Life Tests Under Dependent Competing Causes of Failure

In a life testing situation the failure of an individual, either a living organism or an inanimate object, may be classified into one of k(< 1) mutually exclusive classes, usually causes of failure. One often has dependent causes of failure in actual physical situations, i.e., the theoretical lifetime of an individual failing from one cause may be correlated with the theoretical lifetime of the same individual failing from a different cause. This paper i) discusses some properties of a bivariate Weibull distribution and ii) is concerned with estimating, by the method of maximum likelihood, the unknown parameters of life distributions belonging to two particular parametric families, viz., bivariate normal and bivariate Weibull, when the causes of failure are dependent. An example involving the failure of small electrical appliances is analyzed and compared with an analysis which assumes the causes of failure to be independent.     

波谱图在判断机械故障中的应用体会

分析了利用波谱图判断机械故障问题的几种方法,指出机械波形成的原因十分复杂,涉及 的机构、零件、部件很多,要快速准确地判断特殊和疑难的机械波,除了要善于积累经验,熟悉常见机械波长、波形及不匀率曲线的形态外,还应通过实践摸索掌握隐波、谐波、假波及周期波等特殊机械波的分析方法,从而达到有效控制成纱条干质量的目的。     

基于Delphi的QTM数据采集统计系统的实现

目前车间现有的QTM综合测试台的数据采集系统,无法对QTM进行故障统计和查询,也缺少中文故障信息提示和建议方法等,采用人工记录费时费力且实时性差,为此开发了基于Delphi的QTM数据采集统计系统。该系统通过RS232串行接口实现PC机与QTM之间的串口通信,对QTM的日常状态数据进行实时采集及故障提示,并在SQLServer的支持下通过以太网对数据进行存储及远程查询。同时采用图形方式显示采集数据,并嵌入中文故障信息提示和建议方法,在远程查询终端嵌入QTM故障统计、标准件校准和吸阻线性测试查询等功能。改进后的QTM数据采集统计系统,增加了图形化重复性、线性采集查询,故障统计和远程查询功能,满足了车间烟草检测仪器信息化管理的需求,克服了人工记录费时费力等缺点。经过实际运行和两年同期数据对比分析可见,车间QTM故障率由2.0%降低到0.5%以下,有效控制了故障时间,减少了QTM维修成本。     

表面裂纹结构断裂失效概率计算的线弹簧-响应面法

将线弹簧模型法和响应面法相结合,建立含表面裂纹结构断裂失效概率的计算方法.考虑材料特性、外载荷和裂纹尺寸等参数的不确定性,以含表面裂纹平板为例进行计算,得出失效概率和可靠度指标.与Monte Carlo法结果进行对比,表明该方法合理有效,在大大减小计算量的同时,能够保证很高的精度,适合工程实际应用.     

Influence of surface treatments on topography and bond strength of densely-sintered zirconium-oxide ceramic

The aim of this study was to evaluate the effect of surface treatments on the roughness and bond strength of dental materials containing MDP to zirconium oxide ceramic. Forty square-shaped zirconium-oxide ceramic blocks (Lava Zirconia, 3M-ESPE) were treated as follows: (CT) polished only; (SB) sandblasting (110 µm aluminum oxide particles) or (SC) silica coating (110 µm particles). Roughness of treated surface was measured using a profilometer (Ra) and by atomic force microscope (AFM). Two resin luting agents were used after silane application: self-adhesive (Rely X U200, 3M-ESPE) and dual cure (Rely X Ultimate, 3M-ESPE). The samples were submitted to microshear bond strength test. The failure analysis was performed. Data were submitted to ANOVA and Tukey test (α=0.05). Bond strength results ranged from 20.44 (CT+Ultimate) to 34.37 MPa (SC+U200) after 24 h and from 12.03 (CT+Ultimate) to 27.44 MPa (SC+U200) after 12 months of storage with SC statistically superior to the other treatments. Mean values of roughness varied from 0.07 (CT) to 0.85 µm (SC). The both resin luting agents showed similar results to all surface treatment groups. Silica coating provided the best treatment of the ceramic surface.     

单一节理岩体R—R破坏准则及参数确定

为评价岩体中节理对岩体强度特性的影响，分析了单一节理的分布性状，介绍了单一节理岩体破坏的Ｒａｏ－Ｒａｍａｍｕｒｔｈｙ准则及其参数试验确定方法，并应用于峨口铁矿采场边坡两种典型的单一节理岩体强度的研究。     

在役含缺陷冷凝器的定量风险分析

采用基于风险的检验分析与概率断裂力学相结合的方法,分析了在役含缺陷冷凝器的失效可能性和失效后果,利用API581的风险矩阵确定了冷凝器的使用风险。分析结果表明,该冷凝器的使用风险为“中等”,可以继续使用。     

FANUC Oi C系列CNC数控机床返回参考点故障处理

数控机床在开机之前,通常都要执行回机床参考点的操作,归根于机床断电后,就失去了对各坐标位置的记忆,其回机床参考点的目的在于让坐标轴回到机床一固定点上,即机床的零点,也叫机床参考点(MRP)。回参考点操作是数控机床的重要功能之一,该功能是否正常,将直接影响零件的加工质量。     

基于EMD的卫星动量轮性能可靠性建模

对于某些产品,如卫星动量轮,具有高可靠性、长寿命的特点.在对这类产品进行试验时,其时间相对产品的实际寿命通常相对较短,往往无法取得失效数据,那么利用传统的可靠性理论一般无法评定该类产品的可靠性.文中针对该类产品具有小子样、无失效数据的特点,从性能可靠性出发,提出了一种基于EMD算法的可靠性建模方法,同时,对EMD算法进行了改进,找到了一种简单有效的克服端点问题方法.通过对某型号动量轮的实例分析证明该方法对解决该类问题是行之有效的.     

Modelling the strengthening of glass using epoxy based coatings

Glass strength can be increased by applying epoxy based surface coatings. A number of models have been presented in the literature to explain the strengthening afforded by these coatings but until now there has been no clear evidence to definitively support one model over another. In this work, finite element models (FEM) of four-point bending test specimens have been developed. These models have been used to study the strength of cracked uncoated and surface coated specimens in order to identify the strengthening mechanism. The FEM results showed that full filling of the crack using epoxy coating is sufficient to heal the crack if the coating inside the crack is ideally glued to the crack surfaces. It is also shown that under these circumstances the coating modulus is relatively unimportant parameter. FEA results for partially filled cracks show that increasing the filled percentage increases the strengthening. Fractographic analysis of the 10 kg indented and coated samples showed that the fracture surfaces do not follow the median crack symmetric plane and that fracture started from another plane when coated properly, however the fracture surface of these samples still starts from the indentation site. On the other hand, fractographic analysis of the 1 kg indented and properly coated samples showed that the samples failed from their edges which indicate that the crack was overcome. The finite element results show that the diamond imprint resulting from the Vickers indentation play an important role in this type of fracture.