渗碳齿轮钢的疲劳性能及寿命概率分布研究

利用旋转弯曲疲劳试验方法研究了SCM420齿轮钢经渗碳后的疲劳性能,使用SEM扫描电镜观察统计了夹杂物起裂源的尺寸,并结合日本学者Murakami提出的疲劳极限预测公式,发现钢中出现频率较高的大尺寸(≥38μm)夹杂物对疲劳性能具有很大的损失作用。此外,研究了试验钢在1020 MPa应力级别下疲劳寿命的分布规律。结果表明,对数疲劳寿命符合二参数威布尔分布和正态分布,但威布尔分布更优于正态分布。     

基于EM算法的不完全疲劳寿命数据可靠性分析

针对随机截尾寿命数据模型的参数估计,提出基于EM算法的通用算法,并以疲劳寿命计算中所常用的二参数威布尔分布模型为例,给出基于EM算法的寿命数据拟合通用方法.另外对于服从复杂分布模型的数据,则采用与蒙特卡洛法相结合的EM算法.最后通过计算模拟的不完全疲劳寿命数据,验证了EM算法对于随机截尾寿命数据模型参数估计的有效性.     

P74重轨钢断裂韧性K_(lc)值的统计分析

本文用威布尔分布（Weibull distribution）对131个高碳轨钢试样的K_lc数据进行了拟合,经果表明,高碳轨钢K_(lc)的分布特性基本服从威布尔分布,其形状参数m的估计值为2.3,低限断裂韧性K_（lc）~·的估计值为90kgf·mm~(-3/2),特征断裂韧性K_(lc)~*的估计值为144.5kgf.mm~(-3/2)。统计分析结果表明,“低碳高磷”试样无论是常规机械性能还是断裂韧性水平都与正常的P74轨钢相当;而“高碳高磷”试样的常规机协性能与P74轨钢相差不大,但韧性水平下降,m值减小,K_(lc)的分散性加剧。     

选矿镍精矿品位概率分布研究及其应用

本文从理论上证明镍精矿品位遵循正态分布，从而使统计检验及工序能力计算应用于选矿生产管理过程中有了理论依据，并通过应用实例阐述掌握精矿品位分布规律的意义。     

100Cr6轴承钢的超高周疲劳性能研究

采用旋转弯曲疲劳、SEM+EDS、面扫描等方法,研究了试验用100Cr6轴承钢的高周及超高周疲劳性能,以及传统疲劳极限附近的失效概率分布,并统计了夹杂物的成分、尺寸等信息。结果表明试验钢100Cr6的传统疲劳极限为967 MPa,在其之下的960 MPa应力幅值条件下,部分试样通过107循环周次后仍出现疲劳断裂失效,非无限寿命。在传统疲劳极限附近,相比于正态分布,疲劳寿命数据更符合二参数威布尔分布。相比于金相检验和面扫描,疲劳+EDS方法更能发现尺寸较大且为刚性的D类和Ds类夹杂物。     

新型陶瓷刀具材料抗弯强度的统计特性分析

研究了一种新型陶瓷刀具材料的抗弯强度有其统计特性，并据此优化了热压工艺参数，分析了其断裂特征。线性回归分析和Ｋ－Ｓ分布拟合检验的结果表明：该陶瓷刀具材料的抗弯强度很好地服从三参数威布尔分布，并进一步建立了抗弯强度尺寸效应的统计模型。     

地下矿山生产接续与设备调度集成优化模型

为了实现地下金属矿山生产接续的紧凑性、科学高效地调度生产设备,针对矿山开采工序复杂、设备资源有限、生产任务量大等特点,以最短工序时间间隔和最短总完成时间为共同优化目标构建了地下矿山生产接续与设备调度集成优化模型.通过分析地下矿山生产循环顺序、作业设备类型和生产能力等生产要素,考虑工序闲置期间采场的安全隐患问题,运用改进遗传算法对最优解进行主-从两步骤搜索,得到地下矿山生产接续和设备调度最佳方案.以国内某大型金矿为案例进行了模型的有效性验证,解算出矿山最优的设备调度计划.验证结果表明,与传统的单一目标优化相比,模型在保证完成指定任务的同时,有效缩短工序时间间隔,并且保证了作业的安全要求.      

船闸底枢可靠性模型及其应用

调查了京杭运河上20座人字门船闸底枢的使用寿命,以此作为实际调查数据对船闸的运行可靠性进行研究.根据底枢蘑菇头磨损试验,应用摩擦学理论分析了底枢摩擦副的失效原因,得出运转不稳、旋转精度降低以及润滑不良引起的摩擦阻力矩过大是造成底枢磨损失效的3种主要模式的结论.应用设备故障的威布尔分布函数和可靠性理论,选用与国内船闸运行工况相同的水润滑条件下的人字门船闸底枢摩擦副模拟磨损实验数据和实际调查数据,分别建立了底枢运行可靠性特征量的计算模型,提出了基于威布尔分布的底枢可靠性指标计算方法,绘制了可靠度曲线.运用实验数据与调查数据于2种模型中,所得可靠度曲线相近,表明计算方法合理,研究成果可靠,可供底枢维修更换决策时应用.     

铜吹炼过程中的杂质脱除

吹炼作业是脱除冰铜中杂质的一道工序。本文论述楚基卡马塔冶炼厂吹炼过程中砷、锑、铋、铅、锌和硒等杂质在粗铜、转炉渣和烟气中的分布状况，并专门讨论初始冰铜品位对杂质脱除的影响。文中对吹炼楚基卡马塔成份复杂的冰铜的工业数据与特尼思特自热转炉处理楚基卡马塔精矿所产生的白冰铜的工业数据做了比较。虽然吹炼白冰铜的除杂率低于吹炼低品位冰铜的除杂率，但正常作业的总除杂率与特尼恩特自热转炉加PS转炉工序的总除杂率不相上下。     

二氧化锰电解工序研究

电解二氧化锰作为电池工业中非常重要的原料之一,其生产过程简单分为化合(制液)、净化(除杂)、电解、后处理(再加工)4个部分。在电解工序当中,锰在此工段以二氧化锰的形式电沉积在阳极板上并在剥离后送至后处理进一步加工。而电解作为整个电解二氧化锰的核心工序,其过程工艺对最终产品质量有很大的影响。主要介绍了电解工艺原理、电解生产时的参数控制以及简单作业流程。     

Weibull Analysis of Mechanical Data for Castings: A Guide to the Interpretation of Probability Plots

The Weibull statistics used in the analysis of mechanical data from castings are reviewed. The insight that can be gained from the three-parameter analysis is introduced, and in particular, the meaning of the threshold value in the three-parameter Weibull distribution from a casting process standpoint is discussed. Weibull mixtures, which are necessary when different defect populations are present in castings, are discussed in detail. Data sets from the literature are reinterpreted for demonstration of the guidelines. Step-by-step procedures are outlined for analysis of Weibull mixtures and for fatigue life data sets with run-outs. The results indicate that knowledge of the casting process is necessary for the accurate interpretation of Weibull probability plots. Because the filling systems of most castings currently are designed poorly, a mixture of Weibull distributions can be expected to be the norm rather than the exception. A single Weibull distribution can be expected only in castings whose filling systems were designed so that no new damage to liquid metal takes place during filling.     

A computer simulation on tensile strength of surface-Damaged fibers

The strength of surface-damaged fibers was studied by means of a computer simulation experiment based on the Monte-Carlo method using a simple model which assumes that the surface flaws can be regarded as mode I notches on fiber surfaces, the strength of undamaged fibers obeys the Weibull distribution function, and the largest flaw determines the strength of damaged fibers. Normal and exponential distribution functions were taken as the flaw size distribution function. By employing the present simulation method, the effects of average flaw size, coefficient of variation of flaw size, density of flaws, and gage length on average strength and its coefficient of variation were studied. It was found that the surface-damaged fibers can retain their full strength only when the average flaw size is small, the coefficient of variation of flaw size is small, density of flaw size is low, and gage length is short. Otherwise the average strength of damaged fibers was reduced seriously. It was emphasized that the scatter of size of flaws and density of flaws strongly affect the strength of fibers as well as flaw size and gage length.     

Shapes of reaction-time distributions and shapes of learning curves: A test of the instance theory of automaticity.

The instance theory assumes that automatic performance is based on single-step direct-access retrieval from memory of prior solutions to present problems. The theory predicts that the shape of the learning curve depends on the shape of the distribution of retrieval times. One can deduce from the fundamental assumptions of the theory that (1) the entire distribution of reaction times (RTs), not just the mean, will decrease as a power function of practice; (2) asymptotically, the retrieval-time distribution must be a Weibull distribution; and (3) the exponent of the Weibull, which is the parameter that determines its shape, must be the reciprocal of the exponent of the power function. These predictions were tested and mostly confirmed in 12 data sets from 2 experiments. The ability of the instance theory to predict the power law is contrasted with the ability of other theories to account for it. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exploring a mixture of distributions using Minitab

A set of macros has been developed to help the user explore the characteristics of the two-component mixture of distributions. Five distributions are included: normal; exponential; Weibull; lognormal; and uniform. Using the powerful abilities of Minitab (version 9) the user can produce graphs for the conditional and unconditional density, cumulative density, survival and hazard functions. The mean of the unconditional distribution is calculated as the weighted average of the conditional means. A technique is programmed for calculating the unconditional median which cannot be derived mathematically. A What..if..? approach can be helpful in clarifying concepts such as sufficient conditions for unimodality, identifiability of mixtures, and hazard function of mixture of distributions.     

Delay Time Analysis in Microtunneling Projects

Delay in microtunneling projects is a complex multivariate problem. Delay in microtunneling is defined as the nonworking time of a microtunneling project due to any reason other than scheduled stops. There are many reasons for delay such as mechanical failure of system components, leakage of hydraulic hoses, blockage of slurry pipes, and waiting time for excavated materials hauling equipment. Delay time increases the project duration and consequently the project cost. Delay data were collected from 35 microtunneling projects. Collected delay data were delay duration, delay reason, time, and location from the start to the stopping point. Five categories of delay causes were used in the analysis. Prediction of delay time will enhance the estimation accuracy of microtunneling project duration. A predictive model using a probabilistic approach was selected to represent the delay time. Based on data characteristics, a Weibull distribution was determined to best represent the overall delay duration in microtunneling projects. Using “regression with life data,” expected overall delay in a microtunneling project could be predicted as a function of driven length. The model will help contractors to estimate total project time with reasonable accuracy. Knowing the anticipated delay time will allow contractors to have a point of comparison for actual performance.     

Fracture of glass in tensile and bending tests

To fully characterize the mechanical behavior of ceramics, it is useful to study their response to both tensile and bending tests. In this investigation, a quantitative comparison is made between tensile and bending results from (circularly) cylindrical glass rods of borosilicate glass and of fused silica. These experimental results show that in each material, the Weibull exponentm is approximately the same for both types of test. The fractured samples clearly showed that all failures initiated at surface-located flaws. The stress level at which the probability of fracture in tension equals 50 Pct was determined; the maximum tensile stress for 50 Pct probability of fracture in bending was also determined. The ratio of these two stresses was predicted previously from simple, theoretical considerations based upon the applicability of the Weibull function and on the distribution of defects in the specimens. This theoretical result is inconsistent with the experimental observations in view of the fractography. Therefore, it is concluded that failure in the materials tested is not satisfactorily described by Weibull statistics.     

Mechanical properties distributions of PM manganese steels analysed by Gaussian and Weibull statistics

Abstract

Powder metallurgy (PM) parts acceptance is determined by compositional and processing parameters and their controls. Statistical procedures are used for assessment; normal distribution and 'six sigma' appear to predominate. For fatigue of metallic materials and strengths of ceramics, fibres and composites, however, Weibull probability of survival analyses are widely used. The original analysis considers a threshold stress at which the probability of failure is zero. This stress is frequently taken to be zero, simplifying the analysis to two parameters. The yield stress has been suggested for the threshold stress, probably not sufficiently conservative for less ductile PM materials. A new three-parameter Weibull analysis, in which it is taken to be the fracture strength minus six standard deviations, is presented. Powder metallurgy manganese steels are under commercial consideration and this approach is applied to 12 variants of such laboratory processed specimens. It is compared with the two-parameter Weibull and Gaussian, the least conservative, analyses.     

Equiaxed Grain Count in Aluminum Alloy Castings: Theoretical Background and Experimental Verification

In this work, a theoretical model is proposed for heterogeneous nucleation on substrates the size distributions of which can be described by the Weibull statistics. In particular, the proposed model suggests that the size distribution of the various nucleation sites is exponential in nature. It is found that the nuclei density can be given in terms of the maximum undercooling. Measurements of grain count were carried out on single-phase Al-1.3 Si and Al-5.0 Cu (wt pct) alloys inoculated using an Al-5Ti-1B (wt pct) master alloy. In the single-phase alloys, the area of equiaxed dendritic grains was estimated using EBSD analysis and by stereological means on polished and etched surface sections. In addition, maximum undercoolings were determined by thermal analysis. The experimental outcome indicates that the volumetric grain density can be properly described by an exponential expression. Finally, the magnitudes of the nucleation parameters were experimentally determined in this work.     

The acquisition of conditioned responding.

This report analyzes the acquisition of conditioned responses in rats trained in a magazine approach paradigm. Following the suggestion by Gallistel, Fairhurst, and Balsam (2004), Weibull functions were fitted to the trial-by-trial response rates of individual rats. These showed that the emergence of responding was often delayed, after which the response rate would increase relatively gradually across trials. The fit of the Weibull function to the behavioral data of each rat was equaled by that of a cumulative exponential function incorporating a response threshold. Thus, the growth in conditioning strength on each trial can be modeled by the derivative of the exponential—a difference term of the form used in many models of associative learning (e.g., Rescorla & Wagner, 1972). Further analyses, comparing the acquisition of responding with a continuously reinforced stimulus (CRf) and a partially reinforced stimulus (PRf), provided further evidence in support of the difference term. In conclusion, the results are consistent with conventional models that describe learning as the growth of associative strength, incremented on each trial by an error-correction process. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The instance theory of automaticity: Why the Weibull?

It is shown that in order to derive the Weibull shape for the response time distribution in the instance theory of automaticity (G. D. Logan, 1988) by an asymptotic argument from the theory of extreme value statistics, it is necessary to determine the domain of attraction of the underlying parent distribution. An alternative, nonasymptotic characterization property equivalent to the power law of practice is presented here that gives a more feasible justification for the choice of the Weibull. This result leads to a different emphasis on the empirical conditions testing the theory. Some problems arising from the use of the asymptotic theory of extreme value statistics for the stochastic modeling of behavioral data are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)