Sandoval, Oscar R.Machado, Luiz Henrique JorgeHanriot, Vitor MouraoTroysi, Fernanda...
19页
查看更多>>摘要：The technology of internal combustion engines has improved to meeting international regulations, applying turbocharging as an effective method. However, the works under extreme conditions requires strict maintenance plans, since when it fails, it completely deteriorates the functioning of the turbocharged engine. In this work, two procedures are used to characterize some operating failures. Faulted blades are introduced in the compressor to simulate typical failures observed in automotive turbochargers. Four centrifugal compressors mounted with perfect and defected blades are used to compare changes during three failures steps, using experimental vibration and acoustic analyses. The vibratory response of the compressor is obtained by analyzing the vibration signals measured on the turbochargers. Furthermore, sound pressure measurements are performed to evaluate the noise radiation based on an acoustic wave decomposition technique. The experimental results rendered for the vibratory response and noise generation from the turbocharger compressor permit the characterization of automotive turbocompressor operating failures.
查看更多>>摘要：Solidification cracking is very common in the welding process of austenitic stainless steels and can lead to premature failures. Yet, the main quantitative impact of S, P and Si on solidification cracking is still lacking. In addition, the present solidification cracking prediction diagrams are merely composition based, i.e., Creq/Nieq dependent. Hence, this work aim to highlight the importance of controlling S, P, Si, and delta-ferrite on the susceptibility of AISI 310S to solidification cracking. Penetrant testing, XRF spectrometry, hardness, ferrite measurements, along with microscopic examination were used. XRF spectroscopy revealed 0.09% S, 0.09% P and 2.27% Si at the weld which are deemed to be in critical range according to the reported literature and ASTM A240. Benchmarking the results with the modified Suutala and Pacary curves revealed close results. Therefore, outcomes from this work can aid in the development of such prediction diagrams, along with improvement to the refining industry.
查看更多>>摘要：The occurrence of fracture during wire drawing seriously reduced the quality of steel wire. In this study, the morphology of necking fracture and microstructure of wire are observed by SEM. It is found that there is large off-center inclusion on the surface of some fractures. Meanwhile, void defects appear near the inclusions, especially along the drawing direction. The FEM is employed to simulate multi-pass drawing of wire with and without off-center inclusion under different back tensions. The results show that with the increase of back tension, the damage in the core of wire without inclusion gradually accumulates. When the damage exceeds the critical value, cracks occur preferentially in the wire core and propagate to the surface of wire, thus forming as necking fracture. When the wire contains inclusion, cracks will first occur at both ends of inclusion, and its fracture is formed earlier than the wire without inclusion.
查看更多>>摘要：This paper describes a stress corrosion cracking (SCC) failure case of super 13Cr tubing serviced for six years in a high-pressure, high-temperature (HPHT) gas well. The failure causes and processes were studied by various characterizations and SCC simulation testing. The failure mode of super 13Cr tubing is brittle transgranular fracture, and the dominating role in SCC failure is the synergistic action of KH2PO4 phosphate packer fluid and CO2, leading to corrosion damaged zone, which is a selective corrosion along the martensitic multiscale boundaries. Under tensile stress, cracks developed at the corroded martensitic multiscale boundaries and propagated due to the low structural strength of the corrosion-damaged zone. Due to its compatibility with 13Cr tubing, formate is recommended as an alternate packer fluid for high-pressure, high-temperature (HPHT) gas wells.
Marques, Thais Peres ZantineMarques, Bruno Mikio FujiwaraCandido, Geraldo MauricioRezende, Mirabel Cerqueira...
14页
查看更多>>摘要：This study presents the influence of different geometric arrangements of butt joint formed by plain weave fabric prepreg layers on mechanical and fracture behavior of carbon/epoxy laminates tested under tensile loading. The experimental test results showed a reduction of up to 17% on the tensile failure load, due to the presence of the discontinuity in the reinforcement, when compared to the continuous fiber reinforced composites. However, statistical analyses demonstrated that the different staggering methods of the butt joints did not affect considerably the tensile mechanical behavior of the laminates. The stress concentration in the embedded joint regions was observed by finite element analysis results, which predicted the tensile failure load and also the failure region, according to Hashin criterion. SEM analyses revealed that all specimen configurations exhibited fracture in the butt joint regions, with the occurrence of cohesive failure of the matrix originated in the co-curing process, associated with a strong interfacial adhesion with the fibers. This behavior evidences a high interfacial strength of the co-cured plies joints, which is attributed to the good quality of the prepreg material associated with the efficiency of the laminate manufacturing process. The numerical studies showed a good fit with the available experimental results regarding tensile failure load. Therefore, the implemented finite element model proved to be adequate to accurately predict the tensile strength of plain weave fabric laminates containing layer joints.
查看更多>>摘要：Materials with shape memory effect (SME) can be used as the actuators of self-deforming structures, but the existing ways to design and select actuators with SME are complicated. In this work, an efficient and easy idea was proposed to select the shape memory polyurethane (SMPU) actuator with different designed shapes and sizes. First, the mechanical and shape memory experiments of SMPU were performed to obtain the basic mechanical and shape memory properties. Then, a self-deforming structure was designed by introducing the SMPU actuators with different shapes and sizes. Next, to select the optimal structural SMPU actuators, the finite element analysis was carried out by simulating the self-deforming process. Finally, based on the criteria of the minimal unrecoverable strain and maximum recovery bending moment, two kinds of actuators were chosen to drive the designed self-deforming structure cooperatively. Comparing the simulated and experimental self-deforming process, the feasibility of this method was verified. This work plays a guide in designing and selecting the actuators for self-deforming structures.
查看更多>>摘要：Aiming at the common fault diagnosis problems of rotors in industrial applications. A rotor system fault diagnosis method based on vibration signal feature vector transfer learning is proposed. First, Statistical methods and wavelet packet decomposition are used for vibration signal feature extraction. Then, the ReliefF algorithm is used to evaluate the fault features and screen out the sensitive fault features set. Next, the training data and real time test data are mapped to the kernel Hilbert space using the transfer component analysis method. Finally, the weighted knearest neighbor method is used as the fault feature classifier for fault pattern recognition. Model training and validation using typical failure datasets of different equipment and different operating conditions. Compared with other related methods, the results indicate that the proposed method has better generalization and diagnostic accuracy. This research will promote the engineering application of intelligent fault diagnosis of rotor system.
查看更多>>摘要：Finding the optimized set of manufacturing parameters to produce strong solder-copper connections requires investigating the main and interaction effects of processing variables on the joint strength and microstructure. In this study, solder joint specimens were prepared at different levels of cooling rate, time above liquidus (TAL), and soldering temperature. Mode I fracture experiments were designed and performed at a strain rate of 0.5 s-1. The fracture load remained constant from the cooling rate of 0.1 to 1.4 degrees C/s and then decreased by almost 34% with further increase in the cooling rate to 34 degrees C/s. Increasing TAL from 60 to 120 s reduced the fracture load by almost 27%, while it was almost unchanged from TAL of 120 to 240 s. The influence of soldering temperature on fracture load was negligible. Microstructural examination showed the cooling rate and TAL both affected intermetallic compound (IMC) thickness and this caused the interaction between them.
Nie, HailiangMa, WeifengHe, XueliangHuo, Xiaotong...
11页
查看更多>>摘要：As one of the main forms of pipeline deformation and failure, buckling poses a threat to the service safety of pipelines, seriously leads to oil and gas leakage, pipeline shutdown and environmental pollution. It not only brings huge economic losses, but also leads to fire, explosion and other accidents, which threaten the property and life safety of the country and people. Therefore, it is necessary to study the buckling deformation mechanism and failure rule, so as to lay a foundation for the evaluation and protection of pipeline buckling deformation. In this paper, theory and finite element simulation method has been used to study the buckling failure mechanism of the pipeline crossing road. The form and magnitude of the local load causing pipeline buckling are obtained through theory and vilified by the finite element simulation. The analysis results show that the boundary conditions and stiffness of the pipe are locally changed by the casing, and the deformation of the pipe is concentrated under the external load, such as road load and seismic wave, which leads to buckling. Therefore, the existence of casing will affect the deformation distribution of pipeline, and it is necessary to optimize the design and protect it in practical engineering to avoid buckling caused by deformation concentration.
查看更多>>摘要：The traditional welded connections of steel moment frames are prone to brittle fracture in earthquakes due to the high stress concentration at the beam end, which significantly affects the seismic performance of steel frame structures. A novel type of steel connection with local structural forms is proposed to avoid brittle fracture. The proposed connection is developed by both of cover plate strengthened at the beam flange and the opening weakened at the beam web. The quasi-static tests of 8 welded steel connections were carried out to investigate and validate the proposed connection. The failure mode, hysteretic behavior, strength and cyclic degradation behavior, ductility and rotation behavior, stiffness behavior, and energy dissipation behavior of 8 connections were analyzed and further discussed. Moreover, the effects of different local structural forms, such as length of cover plate and diameter of web opening, on the proposed connection were experimentally investigated in detail. Also, the seismic performance of the proposed connection was comprehensively compared with the traditional connection. The results show that the proposed connection can achieve the plastic hinge away from the face of the column, thereby avoiding the brittle failure at the beam end, exhibiting excellent seismic performance. The comparisons demonstrate that the proposed connection presents a satisfactory ductility and plastic rotation behavior. A good cumulative plastic rotation and cumulative energy consumption can be observed in the proposed connection. However, the traditional connection shows a poor energy dissipation behavior. In addition, the strength and stiffness behavior of the proposed connection are not much different from the traditional connection, but the hysteretic, ductility, plastic rotation, and energy dissipation behavior can be considerably improved. The results confirm that the proposed connection is verified for seismic behavior and can be considered as a reasonable steel welded connection. Consequently, the proposed connection can be recommended to be directly adopted in the beam-to-column connection for steel frame structures under seismic design.
NSTL
Elsevier