Application of a Novel Method for Machine Performance Degradation Assessment Based on Gaussian Mixture Model and Logistic Regression

The currently prevalent machine performance degradation assessment techniques involve estimating a machine’s current condition based upon the recognition of indications of failure features,which entail complete data collected in different conditions.However,failure data are always hard to acquire,thus making those techniques hard to be applied.In this paper,a novel method which does not need failure history data is introduced.Wavelet packet decomposition(WPD) is used to extract features from raw signals,principal component analysis(PCA) is utilized to reduce feature dimensions,and Gaussian mixture model(GMM) is then applied to approximate the feature space distributions.Single-channel confidence value(SCV) is calculated by the overlap between GMM of the monitoring condition and that of the normal condition,which can indicate the performance of single-channel.Furthermore,multi-channel confidence value(MCV),which can be deemed as the overall performance index of multi-channel,is calculated via logistic regression(LR) and that the task of decision-level sensor fusion is also completed.Both SCV and MCV can serve as the basis on which proactive maintenance measures can be taken,thus preventing machine breakdown.The method has been adopted to assess the performance of the turbine of a centrifugal compressor in a factory of Petro-China,and the result shows that it can effectively complete this task.The proposed method has engineering significance for machine performance degradation assessment.     

回转窑轮带在受接触力时的非线性有限元仿真

用有限元非线性分析方法，建立回转窑轮带和托轮接触有限元分析模型；并通过编程计算出轮带和托轮的最佳接触刚度；通过仿真，可绘出整个轮带的应力分布图和变形图。与理论算法比较，此方法所得结果更直接，观察结果更方便，且与理论结果很相近。     

不同形态白炭黑对胎面胶性能的影响

通过选用不同形态的白炭黑,来研究其在同一个胎面胶中的硫化特性和物理机械性能。研究表明,其对胶料的性能影响不大,只是粉末状样品由于颗粒较小,比重较轻,较易产生粉尘较易飞扬,在密炼过程中容易对环境造成污染以及给工人身心健康带来负面影响。故在生产过程中,即使在成本小量增加的前提下也应该选用颗粒状等较不易产生粉尘的白炭黑来使用,以免对员工健康造成危害。     

Interface characterization of Al/Cu 2-ply composites under various loading conditions

The effects of reduction ratio during roll bonding on the microstructural evolution at interface and subsequent mechanical properties of roll-bonded Al/Cu 2-ply sheets were investigated. The interface microstructures for several Al/Cu 2-ply sheets fabricated under different reduction ratios between 30% and 65% were verified by transmission electron microscopy (TEM). Taking the difference of interface microstructure into consideration, 3-point bending and peel tests were performed for obtaining flexural and bonding strengths for Al/Cu 2-ply sheets. The effect of the quantified areas of metallurgical bonding at interfaces on the bonding strength was also discussed. The results show that both the bonding and flexural strengths for Al/Cu 2-ply sheets are reduced by decreasing the reduction ratio during the roll bonding process, which is strongly correlated with the interface microstructure. This was especially verified by observing the interface delamination from the 3-point bent samples.     

电镀锌钢材表面物理气相沉积Zn-Mg合金镀层的电化学性能(英文)

锌合金镀层由于具有较强的耐腐蚀性能而得到广泛的关注,特别是Zn-Mg合金镀层,其耐腐蚀性能能得到显著提高。采用气相沉积方法制备不同镁含量的Zn-Mg合金镀层,研究Zn-Mg合金镀层中镁含量对其耐腐蚀性能的影响。在3%NaCl溶液中进行浸泡试验、动电位测试和电偶腐蚀试验,研究不同Mg含量镀层的耐腐蚀性能。结果表明,Zn-Mg合金镀层的耐腐蚀性能与Mg含量显著相关,镀层的腐蚀电位随着Mg含量的增加而降低,但是腐蚀电流密度却升高,直至15%Mg含量;在Zn-Mg合金镀层中存在钝化区。     

提高虚拟车削仿真质量的工件建模方法

根据车削加工工件的几何外形和成形特点 ,提出了包含加工误差信息的回转体类工件半剖轮廓多边形建模方法和记录、组织加工误差信息的刀具轨迹法。在虚拟加工中 ,刀具扫描体被简化表示为刀具扫描体轮廓多边形 ,简化了仿真计算。同时还对加工过程仿真和反映加工误差的已加工表面形貌的构建等关键问题进行了研究。该建模方法在VMIS虚拟加工与检测系统中获得了应用     

弹性基体磨具的磨抛轨迹与表面加工质量研究

目的 解决以光学玻璃为代表的硬脆材料加工效率与表面质量难以同时得到保证的共性问题。方法 以弹性基体工具磨削抛光技术为基础,分析弹性接触区域内有效工作磨粒的运动行为。基于Preston方程材料去除模型,研究磨抛过程中磨抛接触区域的接触面积、速度分布、多颗磨粒的运动轨迹。基于运动学模型,探究磨抛过程中磨具的运动学参数、磨粒浓度及排布特征等因素对磨粒磨抛轨迹的影响,采用磨具与工件接触区域磨粒运动轨迹相对面积占比和变异系数表征磨粒运动轨迹分布的均匀性,并建立基于轨迹均匀性的加工表面质量评价方法,优化工艺参数。以石英玻璃为加工对象,以硅橡胶中混入金刚石磨粒为基体,通过正交实验研究不同参数对工件表面质量的影响。结果 仿真结果表明,选取自转速度为300 r/min、进给速度为1 mm/s、磨抛进动角为15°,磨粒浓度及排布采用1 mm磨粒理论间距,此时获得的最大磨粒运动轨迹相对面积占比为96.46%,最小变异系数为0.375。通过实验,得到了选取磨抛工艺参数中的最佳参数组合,自转速度为1 200 r/min,进给速度为1 mm/s,磨抛进动角为15°~20°,磨粒浓度及排布采用磨粒间距1 mm,该组合可将工件的表面粗糙度由1.078 μm降至0.057 μm,材料去除率为3.8×10⁸ μm³/min。结论 磨粒运动轨迹的密集程度与自转速度、磨粒浓度及排布呈正相关,与进给速度呈负相关,在考虑加工成本的前提下,采用高自转速度、高磨粒浓度、低进给速度及15°~20°的进动角可以获得密集且均匀的磨粒运动轨迹,提高了工件的表面质量和材料去除效率。     

有限区间内设备顺序预防性维护策略研究

为了克服等周期维护模型忽略设备可靠性要求,以及长期运行期望维护周期模型忽略设备特定阶段维护需求的缺点,通过引入基于役龄递减因子和故障率递增因子的混合式故障率演化规则,建立了有限区间内基于设备可靠性的顺序预防性维护优化模型,并以威布尔分布为例,利用仿真方法对其进行了优化。仿真结果显示,该模型可使设备的维护周期呈递减之势,反映了设备在某一特定阶段的可靠性需求。     

Study of residual stresses in tailor rolled blanked Al5J32-T4 sheets

Several automotive parts such as door panels have been manufactured by using load-adapted blanks for crash optimization and weight minimization.Recently, Tailor Rolled Blanks (TRB) has been introduced to remove the disadvantages of a welding process which was used in joining panel components.TRB offers better structural design capabilities due to the seamless transitions on the panels with different thicknesses.In spite of the advantages of the process, TRB leaves internal stresses in the panel.This residual stresses lower the formability of Tailor Rolled Blanked (TRBed) parts and cause cracks near severe curvature during subsequent forming processes.In this research, the residual stresses of TRBed Al5J32-T4 sheets were studied by X-ray stress analysis, and also microstructure was observed along the rolling direction.In addition, heat treatment was done after TRB process in order to compare the residual stresses to that of the TRBed sheets before the heat treatment.     

空气自然对流式质子交换膜燃料电池的三维建模和实验分析

在空气自然对流式燃料电池内部,速度、温度、组分浓度及电流分布特性有着极强的耦合作用.氧气质量传输限制引起的浓度过电位是这种燃料电池的主要性能损失.从自然对流、传热传质的角度,建立了三维数学模型.利用三维流体动力学软件和用户建立的子程序,对自然对流下Navier-Stokes 方程,能量方程,电化学动力学方程以及组分、水的传输方程进行了数值求解.通过分析数值计算的结果,结合自然对流的特性,设计了实验系统.对温度分布和电池性能进行了测试.对空气湿度对电池性能的影响进行了分析.数值计算结果与实验结果很好地吻合.模型的建立,对于认识空气自然对流式质子交换膜燃料电池内部的耦合传输现象有极大的意义,可以作为质子交换膜燃料电池的计算机辅助优化设计工具.