Failure analysis of connecting bolts and location pins assembled on the plate of main-shaft used in a locomotive turbochanger

Three connecting bolts, three location pins and navel of turbo-disk fractured, which were assembled on the plate of the main-shaft used in a locomotive turbochanger. Detailed fractographic study and metallurgical analysis were focused on the trouble bolts. The fatigue fracture is the main failure mechanism of the bolts. Appearance of the surface decarburization layer in the thread tip and root regions of the three failed bolts make the hardness at the thread regions decrease intensely so that the fatigue cracks initiated form the root at the first engaged thread. Surface damage morphology with cutting, wear and plastic deformation features was found on the working flanks of the engaged threads. Other components fractured in succession after the trouble bolt fractured.     

Failure analysis on fracture of worm gear connecting bolts

The worm gear connecting bolts of refueling machines of a nuclear power plant, with implementing standard of ANSI/ASME B18.3 and ASTM A574-08 and strength grade of 10.9, fractured at the thread neck position after running for about 10 years, and means such as macro examination, chemical compositions analysis, hardness testing, metallographic examination and fracture analysis, were used to analyze the fracture property and reasons of the bolts. The results show that the fracture of the bolts is due to two-way bending fatigue fracture. Surface decarburization of the bolts and stress concentration at the bolt thread neck decreased the fatigue strength of this position and resulted in the initiation of fatigue cracks. By comprehensive analysis and stress estimating, it was concluded that the main reason for fracture of the bolts is that there was a big gap between the bolts and the bolt holes, which resulted in fatigue fracture of the worm gear connecting bolts.     

蜗轮连接螺栓断裂失效分析

装卸料机上的蜗轮连接螺栓材料为35钢,强度等级为10.9级,在设备运行大约10a后发生断裂。对断裂螺栓进行宏观、化学成分、硬度、金相、能谱和断口分析后得出,该螺栓的断裂性质为双向弯曲疲劳断裂,螺栓表面的脱碳和螺纹颈部的应力集中降低了该部位的疲劳性能。通过综合分析和螺栓受力估算后得出,螺栓断裂的主要原因是螺栓和内齿轮螺栓孔之间存在较大的间隙,使螺栓的受力状态和受力大小过早地发生了变化,造成连接螺栓疲劳断裂。     

Metallurgical failure analysis of fasteners in an impeller assembly

This paper examines a failure analysis of the bolts from a failed joint between an impeller blade and a rotating assembly unit. The bolts failed due to poor thread manufacture and installation. Sharpened thread roots led to high stress concentrations that favored crack initiation. An oddly shaped thread profile allowed friction between mismatched thread surfaces. Poor installation procedures allowed for the possibility of overtightening to nucleate cracks in the head-to-shank interface (which had a smaller radius and therefore a higher stress concentration) and possibly also in the thread roots. Each of these influences contributed to crack initiation in the bolts. After cracks had formed, bending fatigue then propagated the nucleated cracks to final fracture. The failure analysis also recommended using bolts with rolled threads, which allow a more complete fit between mating male and female threads, and assuring that an appropriate preload is placed on bolts during installation.     

挤出机摩擦离合器螺栓断裂分析

某挤出机中气动摩擦离合器与减速器端连接的螺栓在使用过程中经常发生断裂,改用另一种材料的螺栓后情况未有很好改善。采用化学成分分析、力学性能测试、断口分析和金相检验等方法,对螺栓断裂的原因进行了分析。结果表明：起裂源位于螺栓的加工刀痕、表面擦伤处及因微动疲劳所致的螺纹微裂纹处,这些部位均存在应力集中,在振动作用下,萌生的裂纹不断扩展,使有效承载面积不断减小,最终引起螺栓疲劳断裂。     

叠层膜片联轴器螺栓断裂原因分析

采用化学成分分析、显微组织检验、硬度测定、断口宏观和微观观察及能谱分析等方法对叠层膜片联轴器断裂螺栓进行了分析.结果表明,螺栓根部的退刀槽因加工质量差造成应力集中,加上材料内部有夹杂物,同时在叠层膜片联轴器安装上有问题及机组中其他部件(如风机叶片和齿轮箱)也有损坏等各种因素的存在,该叠层膜片联轴器螺栓组使用于频繁起动的大载荷工作状态,一旦有超过该螺栓所能承受的工作应力就会引起疲劳而发生断裂,最终导致叠层膜片联轴器损坏.给出了正确设计、制造、安装和使用叠层膜片联轴器的建议.     

CRACK SHAPE EVOLUTION STUDIES IN THREADED CONNECTIONS USING A.C.F.M.

Abstract— Crack shape evolution has been studied in high strength, rolled thread, bolts. It has been found that, using the Crack Microgauge, it is possible to detect and size fatigue cracks, located at the thread root, from depths of less than 0.1 mm up to fracture. This work required a special probe system to be developed and also a theoretical solution for the a.c. field distribution in a thread. Some of the work and results are briefly described in this technical note.     

铁路货车钩缓装置钩尾扁销螺栓断裂原因分析

铁路货车钩缓装置中的钩尾销螺栓在螺杆近方头一侧根部位置发生断裂。采用微观分析方法分析了该螺柱断裂原因。综合分析表明：该断裂螺栓方头一侧可能仅局部加热后锻打成四方头,并发生过热,造成在方头一侧的螺柱根部形成马氏体组织和魏氏体组织过渡的U型区域。不良组织的存在增大了钢的脆性,冷加工性能大大降低,在U型区域和螺柱表面交界处萌生了微细裂纹。当钩尾扁销螺栓在列车运行过程中受到过大的冲击时,该螺栓上的微细裂纹在螺栓靠近方头一侧存在的沿轴向的拉应力和螺栓正常紧固力的合力联合作用下张开并迅速扩展,造成螺栓断裂。     

螺栓断裂分析

采用多种分析手段对螺栓断口及基体进行分析,并从螺栓的使用环境、受力情况及工作状况分析和探讨了断裂的原因。结果表明,螺栓的断裂是由于缝隙腐蚀引起,在应力腐蚀及腐蚀疲劳的作用下最终导致螺栓断裂,是由多种因素综合所致。     

汽轮机高压外缸结合面双头螺栓断裂分析

某电厂汽轮机高压外缸结合面双头20Cr1Mo1VTiB钢螺栓在安装时发生断裂,通过断口分析、化学成分分析、金相检验以及力学性能测试等方法对螺栓的断裂原因进行了分析。结果表明:该螺栓钢存在严重的显微组织缺陷,力学性能指标不符合技术条件要求,减弱了螺栓的承载能力,螺纹处的应力集中效应会加剧螺栓的缺口敏感性,导致螺栓在安装时于螺纹处发生脆性断裂。     

内燃机车用柴油机连杆螺钉断裂分析

内燃机车在检修重组后运行约一个月,其柴油机的两根连杆螺钉发生断裂。采用化学成分分析、硬度测试、断口分析和金相检验等方法,对两螺钉断裂的原因进行了分析。结果表明:两螺钉的断裂均为疲劳型断裂,其中一根螺钉先行断裂,其断裂的根本原因可能是螺钉紧固处于不合理的状态所致。     

吊车转盘连接螺栓断裂分析

吊车转盘后部的连接螺栓发生断裂,通过化学成分分析、宏观和微观检验等方法对断裂原因进行了分析。结果表明：螺栓为疲劳断裂,螺纹根部的细小裂纹是导致螺栓发生疲劳断裂的主要原因;螺栓松动后受到弯曲载荷是引起螺栓发生疲劳断裂的诱因。     

某船用减速器螺栓断口的SEM分析

对某船用减速器断裂螺栓的断口形貌进行了SEM分析,同时结合螺栓的工况条件和受力情况,分析了其疲劳剪切断口形成的机理和过程,推断了引起螺栓断裂的原因,并提出了相应的解决措施,为整机的安全运行和优化结构设计提供了重要的参考依据。     

某电传操纵系统弹簧拉杆可调叉形接头断裂原因

某飞机电传操纵系统弹簧拉杆可调叉形接头在运行过程中发生断裂,通过宏微观分析和金相检验等方法对拉杆接头的断裂原因进行了分析。结果表明:拉杆接头断裂为疲劳断裂,断裂的根本原因是其显微组织不均匀的同时出现了魏氏组织,使接头的抗疲劳性能严重降低,导致疲劳裂纹的萌生与扩展;而拉杆的受力不均匀则加速了其疲劳裂纹的扩展。     

1240MPa级Ti-38644高锁螺栓的拉伸疲劳增寿机理

用扫描电镜和能谱观测分析Ti-38644高强钛合金高锁螺栓的拉伸疲劳断口,揭示了高锁螺栓的疲劳裂纹萌生和扩展的微观特征和疲劳增寿机理。结果表明,Ti-38644高强钛合金高锁螺栓的疲劳断口包括疲劳裂纹萌生区、扩展区和瞬断区:疲劳裂纹从螺栓头下圆角滚压薄弱部位表面萌生,随后在基体中呈放射性扩展;进入扩展区后裂纹的尺寸由微观扩展至宏观,以疲劳条带扩展机制为主,同时也存在解理断裂。头下圆角处的变形层对Ti-38644高锁螺栓的疲劳寿命有显著的影响,变形层使Ti-38644钛合金高锁螺栓的疲劳寿命明显提高。通过微观组织与疲劳寿命的对比,探讨了Ti-38644钛合金高锁螺栓疲劳强化的作用机理。     

轮胎螺栓断裂失效分析

某汽车轮胎螺栓在使用过程中发生断裂。采用宏、微观检验和化学成分分析等方法对失效件进行了检测。结果表明，其断裂形式为弯曲疲劳断裂。疲劳裂纹的形成是由于螺纹牙底存在脱碳和折叠裂纹等缺陷，这些缺陷的存在使该材料产生了较大的应力集中，从而导致螺栓开裂失效。     

HXD1机车牵引电机转轴组件断裂失效分析

HXD1型电力机车的牵引电机转轴和小齿轮轴采用圆锥过盈配合传动结构(下称转轴组件),使用中该组件出现了早期断裂失效.本文通过理化检测、断口和配合面宏/微观形貌观察等失效分析技术对失效组件进行了分析.结果表明,材料成分、组织和显微硬度正常,小齿轮轴和电机转轴的失效形式分别为高周疲劳断裂和微动疲劳断裂.造成组件失效的原因和过程是,小齿轮轴近齿端油槽-油孔交界线处有较大的结构应力集中,油槽底部周向加工刀痕造成附加应力集中,在应力集中和旋转弯曲疲劳载荷作用下油孔边两个应力集中点萌生了疲劳裂纹并扩展;随小齿轮轴裂纹的不断扩展转轴组件结构刚度减小,继而诱发了与小齿轮轴匹配的电机轴配合面的微动疲劳,电机轴疲劳裂纹萌生于微动区的边缘处;电机转轴先于小齿轮轴完全断裂.基于本文的分析结果提出了提高组件抗疲劳断裂的技术措施.     

汽车发动机曲轴断裂失效分析

某厂生产的发动机曲轴在用户使用过程中,3个月内共发生了4起曲轴断裂失效事故,采用化学成分分析、金相检验、硬度测试以及断口的宏、微观形貌分析等方法对断裂曲轴进行了分析。结果表明：曲轴断裂为高周低应力弯曲疲劳断裂,导致其断裂的主要原因是在曲轴第一曲拐过渡圆角R附近的曲柄表面聚集分布着机加工刀痕,形成了应力集中;在用户行驶过程中因车况、路面等复杂因素形成的过载或冲击载荷等作用下,在第一曲拐轴颈尺附近曲柄表面应力集中的机加工刀痕处萌生疲劳裂纹,并逐步扩展直至断裂失效。     

洗衣机螺栓断裂失效分析

某洗衣机螺栓在安装过程中发生断裂失效,为查明螺栓断裂的原因,对断裂螺栓进行了化学成分分析、宏观分析、金相检验和断口微观形貌分析。结果表明：螺栓断裂是由于其制造时产生了严重的带状组织,降低了螺栓的许可扭转力矩,导致螺栓在安装过程中发生扭转断裂。     

Failure Analysis of a Mobile Crane: A Case Study

This paper presents metallurgical failure analysis method to find the root cause of a mobile crane turret bolts failure. Focus of the metallurgical analysis was to identify the root causes of the failure of turret bolts which led to the collapse of the mobile crane. The turret bolts were made of high strength steel. Comprehensive engineering analysis suggested that the turret bolts failure was initiated with fatigue. The fatigue was most likely initiated by the corrosion at the bolt surface and accelerated by the loosening of bolts due to long servicing life and/or fluctuating tensile load. Based on the investigations, recommendations are provided to guide the operation of the mobile crane to prevent the premature failure.