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This research was focused on the failure analysis of a cracked SS304 stainless steel elbow from a chemical plant. The service life of the elbow was 2 years and 8 months. The elbow was welded with two straight pipes at two ends. Cracks were located mainly at positions close to the weld joint and the arc where very strong tensile residual stress existed. Corrosion pits were distributed on the inner surface of the elbow. Cracks were initiated from the corrosion pit bottoms. Branching was observed from the cracks. Cl and S elements were detected in corrosion products from the corrosion pits and the cracks by EDS. SEM results reviewed the intergranular and transgranular brittle nature of the fracture. It is concluded that stress corrosion cracking was the main reason for the cracking of the elbow. [ABSTRACT FROM AUTHOR]

• Failure analysis of bearings over the past 20 years are summarized and reviewed. • Different failure modes and mechanisms of bearings are classified and introduced. • It is described in details based on the corresponding characteristics of the failure mechanisms. • Wear and fatigue are the most common failure modes of bearings. • The main causes of failure are summarized. This work reviews the failure modes, mechanisms and causes of bearings in mechanical equipment. Bearings are among the most important basic mechanical components. Their operating conditions directly affect the safety and stability of mechanical equipment. In industries, users have very high requirements for the quality, accuracy, and service life of bearings and pay much attention to the selection, installation, use, and maintenance of bearings. However, bearing failures during operation has not been eliminated. Possible failure modes of bearings include fracture, corrosion, deformation and wear have been reviewed. Failure analysis is crucial for the safe operation of bearings. By identifying the modes and causes of failure, effective measures can be proposed to improve the service life of the bearings and eliminate potential accidents. Herein, the contributions of various researchers to bearing failure analysis over the past 20 years are reviewed. The failure modes and mechanisms of the bearings are classified and discussed. Typical bearing failure cases are discussed. According to statistical results, wear and fatigue are the most common failure modes of bearings, as bearings are affected by cyclic loads, friction, and lubrication during operation. Incorrect assembly, use, and maintenance is the main causes of bearing failure. The aim of this review is to provide information on systematic failure analysis of bearings, identify the failure mechanisms under different conditions, and propose an effective plan to improve the bearing reliability, reducing the occurrence of similar bearing failures. [ABSTRACT FROM AUTHOR]

Cracking of an oil inlet pipe in an electrohydraulic governing system was detected and analyzed to determine its failure mechanism. Microscopic analysis methods, such as the scanning electron microscopy and energy-dispersive X-ray spectrum, were applied to obtain the effective information. Visual and micro-examination showed that the pipe suffered a brittle cracking at the elbow part. Corrosion pits and branched cracks had formed in the outer surface of the pipe. The element of chlorine was detected both in the corrosion pits and the corrosion products inside the cracks. In addition, the cracks were found initiating from the bottom of the corrosion pit. Transgranular cracking feature was identified for the cracks. All the collected evidences suggested that the EH oil pipe fractured due to the combination of a chloride pitting corrosion and a stress corrosion cracking failure. [ABSTRACT FROM AUTHOR]

Failure analysis was carried out on the stainless steel hooks in a brick kiln to confirm its failure mechanism. The collected evidence indicated that chemical composition of the stainless steel hook was consistent with the standard requirements for 304 stainless steel. The metallographic test showed that the microstructure of the stainless steel hook in the non-damaged areas was normal. However, serious chromium segregation which might be caused by secondary phase formation at the high temperature was found in the damaged material. This dramatically reduced the corrosion resistance of the material. The corrosion elements such as oxygen and sulfur were found playing a major role in the corrosion process. Thus, the failure of the stainless steel hook was induced by corrosion due to the chromium segregation and the existence of corrosive elements including oxygen and sulfur. [ABSTRACT FROM AUTHOR]

Cracks in nano-scale are common defects in the 2D materials fabricated by a chemical vapor deposition method. Mechanical performance of 2D materials might be affected significantly due to the presence of nano-cracks. In this work, the mechanical performance and failure behavior of h -BN sheets with nano-cracks were studied using molecular dynamics methods. The relationship between the mechanical properties of h -BN sheets and the type or size of cracks was analyzed. The effect of temperature and strain rate on the mechanical behaviors of h -BN sheets was discussed. Results showed that when the crack size was larger than the threshold value, the Young’s modulus of h -BN sheets decreased with the increase of the crack size linearly. The increasing crack size resulted in faster decrease of the Young’s modulus of the zigzag h -BN sheet than that of the armchair h -BN sheet. The fracture strength decreased rapidly with the increasing crack size first. Then, when the crack size reached a critical value, change of the fracture strength become minor. The mechanical properties of h -BN sheets with cracks were sensitive to the variation of temperature and strain rate. The information obtained in this work would be useful for estimating the mechanical performance and failure mechanism of h -BN sheets in future application. [ABSTRACT FROM AUTHOR]

• Failure analysis was performed to find out the failure cause of the crankshaft. • Evidences indicated the mechanism of the premature failure was fatigue failure. • Fatigue fracture initiation was induced by the dense inclusions. A sport utility vehicle crankshaft was premature failure after a short service life of about 3 years. The fracture took place at the transition arc between the crankpin and the journal. The fracture surface has an angle of 45° inclination with the axial direction of the crankshaft, which is in accordance with the maximum primary stress plane caused by the torsion. A fractographic study indicates that the fracture surface exhibits a brittle fracture morphology reflective of a low toughness of the material. Macro beach marks and micro striations indicate that the failure mechanism of the crankshaft is fatigue failure. Metallographic analysis shows that flake pearlite and reticular ferrite are the characteristics of the microstructure near the fracture surface, which may lead to the lower plasticity of the material. Reticular ferrite is induced by the heterogeneous inclusion with a chemical structure of CaO-MnS complex. The weaker ferrite destroys the continuous matrix material and reduces the plasticity of the material, resulting in a brittle fracture. Collected evidence reveal that a series of manganese sulfide inclusions are distributed near the crack initiation. According to the quantification analysis of inclusion distribution, the density of inclusions is great enough to act as the initiation of cracks. Moreover, finite element analysis indicates the stress concentration induced by the geometry structure is less than the inclusion. Given all of that, the failed crankshaft is supposed to be initiated by the harmful inclusions. Therefore, it is recommended that rigorous testing of the inclusions and improving the heat treatment quality of crankshafts are effective ways to solve the problem. [ABSTRACT FROM AUTHOR]

The failure mechanism of a clutch shell made from SPCC nitrided steel was analyzed. The component sustained multiple brittle fractures during assembly. Under SEM examination, the fracture surface was found to have facet and cleavage grain appearance. It was predicted that the cleavage fractures started from sites of intergranular fractures. XRD results showed that the nitriding layer contained Fe 3 N (60 wt.%) and Fe 4 N (40 wt.%). It is noted that Fe 3 N is more brittle than Fe 4 N. An impact test was carried out to compare the impact resistance of the failed and normal components. EDS analysis was also carried out, and it was found that the fracture surface contained zinc, which was not an element specified for the SPCC steel or the nitriding salt. As the salt bath nitriding process operated at a temperature higher than the melting point of zinc, failure was most likely due to liquid metal zinc induced embrittlement, as a result of localized salt bath material contamination with zinc. [ABSTRACT FROM AUTHOR]

• The present literature survey reviewed and summarized failure analysis of shafts over the past 20 years. • The different failure modes and mechanisms are classified, and prevention and corrective actions are listed. • The bearing life, service load, macroscopic fracture characteristics and service environment of shafts are introduced in detail. • The main causes of fatigue failure are summarized. Shafts are core mechanical components of equipment. These play a key role in supporting the rotating device and transmitting motion, torque, or bending moment. The quality and performance of shafts are of high significance for the normal and safe operation of the equipment. Failure analysis is of high significance for the safe operation of mechanical equipment and accident prevention. By identifying the modes and causes of failure, effective measures can be proposed to improve the service life of shafts and eliminate potential accidents. In this work, failure analysis cases reported for shafts in the past 20 years are reviewed. Typical failure modes including fracture, corrosion, wear, and deformation failures are summarized. Fatigue fracture is the most common failure mechanism of shafts owing to the influence of cyclic loads on shafts under normal working conditions. The fatigue failure characteristics, environmental factors, wear fatigue, and causes of fatigue failure of shafts are described in detail. The objective of this review is to provide systematic failure analysis information of shafts and thereby, aid engineering communities to identify the failure mechanisms of shafts under different conditions. [ABSTRACT FROM AUTHOR]

• The fractured droppers due to fatigue crack propagation were analyzed. • The initial region was located at a notch near the bending place of droppers. • The residual strength will increase as the increasing of the chamfering radius. • Improvement the manufacturing tool was an effective way to improve the service life. The failure mechanism of the fractured droppers used in power supply systems for subway was analyzed with various technologies. Collected evidences indicated that the droppers fracture due to fatigue crack propagation. The chemical composition and mechanical properties of the dropper material were both complied with the normal 304 stainless steel standard. The metallographic examination showed that the microstructure of the failed dropper was normal. The initial region of the fatigue damage was located at a notch near the bending place. Under the cyclic loads caused by the up and downs of the dropper when the train passes by, the crack initiated, propagated and ruptured finally. Results of finite element simulations suggested that the residual force of the droppers will increase as the chamfering radius is. Improving the manufacturing tool was an effective way to reduce the stress concentration and to increase the residual force of the droppers, thus, to improve the service life of the droppers. [ABSTRACT FROM AUTHOR]

Premature failure of headspan suspensions was mainly attributed to the fracture failure of the droppers. Various experiments were conducted to explore the fracture failure mechanism of the droppers used in headspan suspensions. Four notches along the axial direction of the dropper, corrosion pits and corrosion products were observed by visual examination. Although the axial cracks have little effect on the structural strength, they make it easier to form corrosion environment in the notches than on the exposed outer surfaces. Furthermore, energy spectrum analysis indicated the presence of chlorine and sulfur both in the corrosion products inside of axial cracks and corrosion pits. Meanwhile, typical microstructural features of intergranular cracking and corrosion products were observed by the scanning electron microscopy. Finally, finite element analysis was conducted to characterize the stress distribution near the corrosion pits. The simulation results showed that obvious stress concentration was formed near the corrosion area. All the results indicated that the droppers failed due to the combination of pitting corrosion and stress corrosion cracking. [ABSTRACT FROM AUTHOR]

The failure mechanism of the connectors assembled on the isolating switches was analyzed. Under SEM examination, the fracture surface showed obvious crack propagation traces. Beach marks with a reverse bending pattern were found on the fracture surface. Fatigue striations, which were the micro-evidence of fatigue, were observed clearly on the propagation zone. Both the metallurgical examinations and XRD analysis showed that the material of the connector only contained the austenite phase. The collected evidence suggests that that failure of the connectors was induced by fatigue. The vibration of the specimen during transport was the most probable source of the alternating stress. The stretching assembly stress of the connector could increase the fatigue stress ratios of the specimen. Defects existing in the material might destroy the continuity of the material substrate and reduce the fatigue performance of the material. [ABSTRACT FROM AUTHOR]

• The fractured spring due to bending fatigue crack propagation were analyzed. • The failed spring has obvious external defects. • The precise characterization of the defects was measured by CT. • The effect of the defect on the stress distribution was analyzed. The torsion spring is an important component for vehicle steering system. The torsion spring in this study was manufactured using high quality carbon structural steel. In order to study the failure mechanism of the spring, a series of experiments were carried out. All the collected evidences indicated that the spring fracture was due to fatigue crack propagation. At the same time, an obvious machining defect was observed on the inner surface of the ring. There are two crack initiation regions which are located at the areas near and opposite side of the machining defect. Under the cyclic loading induced by the repeated turning, the crack propagated and fractured finally. In order to analyze the effect of the machining defect on the fatigue failure, a computed tomography experiment was conducted. The precise characters of the defect were measured by computed tomography experiments. Then a finite element model was established according to the actual defect size and the stress distribution of the torsion spring was analyzed. The results showed that the local stress of the spring and the area of stress concentration are closely related to the machining defect and the gap between the spring and the two cylindrical objects. Under the actual condition of the torsion spring in service, the severe stress was located on the fracture location, which indicating that the machining defect is the efficient cause of spring failure. [ABSTRACT FROM AUTHOR]