板料渐进成形数值模拟与实验研究

为提高渐进成形的成形效率和成形质量,了解板料渐进成形的变形规律及工艺参数对成形的影响,采用有限元方法对板料渐进成形过程进行了数值模拟研究,分析了斜壁盒形件渐进成形过程应力分布和厚度变化趋势,通过对不同进给量和不同成形路径进行数值模拟,分析了工艺参数对成形的影响.结果表明,斜壁盒形件最大应力和最大厚度减薄发生在底面拐角处;成形过程中工具头运动轨迹应尽量采用走螺旋线的方式,可以提高成形件的成形能力和成形质量.渐进成形实验表明,数值模拟结果与实验结果基本吻合.     

板材软模成形数值模拟研究现状

分析了板材软模成形数值模拟的特点,对目前主要采用的软模成形数值模拟方法进行了阐述和评价,并对三类典型软模成形(液压成形,橡皮成形及粘性介质压力成形)过程数值模拟应用进行了综述,最后对板材软模成形数值模拟发展趋势进行了展望.     

法兰盘热挤压工艺设计

以法兰盘为研究对象,对法兰盘进行了结构及工艺性分析,并对变形程度进行了校核,拟定了先镦挤法兰和台阶,然后分步成形中心孔的工艺方案。 利用有限元分析软件对法兰盘成形过程进行了模拟分析,预测了法兰盘成形过程中的缺陷,缩短了试模周期。 用方案一镦挤法兰和台阶时变形量过大,无法同时成形,因此提出先成形法兰后成形台阶的方案二,但成形台阶时坯料受力不均匀且变形量很大,也无法成形。方案三先成形台阶,后成形法兰,最后反挤中心孔,并对成形过程各工步成形载荷进行了校核,结果显示,各工步成形效果良好,单工步最大载荷及总的载荷均满足设备要求。     

金属板材数控渐进成形工艺的研究进展

为了总结过去十几年国内外学者对板材数控渐进成形工艺技术的研究进展,对渐进成形工艺成形机理方面的研究成果进行了综述,分析了其材料变形的特点;全面概述了近年来国内外学者有关成形工艺参数对成形极限、成形精度、表面质量及能耗和效率的影响方面的研究成果,并介绍了国内外金属板材渐进成形装备的研究进展,最后对新兴的板材渐进成形工艺进行了总结概括。现有研究表明,成形件几何精度、表面质量和成形效率等方面的不足仍然是制约该技术广泛工业化应用的关键问题,同时渐进成形件的形性协同控制机理也亟待研究。     

多点复合渐进成形与单点渐进成形的对比分析

为提高金属板材渐进成形的成形质量、成形精度、成形效率和成形极限,了解不同渐进成形工艺对制件成形性能的影响,本文以典型方锥台制件为研究对象,利用有限元软件MSC.Marc对2种渐进成形工艺进行了三维建模,对比分析了单点渐进成形和多点复合渐进成形对制件等效塑性应变、厚度分布和成形精度的影响.数值模拟结果表明:单点渐进成形的等效塑性应变和厚度减薄主要集中在制件相邻侧壁间的拐角处,而多点复合渐进成形的等效塑性应变和厚度减薄均匀地分布在制件成形区;相同成形工艺参数下,相比单点渐进成形,多点复合渐进成形更有利于制件的成形效率、成形质量、成形精度和成形极限的提高,更有利于抑制破裂等失稳现象的产生.2种渐进成形工艺的成形试验表明,数值模拟结果与试验相符.     

超声振动辅助塑性成形及形性预测研究进展

随着微机电系统等领域的快速发展,对零件成形精度与性能的要求日益增加。超声振动辅助塑性成形是一种典型的能场辅助塑性成形工艺,相比于传统塑性成形工艺,具有流动应力低、材料成形能力高、界面摩擦少、成形质量较好等优势,被广泛应用于难成形材料加工、微成形、复杂构件成形等塑性成形过程。然而,由于不同塑性成形工艺中金属的变形行为特性存在较大差异,对塑性成形质量与成形性能进行预测有利于实现成形过程的形性协同控制。介绍了超声振动辅助塑性成形在体积成形工艺（镦粗、挤压、拉拔等）与板料成形工艺（拉伸、拉深、渐进成形、冲压等）中的应用及发展概况,讨论了超声振动对材料塑性变形过程中宏观表现与微观演化的影响。在已有研究基础上,重点分析了超声振动辅助塑性成形过程中成形能力预测（流动应力、成形极限等方面）和成形性能预测（表面性能、力学性能、微观组织等方面）的研究进展,为金属零部件成形高质量形性调控提供理论参考,并展望了超声辅助塑性成形工艺的发展趋势。     

成形工艺对轿车减振器座应变状态影响的研究

通过网格应变分析技术,对某轿车采用一次成形、两次成形工艺冲制减振器座的应变状态进行了定量研究,结果表明,成形工艺对减振器座的应变分布、应变路径、应变大小影响很大,一次成形较两次成形对材料的成形性能要求较高,两次成形工艺更有利于零件成形.     

金属板材单点渐进塑性成形过程的计算机模拟

研究了金属板材单点渐进塑性成形的成形机理,通过建立渐进成形的变形模型,详细分析了变形过程中受力的情况及成形过程,利用ANSYS软件对成形过程进行了计算机模拟.     

超混杂纤维金属层板成形方法研究进展

纤维金属层板(Fiber Metal Laminate, FMLs)作为一类兼具金属和复合材料优势的超混杂材料,凭借其优异的性能在航空航天和汽车领域应用广泛,其中商业化最成功的是玻璃纤维增强铝合金层板。首先按照组成金属与增强纤维的种类将纤维金属层板的分类进行介绍,并对其历史背景与研究进展进行了回顾。由于各成形方法涉及的变形机理不同,结合成形过程中几何尺寸和工艺参数对FMLs成形性能的影响,对其回弹、起皱、分层和开裂等成形缺陷和成形难点进行了分析。综述了现阶段国内外自成形、冲压成形、喷丸成形、充液成形和激光成形等技术的发展与应用现状,并对每种技术的优缺点及适用零件的类型进行探究。深入讨论了现有成形技术所遇到的挑战,其中重点对充液成形与冲压成形进行介绍。此外,简要介绍了FMLs在成形过程中的变形机理、变形模式和成形质量。在对各方面因素进行全面分析的基础上,讨论了FMLs成形技术未来的发展方向与挑战,此工作对科研人员未来开发新的成形方法具有一定意义。     

铝合金板料电磁成形工艺与理论的研究进展

将电磁成形与现有板料成形工艺相结合,能够有效拓宽电磁成形应用领域,可为汽车、航空、航天等高端装备中铝合金零件高性能精确成形带来新的突破.主要综述了电磁复合成形工艺、多物理场耦合数值模拟与本构建模、铝合金板料电磁成形性能与组织演变等3个方面的研究进展,并结合笔者的研究工作对电磁成形工艺与理论研究中存在的问题进行了简要分析.着重综述了以电磁辅助冲压与电磁渐进成形为典型代表的电磁复合成形工艺,阐述了电磁成形过程多物理场耦合数值模拟分析方法,介绍了基于管材电磁成形或板材电磁胀形实验的高应变速率本构模型参数逆向识别方法,为电磁成形数值分析提供必要的材料模型.阐明了电磁成形能够有效提高铝合金板料成形性能,并揭示了多物理场耦合作用下铝合金板塑性变形机理与组织性能演变规律,为电磁成形工艺研究打下重要理论基础.最后,对铝合金板料电磁成形工艺与理论的研究进展进行了总结,并对其发展前景和研究方向进行了展望.     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Assessment of intakes of mixtures of radionuclides

Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Numerical study of methods of linearization of the output characteristics of radio-frequency sensors of the level of dielectric media

Different constructions of the sensing elements of radio-frequency level sensors based on sections of long lines are numerically investigated by means of the Matlab program for the purpose of minimizing the measurement error caused by the nonlinearity of the output characteristic. It is shown that the nonlinearity is lowest for U-shaped designs. The nonlinearity factor KN may be regulated by varying the capacitance of a correcting capacitor connected to the input of the sensing element and (or) the length of one of the sections of the long line. In selecting an optimal capacitance of the correcting capacitor KN ≤ 0.15% for control media with dielectric permittivity in the range 2.2–30.     

Possibilities of Decreasing the Errors of Determination of the Height of the Pole of a Sessile Drop of Melt

We analyze the possibilities of decreasing the errors of measuring the height of the pole of a sessile drop of melt above its equator by determining the position of the equator according to the midpoints of vertical chords of the image of the drop. The optimal distance between these chords and the edge of the image of the drop is chosen within 10–20% of the radius of the equator. The proposed method guarantees the same level of errors of evaluation of the height of the pole and the radius of the equator, which enables one to substantially increase the accuracy of evaluation of the capillary constant and the surface energy of the melt according to the geometric parameters of the sessile drop.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.