Case studies in engineering failure analysis最新文献

The analysis of an abnormal failure of forklift forks is presented in this work. The investigation results suggested that failure occurred due to fatigue mechanism followed by sudden overload fracture. The orientation of fatigue fracture indicates abnormal lifting operation, favouring crack initiation from outer fork area which is the compression designed zone. Moreover, various surface flaws and weakness areas (such as surface marks, decarburized microstructures and weld zones) identified on the outer fork zone, compromise fatigue strength inducing premature crack nucleation and fast growth towards final failure.

Failure analysis of a shaft used in a bridge crane has been carried out. The shaft fractured in the keyway with evidence of fatigue. Chemical analysis, micro-structural characterization, fractography, hardness measurements, and finite element simulation were used for the analysis. The microstructure was predominantly tempered martensite; large amounts of oxides, micropores, and manganese sulfide inclusions were found. The geometry of the keyway also promoted the initiation crack because the width and height were erroneously designed. It was concluded that all these factors produced fatigue failure. It is recommended to first guarantee the chemical composition and microstructure of the material. Secondly, use magnesium or calcium additions in the steel casting process to obtain better shape control of inclusions and, finally, accomplish the geometric parameters recommended by the standard to avoid high stress concentration factors.

This paper investigated the brittle fracture mechanism of a grade E cast steel knuckle that is one of the key components of the coupler for railway wagon by using scanning electronic microscope, optical microscope, energy dispersive spectroscopy as well as mechanical property testing methods. It is found that large amounts of developed coarse dendrites and shrinkage porosity existed in the knuckle's microstructure, the plasticity and impact toughness of the knuckle entity are very bad and far below that of the Keel block represented this knuckle. Apparently, the shrinkage porosity resulted in the knuckle unsound metallic matrix and poor mechanical properties. The fracture morphology mainly shows the characteristic of cleavage, quasi-cleavage fracture as well as a little ductile fracture, so the failure of the knuckle can be attributed to brittle fracture distinctly. Moreover, a welding repair area with high hardness is also found in the fracture region, which might initiate micro-cracks on the surface of the knuckle. As a result, it can be inferred that under an impact load that did not exceed material fracture limit, the micro-cracks initiated from weld repair zone propagated rapidly into the inner matrix by continuously fracturing the dendrites along shrinkage porosity regions until the knuckle failed instantly.

The tapered joints of modular hip implants are prone to fretting and crevice-corrosion. This can lead to total failure in under a year, especially for heavier, more active implant recipients. In this study, fractography of a failed Profemur Z implant showed that a life limiting fatigue crack was nucleated on the anterolateral surface of the implant's neck. The fatigue crack nucleation area appeared to have both more fretting damage and a higher corrosion rate than on other surfaces of the neck.

Failure of a subsea crude oil API 5L X52 steel pipeline which led to oil leakage has been reported to occur after 27 years in service. Some leaks were found to form at the bottom of the horizontal API 5L X52 steel pipeline near an elbow section which connected the pipeline to a riser. The present investigation aims to analyze the main cause of failure by conducting standard failure analysis methods including visual examination, chemical and mechanical characterizations, metallurgical examinations using optical microscopy in combination with scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) analysis and corrosion test using a three-electrode potential technique. Results of this investigation suggest that the cause of failure is electrochemical corrosion combined with mechanical process known as flow-induced corrosion. The failure mechanism is discussed with specific attentions are paid to fluid flow rate and chloride-containing water phase.

Evaluating and analyzing the risk in the mining industry is a new approach for improving the machinery performance. Reliability, safety, and maintenance management based on the risk analysis can enhance the overall availability and utilization of the mining technological systems. This study investigates the failure occurrence probability of the crushing and mixing bed hall department at Azarabadegan Khoy cement plant by using fault tree analysis (FTA) method. The results of the analysis in 200 h operating interval show that the probability of failure occurrence for crushing, conveyor systems, crushing and mixing bed hall department is 73, 64, and 95 percent respectively and the conveyor belt subsystem found as the most probable system for failure. Finally, maintenance as a method of control and prevent the occurrence of failure is proposed.

In this case study, a failed railway rail which was used for heavy cargo trains was investigated in order to find out its root cause. The macroscopic beach marks and microscopic fatigue striations were not observed by macro and microscopic observations. The chevron patterns were observed by macro observations. The crack origin was at the tip of chevron patterns. The fan-shaped patterns, cleavage step and the river patterns were observed at the crack origin, which demonstrated the feature of cleavage fracture. The metallurgical structures at the crack origin were pearlite and ferrite networks. The crack is supposed to be initiated from the weaker ferrite networks. Given all of that, the failed railway rail is considered to be caused by overload. It is of great importance to improve the welding technology, and control the load of train in order to prevent similar failure in future.