断裂失效分析(续)

3.3疲劳断裂失效分析　疲劳断裂失效分析的内容包括：分析判断零件的断裂失效是否属于疲劳断裂与疲劳断裂的类别;引起疲劳断裂的载荷类型与大小以及疲劳断裂的起源等.疲劳断裂失效分析的目的则是找出引起疲劳断裂的确切原因,从而为防止同类疲劳断裂失效再次出现所要采取的措施提供依据.     

高强度套管断裂失效预防及标准化

通过对高强度套管断裂原因进行大量调查研究和失效分析,认为套管材料钢级越高,需要匹配的韧性也越高,高强度(屈服强度≥140ksi,即965MPa)套管断裂原因主要与材料强度和韧性不匹配有关。要从根本上解决高强度套管断裂问题,首先应当对高强度套管断裂原因进行失效分析和研究,找出其断裂原因;然后依据失效分析和研究成果制定严格的订货技术标准,并采取一定的措施落实订货技术标准。     

某油田钻杆旋塞阀断裂原因分析

近年来,油田钻杆用旋塞阀频繁发生失效事故,如密封失效、无法旋转、本体断裂等。该试验针对某油田发生的一起钻杆旋塞阀横向断裂事件,通过宏观分析、化学成分分析、力学性能测试、金相分析及微观形貌分析,对旋塞阀的断裂原因进行了分析。结果表明:旋塞阀的断裂机理为疲劳断裂,断裂的主要原因是材料的冲击韧度过低,导致早期裂纹的萌生和扩展,最后根据失效原因提出了相应建议。     

轿车后桥轴头断裂失效分析

轿车在公路上正常行驶时突发事故,后桥轴头断裂失效.应用扫描电子显微镜、金相显微镜、直读光谱仪等对失效件断口、焊接质量、断裂原因进行试验分析.结果表明,断裂属于应力集中型疲劳扩展加快速撕裂,断裂失效的主要原因是严重的焊接不连续性缺陷,减少有效截面面积的同时,极大降低断裂应力,并起到应力提升源的作用.     

机械零件断裂失效分析

断裂失效是最主要,危害最大的一种零件失效模式。断裂失效分析是从断口的宏观、微观特征入手,研究断裂过程和形貌特征与材料的性能、显微组织、零件的受力状态及环境条件之间的关系,从而提出断裂的原因。     

失效分析技术(续)

断口是断裂失效中两断裂分离面的简称。由于断口真实地记录了裂纹由萌生、扩展直至失稳断裂全过程的各种与断裂有关的信息。因此,断口上的各种断裂信息是断裂力学、断裂化学和断裂物理等诸多内外因素综合作用的结果,对断口进行定性和定量分析,可为断裂失效模式的确定提供有力依据,为断裂失效原因的诊断提供线索。     

飞机舵机失效分析及首断件判定

某飞机舵机在地面随机振动试验后其电传功能失效,分解发现其中的电门支架和传感器支架均已断裂。采用断口分析、化学成分分析、硬度测试和金相检验等手段对该舵机失效原因及首断件进行了分析。结果表明:电门支架为该失效舵机各断裂件中的首断件,电门支架断裂的主要原因是其断裂处在振动试验前就已存在裂纹;舵机失效过程为电门支架首先发生准解理断裂后,其中一块断口由于失去固定作用对传感器支架产生撞击,进而又引起传感器支架发生疲劳断裂。     

某压缩机45钢转轴断裂原因分析

某压缩机转轴在正常工作中突然发生断裂,通过对失效转轴的化学成分、力学性能、显微组织、裂纹及断口形貌进行分析和检验,查明了其断裂原因。结果表明:该转轴断裂为旋转弯曲疲劳断裂;断裂起源于转轴补焊热影响区的沿晶微裂纹,转轴加工过程中表面进行补焊并且补焊工艺控制不当是导致其断裂失效的主要原因。     

高压压缩机联轴器用螺栓失效分析

针对现场一起国产化联轴器法兰紧固螺栓的断裂失效事故,采用多种典型失效分析方法分析了螺栓失效的过程和螺栓的材质,认为对螺栓受力环境的低估和选材不当是导致螺栓无法承受工作载荷而产生疲劳断裂失效的主要原因.     

TDJ型减速顶构件失效分析

本文分析了ＴＤＪ型火车减速顶的受力状况，采用ＳＥＭ及金相物理等手段观察减速项构件失效断口的微观形貌，对构件断裂失效原因进行了详细的研究，并得出应力集中造成的疲劳断裂是减速顶构件失效原因的结论     

减震器托架断裂失效分析

目的解决减震器托架断裂失效的问题。方法通过化学成分分析、力学性能分析、断口扫描分析、金相组织分析、氢含量测试等手段,确定了减震器托架断裂性质及原因。结果减震器托架发生氢脆断裂。结论由于酸洗过程中材料渗入过量氢,导致氢脆并发生断裂。为防止类似的失效事故再次发生,提供了一些指导性建议。     

Brittle Fracture of Hot-Forging Cast Dies

The site applications of cast hot-forging dies made from a new type cast steel were performed and several of the dies experienced brittle fracture. Analysis of the operating modes and evaluation of mechanical properties were used to establish relations among failure patterns and lives of dies. The results show that the dies experience elevated-temperature wear, plastic deformation and thermal fatigue and that brittle fracture was the predominant failure pattern. Brittle fracture of cast dies has two patterns: early brittle fracture and impact fatigue fracture. The early brittle fractures seldom occur but, when this failure mode occurs, the failure severely shortens the life of the cast dies. The early brittle fracture is attributed to abnormal heat-treatment and operation. Impact fatigue fracture is the dominant failure pattern in the cast dies. This failure mode usually initiates from sand inclusions, micro-cracks and/or thermal fatigue cracks. The specifications of the die material should include a requirement for impact toughness to assure that the dies are resistant to multiple impact loads. This means that strength-dominant toughness must be controlled and optimization of the heat-treatment processes must focus on this requirement.     

Failure of amorphous polystyrene

The failure behaviour of amorphous polystyrene was studied in methanol and ambient air under constant load and strain rate conditions. The good correlation found between fracture mechanics theory and the test results of both crazing and fracture indicates that fracture mechanics theory can be used in predicting failure of amorphous polystyrene. From the fracture mechanics analysis of the results it is inferred that the kinetics associated with craze initiation and crack propagation are similar and that the inherent flaw responsible for failure first initiates the craze in which a crack is then formed. Both the distribution of inherent flaws and the kinetics of crazing and fracture are dependent on the test environment.     

Insights into the effects of tensile and compressive loadings on microstructure dependent fracture of trabecular bone

The micro-scale finite element models used in the past to understand yielding failure of trabecular bone have not addressed the microcrack formation and its effect on microstructure dependent fracture. An understanding of microcrack based failure mechanisms can be important to develop insights into response of trabecular bone to external loading before final failure. With this goal, we analyze tensile and compressive fracture failure at two different ages in two trabecular bone micrographs obtained from an ovine femur using a recently developed cohesive finite element method (CFEM) framework. The results and analyses indicate that examined trabecular microstructures are optimally designed for resisting compressive loading. Under tensile loading, initial damage in a microstructure is localized in a single random trabecula. Final microstructure failure occurs immediately after the failure of the trabecula. However, under compressive loading, failure of the first trabecula does not precede immediate complete failure of microstructure. Under compression the propagation fracture toughness (characterized by change in energy release rate as a function of crack density) increases with increase in crack density. However, under tension the propagation fracture toughness decreases with increasing crack density. The fracture mechanism remains unaffected by age variation. Effect of tissue property random variation on the variation in fracture strength diminishes under tension and increases under compression with increase in the age. Overall, results indicate that structural arrangement of the trabecular bone (besides the hierarchical chemical composition) can be an important contributor to its unique fracture resistance properties.     

Fracture mechanics as a tool in failure analysis — Prospects and limitations

Although fatigue crack propagation and fracture cause a large part of failure events in industrial practice, fracture mechanics in failure analysis seems to be still a side issue. Starting from an introduction into important basic questions of failure analysis and fracture mechanics, the authors specify what kind of questions in failure analysis can be effectively solved by fracture mechanics (and which can't). They illustrate their discussion with a number of 13 case studies from the literature. Much more pronounced than in the design stage the benefit of fracture mechanics in failure analysis depends on its accuracy. This is limited by both, intrinsic factors of the method and the availability and quality of the input information. The authors discuss the various aspects and provide the reader with some background information which, as they believe, will be helpful for better understanding the prospects and limitations of fracture mechanics in failure analysis and the conditions of its application.     

电站装备失效分析及其预防

简叙了电站装备失效分析程序、失效原因及其失效机理。大量的各种各样的失效，常常涉及一种或多种的失效机理。在众机理中，主要是：腐蚀失效、环境断裂失效、变形失效和断理解失效。     

自行车多飞飞轮轮芯冷挤压凸模具断裂失效原因探析

本文以某自行车集团多飞飞轮轮芯冷挤压模具的凸模为研究对象,通过模具结构的分析、挤压力计算、光学显微镜与扫描电子显微镜的组织结构观察、失效模具断口形貌分析及微区成分测试等探讨了自行车多飞飞轮轮芯冷挤压模具断裂失效的原因。实验发现,失效模具的显微组织中明显存在不均匀带状分布的碳化物,而断裂裂纹发生部位为碳化物集中区。模具组织中存在不均匀带状分布的碳化物是产生断裂失效的主要原因。     

Hygrothermal ageing and fracture of glass fibre-epoxy composites

The effects of hygrothermal ageing upon the failure characteristics and work of fracture of glass fibres in epoxy are described. A collection of data based on the direct observation and measurement of fibre debond length and fibre pull-out length after fracture is displayed in empirical failure diagrams. Similarly, a vast number of experimental measurements of work of fracture is displayed in a three-dimensional diagram where the axes are work of fracture, humidity and ageing time. This information is combined with models of fracture in the construction of a fracture map which is used to interpret hygrothermal ageing phenomena.     

Scanning electron microscopy studies on tensile,tear and abrasion failure of plasticized poly (vinyl chloride) and copolyester thermoplastic elastomers

Scanning electron microscopic observations on the tensile, tear and abrasion failure of plasticized poly (vinyl chloride) (PVC) and copdyester (Hytrel 40D) thermoplastic elastomers showed that the patterns developed on the fracture surfaces could be correlated with the strength and type of failure of these materials. Hytrel was found to undergo ductile failure whereas PVC showed shear fracture under tensile stress. The higher tear and abrasion resistances of Hytrel than those of PVC were also manifested by the difference in fracture patterns on the failure surfaces of these samples.     

Computational homogenization of discrete fracture in fibre-epoxy systems

In the present paper the effective mesoscale failure response of a fibre-epoxy sample is computed from its complex microscale fracture behaviour. The mesoscale failure response is represented by a traction-separation curve derived from numerically homogenizing the fracture response of a periodic fibre-epoxy microstructure loaded under uniaxial tension. The traction-separation curve can be applied in material points of interface elements that are used for simulating mode I mesoscopic fracture in macroscopic laminate failure problems. The effect of the size of the microscopic fibre-epoxy sample on the mesoscale failure response is examined, as well as the effect of local imperfections at fibre- epoxy interfaces.