550kV断路器操作机构轴销的断裂原因分析

在断路器1 000~2 000次机械操作试验中,30CrNi3合金钢渗氮轴销发生断裂。通过化学成分分析、断口分析、低倍检验、金相检验、力学性能测试的方法,对轴销的断裂原因进行了分析。结果表明:该轴销的断裂性质为双向弯曲疲劳断裂;轴销材料渗氮层存在脉状氮化物,内部存在疏松、大尺寸夹杂物和气泡缺陷,降低了材料的力学性能;在周期性旋转弯曲力作用下,轴销表面缺陷处出现裂纹并不断扩展,最终导致轴销疲劳断裂。     

飞机操纵系统链条销轴断裂分析

某型飞机操纵系统链条销轴在使用中断裂。采用化学成分分析、外观检查、断口分析和表面质量检验等方法对断裂销轴进行了分析,又对有裂纹的销轴与断裂销轴进行了对比分析。结果表明：销轴表面存在原始缺陷,加上链条链板在长期使用中的磨损使得链板间隙增大,导致销轴承受剪切力的同时又承受弯曲载荷,最终导致销轴发生疲劳断裂。     

45B钢链轨销轴断裂原因分析

某45B钢链轨销轴在使用过程中发生早期断裂。通过化学成分分析、硬度测试、有效硬化层深度测定、金相检验、断口分析等方法,对销轴的断裂原因进行了分析。结果表明:销轴断裂机制为准解理断裂+韧性断裂的混合型断裂;在使用过程中,45B钢材料中的球状氧化物剥落留下微孔洞形成裂纹源,在弯曲应力的作用下,裂纹源迅速放射扩展,造成销轴早期断裂。     

某电动泵传动轴断裂原因分析

某电动泵传动轴在使用过程中发生早期断裂,采用断口分析、金相检验、硬度测试、化学成分分析、表面质量检查等方法对传动轴断裂的原因进行了分析。结果表明:该传动轴的断裂模式为疲劳断裂;由于电火花加工工艺设置不当,使传动轴的销孔表面产生了微裂纹,在交变载荷作用下,微裂纹不断扩展直至传动轴发生断裂。     

汽车右后拖曳臂轴断裂原因分析

某汽车仅使用2d(天)、行驶56km,其右后拖曳臂轴即发生断裂。采用断口宏观和微观检验、硬度测试、金相检验、化学成分分析等方法,对该右后拖曳臂轴断裂的原因进行了分析。结果表明:该轴断裂性质为沿晶脆性断裂,断裂的主要原因是其锻造组织存在缺陷及未经调质处理,使轴的强度大大降低;次要原因是轴表面因磨削加工过热形成了表面磨削淬火层,增加了轴表面的脆性及拉应力,使微裂纹在轴表面产生。     

调速器步进电机轴断裂失效分析

某电厂调速器步进电机轴在开机调负荷过程中发生断裂,对断裂电机轴进行了宏观检验、化学成分分析、硬度测试、金相检验和断口分析,并对步进电机轴材料进行了切应力校核。结果表明:该调速器步进电机轴断裂失效为低应力高周旋转/弯曲疲劳断裂。电机轴断裂失效的主要原因一方面是因为变径部位退刀槽位置容易造成应力集中现象,从而促使步进电机轴表面产生疲劳裂纹;另一方面是因为硫化物、碳化物等夹杂物的存在会降低材料的塑性、韧性和疲劳强度,进一步造成应力叠加,材料力学性能降低,加速疲劳裂纹的形成和扩展。     

曲柄销轴断裂分析

对曲柄销轴在采油设备上的安装配合情况进行了调查，在此基础上，分析了销轴在采油设备工作时的受力情况，并通过化学分析、金相检验和扫描电镜等方法对销轴断裂失效进行了分析。结果表明，该销轴在交变偏斜拉应力的作用下，在销轴的应力集中处——退刀槽根部产生疲劳裂纹，最终导致疲劳断裂。另外钢材质量欠佳、组织不良也促进了断裂过程的进行。     

空压机曲轴断裂失效分析

某空压机曲轴在运行约5 000h后发生断裂失效,通过宏观检验、断口分析、金相检验以及硬度测试等方法,对空压机曲轴断裂原因进行了分析。结果表明:由于曲轴中存在严重的疏松缺陷,在运行过程中于曲轴轴颈和轴拐R过渡表面疏松处萌生裂纹,在交变应力作用下,裂纹以疲劳方式扩展直至曲轴断裂失效。     

汽车变速器输入轴校直断裂失效分析

某汽车变速器输入轴在渗碳淬火热处理后校直时断裂,采用断口宏微观分析、低倍酸蚀检验、金相检验及硬度测试等方法对输入轴断裂原因进行了分析。结果表明:该输入轴断裂部位的横向剖面存在棒料未切除干净的残余缩孔缺陷,使轴直径变化的R部位有效承载面积减小,成为结构上的危险截面;加之输入轴表面渗碳层存在粗大的马氏体,脆性较大,从而导致输入轴在较大的校直外力作用下于应力集中的R部位表面萌生裂纹,并迅速扩展发生一次性断裂。     

电梯驱动轴断裂原因分析

某电梯公司生产的材料为Q345A钢的电梯驱动轴在短期内发生断裂失效,采用化学成分分析、金相检验、硬度测试、扫描电子显微镜分析等方法对驱动轴断裂原因进行了分析。结果表明:该驱动轴断裂属性为多源旋转弯曲疲劳断裂;断裂源位于驱动轮盘和驱动轴过渡的环焊缝热影响区的应力集中处,加之驱动轴表面加工刀痕明显,且存在硬而脆的马氏体非正常组织,进一步加剧了该处的应力集中,在扭转力作用下萌生多源裂纹,裂纹不断扩展最终导致断裂。     

Stress and failure analysis of the crankshaft of diesel engine

In this work the failure analysis of the crankshaft of diesel engine was performed. Visual examination of the crankshaft fracture showed that beach marks, typical for fatigue failure were observed. Additional observations of the crack initiation zone indicated that crack origin was not covered by material defects or corrosion products. Performed hardness test of the fractured crank pin showed that large HRC values were observed in central part of the pin only. On the corner of cylindrical pin surface where the crack origin was located the hardness of material was much smaller. In order to explain the reason of premature crankshaft damage, the finite element method was utilized. The results of nonlinear static analysis showed that during work of the engine with maximum power the high stress area was located in crack initiation zone. Based on results of performed investigations it was concluded that the main reason of premature fatigue failure was high-cycle fatigue of the material in external zone of the crank pin where the small structural radius was designed. In final part of the work the recommendations for increase of the fatigue life of analyzed crankshaft were formulated.     

分动箱齿轮断裂原因

某分动箱的20CrMnTi钢齿轮在工作过程中发生断裂.采用宏观分析、微观分析、化学成分分析、硬度测试、硬化层深度测量、非金属夹杂物分析、金相检验等方法对齿轮的断裂原因进行了分析.结果表明:齿面上残留的加工刀痕导致应力集中,在周期载荷的作用下,疲劳裂纹源首先在残留的加工刀痕较深处形成,随后裂纹逐渐扩展,最终齿轮发生疲劳断...     

活塞销失效原因分析

某发动机活塞销失效导致发动机损毁.采用磁粉探伤、宏微观断口分析、化学成分、金相组织及硬度分析等方法对失效的活塞销进行了分析,同时还对活塞销在服役过程中的应力状态进行了有限元模拟计算.结果表明,导致活塞销疲劳断裂的原因是活塞销端面存在磨削裂纹.     

某型火炮击针失效分析

目的为了解决火炮击针断裂的问题。方法对断裂的火炮击针进行了宏观检查、化学成分分析、机械性能测试、断口分析、宏微观组织检测,确定了击针断裂的性质和产生原因。结果火炮击针断口属多源疲劳断口。结论击针断裂的主要原因:一是螺纹槽根部半径R较小,截面过渡不够平滑和自然,形成了较大的应力集中;二是螺纹槽根部的加工比较粗糙,进一步加剧了应力集中;另外,发射药形成的高温气体对火炮击针螺纹槽根部有腐蚀作用,导致击针螺纹槽根部R处出现点蚀坑,点蚀坑破坏了该处的表面完整性,形成了较大的应力集中,导致在点蚀坑处萌生了早期疲劳裂纹。建议改进工艺设计,增大螺纹槽根部R,确保截面过渡平滑自然,以降低颈部的应力集中系数;改进加工能力和水平,防止出现机加工缺陷。     

Influence of laser shock peening on fatigue performance of LZ50 axle steel for railway wheel set

Laser shock peening (LSP) is a surface treatment technique that forms a strengthened layer on the metal surfaces. In this study, the LSP was applied on the locomotive LZ50 axle steel surface which was interference fitted with the wheel. The microstructures, fracture morphologies and fatigue performances of LSP‐treated and untreated axle steels were explored. The results indicated that after the LSP treatment, a strengthened layer was generated on the axle steel surface. The surface hardness was increased by 25%, that is, from around 204 to around 255 HV_0.3. The residual compressive stresses were improved from 260 to 345 MPa along the axial direction and from 165 to 225 MPa along the radial direction. The fatigue limit was increased by 30%, that is, from around 130 to around 170 MPa. The fracture surfaces could be divided into three regions: crack initiation, crack propagation, and short‐break regions. In the crack initiation region, the fatigue striation of the LSP‐treated steel was denser than the untreated steel. In the crack propagation and short‐break regions, the fracture morphologies of the LSP‐treated and the untreated axle steels were similar.     

Fracture Failure Analysis of Ductile Cast Iron Crankshaft in a Vehicle Engine

The engine crankshaft of a vehicle suddenly fractured, as the vehicle was running normally on a highway. The engine crankshaft was made from ductile cast iron. The failure cause was analyzed by chemical and metallographic examination, evaluation of mechanical properties, determination of depth of the quenched layer, measurement of distance between the quenched layer and the web, observation on the fracture surface as well as value determination of the fillet radius. The results showed that the failure mechanism of the crankshaft was fatigue fracture resulting from co-effect of bending and twisting, and the crack originated from the subsurface shrinkage in the unquenched layer of the crankshaft journal. Several aspects of the crankshaft were not up to the technical standards, such as distance between the quenched layer and the web, chemical composition, hardness and microstructure of the quenched layer, yield strength, and impact toughness.     

ZM6尾减机匣开裂失效分析

某型号飞机尾减机匣试验过程中出现异常,荧光检查发现裂纹.通过故障机匣外观检查、裂纹断口宏微观观察及能谱分析、材料硬度检测、金相检查等试验得出结论,尾减机匣失效属低周疲劳开裂,机匣表面Nd元素偏析是导致机匣疲劳裂纹形成的直接原因,材料韧性不足一定程度上促进了裂纹的疲劳扩展,根据分析结果,给出提高尾减机匣受力部位的疲劳抗力,避免故障再次发生的有效方法.     

Failure Analysis of a Cylindrical Roller Bearing from a Rolling Mill

Premature failure of a cylindrical roller bearing of a gear box input shaft from a hot strip mill has been investigated. The pins of the cylindrical rollers of the bearing broke from the welded joints at their ends on the cage ring. Investigations were carried out on the failed roller pin and the welded joint. The investigation consists of visual observation, chemical analysis, characterization of macro- and microstructures, measurement of hardness profile, fractography, and energy dispersive spectroscopy (EDS). The fracture surface of the roller pins exhibits beach marks. Scanning electron microscopy (SEM) of the fracture surfaces reveals striations suggesting fatigue failure. The measured hardness profile along the welded joint shows very high hardness due to the presence of untempered martensite at the fusion boundary as revealed by the microstructural examination. Analyses of the results infer that the roller pins failed by the initiation of fatigue cracks from the welded joint because of the presence of untempered martensite originated due to improper welding process.     

汽车板簧的断裂分析

汽车板簧在路试中出现早期疲劳断裂。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断裂的汽车板簧进行了分析。结果表明,焊接时,飞溅的熔滴在板簧表面形成烧伤坑并形成淬火马氏体及淬火裂纹,在路试中产生应力集中而成为疲劳源,在交变应力作用下使裂纹扩展而最终断裂。