with relative outer corner radius of 3.0 was obtained by warm hydroforming at 240℃. The minimum thickness of the formed square section was located in the transition position between the corner and the straight wall. The thinning ratio of the round corner increased with the increase of forming temperature. Fotmability of the magnesium tube was improved by raising temperature under the effect of dynamic recrystallization at 240℃.

Modal analysis and pulse response of mobile hard disk head actuator arm assembly

Head actuator arm assembly (HAA) is the most important mechanical component of a mobile hard disk drive (HDD) and its shock dynamic response is a principal index of vibration resistance. In this paper,a finite element (FE) model is firstly developed in ANSYS of 2.5 inch (1 inch=25.4 mm) mobile hard disk. This model includes actuator arm,voice coil motor (VCM) and pivot bearing. The various step modal of HAA is calculated by FE model. Then the actuator arm vibration behavior is simulated with LS-DYNA procedure. The influence of pulse waveform,pulse amplitude and pulse width on the shock response of the relative displacement of the head actuator arm assembly is studied.

SCIENCE OF WINNING SOCCER:EMERGENT PATTERN-FORMING DYNAMICS IN ASSOCIATION FOOTBALL

Quantitative analysis is increasingly being used in team sports to better understand performance in these stylized,delineated,complex social systems.Here,the authors provide a first step toward understanding the pattern-forming dynamics that emerge from collective offensive and defensive behavior in team sports.The authors propose a novel method of analysis that captures how teams occupy sub-areas of the field as the ball changes location.The authors use this method to analyze a game of association football(soccer) based upon a hypothesis that local player numerical dominance is key to defensive stability and offensive opportunity.The authors find that the teams consistently allocated more players than their opponents in sub-areas of play closer to their own goal.This is consistent with a predominantly defensive strategy intended to prevent yielding even a single goal.The authors also find differences between the two teams' strategies:while both adopted the same distribution of defensive,midfield,and attacking players(a 4:3:3 system of play),one team was significantly more effective in maintaining both defensive and offensive numerical dominance for defensive stability and offensive opportunity.That team indeed won the match with an advantage of one goal(2 to 1) but the analysis shows the advantage in play was more pervasive than the single goal victory would indicate.The proposed focus on the local dynamics of team collective behavior is distinct from the traditional focus on individual player capability.It supports a broader view in which specific player abilities contribute within the context of the dynamics of multiplayer team coordination and coaching strategy.By applying this complex system analysis to association football,the authors can understand how players' and teams' strategies result in successful and unsuccessful relationships between teammates and opponents in the area of play.

Simulation of construction shape-forming process of cable domes

A cable dome has no stiffness or load carrying capacity unless it has been prestressed.Analyses of cable domes are based on successful prestressing designs,making force finding analysis very important.A new force finding method named the imbal-ance force iterative method is proposed,which can overcome some limitations of the integrity feasible prestressing method.For instance,even if groups are assigned by mistake,the pretension distribution that satisfies the known geometry form can also be found.This method possess good stability and calculation efficiency,and a case study indicates that it is applicable to the force finding of large and complicated cable domes.On the other hand,form finding analysis of cable domes is also a key engineering problem.However,rigid displacement occurs in this process,which makes the analysis more complex.In this pa-per,the dynamic relaxation method was selected,and the problem of rigid displacement was therefore effectively solved.The method includes two steps:first,the stretching cables are released,and secondly,an axial force is imposed on the two ends of each released cable.This method is convenient in its calculation and clear in its conception.A case study indicates that the method is suitable for the simulation of the construction process of various cable domes and cable-strut tension structures.Moreover,a form finding experiment was conducted on a model of a cable dome with a diameter of 4.8 m by tensing diagonal cables.The behavior of the model in the form finding process was investigated.The experimental results indicate that the ini-tial lengths of members and prestress loss are key issues in cable domes design.The results also prove that the methods of form finding and force finding proposed in this paper are reliable and effective.