Papers by Keyword: Failure Analysis

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Authors: Qun Wang, Yu Lei Li, Jin Jun Tang, Xing Wang, Xiao Yu Jin, Zi Yu Liu
Abstract: Based on the understanding of material characteristics and interaction between projectile and target, a lightweight hybrid composite armor target consisting of alumina ceramics pellets and ultrahigh molecular weight polyethylene (UHMWPE) was designed and prepared. The target areal density of the armor panel was 7.5 g/cm2. The standard size of the armor panel was 150mm×150mm×43mm. The Ballistic Performance of Alumina/UHMWPE composite armor against an impact of 12.7 mm armor piercing (AP) projectile was investigated at the nominal velocity of 818 m/s. The energy absorbing mechanism revealed that the armor was able to protect against the projectile, together with weight saving.
Authors: Wei Shi, Yi Shi Lv, Zhong Bing Chen, Ling Hui Meng, Li Jun Zhang, Jian Lin Zhang
Abstract: Characteristics and forming causes of the cracks in welded joint of 15Cr1Mo1V steel serviced 70000h are investigated by mechanical and chemical testing and crack morphology observation. Results show that the cracks initiate from welded metal or coarse grain heat affect zone (CGHAZ) near fusion line, and there are three kinds of defects observed in the crack region, which are macrocracks, microcracks and voids. According to the forming position, process and morphology of the cracks, it is estimated that the cracks are a kind of stress relief crack (SRC). The main reasons of the cracking are because of residual stress caused by improper temperature field during post welding heat treatment, strong stress concentration caused by welding structure, additional stress caused by abnormal hangers & supports and decreased ductility of welded joint in service. The SRC in welded joint can be avoided through optimizing the welding process and postweld heat treatment(PWHT) process to ensure enough critical ductility deformation ability εc and avoiding and reducing stress concentration and additional stress to decrease ductility deformation εP of welded joint which make εc>εp consistently.
Authors: P. Promdirek, Somrerk Chandra-Ambhorn, C. Tongtae, C. Anantawirun, C. Buaphuen
Abstract: In the present study, a thermowell made of Incoloy 800 (33Ni-21Cr-46Fe) was used as a part to cover and therefore to protect a thermocouple inserted in a tube used in petrochemical process. It was then subjected to the atmosphere in the tube containing moving carbon particles at 900°C. One of the critical failure types observed was the combination of both solid particle erosion and oxidation. Thermowell degradation, which accounted for the corrosion-affected-erosion of materials, was significantly observed in the area where impingement at the head surface area of thermowell. The physicochemical characterization revealed that the thermowell consisted of two layers. The inner one is the incoloy 800 base metal, whereas the outer layer was clad with a cobalt base superalloy. Kinetic of oxidation of both materials in each layer, which was performed in air at 1173K presented the different parabolic rate. Metal oxide and surface morphology of thermowell, which was investigated in the simulated condition, were then examined by XRD, OM and SEM. A finite element software was furthermore applied to simulate the flow direction and the velocity of the particles. It was found that the maximum speed of particles (180 m s-1) was at the surface where the impingement angle of particle is 90°. Comparing to the failure of themowell in service, it was concluded that the failure of thermowell depends primarily on the impingement angle of particle. Design of the shape of thermowell, as well as the cladding with the higher erosion-corrosion resistance materials, were recommended to be carried out to improve the erosion-corrosion resistance of this part.
Authors: Jin Wei Fan, Xiao Long Yi, Chao Liu, Yong Jun Liu
Abstract: CNC cylindrical grinding machine reliability is an important performance indicators, the level of reliability will directly affect the use of CNC cylindrical grinding machine. Reliability of the traditional classification method is not clear, standards are not uniform, the paper application taxonomy for 12 CNC grinding machines from September 2012 to July 2014 for two years more than 600 pieces complete failure and repair data for statistical analysis to identify a greater impact on the overall reliability of the fault location and cause of the malfunction. According to the probability of occurrence of each failure mode, the severity of harm's comprehensive evaluation of the degree of fault of each site, identify the weak links of the whole system. As a result, the reliability of CNC cylindrical grinding machine will be greatly improved.
Authors: Asim Ghaffar, Mahir Hassan
Abstract: In this study, ship position optimization is conducted on a cable-driven parallel manipulator (CPM) operating inside deep sea. The workspace and stiffness of the manipulator is analysed as well as cable tensions after failure are reported and a combined criterion of ship position optimization has been established. Based on the criterion, the CPM will have maximum workspace and stiffness as well as minimum cable tensions in case of a failure. The optimization is demonstrated with six, eight and ten ships CPMs. The performance of the system is improved with higher number of cables in a CPM.
Authors: Miao Shang, Guo Min Lin, Wen Guang Zhang, Fei Zhou
Abstract: The common failures of three-phase motor are described, the specific reasons of failure are analyzed, the treatment of common failures are illustrated, the motor repair methods are summarized, the troubleshooting process is pointed out, the developing direction of common troubleshooting is put forward. For saving production resources, improving the efficiency of enterprise's safety production and economic benefit, it has important guiding significance.
Authors: Diane Perle Sadik, Jang Kwon Lim, Juan Colmenares, Mietek Bakowski, Hans Peter Nee
Abstract: The temperature evolution during a short-circuit in the die of three different Silicon Carbide1200-V power devices is presented. A transient thermal simulation was performed based on the reconstructedstructure of commercially available devices. The location of the hottest point in the device iscompared. Finally, the analysis supports the necessity to turn off short-circuit events rapidly in orderto protect the device after a fault.
Authors: Huan Xin Cheng
Abstract: Some composite material characteristics are summarized and main advantages of composite material are analyzed in the paper. In addition, stress analysis methods, failure rules and design techniques of a pressure vessel are also recommended. Finally, the importance of composite material has been summed up . The paper has some reference values to investigation of a composite material pressure vessel.
Abstract: A high strength bolt with hot dip galvanizing treatment failed shortly after being installed for two days on a padeye of mooring dolphin. The bolt was installed with increasing stress on the second day in which the value was nearly twice. Investigation results showed the bolt fractured with the nut head separated from the pin. Corroded fracture surface with brittle characteristic and no plastic deformation observed dominating the failed area. Characterization of hardness and chemical composition followed with microstructure and fractography observation on the fracture surface then conducted in order to analyze the reason for this brittle fracture occurrence. Results indicate that, while the bolt conforms to the material specification in term of chemical composition, the hardness value was high. The microstructure observation reveals a transgranular crack propagation and cleavage failure occurred. The cleavage failure was clearly observed under fractography observation using scanning electron microscope. Failed galvanize layer due to mechanical failure becomes preferential site for hydrogen evolution in marine environment, which leads to hydrogen diffusion into the matrix, thus results in hardness increase. The increasing stress during installation become detrimental to the bolt and facilitate the hydrogen induce cracking. Detrimental effect of hot dip galvanize layer is pointed out in the application of high strength material in marine environment.
Authors: Zhen Hua Zhou, Dong Jian Xue, Sheng Jie Qian
Abstract: Failure analysis was carried out to find out the causes of burst on water-cooled wall tubes elbow for circulating fluidized bed (CFB) boiler.Through macro-observations, chemical composition analysis, macro structure observations,grain size measurements and water quality examinations, it can conclude that the high pH value of boiler water at the fire-facing side of weld dense phase zone will lead to alkali concentration that will cause alkali corrosion. The existence of residual stress in elbow under strong alkaline environment will cause alkali stress corrosion. Research results show that the tube failure is caused by both alkali corrosion and alkali stress corrosion. Strengthen water quality monitoring and elimination of stress can effectively prevent the alkali corrosion and alkali stress corrosion.
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