基于3种驱动方式的镁合金覆盖件柔性砂模拉深试验与仿真研究

选择砂子作为柔性介质,通过砂子摆放位置的不同实现不同驱动方式,并针对复杂镁合金覆盖件进行研究。采用有限元模拟与拉深试验对比验证的方法,针对差异化驱动方式探究了拉深温度、板厚以及填砂高度对镁合金板材成形结果的影响,并采用宏微观协同验证的方法对有限元模拟进行验证。针对复杂镁合金覆盖件,最终提出了能够改善其拉深性能的优化策略。

丁醇汽油混合燃料在缸内直喷发动机中的燃烧特性研究

为探究丁醇对发动机燃烧的影响,选取甲苯标准参考燃料(TPRF)与各类丁醇的同分异构体的混合燃料进行了发动机可视化试验研究。试验基于直喷点燃式光学发动机,结合高速摄影及缸内压力测试等手段,进行了不同TPRF-丁醇燃料的火焰图像处理及分析,并结合燃烧分析仪测试了发动机的燃烧性能。试验结果表明:正丁醇与TPRF的混合燃料的火焰速率及火焰面积扩张速率最高,而叔丁醇与TPRF的混合燃料最低;丁醇的添加会抑制TPRF的着火倾向,导致燃烧持续期和着火延迟期明显延长,延长效果由大到小依次为叔丁醇、仲丁醇、异丁醇、正丁醇;由于丁醇的热值更低,黏度和汽化潜热更高,掺混丁醇后发动机平均有效指示压力也有显著降低。

Nominal friction coefficient in spread formulas based on lead rolling experiments

Friction coefficients in spread formulas were studied under low width-to-thickness ratio. The effects of all the factors on friction were considered as different roughness of surfaces. After lead rolling experiments in 5 different roughness grades, friction coefficients were obtained. With changing width-to-thickness ratio, reduction rate and ratio of diameter of roller to thickness, all the nominal friction coefficients which can be used in these formulas were calculated. Then, a fitting expression was proposed, comparing with the results measured in 232 times tests, the errors of the nominal friction coefficients calculated by the expression are mostly less than 12%. After a certain times self-learning, the errors are no more than 2%. With the varying nominal friction coefficients, the spread will be predicted more accurately. When the nominal friction coefficient is used to predict the spread under the real working condition, the results calculated are also in agreement with the measured ones, and the errors are less than 2%. This credible reference and solution about how to set the friction coefficient in spread formulas would also be used in practical industrial production.

低速稀薄燃烧工况下闪沸喷雾燃烧特性

均质稀薄燃烧已被证实是未来进一步优化直喷汽油机燃烧、节能减排的关键技术.然而,稀薄燃烧的控制应用面临巨大挑战,特别是在低速稀薄燃烧工况下,温度较低,气流速度较弱,火核形成以及火焰传播速度较慢,对油气混合均匀度要求较高.本文针对一台直喷光学发动机中闪沸喷雾的应用,对低速稀薄燃烧工况下火焰发展规律、放热规律等进行了分析.结果显示,闪沸喷雾可以有效提升燃烧放热速度,改善缸内指示平均有效压力(IMEP).

Dynamic matrix predictive control for a hydraulic looper system in hot strip mills

Controlling the looper height and strip tension is important in hot strip mills because these variables affect both the strip quality and strip threading. Many researchers have proposed and applied a variety of control schemes for this problem, but the increasingly strict market demand for strip quality requires further improvements. This work describes a dynamic matrix predictive control(DMC) strategy that realizes the optimal control of a hydraulic looper multivariable system. Simulation experiments for a traditional controller and the proposed DMC controller were conducted using MATLAB/Simulink software. The simulation results show that both controllers acquire good control effects with model matching. However, when the model is mismatched, the traditional controller produces an overshoot of 32.4% and a rising time of up to 2120.2 ms, which is unacceptable in a hydraulic looper system. The DMC controller restricts the overshoot to less than 0.08%, and the rising time is less than 48.6 ms in all cases.

Analysis and prediction of fishtail during V-H hot rolling process

The fishtail in head and tail of the slabs was studied during V-H hot rolling process. With the application of ANSYS/LS-DYNA, simulation analysis was used to research this process. The various factors which have a great influence on fishtail shapes were analysed, such as initial width, initial thickness, radius of the edger roll and horizontal roll, edging draught,horizontal reduction rate, and friction coefficient of the surface. Then the curves that can describe the shapes were obtained. After a certain time of self-learning, the optimized curves were given out. At last, through the fitting of the simulation test results, the math models for the area of fishtail defect changing with the presented factors were received. The experimental results show that the accuracy of the prediction for the fishtail shapes is more than 95%. With the application of the prediction for the fishtail shapes and the area of the fishtail defect, the loss rate of the slab is decreased by about 0.1%.

以金相技能大赛推进材料专业实验教学改革

以培训学生参加全国大学生金相技能大赛为契机,分析材料专业实验教学的现状与存在的问题,对材料专业的实验教学进行了改革,通过修订实验教学大纲、扩展实验教学内容、规范实验教学方案、创新实验室管理模式等措施,拓展实验受众,全面提高学生的金相技能。

基于有限元仿真的航空发动机叶片辊轧成形过程参数优化

精密辊轧是航空发动机叶片的重要加工方式,其工艺参数难以确定,导致叶片成形效果难以控制。提出使用ABAQUS有限元仿真方法对辊轧过程进行模拟,通过改变辊轧压下量以及摩擦因数,研究压下量和摩擦因数对叶片成形结果的耦合影响,从而优化工艺参数,获得最优的参数设定。研究结果表明:随着摩擦因数的增加,该辊轧模型叶片的宽展整体增加,且所受轧制力与摩擦因数呈线性正相关;随着端口压下量的增加,叶片所受轧制力以及叶片宽展均有所提升,但当压下量增加超过0.06 mm时,轧制力以及宽展发生突增,叶片变形集中于边缘局部区域,不利于成形结果的精密控制。