恒压时间对ADC12合金恒流-恒压微弧氧化膜层组织与性能的影响

目的 探究先恒流一定时间再恒压不同时间对ADC12高硅铝合金微弧氧化膜层组织与性能的影响,并从中选择较优的氧化时间组合.方法 选择双极性脉冲电源,在先恒流(11 A/dm2)35 min后,再恒压(550 V)不同时间(5、15、25、35 min),制备微弧氧化陶瓷膜层.通过采用扫描电子显微镜(SEM)、金相显微镜、X射线衍射仪(XRD)、HT-600摩擦磨损试验机、电化学工作站(极化曲线、阻抗谱)等设备来表征表面形貌、膜层厚度、物相组成、磨损率以及耐腐蚀性.结果 在先恒流再恒压下制备的微弧氧化膜层,其厚度随着氧化时间的延长呈现先增长后下降的趋势.先恒流35 min再恒压25 min所制备的膜层厚度最厚,为25μm;微弧氧化膜层中都存在α-Al2O3、Y-Al2O3和Al2SiO5相;随着氧化时间的延长,微弧氧化膜层的磨损率出现先增长后下降的趋势.在先恒流35 min再恒压5 min所制备膜层的摩擦系数最小,仅为0.78.氧化时间的变化对ADC12铝合金MAO膜层耐蚀性的影响较大,腐蚀电位随着氧化时间的延长呈现先上升后下降的趋势,同时腐蚀电流的变化趋势也与腐蚀电位相同.综合考虑,在先恒流35 min再恒压25 min所制备的膜层,其耐腐蚀性较好.结论 先恒流(11 A/dm2)35 min再恒压(550 V)25 min时所制备的微弧氧化膜层较厚,致密性较好,耐蚀性最佳.     

基于响应曲面法的盾构机单唇形铰接密封性能研究

为提升盾构机铰接密封性能和使用寿命,研究其密封机制及主要失效形式,使用ANSYS Workbench软件建立密封二维轴对称模型,基于响应曲面法分析各影响因子对密封性能的灵敏度和影响趋势,并进行油脂用量的量化研究。结果表明：影响因子的灵敏度由大到小依次为材料的弹性模量、润滑油脂压力、倾斜角度和密封油脂压力;通过合理构建背压能够提高密封的耐压能力;随着材料弹性模量的增大,密封最大等效应力和最大接触压力呈现线性增大;倾斜角度的增大会引起外侧密封压缩量减小,使最大等效应力和最大接触压力减小;材料弹性模量、倾斜角度和润滑油脂压力的交互效应对外侧密封最大接触压力的影响均较显著。对密封性能进行多目标参数优化,获得油脂压力的最优组合方案,为实际工程施工提供参考。     

弹塑性大应变双重非线性问题分析的再生核质点法研究

再生核质点法是一种新型无网格方法,只需质点信息而无需划分网格,在大变形大应变分析中能够方便适应计算中网格畸变。在大应变情况下引入Jaumann应力率和应变速率来表征材料的弹塑性本构关系,并将再生核质点法的插值方法引入虚位移原理,推导了弹塑性大应变再生核质点法计算控制方程,给出了方程计算格式。通过对具体算例的分析研究表明了,此方法对弹塑性大应变分析的有效性。     

Attenuating water hammer pressure by means of gas storage tank

1　ＩＮＴＲＯＤＵＣＴＩＯＮＩｎｔｈｅｄｅｓｉｇｎａｎｄｏｐｅｒａｔｉｏｎｏｆｐｉｐｅｌｉｎｅｓｏｆｌｏｎｇ ｄｉｓｔａｎｃｅｈｙｄｒａｕｌｉｃｓｏｌｉｄｐａｒｔｉｃｌｅｓｔｒａｎｓｐｏｒｔａｔｉｏｎ ,ｎｏｔｏｎｌｙｔｈｅｓｔｅａｄｙｆｌｏｗｓｗｉｔｈｕｎｉｆｏｒｍｄｉｓｃｈａｒｇｅａｎｄｐｒｅｓｓｕｒｅ ,ｂｕｔａｌｓｏｔｈｅｕｎｓｔｅａｄｙｏｎｅｓｗｉｔｈｎｏｎ ｕｎｉ ｆｏｒｍｄｉｓｃｈａｒｇｅａｎｄ ｐｒｅｓｓｕｒｅｓｈｏｕｌｄｂｅｃｏｎｓｉｄｅｒｅｄ .Ｔｈｅｖａｒｉａｔｉｏｎｏｆｄｉｓｃｈａ…     

我国皮江法炼镁的现状与分析

我国已连续几年成为世界第一产镁大国，镁及其产品出口第一大国。但产镁大国的称号，是由落后的皮江法支撑起来的。我国的皮江法炼镁，在各个工艺环节上都与国外的镁厂有差别，最终导致整个工厂的指标与国外的镁厂有较大的差距。本文分析了问题产生的原因，并尝试提出了一些解决办法。     

硬线盘条拉拔断裂原因初步判断

从原料和加工工艺方面对拉拔断裂原因进行分类;介绍了根据拉拔工艺、宏观断口分类分析来判断硬闰拔断理解原因的广阔才部分典型事例。     

Discriminating surface-breaking from subsurface cracks in pressurized water pipes by means of a parametric modulation technique

The discrimination of surface-breaking cracks from cracks that are entirely embedded within the material is paramount to the assessment of the integrity of pressurized water pipes. This work addresses this issue investigating the use of a parametric modulation technique towards this end. Tests are conducted on 1D surface-breaking cracks that are either dry or contain water. The response of these defects is investigated as a function of crack depth and closure, as well as of amplitude and frequency of the modulation. The ensuing results suggest that fluid-filled and dry cracks can be discriminated from each other. The origin of the different response of these defects is discussed in terms of both crack's stiffness and modulation-induced dynamics.     

Tool wear-dependent process analysis by means of a statistical online monitoring system

Simulating milling processes can provide numerous optimization possibilities regarding process stability and surface quality. In tool and die manufacturing often long-running processes are necessary. In contrast to very time-consuming Finite-Element-based approaches, geometric physically-based simulation systems allow predictions for such processes because of their relatively short runtime. The machining of hardened material and varying engagement conditions between the tool and the workpiece provoke a gradually increasing influence of tool wear on the cutting edges. To consider these alterations while simulating milling processes, different approaches can be used. Because of the complex characteristics of tool wear, methods, which result in an increased simulation runtime, have to be used for the geometric modeling of tool wear. In this paper, a novel approach for monitoring a milling process is presented, which utilizes an online-selection of pre-calculated simulation data to predict the process stability for different states of tool wear. To achieve this, measured data are compared to simulated data, which result from offline simulation conductions for each defined state of tool wear. As tool wear changes when the process is progressing, different simulation data for different states of tool wear have to be selected to ensure a valid stability prediction.     

Fatigue analysis of a mechanical press by means of the hybrid multi-body simulation

During the past decade in the automotive industry more and more conventional sheet metal components were replaced by high-strength sheet metal components. The processing of these modern sheet metals lead to an increase of the loads applied to the metal forming machines. In comparison to conventional sheet metals an extensive cutting-shock can be observed while cutting high-strength sheet metals. Hence, the components of the press start to oscillate and therefore the possibility of an early crack initiation increases. Thus, it has become necessary to investigate the specific demands while cutting modern sheet metals and take them into account during the design process of further presses. Within the framework of the presented project, conventional as well as high-strength sheet metals were cut and their loads were recorded. Additionally, a hybrid multi-body simulation model of a mechanical press was established and validated by means of measurements at a real press available at the Institute of Forming Technology and Machines (IFUM). Subsequently, the multi-body simulation model was coupled with a fatigue analysis software package. By means of the coupled simulation the fatigue life of the structural components of the press was determined. The entire approach was validated by means of test structures. The test structures were designed for a short fatigue life, manufactured and mounted the press available at the IFUM. A good correlation of the virtually determined and real fatigue life of the test structures was achieved.     

Revisiting the fundamentals of single point incremental forming by means of membrane analysis

Knowledge of the physics behind the fracture of material at the transition between the inclined wall and the corner radius of the sheet is of great importance for understanding the fundamentals of single point incremental forming (SPIF). How the material fractures, what is the state of strain and stress in the small localized deformation zone and how these two subjects are brought together in order to explain the overall formability of SPIF in terms of ductile damage are still not well understood. However, they are of great importance for improving the robustness and enhancing the predictability of currently existing numerical models and for extending the scope of industrial applications of the process. This paper attempts to provide answers to these questions by means of a new theoretical model for rotational symmetric SPIF that was developed under membrane analysis with bi-directional in-plane contact friction forces.     

High-Performance NC for HSM by means of Polynomial Trajectories

This paper summarises works carried out for defining tool trajectory formats well adapted to High Speed Machining (HSM). Advantages in using native polynomial formats, calculated directly from the CAD model, are highlighted. In particular, polynomial surface formats are presented as a generic format for tool trajectory. Illustrations show that surface formats represent a good compromise between smoothness machining time, and surface quality.     

基于神经--模糊推理系统的发动机相关数据处理

提出应用一种神经—模糊推理系统对发动机有关设计计算中的数据进行映射辩识，以提高数据的结构化程度、加快计算速度，以利于编程处理，消除知识的“组合爆炸”现象。建立了一个神经网络系统与之进行应用比较，通过对具体数据的实际操作表明，应用这种方法能够很好地表达原图表数据关系。同时相对于单纯应用人工神经网络方法，它的数据识别精度更高，速度更快，能够满足设计计算要求。     

Development of hard intermetallic coatings on austenitic stainless steel by hot dipping in an Al-Si alloy

The austenitic stainless steel was coated by dipping it into a molten Al-12.4%Si alloy at 765 °C. The effect of immersion times in the range of 60 to 900 s was investigated with respect to the crystalline structure, thickness, and microhardness of the coating. A uniform layer (~ 12 µm) of intermetallic Al₁₂(Fe,Cr)₃Si₂ with hexagonal crystalline structure is formed, irrespective of the immersion time. Incorporation of Si to the coating changes the growth mode of the coating from inwards to outwards, which favours the development of a flat substrate/coating interface. Microhardness of the coating decreases with increasing dipping time, ranging between 850 and 600 HV for the shortest and longest immersion time, respectively. These hardness values are higher than that for the substrate of about 200 HV, irrespective of the immersion time.