共查询到14条相似文献,搜索用时 15 毫秒
1.
陈渝 《理化检验(物理分册)》2012,(8):551-554
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。 相似文献
2.
We present a procedure of studying the fatigue strength of crankshafts of a two-cylinder motorcycle engine. The use of a unique loading scheme provided obtaining patterns of in-service fracture of the tested crankshafts. The results of comparative fatigue tests of some series of crankshafts of various design and technological versions, namely, nonhardened crankshafts with a fillet and hardened and nonhardened crankshafts without a fillet (zero fillet) are given and analyzed. 相似文献
3.
Failure Analysis of a Vehicle Engine Crankshaft 总被引:1,自引:0,他引:1
An investigation of a damaged crankshaft from a horizontal, six-cylinder, in-line diesel engine of a public bus was conducted
after several failure cases were reported by the bus company. All crankshafts were made from forged and nitrided steel. Each
crankshaft was sent for grinding, after a life of approximately 300,000 km of service, as requested by the engine manufacturer.
After grinding and assembling in the engine, some crankshafts lasted barely 15,000 km before serious fractures took place.
Few other crankshafts demonstrated higher lives. Several vital components were damaged as a result of crankshaft failures.
It was then decided to send the crankshafts for laboratory investigation to determine the cause of failure. The depth of the
nitrided layer near fracture locations in the crankshaft, particularly at the fillet region where cracks were initiated, was
determined by scanning electron microscope (SEM) equipped with electron-dispersive X-ray analysis (EDAX). Microhardness gradient
through the nitrided layer close to fracture, surface hardness, and macrohardness at the journals were all measured. Fractographic
analysis indicated that fatigue was the dominant mechanism of failure of the crankshaft. The partial absence of the nitrided
layer in the fillet region, due to over-grinding, caused a decrease in the fatigue strength which, in turn, led to crack initiation
and propagation, and eventually premature fracture. Signs of crankshaft misalignment during installation were also suspected
as a possible cause of failure. In order to prevent fillet fatigue failure, final grinding should be done carefully and the
grinding amount must be controlled to avoid substantial removal of the nitrided layer. Crankshaft alignment during assembly
and proper bearing selection should be done carefully. 相似文献
4.
针对某型号发动机曲轴疲劳试验未达到规定载荷累计循环次数,早期疲劳开裂的问题,采用化学成分分析、力学性能测试、断口分析、金相检验和表面氮化层检验等方法对其进行了失效分析。结果表明:该曲轴为疲劳开裂,曲轴过渡圆角处的高应力区存在大尺寸硬质非金属夹杂物是导致曲轴过早疲劳开裂的主要原因;另曲轴过渡圆角处加工质量差,使得该处应力集中加剧,也是致使该曲轴过早疲劳开裂的重要因素。 相似文献
5.
利用扫描电子显微镜及附带的能谱分析仪对飞机发动机尾喷口调节片断口进行了微观分析研究。结果表明:调节片边缘的损伤特征以磨损为主,而中部则以接触疲劳为主,疲劳裂纹易在微动区产生。根据上述结果讨论了促使疲劳裂纹萌生的因素,即循环应力和摩擦力引起材料表层塑性变形,以及磨损破坏了材料表面的完整性,造成裂纹尖端应力集中效应。 相似文献
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8.
Michael J. Mullen Arthur H. Griebel John M. Tartaglia 《Journal of Failure Analysis and Prevention》2008,8(1):12-19
To Clean Or Not To Clean? In many failure analyses, adherent rust limits the scope of the fracture surface examinations and presents dilemmas for the failure analyst. The rust must be removed to identify fracture initiation sites and crack propagation modes, and the cleaning methodology varies with service life and type of environmental exposure that the component experienced. In this study, failure analysts examined laboratory fracture samples in a scanning electron microscope (SEM). The fractures were then subjected to controlled rusting conditions, and subsequently varying exposures to inhibited acid were used to remove the rust. The fracture surfaces were again examined in the SEM, after rust removal. The ideal immersion time in the inhibited acid varied with the desired inspection. Although large fracture surface features remained visible after long cleaning times, fine features were damaged by even brief exposure to inhibited acid. However, inhibited acid cleaning is extremely helpful and remains the only means of obtaining useable fractographic results in many situations. 相似文献
9.
Austenitic stainless steel pipelines are used as a conduit for gaseous nitrogen to ejector flow lines of propulsion engine
test facility. Leakage was noticed near a welded T-joint of such a pipeline system that was in service for years. Detailed
metallurgical investigations were carried out to understand the cause of failure. Synergistic effect of chloride ions, thermal
stresses from welding, and the presence of sensitized grains of the material led to stress-corrosion cracking of the steel.
This paper highlights details of investigation. 相似文献
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11.
Susil K. Putatunda Codrick MartisJames Boileau 《Materials Science and Engineering: A》2011,528(15):5053-5059
In this investigation, a new low alloy and low carbon steel with exceptionally high strength and high fracture toughness has been developed. The effect of austempering temperature on the microstructure and mechanical properties of this new steel was examined. The influence of the microstructure on the mechanical properties and the fracture toughness of this steel was also studied.Test results show that the austempering produces a unique microstructure consisting of bainitic ferrite and austenite in this steel. There were significant improvement in mechanical properties and fracture toughness as a result of austempering heat treatments. The mechanical properties as well as the fracture toughness were found to decrease as the austempering temperature increases. On the other hand, the strain hardening rate of steel increases at higher austempering temperature. A linear relationship was observed between strain hardening exponent and the austenitic carbon content. 相似文献
12.
The characteristics of friction-welded joint between commercially pure-titanium (CP-Ti) and low carbon steel, of which was subjected to post-weld heat-treatment (PWHT), was investigated. When the joint was made with friction speed of 25?s?1, friction pressure of 200?MPa, friction time of 2.5?s and forge pressure of 250?MPa, it had the same tensile strength as that of the CP-Ti base metal. The joint had no intermediate layer consisting of intermetallic compound (IMC interlayer) at the weld interface. The joint efficiency of the joint subjected to PWHT decreased with increasing heating temperature and its holding time, and the joint fractured at the weld interface although it had no IMC interlayer. The void was generated on the weld interface of the joint during PWHT process. 相似文献
13.
An extensive study on the fatigue performance of friction stir welded DH36 steel was carried out. The main focus of this experimental testing programme was fatigue testing accompanied by tensile tests, geometry measurements, hardness and residual stress measurements, and fracture surface examination. The S–N curve for friction stir butt welded joints was generated and compared with the International Institute of Welding recommendations for conventional fusion butt welds. Friction stir welds of marine grade steel exceeded the relevant rules for fusion welding. This newly developed S–N curve is being proposed for use in the relevant fatigue assessment guidelines for friction stir welding of low alloy steel. Fracture surfaces were examined to investigate the fatigue failure mechanism, which was found to be affected by the processing features generated by the friction stir welding tool. 相似文献
14.
本文利用悬臂梁试验机,测定了40Cr 钢的断裂韧性 K_(1c)和在3.5%NaCl溶液中,充氢达饱和条件下的氢脆临界应力场强度因子 K_(IH),以及在不同的应力场强度因子 K_(Ii)下的裂纹扩展速率 da/dt,并结合 SEM 对断裂形态进行了分析。 相似文献