基于Hyperworks/LS-Dyna的包装件跌落仿真及包装优化

目的针对嵌入式洗碗机的包装设计方案进行跌落仿真分析,进一步优化降低方案成本,得出符合生产制造的轻量化设计理论。方法首先使用Hypermesh与LS-DYNA进行联合仿真,模拟包装件六面工况下跌落的响应情况;其次使用OptiStruct优化模块对下衬垫进行拓扑优化设计,根据衬垫变形情况设置合理优化工况,优化的约束条件加入衬垫制造约束,得到满足包装需求的最轻量化的方案。结果优化后的最终方案可制造性加强,成本降低1.1元,且优化前后试验采集的易损件响应加速度有不同程度降低,达到优化目标。结论轻量化设计理论在包装领域具有普适性,设计完成后,可以通过拓扑优化的技术路线进一步优化设计方案,降低包装成本,达到降本增效的目的。     

正棱台缓冲垫结构参数对静态缓冲性能的影响

目的研究不同结构参数的正棱台缓冲垫(EPS)在接触面积相同且体积相同时静态缓冲性能的差异。方法以发泡聚苯乙烯(EPS)为试验材料,设立10组接触面积相同,体积相同,厚度及斜面倾角不同的正棱台结构样本,利用万能材料试验机对10组样本进行静态压缩试验,得到10组不同结构参数的应力-应变曲线、应变能-应变曲线、应变能-应力曲线及缓冲系数-静应力曲线。结果随着斜面倾角的增大,缓冲垫的刚度逐渐增大,能量吸收增大,当斜面倾角大于等于70°后,缓冲性能基本相同;在缓冲垫受到同等冲击强度条件下,斜面倾角为80°时正棱台缓冲垫的缓冲性能最好,应变能最大,且其产生的变形量及应力均小于普通六面体缓冲垫。结论在包装设计过程中,可将接触面的侧面设置为80°倾角,按照此结构设计包装,产品更安全,接触部位厚度可降低25.12%,真正实现了降本增效。     

Simple bounds for counting processes with monotone rate of occurrence of failures

The article discusses some aspects of analogy between certain classes of distributions used as models for time to failure of nonrepairable objects, and the counting processes used as models for failure process for repairable objects. The notion of quantiles for the counting processes with strictly increasing cumulative intensity function is introduced. The classes of counting processes with increasing (decreasing) rate of occurrence of failures are considered. For these classes, the useful nonparametric bounds for cumulative intensity function based on one known quantile are obtained. These bounds, which can be used for repairable objects, are similar to the bounds introduced by Barlow and Marshall [Barlow, R. Marshall, A. Bounds for distributions with monotone hazard rate, I and II. Ann Math Stat 1964; 35: 1234–74] for IFRA (DFRA) time to failure distributions applicable to nonrepairable objects.     

纯介质光子晶体非线性效应研究进展

如何在低阈值小尺度(毫瓦或皮焦量级、微米以下)情况下激发非线性光学效应是近年来光学领域研究的重要课题。该研究最直接的应用需求就是光子集成芯片,这是未来实现超高速、大容量信息网络体系的基础。光子晶体具有类似于半导体能带的光子禁带(PBG),被誉为“光子半导体”,为人们提供了一种新颖而又实用的操纵光子的物理手段,使低阈值、可集成非线性效应产生成为可能。越来越多的非线性效应在光子晶体中已经被发现,例如光子晶体慢光、带隙孤子、电磁感应透明、二次谐波产生、光学双稳态等,本文将着重对可用于光子集成器件开发的光子晶体非线性效应研究领域的一些主要成果和进展进行总结,介绍其相关应用并对光子晶体非线性效应研究作出展望。

     

Theoretical principles for the experimental determination of errors due to instability of measuring instruments over time

Conditions are formulated for the experimental determination of error from the time instability of measuring instruments. Translated from Izmeritel’naya Tekhnika, No. 3, pp. 11–12, March, 2009.     

Failure Rate Estimation from Field Data under Time‐Varying Stress

A model to assess the failure rate of equipment under use conditions is proposed. This model links noncontrolled variables to a piecewise failure rate combined with a proportional hazard model. Two influential variables are considered. One is the temperature characterizing the outdoor climate, and the other one is moisture—as an intrinsic variable. The maximum likelihood estimates of the model parameters are obtained. The efficiency of the method is evaluated through simulated data. Results on data from the field are provided. Copyright © 2012 John Wiley & Sons, Ltd.     

国产环氧沥青混合料固化强度增长规律研究

研究了环氧沥青混合料的强度形成机理,在此基础上对影响环氧沥青混合料强度的两个重要因素即混合料的容留时间、养生温度进行了研究,确定了不同温度下环氧沥青混合料的容留时间范围及强度增长规律;采用差示扫描量热法（DSC）测得环氧沥青结合料在不同升温速率下的动态DSC曲线,通过非线性回归求得固化动力学关键参数,建立环氧沥青结合料的固化反应模型。研究结果可以指导环氧沥青混合料的生产与施工,同时对铺装层开放交通时间的确定有参考意义。     

Failure event prediction using the Cox proportional hazard model driven by frequent failure signatures

The analysis of event sequence data that contains system failures is becoming increasingly important in the design of service and maintenance policies. This paper presents a systematic methodology to construct a statistical prediction model for failure event based on event sequence data. First, frequent failure signatures, defined as a group of events/errors that repeatedly occur together, are identified automatically from the event sequence by use of an efficient algorithm. Then, the Cox proportional hazard model, that is extensively used in biomedical survival analysis, is used to provide a statistically rigorous prediction of system failures based on the time-to-failure data extracted from the event sequences. The identified failure signatures are used to select significant covariates for the Cox model, i.e., only the events and/or event combinations in the signatures are treated as explanatory variables in the Cox model fitting. By combining the failure signature and Cox model approaches the proposed method can effectively handle the situation of a long event sequence and a large number of event types in the sequence. Its effectiveness is illustrated by a numerical study and analysis of real-world data. The proposed method can help proactively diagnose machine faults with a sufficient lead time before actual system failures to allow preventive maintenance to be scheduled thereby reducing the downtime costs.     

Degradation models and implied lifetime distributions

In experiments where failure times are sparse, degradation analysis is useful for the analysis of failure time distributions in reliability studies. This research investigates the link between a practitioner's selected degradation model and the resulting lifetime model. Simple additive and multiplicative models with single random effects are featured. Results show that seemingly innocuous assumptions of the degradation path create surprising restrictions on the lifetime distribution. These constraints are described in terms of failure rate and distribution classes.     

从CAD／CAPP集成看轴类零件的产品模型合理表示

本课题组在开发CIMS特征造型软件过程中试作了CAD与CAPP的直接接口,从中发现CAD与CAPP对于零件的特征建模表示方法有不同的理解和要求。本文列举这些差异,以供CIMS和并行工程环境下建立更完善的集成产品信息模型作参考。     

基于比例危险模型的产品竞争失效分析

突发型失效与退化型失效共存的竞争失效问题在实践中大量存在，一般情况下突发失效是受退化量大小影响的。文中利用比例危险模型分析了突发失效与退化量的关系，给出了竞争失效的一般模型及模型的参数估计方法，最后利用所给模型对强激光装置所用的金属化膜脉冲电容器进行了可靠性分析。     

Optimal burn-in time under cumulative free replacement warranty

In this paper, optimal burn-in time to minimize the total mean cost, which is the sum of manufacturing cost with burn-in and cumulative warranty-related cost, is studied. When the products with cumulative warranty have high failure rate in the early period (infant mortality period), burn-in procedure is considered to eliminate the early product failures. After burn-in, the posterior product life distribution and the cumulative warranty-related cost are dependent on burn-in time; long burn-in period decreases the warranty-related cost, but it increases the manufacturing cost. The paper provides a methodology to obtain the total mean cost under burn-in and cumulative warranty. Properties of the optimal burn-in time are analyzed here. Numerical examples and sensitivity analysis are used to demonstrate the applicability of the methodology derived in the paper.