Prediction of tri-modal microstructure under complex thermomechanical processing history in isothermal local loading forming of titanium alloy

To control the tri-modal microstructure and performance,a prediction model of tri-modal microstructure in the isothermal local loading forming of titanium alloy was developed.The staged isothermal local loading experiment on TA15alloy indicates that there exist four important microstructure evolution phenomena in the development of tri-modal microstructure,i.e.,the generation of lamellarα,content variation of equiaxedα,spatial orientation change of lamellarαand globularization of lamellarα.Considering the laws of these microstructure phenomena,the microstructure model was established to correlate the parameters of tri-modal microstructure and processing conditions.Then,the developed microstructure model was integrated with finite element(FE)model to predict the tri-modal microstructure in the isothermal local loading forming.Its reliability and accuracy were verified by the microstructure observation at different locations of sample.Good agreements between the predicted and experimental results suggest that the developed microstructure model and its combination with FE model are effective in the prediction of tri-modal microstructure in the isothermal local loading forming of TA15alloy.

Finite element simulation of aluminum alloy cross valve forming by multi-way loading

Deformation behavior,temperature evolution and coupled effects have a significant influence on forming process and quality of component formed,which are very complex in forming process of aluminum alloy 7075 cross valve under multi-way loading due to the complexity of loading path and the multiplicity of associated processing parameters.A model of the process was developed under DFEORM-3D environment based on the coupled thermo-mechanical finite element method.The comparison between two process models,the conventional isothermal process model and the non-isothermal process model developed in this study,was carried out,and the results indicate that the thermal events play an important role in the aluminum alloy forming process under multi-way loading.The distributions and evolutions of the temperature field and strain filed are obtained by non-isothermal process simulation.The plastic zone and its extension in forming process of cross valve were analyzed.The results may provide guidelines for the determination of multi-way loading forming scheme and loading conditions of the forming cross valve components.

Prediction and Verifcation of Forming Limit Diagrams Based on a Modifed Shear Failure Criterion

The forming limit diagram plays an important role in predicting the forming limit of sheet metals.Previous studies have shown that,the method to construct the forming limit diagram based on instability theory of the original shear failure criterion is efective and simple.The original shear instability criterion can accurately predict the left area of the forming limit diagram but not the right area.In this study,in order to improve the accuracy of the original shear failure criterion,a modifed shear failure criterion was proposed based on in-depth analysis of the original shear failure criterion.The detailed improvement strategies of the shear failure criterion and the complete calculation process are given.Based on the modifed shear failure criterion and diferent constitutive equations,the theoretical forming limit of TRIP780 steel and 5754O aluminum alloy sheet metals are calculated.By comparing the theoretical and experimental results,it is shown that proposed modifed shear failure criterion can predict the right area of forming limit more reasonably than the original shear failure criterion.The efect of the pre-strain and constitutive equation on the forming limits are also analyzed in depth.The modifed shear failure criterion proposed in this study provides an alternative and reliable method to predict forming limit of sheet metals.

Investigation of Excavator Performance Factors in an Open-Pit Mine Using Loading Cycle Time

This study presents the effect of excavator model, loading operation location, shift availability and truck-shovel combination on loading cycle time and productivity of an open-pit mine. The loading cycle time was used to assess the material loading system performance which is one of the key components of the total cycle time for material transportation in an open-pit mine. Loading is among the components of cycle time during which material is being handled. The data analyzed?was?collected from a computerized dispatch system at GGM from which 62,000 loading dispatches per month involving several shifts, 14 excavators and 49 trucks were loaded. About 4465 dispatches per excavator and 1276 dispatches per truck were assessed using loading cycle time data for each dispatch for a period of four months (between August and December). Under fixed tonnage loaded and waste type (33 t of non-acid forming waste rock),?it was observed that loading cycle time depends on excavator model, location and truck being loaded. Average cycle times, PDFS?and CDFS of loading cycle time series were used to identify differences in performance under different situations. It was concluded that shift availability for excavators, loading location, excavator model and truck-shovel combinations strongly affect the productivity during loading process in an open-pit mine.

THE CHANGE OF THE GENERAL FORM AND THE TRANSPORT OF THE WATER， LOAD AND SALT ABOUT THE NORTH－BRANCH OF THE CHANGJIANG RIVER MOUTH

The general form of the north-branch of the Changjiang River mouth has changed much as a result of the change of the main stream lines of the Nantong reach of the Changjiang River and the influence of human activities since 1915. By the 1930s, the main stream lines of the Nantong reach of the Changjiang River has shifted to the Tongzhou Bar west channel. The north-branch at the Changjiang River mouth has become atrophic because of Tongzhou Bar east channel's deposition. After 1958, Toughal Bar and Jiangxin Bar were exploited. And in 1970, the north channel of Jiangxin Bar was blocked up. All these things make the water of the north-branch more difficult to pass through. It leads to the decline of the total discharge percentage of the north-branch. And it causes the rising tide to go back to the south-branch. However, since 1978, with the development of Tongzhou Bar east channel and its left bank being scoured, the water amount of the north-branch has been increasing. And the water,load and salt of going back to the south-branch has been becoming less.

汽车B柱Rollforming成型的有限元仿真

在汽车车体构件制造中的辊弯成型工艺应用项目研究中,利用大型非线性有限元分析软件MSC.Marc研究了汽车B柱变截面辊弯成型仿真的有限元建模方法,主要包括板料模型和成型辊模型的建立、单元选择、边界条件、各种参数的设置及成型辊的速度加载等内容,然后采用刚性轧辊沿板料长度方向平动的方式对板料成型过程进行仿真模拟,分析了板料在成型初期、成型中期、变截面成型期三个阶段的变形特点及应力应变分布,得出了与实际成型规律相符合的结论,验证了模型的正确性,为辊弯成型FEA研究提供技术支持。

Nitrogen forms and pollution load of Dianchi Lake inflow river runoff in rainy season

With the control of point source pollution in Dianchi Lake basin, and the expansion of Kunming city, non-point source pollution has become the main source pollution of urban water environment and Dianchi Lake. To reveal the nitrogen pollution characteristics in watershed, this research selected key monitoring points and sections at Baoxiang river basin in rainy season which is the peak transported time of non-point source pollution, the nitrogen and hydrological indicators are monitored systematically. The different forms of nitrogen are analyzed, the pollution load of nitrogen are calculated and studied at cardinal sections; combined with the literature data, we compared the water nitrogen characteristics of Dianchi basin and Taihu basin, the main results are as follows:(1) In summer, water nitrogen form of Baoxiang river in the Caohe area is dominated by nitrate nitrogen, while in other areas it is dominated by ammonia nitrogen which is accounted for 31%-50% of total nitrogen;(2) The water pollution loads of Baoxiang river tended to increase from upstream to downstream, from June to August the total nitrogen pollution mainly comes from urban areas and the pollution load is 166.408 t;(3) In Dianchi Lake watershed and Taihu Lake watershed nitrogen concentration of inflow river is higher than that of the lake, nitrate nitrogen concentration between inflow river and lake shows a little difference, while ammonia nitrogen concentration of inflow river is higher than that of the lake. The results can provide the theoretical basis for nonpoint source pollution control and urban water environment planning and improvement in Dianchi Lake Basin.

嵌套加强的LQ550高强冷弯薄壁C型钢连续檩条受力性能研究

为提高LQ550级高强冷弯薄壁C型钢连续檩条的承载能力,采用在支座处嵌套的方法来加强连续檩条。对未加强和采用两种嵌套方式加强的檩条共7组试件进行三点受弯试验,得到了试件的承载性能和破坏形态,试验结果表明加强后的试件出现跨中局部屈曲和嵌套端部局部屈曲两种破坏形态。采用ABAQUS软件建立了非线性有限元模型对嵌套加强的檩条进行数值模拟,有限元分析得到的承载力和破坏形态与试验结果吻合良好,验证了有限元模型的准确性。基于验证的有限元模型,分析了两种嵌套方式和不同嵌套长度对檩条承载力的提升,且表明嵌套檩条的长度宜取为连续檩条跨度的1/5~1/4。

轴向载荷下双金属机械复合管界面紧密度研究

为研究应用于油气田集输和海洋工程等领域的双金属机械复合管界面的紧密度特性,建立了液压成型及轴向载荷下双金属机械复合管力学模型,对比了梯形加载、递增式加载与脉动加载液压成型工艺对复合管界面紧密度的影响,探究了轴向载荷下成型压力与结构参数对复合管界面紧密度的影响规律。结果表明,脉动加载液压成型工艺与梯形加载、递增式加载加工工艺相比,管间残余接触压力提升45%,可以更好地保证双金属复合管成型的稳定性;提高成型后的残余接触压力,有助于增强复合管抗载能力;外基管壁厚对复合管承载力的影响最大;内衬管单独承受拉伸载荷时界面分离现象最明显,增加内衬管壁厚能延缓界面分离。

弯曲载荷下双金属机械复合管内衬层屈曲失效机理

双金属机械复合管是油气田集输管线防腐控制的主要措施之一,而内衬层的失效是制约复合管工程应用的关键难题。为研究双金属机械复合管内衬层屈曲失效机理,建立弯曲载荷下复合管力学模型,研究成型压力、工作内压及复合管结构参数对内衬层失效模式的影响规律。结果表明:增加成型后的残余接触压力有助于提高内衬层的抗屈曲能力;较高的工作内压能够延缓内衬层屈曲时间,减小其褶皱幅值;成型前复合管层间初始间隙减小有利于提高内衬层抗屈曲能力;随着外基管壁厚、内衬管壁厚、复合管内径的增加,内衬管的抗屈曲能力增强。

横向冲击载荷下齿形双螺母防松性能

针对螺栓连接结构在舰船爆炸冲击中容易发生松动的现象,设计了一种齿形双螺母的防松结构。利用局部滑移理论分析齿形双螺母的防松原理,采用有限元仿真法,通过预紧力和微滑移的变化量对其防松性能进行分析,并研究了齿形双螺母防松性能的影响因素及其影响规律。研究结果表明:横向冲击载荷下,齿形双螺母预紧力下降慢,微滑移变化小,具有较好的防松性能;当楔形角与螺纹升角相同时,防松效果最差;楔形角越大,齿形数量越多,齿形双螺母的防松效果越好。

冷弯薄壁型钢-结构防火一体板自攻螺钉连接性能试验研究

开展冷弯薄壁型钢-结构防火一体板自攻螺钉连接抗剪性能试验研究,完成35个典型试件单调拉伸及低周往复加载试验,分析结构防火一体板厚度、螺钉直径、螺钉端距及加载角度等因素对其抗剪性能的影响。结果表明:不同加载角度及螺钉端距的试件呈现不同的破坏模式,主要包括板材端部撕裂破坏、板材孔壁承压破坏、板材被拉断破坏等,且破坏时试件的自攻螺钉存在不同程度的倾斜。对于试验端分别采用直径为4.8、5.5 mm螺钉的试件,试件的峰值荷载及延性系数与螺钉直径无明显相关性,弹性刚度随着螺钉直径增大而显著提升;随着螺钉端距由15 mm增大至25 mm,试件的弹性刚度无明显变化,而峰值荷载和延性系数提高了约35%;随着板厚由12 mm增大到20 mm,试件的峰值荷载提高了约40%,弹性刚度提高了约90%,延性系数降低了约30%;与加载角度为0°的试件的特征参数相比,加载角度为45°时,试件弹性刚度提高了约100%,峰值荷载及延性系数无明显差别;加载角度为90°时,试件弹性刚度及峰值荷载无明显差别,延性系数降低了约40%。

镁合金尾翼类构件径向同步加载工艺研究

目的针对常规挤压工艺成形尾翼类构件飞行时翼片径向产生挠曲变形的问题,提出了一种可调控金属流动的径向同步加载成形方法。方法结合ANSYS、Deform-3D有限元模拟和物理实验,分析径向同步加载的金属流动行为、等效应变和金属流线分布,通过拉伸实验测试成形翼片挤压方向(Extrusion Direction,ED)和横截面方向(Transverse Direction,TD)的力学性能,并通过观察显微组织揭示径向强化机理。结果径向同步加载通过对坯料施加周向压应力促进了金属径向流动,形成了沿径向分布良好的金属流线,有利于提升径向力学性能;采用该工艺试制构件表面质量良好,无宏观缺陷,且形成沿径向分布的宏观流线;翼片径向力学性能显著提升,屈服强度提升了57.8 MPa,抗拉强度提升了80.1 MPa,延伸率提升了1.4%,其强塑性的提升与纤维组织和块状LPSO相的纤维强化密切相关。结论实现了尾翼类构件的径向同步加载整体成形,通过调控金属流动形成径向分布良好的金属流线,提升了成形翼片径向强度,为高性能镁合金尾翼类构件的整体成形提供了理论基础和技术支撑。

电网的分散负荷安全域及其应用(二):线路静态失稳的边界-本质-形态及负荷安全域的稳定裕度

交流线路承载的静态稳定边界问题一直悬而未决。负荷安全域可约束线路压差、维持多级电网电压安全水平,但稳定裕度未知。传统静态功角稳定与电压稳定的概念、机理及分析方法都不相同。研究发现,针对线路两种静态稳定可形成统一的概念、机理,而全网静态稳定的充要条件是每条支路都满足静态稳定。基于线路的复变量状态方程,得到末端的复功率-电压(即P_(j)-Q_(j)-U_(j))、复功率-功角(即P_(j)-Q_(j)-θ_(ij))的独立方程;通过可解条件分析、偏导证明,得到唯一的P_(j)-Q_(j)稳定边界及其特征,证明两种失稳的同质性;通过解析几何分析,推导U_(j)和θ_(ij)的稳定边界及其特征,得到符合实际情况的失稳形态解释。基于P_(j)-Q_(j)稳定边界,提出线路负荷安全域的稳定裕度指标以及电压安全水平的修正方法。理论验证基于首端参考系线路模型分析的可行性,提出电网上下级拓扑的稳定域匹配方法。最后,基于状态可观性判据、方程独立性以及平衡点生成原理,分析线路功-角特性的局限性。算例表明,所提的稳定边界、稳定域匹配方法都与PSASP程序收敛性结果吻合。在新能源大量接入导致线路潮流波动性大的背景下,该研究更具理论价值及现实意义。

多楔带轮旋压工艺参数优化研究

针对多楔带轮旋压过程中成形质量较差和旋轮寿命较低的问题,以东安513型发动机多楔带轮为研究对象,基于Deform平台对冷轧钢板08Al多楔带轮成形过程进行数值仿真,通过筛选旋压工艺参数,确定设计变量,并分析主轴转速、旋轮进给速度和旋轮半径对毛坯等效应力、旋轮成形载荷的影响;基于Design-Expert软件对旋压过程的各设计变量以多目标遗传优化算法进行优化设计,并通过试验验证了有限元仿真的可靠性。经过优化后,成形后的带轮等效应力减少了39 MPa,旋轮所受成形载荷减小了10.64%。

轻质高强异形管件充液压制成形技术

目的针对轻质高强异形管状构件的迫切需求,研发了充液压制成形技术,以在低载荷下成形出具有高强度、大尺寸、小圆角等特征的异形空心薄壁管状构件。方法给出了充液压制成形的力学原理,建立了成形过程压制力计算模型与临界支撑内压理论模型,分析了充液压制成形过程失稳屈曲/起皱规律、圆角充填机理与壁厚分布规律。结果当管材充液压制过程所需的支撑内压为内高压成形压力的1/10~1/20时,就可以避免管坯发生失稳屈曲与起皱,同时使压制力大幅降低。在弯曲与压缩应力复合作用下对管坯进行圆角充填,充液压制成形得到的管件壁厚减薄非常小。结论利用小吨位合模压力机在超低压条件下可以充液压制成形出具有小圆角与均匀壁厚的轻质高强异形管件,解决了传统内高压成形压力高、易发生开裂等难题。

非线性加载路径下金属薄板成形极限研究进展

成形极限图是评判金属薄板局部成形能力的重要工具,研究非线性加载路径下的成形极限图对提高实际生产过程中工艺设计的合理性和板料的成形性具有重要意义。总结分析了国内外学者对非线性加载路径下金属薄板成形极限的研究进展,主要包括试验方法、理论预测模型及路径无关成形极限图3个方面。重点研究了不同试验方法的适用范围及优缺点,阐述了多种预测非线性加载路径下成形极限图的理论模型及应用实例,并归纳了当前在应变路径无关的成形极限图方面取得的研究成果。最后,从上述3个方面总结了当前更具潜力的研究方向,并对未来的发展趋势以及面临的困难和挑战进行了展望。

考虑构网型和跟网型变流器的孤岛微电网小信号稳定性分析

由电力电子设备主导的孤岛微电网面临系统惯量小、无频率支持而导致的稳定性问题,恒功率负荷的渗透也加剧了系统的失稳风险。研究了由构网型变流器和跟网型变流器为主导的,计及恒功率负荷的孤岛微电网稳定性。首先,建立了孤岛微电网系统的全阶小信号模型,通过特征值分析法研究了构网型变流器控制中下垂系数对稳定性的影响并得到了下垂系数的数值上界;其次,通过参与因子法揭示了系统参数和控制参数对小信号稳定性的影响;最后,在Matlab Simulink中建立了该孤岛微电网的开关模型,仿真验证了小信号分析结果的准确性。

双腹板工字型GFRP腰梁机械连接力学性能试验研究

为深入研究双腹板工字型玻璃纤维增强复合材料(glass fiber reinforced polymer,GFRP)腰梁机械连接节点的力学性能,基于无连接和有机械连接2种类型GFRP腰梁的静载试验,分析双腹板工字型GFRP腰梁在三分点对称加荷下的受力特征,明确2种类型腰梁的极限状态和破坏形式。结果表明:GFRP腰梁采用双腹板工字型截面型式,截面的最大应力为183 MPa,是GFRP腰梁纵向抗拉强度的62%,纵向抗压强度的73%(容许压缩承载力的205%),可以使GFRP材料强度得到充分发挥,腰梁稳定性能良好;GFRP腰梁容易出现局部破坏,首先在翼缘板处发生局部失稳,随即引起腹板产生屈曲破坏,翼缘和腹板连接处出现面层剥离和鼓起,腰梁连接处增设的缀板和螺栓可有效地抑制该局部破坏变形;采用螺栓机械连接并在连接处增设同材质缀板,可降低螺栓钻孔对梁体本身截面的削弱作用,使GFRP腰梁的刚度和极限承载能力分别提高17.9%和44.9%,是GFRP腰梁的合理连接方式。研究成果可为GFRP腰梁的推广应用提供参考和借鉴。

基于Deform的精冲模具磨损特性研究

建立精冲模具磨损有限元分析模型,采用有限元软件Deform-3D对常温下的精冲凸模磨损进行仿真分析,研究模具材料的硬度、毛坯与模具间摩擦因数和成型载荷等工艺参数对模具磨损的影响。结果表明:凸模边缘的磨损严重,而侧面的磨损量较小;最大磨损深度随着模具材料硬度的增大而减小,随着摩擦因数的增大而增大;反顶力也是影响对凸模磨损的重要因素,最大磨损深度随着反顶力的增大而增大。