Void Shape Effects on Void Growth and Slip Systems Activity in Single Crystals

建立了含椭球形微孔的三维体胞,该模型包含了椭球形微孔的一种特例:即球形微孔。采用晶体塑性滑移理论对不同取向下,单晶合金铸造微孔形状对微孔生长和滑移系激活的影响进行了研究。结果表明,材料的晶体坐标系、椭球微孔坐标系和载荷坐标系之间的坐标转换角度以及椭球微孔的形状对于微孔的演化具有非常重要的影响。对于三维应变状态下,椭球微孔的形状、晶体取向与载荷之间的相互关系共同决定了铸造微孔体积的增长、滑移系的激活和微孔旋转。当单胞滑移系的对称性被椭球型微孔破坏,即使载荷与滑移系统具有对称性,铸造微孔也会发生旋转。虽然单晶合金具有强烈的正交各向异性,但是当铸造微孔初始形状不为球形时,材料性能的正交各向异性对铸造微孔体积增长的影响被削弱。     

Effects of Two Different Dynamic Loading Conditions on Spall and Damage of 7075 Aluminum Alloy

The fracture behaviors of the 7075 aluminum alloy under two different dynamic loading conditions are investigated by means of a light-gas gun. The fracture surfaces obtained in the spall test are compared to the fracture surfaces obtained with a blunt projectile struck to the aluminum alloy plate. Optical and scanning electron microscopes are used in the investigation. For the plate-impact test, spall of the target was attributed to intergranular fracture caused by the tensile stress. The fracture behavior during projectile penetration is complex and consists of several fracture modes in addition to that the fracture is also of dynamic character. The penetration process of aluminum alloy target included: plugging stage, the microcracks nucleation stage, and the final tensile fracture stage. Mixed intergranular brittle/ductile fracture was observed, and brittle fracture played a dominate role.     

粉末冶金材料空穴和夹杂的疲劳蠕变损伤分析

基于Gurson塑性本构模型对含空穴和夹杂的镍基粉末冶金材料Fgh95进行了疲劳蠕变性能分析.采用K-R损伤模型对含空穴和夹杂的粉末冶金材料Fgh95进行了高温蠕变及疲劳-蠕变交互作用性能研究.结果表明:在疲劳载荷和高温蠕变载荷作用下,空穴比夹杂更易引起粉末冶金材料的损伤失效,相对高温蠕变载荷而言,疲劳-蠕变交互作用更易引起材料的破坏,且疲劳-蠕变交互作用对含夹杂材料的影响大于含空穴材料.     

相同形状尺寸的孔洞不同数量分布对多孔铝演变行为的影响

采用分子动力学模拟相同的孔洞总尺寸不同等间距孔洞的数量对多孔铝演变行为的影响。结果表明：在孔洞形状尺寸相同的情况下,随着等间距孔洞数量的增多,导致体系被拉开时间缩短,体系更容易被拉开;含孔洞的体系在加载过程中孔洞演变行为（裂纹尖端无序→尖端钝化→晶格畸变→母裂纹产生子裂纹）中的持续时间越来越短、波动次数越来越小。     

Mechanical Behavior of Shape Memory Alloys Under Complex Loading Conditions of Stress, Strain, and Temperature

The transformation behavior of shape memory alloys is simulated for complex loadings of stress, strain, and temperature. Calculations are made by using the ??Accommodation Model?? which is a constitutive model for shape memory alloys considering the accommodation behavior of the transformation strain. Calculated results are given for the superelastic behavior, the shape memory effect, the transformation behavior under temperature change with stress or strain holding, the structural behavior of a shape memory wire with a bias spring, etc. The effect of the plastic strain on the transformation strain is also investigated.     

胶接结构破坏模式及失效机理

以航空航天领域应用较为广泛的胶接结构为研究对象,以板-板胶接的拉伸剪切强度为评估指标,通过加速湿热老化试验对胶接结构的破坏模式和失效机理进行了研究。结果表明:胶接结构的断裂性质为韧性断裂,且随着老化时间的增加,其破坏模式为由内聚破坏向内聚破坏+界面破坏转变。在湿热老化试验前期,温度对拉伸剪切试样性能起主要作用,在老化后期,湿度起主导作用。     

堇青石表面化学气相沉积二氧化钛的负载机理及负载动力学

以酸蚀改性堇青石为基体,利用化学气相沉积法（CVD）在基体上负载TiO₂,采用扫描电子显微镜、能谱仪、X射线衍射仪、BET比表面积法等对负载了TiO₂的堇青石进行表征,测定不同温度下的负载速度。结果表明：负载了TiO₂的堇青石主要由（211）及（200）取向的锐钛矿TiO₂组成,呈八面体和立方体形态,BET比表面积达78.80 m²·g^-1,平均孔径为9.80 nm,具有双峰分布特征。负载过程为TiCl₄及O₂向堇青石基体扩散吸附,TiCl₄分解为Ti⁴⁺并在高氧势下进入基体晶格形成TiO₂晶核,并经过择优取向和外延式生长,其负载沉积速率方程为,其中T为负载温度,为气相TiCl₄的分压。     

Correlations Between Growth Kinetics and Microstructure for Scales Formed by High-Temperature Oxidation of Pure Nickel. II. Growth Kinetics

The oxidation kinetics of high-purity nickel were studied between 500 and 1200°C, in pure oxygen at atmospheric pressure, for average oxide-scale thicknesses of 1, 5, 10, and 30 m. In the overall temperature range studied, a decrease in the parabolic rate constant k_p with increasing scale thickness was observed. Depending on temperature and oxide-scale thickness, growth kinetics can be interpreted as a mixture of parabolic- and cubic-growth kinetics. Possible correlations between growth kinetics and microstructures of the oxide scales were investigated. From this set of experimental data, oxidation-kinetics models were tested. In particular, the effect of grain-boundary diffusion on NiO-growth kinetics was discussed. The correlations between growth kinetics and oxide microstructures appear to be more complex than usually reported.     

装载系统机器人化的动力学模型与自适应控制

从控制的观点来看,装载系统代表多变量的、非线性的和复杂的动力学耦合系统。考虑到拉格朗日法建立的二自由度装载系统动力学模型在现实情况中存在不稳定性和建模误差。在J.E SLOTINE提出的自适应控制方法的基础上,构造李雅谱诺夫（Lyapunov）函数,设计自适应控制器,对关节位置和速度进行轨迹跟踪研究,并用Matlab进行仿真。仿真结果表明关节速度稳态误差和位置稳态误差为零,验证了控制器的有效性和可行性。     

含铸造微孔镍基单晶合金蠕变损伤和裂纹萌生的模拟计算

基于镍基单晶合金蠕变变形过程中的细、微观组织结构变化及损伤特点,建立了考虑材质劣化和孔洞损伤的双参数蠕变损伤本构方程。利用所建模型对裂纹前缘含铸造缺陷（孔洞）的镍基单晶合金紧凑拉伸（CT）试样蠕变损伤和裂纹萌生进行了模拟计算,并考虑了晶体取向偏差和随机性的影响。计算结果表明：晶体取向和孔洞位置对试样蠕变损伤和裂纹萌生行为有着显著的影响。当孔洞距切口根部距离较近时,裂纹形核于切口附近的孔洞表面,裂纹形核时间较短;孔洞距切口根部距离较远时,裂纹形核位置位于切口表面,具体位置取决于试样的晶体取向,裂纹形核时间较长。随着加载轴晶体取向偏角的增大,裂纹形核时间明显缩短,其分散性加大,最大有34.7%的变化幅度;试样在2个不受控的晶体取向变化时,在偏角为45°和80°出现极值,裂纹形核时间最大偏差达3倍。     

Effect of Mechanical Loading on the Oxidation Kinetics and Oxide-Scale Failure of Pure Ni

The oxidation kinetics and mechanism of oxide-scale failure of pure Ni oxidized under external static compressive and tensile loads were studied. The results showed that both types of mechanical loads accelerated the oxidation rate, but the effect was different for the two types. Compressive loading (CL) affected it by improving the plasticity of oxide scales, and tensile loading (TL) affected it by amplifying the compaction of the oxide–metal interface. As for the oxide-scale failure, CL can delayed cracking, TL accelerated brittle failure. The study analyzed the effect of external load on the oxidation kinetics and the failure mechanism of oxide scales.     

电铲-汽车联合装运中两种调车方式的随机模拟与对比

矿山生产过程受复杂的环境影响，有很大的随机性和不确定性，计算机随机模拟就是根据各变量的概率规律建立一个虚拟模型并使之在计算机上运转。本文把矿山开采过程中电铲——汽车联合装运中两种调车方式中的几个变量，即分析电铲故障频率、每次故障持续时间、电铲装车时间、运行时间、卸载时间、空车运行时间等变量的概率分布规律。然后在计算机中产生符合这些概率分布的随机数，通过改变不同调车方式，找出尽可能发挥设备效率的途径。     

Effects of Loading and Constraining Conditions on the Thermomechanical Fatigue Life of NiTi Shape Memory Wires

The availability of engineering strength data on shape memory alloys (SMAs) under cyclic thermal activation (thermomechanical fatigue) is central to the rational design of smart actuators based on these materials. Test results on SMAs under thermomechanical fatigue are scarce in the technical literature, and even the few data that are available are mainly limited to constant-stress loading. Since the SMA elements used within actuators are normally biased by elastic springs or by antagonist SMA elements, their stress states are far from being constant in operation. The mismatch between actual working conditions and laboratory settings leads to suboptimal designs and undermines the prediction of the actuator lifetime. This paper aims at bridging the gap between experiment and reality by completing an experimental campaign involving four fatigue test conditions, which cover most of the typical situations occurring in practice: constant stress, constant-strain, constant stress with limited maximum strain, and linear stress-strain variation with limited maximum strain. The results from the first three test settings, recovered from the previously published works, are critically reviewed and compared with the outcome of the newly performed tests under the fourth arrangement (linear stress-strain variation). General design recommendations emerging from the experimental data are put forward for engineering use.     

钨合金在高速加载条件下的动态力学性能和失效机理

钨合金与贫铀弹相比,在穿甲过程中由于形成“蘑菇头”而不能形成很好的绝热剪切带而使其穿甲性能不及贫铀弹.钨合金在高速冲击加载下的动态力学性能和失效决定着钨合金穿甲性能,为此,本文综述了十多年来国内外对钨合金在高速冲击加载下的动态力学性能和失效机理的研究现状.     

基于直线电机的新型动态加载系统建模与仿真

针对伺服作动器动态性能测试需求,充分发挥电动加载便于安装维护、控制灵活以及直线电机高动态特性的优势,提出由直线电机驱动增力模块,通过机液融合的方式实现小位移、大推力、高频响的动态加载方案。在建立加载系统与伺服作动器系统数学模型的基础上,为提高力加载精度、改善系统稳定性和响应速度,引入多环级联控制与前馈控制的复合控制方案,并基于结构不变性原理通过前馈补偿抑制多余力。MATLAB/Simulink仿真结果表明:提出的伺服作动器动态加载方案与控制策略能够有效改善系统加载性能和抑制多余力,具有良好的工程参考价值。     

Kinetics of Failure Rate Accumulation and TiNi Shape Memory Effect Alloy Fracture Under Mechanical Cycling

Wire specimens, d = 0.1 mm, made of Ti-(50.6-50.8)at.%-Ni alloy were exposed to thermo-mechanical treatment (TMT), thus making the samples straight and providing them with high superelasticity (ε_se). It was established that the most effective method of TMT is annealing with deformation at 500 and 300 °C. The optimum mode of treatment was used in the research of mechanical fatigue of alloys with high superelastic properties. Two stages characterizing the alloy behavior under mechanical cycling were found out: failure accumulation and fracture. It was shown that the duration of the cycles is determined by the value of the preset deformation (σ_set) in relation to the deformation on the plateau-shaped area. The results of low-cycle fatigue of the alloys under investigation were processed by means of the method of least squares. The equations of prognosis of longetivity at the preset level of deformation are presented.     

舵机动刚度加载系统设计与分析

动刚度是舵机不可忽视的一项动态性能,加载系统的性能直接影响动刚度的测试结果。分析系统的原理结构,从静压支承伺服作动器的计算设计、伺服阀的选型、回油系统与安全保护措施的设计等方面对加载系统进行了全面设计。该系统已经投入使用,性能表现良好。     

Effects of Parameters on Inhomogeneous Deformation and Damage in Isothermal Local Loading Forming of Ti-Alloy Component

Isothermal local loading (ILL) forming technology provides a new way to form largescale rib-web (LSRW) components of Ti-alloy, widely used in the aero-space fields as key load-bearing structures. However, the metal undergoes complex plastic inhomogeneous deformation and microstructural evolution, this will lead to macroscopical forming defects and further damage due to multi-process parameters and local loading method, making the process and forming quality hard to control. Using numerical simulation, combined with experiment, influences of various process parameters on forming process, inhomogeneous deformation and damage have been explored for ILL of LSRW components, such as the types of die-forging mode, frictional conditions, and local loading parameters (partitioning of the loading zone, constraint conditions, and loading pass). Then the reasonable forming conditions for LSRW components of Ti-alloy to be studied are proposed. The practical forming experiment of TA15 LSRW component was achieved successfully and the forging with good forming quality, excellent microstructure, and comprehensive mechanical properties was obtained, which indicates the reliability and practical value of results obtained in this article.