皮卡车钢板弹簧断裂分析

通过断口分析、化学成分分析、金相检验和硬度测试对皮卡车的钢板弹簧断裂的原因进行了分析。结果表明:钢板弹簧表面存在凹坑造成了应力集中,而且板材的非金属夹杂物超标,降低了疲劳强度,在交变应力载荷的作用下,最终造成钢板弹簧发生了早期疲劳断裂。     

汽车钢板弹簧断裂失效分析

采用金相及断口分析等方法,对早期疲劳断裂失效的汽车钢板弹簧进行了综合分析,得出,钢板弹簧产生疲劳断裂的主要原因是由于喷丸工艺控制不当,致使弹簧表面存在较多较多较深的弹坑,这些凹坑在弹簧工作时成为应力集中点而形成疲劳源,另上,弹簧表面局部区域存在脱碳,降低了材料的疲劳强度。     

列车用弹簧断裂原因分析

采用直读光谱仪、光学显微镜和扫描电子显微镜等分析手段对断裂弹簧进行了失效分析。结果表明,该弹簧断裂性质为腐蚀疲劳断裂。弹簧表面与表面的有机涂层存在一定的间隙,外界的水蒸气和腐蚀性离子会穿透有机涂层,对基体材料造成腐蚀,产生腐蚀坑,形成应力集中点,在交变载荷和腐蚀性介质的共同作用下产生裂纹源,最终发生腐蚀疲劳断裂。     

60Si2MnA钢弹簧压力试验断裂原因分析

某60Si2MnA钢弹簧在压力试验过程中发生断裂失效,采用断口宏微观分析、扫描电镜及能谱分析、金相分析等方法对其断裂原因进行了分析。结果表明:弹簧表面存在较多的酸洗腐蚀坑,在压力试验过程中成为应力集中点,于腐蚀坑底萌生微裂纹,微裂纹不断扩展最终导致弹簧断裂失效。最后根据弹簧断裂原因提出了改进建议。     

铁路轴箱弹簧断裂原因分析

某铁路轴箱弹簧在服役过程中发生断裂。采用化学成分分析、非金属夹杂物检验、硬度测试、显微组织及表面脱碳层检验、断口分析等方法,对弹簧断裂的原因进行了分析。结果表明:在服役过程中,弹簧表面存在的不连续凹痕处产生应力集中并形成裂纹源,疲劳裂纹不断扩展,导致弹簧最终发生疲劳断裂。     

汽车钢板弹簧断裂分析

用化学分析、断口分析和金相检验等方法对断裂汽车钢板弹簧进行了分析。结果表明,钢板弹簧材质存在的夹杂物、带状组织和不同程度的表面脱碳,是导致钢板弹簧断裂的主要原因。     

大型轧钢卷曲机环型弹簧的断裂分析

对大型轧钢卷曲机四棱锥部件环型弹簧的断裂从化学成分、金相、断口等方面做了综合分析.断口分析表明,弹簧的断裂性质为疲劳.疲劳源起源于零件锥面与横端面相交的应力集中处.金相分析表明,裂纹源大致和主应力方向呈45°,弹簧使用过程承受着剪切应力和拉应力的共同作用.讨论了实际应力、显微组织等对弹簧的使用寿命的影响.显微组织中存在贝氏体组织,直接导致弹簧的硬度大幅度下降,从而会造成弹簧的主要力学指标切变模量以及疲劳强度等大大降低.分析结果认为,弹簧是在较大的应力作用下,由内壁锥面损伤处引发裂纹源,沿主应力方向产生的断裂.显微组织较差、硬度偏低对弹簧的早期断裂有重大的影响.     

气门弹簧断裂分析

通过对断裂气门弹簧进行硬度、化学成分、扫描电镜和能谱仪等分析,其结果表明,气门弹簧断裂是由于残存在弹簧表面的清洗剂腐蚀作用造成的.喷丸过程中的撞击凹坑也促进了这一过程的发生.     

60Si2MnA钢片弹簧断裂失效分析

某60Si2MnA钢片弹簧在使用10h后出现批量断裂,对断裂片弹簧进行了化学成分分析、硬度测试、金相检验以及断口微观形貌观察,以查明其断裂原因。结果表明:片弹簧断裂是由于在酸洗、电镀过程中析氢反应的发生,使其产生氢脆现象;同时由于热处理工艺过程控制不当,造成组织异常,硬度高于技术要求,加快了其氢脆倾向,最终导致片弹簧在外应力作用下发生氢脆断裂。     

列车车轮辐板断裂原因分析

通过化学成分分析、宏观及微观检验、力学性能测试、有限元分析等方法对列车车轮辐板断裂的原因进行了分析。结果表明:车轮辐板内侧面存在明显的点腐蚀,在辐板表面交变应力的作用下发生疲劳开裂,当疲劳裂纹扩展到一定长度时车轮发生断裂。点腐蚀不仅破坏了辐板表面喷丸加工所形成的高硬度残余压应力层,并在点蚀坑内部造成应力集中,形成疲劳裂纹源。因此车轮在运输、存放及使用过程中应注意防护,避免腐蚀的发生。     

Investigation into recurring military helicopter landing gear failure

The skid landing gear of a military helicopter failed while the helicopter was moored on the ground at the airport. The rear cross tube of the landing gear assembly was found fractured into two separated pieces. The fracture occurred in the right flange of the rear cross tube, where a connection with the spring tube is established using a clamp. The initial visual inspection of the fracture zone revealed a presence of heavy corrosion and significant damage of the anti-corrosion protective layer on the outer surface of the flange of the rear cross tube. Fractographic analysis highlighted corrosion as the main cause of the failure. Evidence was found to show that the fracture was initiated from corrosion pits located on the exterior, underside of the cylindrical part of the flange. Metallographic examination discovered corrosion pits with micro cracks and multiple branched secondary cracks in the crack origin area, indicating the occurrence of stress corrosion cracking. Chemical analysis of the corrosion deposits showed the presence of sodium, chlorine, calcium and sulfur. The stress analysis of the helicopter landing gear assembly, carried out by means of finite element method, confirmed that the crack origin was located at the area with the maximum tensile stress in the flange.     

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。     

钻杆接头台肩根部刺漏失效分析

通过力学性能测试、化学成分分析、金相检验和断口分析等方法对某井发生的钻杆接头台肩根部刺漏失效原因进行了分析。结果表明：材料冲击功低于标准要求,接头台肩根部受到严重腐蚀,形成大而深的腐蚀坑,在交变应力作用下,裂纹萌生于腐蚀坑底部,并迅速扩展,最终导致钻杆接头发生早期腐蚀疲劳失效。     

加氢装置中管道法兰密封钢圈的断裂分析

采用宏观及断口分析、金相与硬度检测、扫描电镜与能谱分析等方法,对加氢装置中管道法兰密封钢圈的断裂原因进行了分析。结果表明,断裂是由于管道中气体所含的H2S对钢圈内表面产生严重点蚀和钢圈组织不合理所致。当法兰螺栓紧固时,钢圈内表面所受的强大拉应力造成蚀坑底部的应力集中而形成裂纹源,而钢圈硬脆的淬火组织促进了裂纹在基体中的快速扩展,最终导致断裂。     

Corrosion induced fatigue failure of railway wheels

Two AAR class B rolled wheels for locomotives failed after about two years of service. The fracture surfaces of the failed railway wheels were examined. The examination showed that there were corrosion pits on the back plate surface of the failed wheels. All of the fracture originated from corrosion pits at the wheel plate surface and fatigue propagated to a length and then expanded rapidly by cleavage. Fatigue specimens cut from the wheel plate were corroded with different time duration in an artificial corrosion environment to simulate the corrosion states of the wheels. The fatigue properties of the un-corroded specimens and the specimens corroded with different times were tested in air. Finite element method (FEM) and Sines' criterion were used to evaluate the safety of the wheels. The results showed that the wheel plates without corrosion pits exhibited an excellent resistance to failure. The corrosion pits could promote the initiation of fatigue cracks and drastically lower the fatigue limits of corroded specimens. The real root cause of the failure of the subject wheels was due to the corrosion pits at the wheel plate surfaces. A critical depth of the corrosion pit on the wheel plate 300 μm was recommended. Protection of the wheel plate was important to ensure the safety of wheels and the rust prevention oil was recommended to be applied on the wheel plate regularly.     

The failure of an armour faced conveyor connector

The combined use of modern metallurgical techniques for fracture examination, laboratory test data and fracture mechanics calculations allows metallurgical failures to be examined in a quantitative manner. Complex load histories and environments can result in more than one sub-critical cracking mechanism occurring in a component. Quantitative understanding of the rate determining cracking process is a necessary prerequisite to rectifying the problem. The following case study describes a connector from an armour faced conveyor which failed in service. The failure investigation involved fractography, stress analysis, material property evaluation and fracture mechanics calculations. Fractographic evidence indicated a stress corrosion failure mechanism. Calculations of critical crack sizes showed that stress corrosion cracking alone could not account for the fracture. It was concluded that the failure was due to a sequence of three cracking processes which preceded unstable ductile fracture. Firstly, frictional heating caused rubbing or quench cracks typically 0.5–1 mm deep. Secondly, corrosion fatigue cracks grew several millimetres allowing the third fracture process, stress corrosion cracking, (SCC) to initiate and grow. In the situation described here, this process was much faster than corrosion fatigue. The influence of defect size due to rubbing cracks and the influence of K_ISCC have been compared with the corrosion fatigue life of the component. An increase in K_ISCC and hence critical defect size for SCC has been shown to increase the corrosion fatigue life of the component by a large factor. A change in design would also alleviate the problem of SCC by reducing the static stress, which is the driving force for SCC.     

Challenges in modelling the evolution of stress corrosion cracks from pits

The evolution of stress corrosion cracks from pits is important in many industrial applications but continues to be a challenge in both measurement and prediction. Life prediction in these circumstances has to account for pit growth kinetics, the conditions for the transition from pits to cracks, and the growth rate of cracks in the short and long crack domain. An example of importance is the performance of steam turbine rotors in power generation. Although stress corrosion failures are comparatively rare, the consequences can be severe and occasionally catastrophic. Consequently, considerable effort is being focused on evaluating the effect of operational variables on pitting and crack growth and in developing an improved basis for structural integrity assessment. A preliminary mathematical model based on deterministic equations with statistically variable input parameters was developed for simulating the evolution of the pit depth distribution at different exposure times, and the transformation to stress corrosion cracks was based on the Kondo criteria. The model predicted some features of the damage well but recent novel measurements of the evolution of stress corrosion cracks from pits combined with finite element analysis of the strain distribution suggest that the transition from a pit to a crack is more complex than can be accounted for by the Kondo approach.