浅谈机械产品失效模式

机械设备中各种零部件都具有一定的功能,当机件在载荷的作用下丧失最初规定的功能时为失效,通过对失效件的分析和验证,模拟重现失效现象,找出失效原因、机理、原因和规律,并提出改进措施和预防对策,可提高产品质量,对产品修复、改进及仲裁失效事故等方面具有很强的实际意义。机械产品的失效通常分为两大类,一类是断裂失效,另一类是非断裂失效,断裂失效常按断裂性质分为韧性断裂、脆性断裂和疲劳断裂,非断裂失效主要有磨损失效和腐蚀失效。     

机械零部件失效浅析

介绍了机械零部件的失效形式以及失效分析的具体方法,并结合典型的机械零件的失效情况,对其失效的原因和分析步骤进行了讨论,提出了改进措施.     

滚动轴承的白色腐蚀裂纹失效

白色腐蚀裂纹(WEC)为不同于经典滚动接触疲劳(RCF)的轴承失效机制,因通常导致轴承早期失效而成为目前最受关注的轴承失效机制之一。对WEC失效与经典RCF的差异进行了概述,并以台架测试研究了多种附加载荷、轴承材料及其热处理和表面涂层对轴承WEC失效寿命的作用,以及钢的洁净度对轴承WEC失效和经典RCF寿命的不同影响。证实了附加载荷是发生WEC失效的必要条件,改善钢的洁净度可显著提高轴承经典RCF寿命,但不能作为提高轴承WEC失效寿命的有效方法。     

高铬离心复合铸铁轧辊的非正常失效及预防

简单介绍了高铬离心复合铸铁轧辊的技术特性和失效形式,并分析了非正常失效的原因,同时针对非正常失效提出了预防措施.     

高炉铁沟浇注料的失效分析与原因探讨

对高炉Al2O3-SiC-C质浇注料的失效原因进行了分析,认为浇注料的失效主要与水泥失效有关,浇注件中氯离子过量也会影响凝固的效果.通过加入少量铝酸钙水泥,可以使得失效浇注料重新产生强度,投入使用后,无不良影响.     

高铬离心复合铸铁轧辊的非正常失效及预防

简单介绍高铬离心复合铸铁轧辊的技术特性和失效形式,并分析非正常失效的原因,同时针对非正常失效提出预防措施.     

粉末热锻用3Cr2W8V钢模具热处理工艺的改进

粉末冶金热锻模具一般采用3Cr2W8V钢制造。在热锻时它的主要失效形式是热疲劳失效。热疲劳失效又分热应力疲劳失效和机械疲劳失效两大类。粉末热锻模具的失效属于内约束型的热应力疲劳失效。由于模具在循环加热和冷却过程中,截面上存在温度梯度,心部材料对模腔表层的自由热胀冷缩有约束作用,使表层在加热时受压缩热应     

称重油缸失效原因分析与改进

通过对称重油缸的工作原理和失效方式的分析,得出造成油缸失效的几种原因,进而针对性地提出了解决油缸失效的方法。     

轧辊失效的原因及预防措施的研究

介绍轧机轧辊的常见失效形式。着重分析了轧辊失效的原因及预防失效的措施。     

连轧管机轧辊失效分析

分析了连轧机轧辊的失效形式及失效原因,并提出了对应的解决措施,提高了轧辊的使用寿命,避免了轧辊的非正常失效,有效提高了工厂的生产效率。     

Analytical Approach to Calculate Rate of Bank Erosion

Bank erosion consists of two processes: basal erosion due to fluvial hydraulic force and bank failure under the influence of gravity. Because bank resistance force varies with the degree of saturation of bank material, the probability of bank failure is the probability of the driving force of bank failure being greater than the bank resistance force. The degree of saturation of bank material increases with river stage; therefore, the frequency of bank failure is correlated to the frequency of flooding. Consequently, the rate of bank erosion is due to both basal erosion and bank failure, and bank failure is a probabilistic phenomenon. In this paper, for cohesive bank material experiencing planar bank failure, a deterministic approach was adopted for basal erosion analysis, whereas the probability of bank failure was included in the analysis of bank failure. A method for calculating the rate of bank erosion was derived that integrates both basal erosion and bank failure processes, and accounts for the effects of hydraulic force, bank geometry, bank material properties, and probability of bank failure.     

宝钢RH真空系统稳定运行的研究与实践

在炼钢厂生产高附加值的品种钢必须通过RH精炼工序,而RH装置中的真空系统是否稳定是决定钢水质量的关键因素。介绍RH真空系统故障的分类,包括能源介质的故障、漏气故障及真空元件的故障。对每类故障的原因进行分析,并结合现场实际案例,快速确认故障原因。从真空度维护方面介绍了几种有助于真空系统稳定运行的措施,经实践证明非常有效,对同类真空系统的运行有一定借鉴意义。     

Tensile fracture of brittle matrix composites: Influence of fiber strength

A stress intensity approach is used to analyze tensile failure of brittle matrix composites that contain unidirectionally aligned fibers held in place by friction. In general, failure may initiate either by growth of a crack in the matrix, or by fracture of fibers that bridge the matrix crack. Subsequently, these failure processes may continue either unstably or stably with increasing applied stress. Solutions to the fracture mechanics analysis are obtained numerically in normalized form, with one microstructural variable, the normalized fiber strength. The analysis defines transitions between failure mechanisms and provides strength/crack-size relations for each mechanism. Explicit relations are derived for the matrix cracking stress (noncatastrophic failure mode), the condition for transition to a catastrophic failure mode, and the fracture toughness in a region of catastrophic failure, in terms of microstructural properties of the composite.     

Analysis of Test Specimens for Cohesive Near-Bond Failure of Fiber-Reinforced Polymer-Plated Concrete

The failure mechanisms of reinforced concrete (RC) members change due to the application of externally bonded fiber-reinforced polymer reinforcement. Although an extensive literature is available describing the failure mechanisms of poststrengthened flexural systems, brittle failure modes caused by bond failure, such as midspan debonding and end peeling, need to be further investigated in order to identify and quantify the fracture processes that result in bond failure. Simplified experimental tests have been designed to idealize the bond between the laminate and the RC member. However, it is unclear how the simplified test results can be related to the actual flexural debonding failures. This paper investigates and compares two bond failure tests: a simplified test (or simple shear test) and a recently proposed shear/normal test. After discussing the characteristics of both tests and how they relate to the midspan debonding and end peeling failures, the shear/normal test is studied in more detail using a nonlinear finite-element fracture mechanics program. The program accounts for cohesive localized and distributed concrete crack damage and is capable of describing the geometrical discontinuities that induce different brittle failure mechanisms. The numerical results compare well with available experimental data and help explain the crack formation and propagation pattern up to specimen failure. Parametric studies are presented to elucidate the influence of different material parameters on the failure mechanisms.     

Failure of resistance spot welds: tensile shear versus coach peel loading conditions

Abstract

This paper aims at investigating the failure behaviour of resistance spot welds under tensile shear (TS) and coach peel (CP) loading conditions. A failure mechanism was proposed to describe both interfacial and pullout failure modes in each loading condition. The mechanisms were confirmed by SEM investigations, examining the cross-sections of the fractured welds to detail the fracture path. The experimental results showed that in the pullout failure mode during TS testing, necking is initiated at the nugget circumference in the base metal, and then failure propagates along the nugget circumference in the sheet, leading to the final fracture, while pullout failure during the CP test occurred by crack initiation and propagation near the weld nugget/heat affected zone boundary. The interfacial failure to pullout failure mode transition in the TS and CP tests was also studied. The critical weld nugget size required to ensure the pullout failure mode was obtained for each loading condition. The critical fusion zone size to ensure pullout failure mode during the TS test was larger than that of the CP test. It was found that the load bearing capacity of the spot welds under CP is significantly lower than that of the TS test.     

Methods of the use of ketorolac tromethamine in patients during the early postoperative period

An evaluation was done of respiratory failure in 149 children aged 3 to 15 presenting with funnel-shaped chest deformity (FCD). An original classification is suggested of degree of respiratory failure in FCD in children. Based on the index assessment of clinical and functional parameters an outline has been worked out for degree of respiratory failure. The criteria obtained are statistically significant; being able of giving quantitative assessment of degree of respiratory failure they can serve as control figures to be used in evaluations designed to study time course of changes in respiratory failure.     

Prognosis of heart failure and factors influencing mortality

According to the recent concept, heart failure has been regarded as the syndrome in which left ventricular function is associated with shortened life expectancy. Thus, an understanding of heart failure is of the utmost importance in understanding the mortality. Five primary factors that appear to influence prognosis in heart failure are an etiology of heart failure, the severity of ventricular dysfunction, the degree of impairment of exercise capacity, the activation of neurohumoral factors, and high incidence of ventricular arrhythmias. Both left ventricular ejection fraction and exercise tolerance bear a close relationship to survival in heart failure but there is only weak correlation between these two parameters indicating that each factor may be an independent determinant of survival. Sympathetic stimulation could certainly increase the likelihood of lethal ventricular arrhythmias and contribute to sudden death in heart failure. However, the result of recent large scale trials have indicated that reduction of mortality in patients with chronic heart failure and low ejection fraction by medical treatment was not necessarily a result of the reduced mortality due to an arrhythmia but that due to progressive heart failure. Establishing the prognosis of a patient with heart failure may be of considerable importance in patient management.     

Model Tests and Analyses of Bearing Capacity of Strip Footing on Stiff Ground with Voids

A series of 1G loading tests under the plane-strain condition were conducted on stiff ground with continuous square voids with the view of shallow foundation on calcareous sediment rocks, which contain voids because of their susceptibility to water dissolution. Detailed experimental observation revealed three types of failure modes for a single void: bearing failure without void failure, bearing failure with void failure, and void failure without bearing failure, depending on the location of the void as well as the size of the void. Upper-bound calculations were presented to interpret the changes of bearing capacity observed because of the existence of a void.     

高压空气环境下钨电极失效的研究

在模拟试验舱中进行了高压TIG焊试验,钨极的失效形式主要有烧蚀、钨极尖端粘上金属、钨极熔化3种形式,烧蚀占总失效的90%,钨极尖端粘上金属占到9%,钨极熔化占到1%;给出了钨极失效的几何判据。对钨极凸缘形成机理进行了研究,研究表明,凸缘是电极尖端温度合适的C粗糙区内,钨重结晶和钨的氧化物分解、沉积共同作用的结果。分析了影响高压焊接钨极失效的因素,建立了高压TIG焊钨极失效的故障树,对故障树进行了定性和定量分析,找出它的最小割集,计算出事件的结构重要度系数。在此基础上,提出了防止钨极失效的措施。