查看更多>>摘要：? 2022 Elsevier LtdIn this paper, the effect of impeller eccentricity caused by parallel misalignment of the coupling is considered, and the impact of the impeller eccentricity on the hydrodynamic characteristics of a centrifugal pump is numerically investigated. The finite volume method is adopted to simulate the dynamic process. The results show that the eccentric impeller will deteriorate the hydraulic performance of the pump, nonetheless the influence is limited. However, it significantly affects the amplitude of the flow-induced force at shaft frequency, and the amplitude is proportional to the eccentricity ratio to some extent. The influence of impeller eccentricity on pressure pulsation can be evaluated by the shaft orbit. The crest factor of the impeller trajectory is positively correlated with the pressure pulsation intensity. The minimum value of the impeller trajectory has a negative relationship with the average radial force of the impeller. The clocking position of the eccentric impeller primarily affects the phase relationship between the shaft frequency and the blade passing frequency. A function is proposed to characterize the fluctuating pressure distribution with a spatially periodic pattern around the volute under eccentric conditions. This research can provide an essential reference for fault diagnosis and vibration control of the centrifugal pump.
查看更多>>摘要：? 2022 Elsevier LtdThis paper is devoted to Reinforced Concrete (RC) beams that can be subjected to accidental falls of substantial masses (hard impacts at low velocities), such as the beams of bridges, industrial buildings, or factories. Here the reference is to existing RC beams, which have no purposely designed reinforcement to resist impacts. The paper focuses on a mass that falls around the midspan, where the capacity of a RC beam to resist an impact is minimum, due to a potential primary cracking pattern that consists of vertical cracks. The impact here is defined by the combination of the mass that falls down and its velocity at the impact. The paper provides an analytical formulation to predict the combinations that trigger the collapse of a RC beam (i.e., ultimate combinations). After having framed the research question, the paper presents the two possible failure modes, the derivation of the equations, the sensitivity of the bearing capacity to the main parameters, comparisons with existing results from literature, and two applications, whose results are discussed.
查看更多>>摘要：? 2022 Elsevier LtdThis paper studies the influence of varying the proportion and configuration of steel and glass fiber-reinforced-polymer (GFRP) rebars on the flexural behavior of reinforced concrete (RC) beams. The influence of adding steel fibers in concrete used for the hybrid reinforced beams is also studied. A total of sixteen under-reinforced concrete beams of 200 × 450 × 3000 mm were tested to failure under four-point flexure. The parameters investigated were first-crack load, initial stiffness, ultimate load, ductility, service load, and deflection at 50% and 100% of ultimate load. The increase in the area of steel rebars caused improvement in serviceability and enhancement in ductility. The incorporation of steel fibers in concrete improved the first crack-load and initial stiffness. The flexural capacity of hybrid reinforced beams was assessed based on the section analysis by incorporating strain hardening in steel rebars, which showed a reasonably good correlation with the experimental results.
查看更多>>摘要：? 2022 Elsevier LtdThe crack fault often appears in the complicated gear system, and even causes tooth broken. To solve this problem, an improved model is proposed in this paper, which considers the coupling effect of cracks on both gear tooth and gear foundation, and a 2D finite element model is established to verify the proposed method. The influences of crack size and inclination angle on meshing stiffness are investigated. The results are used to simulate the situation of the crack occurring at the sun gear in an 18 degrees of freedom dynamic model of the planetary gear set, so as to obtain the dynamic responses of the crack gear system both in time domain and frequency domain. Finally, two different methods are used to process the original vibration signals to obtain the residual signals. Combining the residual signals, several statistical indicators are employed to characterize the evolution of crack propagation.
查看更多>>摘要：? 2022 Elsevier LtdA burst failure occurred in a reinforced thermoplastic pipe used in an oil transportation system for 5 years. Visual inspection, tensile test, FTIR, TGA, VST, DSC, and pressure test were conducted to find out the failure cause. The results show that the damage to sealing rings led to the leakage of conveying medium in the joint. The fibers in the reinforcement layer were contaminated by the leaked conveying medium, resulting in performance degradation. The tensile strength and elongation at break of the fiber all decreased by 60 ～ 80%. The burst pressure of the contaminated pipe is only 6 ～ 7 MPa, far lower than its PN. According to the operating record, the highest working pressure ever reached 5.2 MPa during the operation, which approached its burst pressure. Meanwhile, there were pressure fluctuations during the operation. When the transient pressure was higher than the burst pressure of the contaminated pipes, burst failure occurred.
查看更多>>摘要：? 2022 Elsevier LtdThe aim of this study is to evaluate the behavior of a discharge manifold that has space restrictions. These restrictions do not allow a suitable design by the usual practice. Thus, for its evaluation an upgraded methodology was necessary for structural analysis and revision. The upgrade includes the soil-thrust blocks-pipeline interaction and the influence of fittings outside the blocks using a simplified model. The manifold was assumed as a whole structure. The pipeline was modelled with frame elements. The behavior of the thrust blocks was simulated by means of a Winkler-like model with torsional and horizontal springs. Additionally, the influence of reducers and valves lying outside the blocks was included. Two analyses were performed. The first one, the interaction between soil, thrust blocks and pipeline is neglected; the second one includes the interaction among the elements. It is concluded that the overall capacity of the structural system increases when the interaction among elements is considered. The effects due to the interaction and the fittings lying outside the blocks can be estimated with the proposed model. Finally, it is shown that the reducers not embedded in the blocks produce a significant increment (up to 47%) in the pipeline longitudinal stresses. Nevertheless, the manifold resulted suitable for its operation. Thus, to evaluate a manifold that has space restrictions the enhanced methodology described in this paper can be used.
查看更多>>摘要：? 2022 Elsevier LtdThe paper aims to analyze the cause of failure of a wear ring impeller and to analyze the quality of the wear ring material. The analysis was conducted by common failure analysis procedure including chemical composition test, visual examination, microstructure examination, microhardness, and macrohardness. The results show that the sliding wear, softened material, and adhesion wear are found on the outer surface of the wear ring, and the deflection occurs on the fracture surface. The fractography analysis indicates that the initial crack occurs due to the valley that acts as a stress concentrator geometry, and the failure is caused by the fatigue stress. The chemical composition test shows that the overlay material is not in accordance with technical data. The suggestion for the corrective action is to ensure the eccentricity of the overall rotary part, and it must use the proper material to prevent sudden failure.
查看更多>>摘要：? 2022 Elsevier LtdSign and traffic signal structures are susceptible to fatigue damages caused by wind, temperature change, and road-induced excitation. This study focuses on the stress intensity factor (SIF) ranges for octagonal tube-to-transverse plate joints widely used in sign and traffic signal structures. The finite element (FE) models were established and calibrated by using Newman and Bowness equations. The SIF ranges of the joints with fillet weld and full-penetration groove weld were compared. The effects of initial crack location, transverse plate thickness, tube diameter and thickness, taper ratio of tube, weld size, and number of bolts, on the SIF ranges of tube-to-transverse plate joint with fillet weld were intensively investigated. The suggestions for improving the remaining fatigue life of the joint were offered.
查看更多>>摘要：? 2022 Elsevier LtdCopper anode (～98%) is widely used to produce the cathode (99.995 wt%) in electrorefining process. These anodes sometimes become problematic from the production line due to the presence of bumps/holes on their surface. To find the reason of this defect, chemical composition of the three casted anodes was determined by the quantmeter analysis. Also, the microscopic and phase analysis were done by FESEM, EDS, XRD, and XRF for three types of anodes bump. The chemical analysis of anodes confirmed a high level of sulfur and oxygen, which have a key role in the formation of bumps. The results confirmed the presence of impurities including Cu2S, BaSO4, CaCO3 and MgCO3, which cause the formation of gas bubbles at the final stage of solidification. The main source of these impurities was barium sulfate as mold covering and magnesia-chrome bricks (as refractories). To prevent bumps phenomena, the control of impurities content is necessary.
查看更多>>摘要：? 2022 Elsevier LtdThe stress arching mechanism of longwall panel floor were studied by theoretical analysis, numerical simulation and field observation. The study results show that: the direction of the principal stress on the floor is deflected in the process of mining, so the concentrated stress of floor transmits along an arching line. The goaf floor went through a process of high unloading, which intensifies the degree of crack propagation and fracture of the floor. Microcracks in floor are likely to connect with each other to form a macroscopic fracture surface, which leads to a significant volume expansion of goaf floor. There is a terrace-like tensile plastic zone in the goaf floor and an arched shear failure zone exists outside the tensile plastic zone. Field monitoring results reveal that the goaf floor is dominated by unloading tensile failure, and the floor in front of the mining face is dominated by shear failure.
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