查看更多>>摘要：? 2022 Elsevier LtdThere is no existing effective analytical method for calculating the mesh stiffness of spur gears with tooth root crack when the interactions between the neighboring teeth induced by gear body flexibility are considered, while this factor has been demonstrated to have a considerable effect on the mesh stiffness. In this paper, an improved method of spur gear mesh stiffness is proposed based on the theory of elastic mechanics for circular ring, which is capable of calculating the mesh stiffness with tooth root crack accurately. Then, the calculated gear body-induced stiffness results considering structural coupling effect with tooth root crack is validated by the finite element method. In addition, the effect of different hub hole radius and crack lengths on the stiffness caused by the structural coupling effect are investigated. The results indicate that the proposed analytical method is more accurate for spur gear mesh stiffness calculation with tooth root crack.
查看更多>>摘要：? 2022 Elsevier LtdThe risk of burn-through is a major concern when conducting in-service welding repair for oil-gas pipelines. The governing mechanism of burn-through has not hitherto been studied systematically. During in-service welding, different micro-zones of the pipe wall metal below the molten pool have different crack initiation mechanisms due to different temperature and stress conditions. This paper uses molecular dynamics to study the initiation and evolution of micro-defects in different micro-zones of the pipe wall under the in-service welding pool and reveals the microscopic mechanism of in-service welding damage and failure. The research found that the pipe wall under the in-service welding pool is divided into a fusion zone and a coarse grain zone. For the coarse grain zone, the grain boundary region is subjected to large deformations and causes high strain. The stress concentration at the grain boundary (especially the triple junctions) is caused by the arrest of grain boundary slip, which leads to the initiation and propagation of microcracks in the grain boundary region. The displacement vector of atoms at the grain boundaries is generally larger than that of the atoms in the crystal, further indicating that grain boundary slip is the primary mechanism of microcrack initiation in the coarse grain zone. Compared with the coarse grain zone, the grain boundary width of the fusion zone increases, and the grain boundary atoms show apparent disorder. The peak value of the radial distribution function decreases, and the peak becomes wider, indicating that the grain boundary pre-melting phenomenon occurs in the fusion zone. In addition, as the tensile strain increases, the instability of the pre-melting zone expands rapidly and advances into the crystal grain. During in-service welding, the high-temperature deformation of the coarse grain zone and the fusion zone of the tube wall are mainly controlled by the intergranular mechanism. Through molecular dynamics, the mechanism of grain boundary slip in coarse grain zone and grain boundary pre-melting in fusion zone were studied from the microscopic scale. Thereby the microscopic mechanism of in-service welding damage failure was further clarified.
查看更多>>摘要：? 2022 Elsevier LtdA water filter was inspected in order to determine the origin and chemical nature of several corrosion products on its surface. The metallic material base was analyzed to be a lead brass with a nickel coating of 4–5 μm thickness. The plastic base, as well as the rod and nut, was impregnated by similar deposits whose chemical nature was mainly oxides, carbonates and chlorides, according to the EDX analysis. Some white deposits were observed in the nut and rod, probably corresponding to zinc oxide. These deposits may be formed upstream by the pipe materials or the sediments that the fluid may carried inside the pipe. The absence of a nickel coating leaded to corrosion pits in some areas of the rod and nut. This corrosion has initiated on the surface, and has progressed through the beta phase that was zinc impoverished, to the inner zone of the filter.
查看更多>>摘要：? 2022 Elsevier LtdAncient southern Chinese timber buildings, built in the Song and Yuan dynasties (AD 960–1368), play an important role in Chinese cultural heritage. Nowadays, such buildings collapse more frequently than before due to local member failures. This study focuses on a special construction arrangement of ancient Chinese timber buildings, called Pu-zuo, and its effect in the progressive collapse of the building is experimentally studied in detail. Five 2-bay frames are designed for this experiment, one without Pu-zuo and four with Pu-zuos, considering different arrangements and types of Pu-zuo. A downward load is applied at the middle column until failure occurs. The progressive collapse mechanism of the frames and the mechanical performance of the joints and components during the collapse process are investigated. Finally, comparing the results between the five frames, the structural effect of Pu-zuo resisting the progressive collapse is studied. The results show that the main beam of the frames, called Lan-e, is a key component to transfer the load to the side columns when the structure collapses due to middle column failure. Compared with the frames without Pu-zuo, the bearing capacity of the frames with column and intermediate Pu-zuos increases by 138%～158% and the one of the frames with only column Pu-zuos increases by 45%～60%. Hence, intermediate Pu-zuos further improve the stiffness, bearing capacity and ductility of the structure in progressive collapse.
查看更多>>摘要：? 2022 Elsevier LtdDue to the influence of signal modulation and multi-stage coupling, the fault diagnosis of multi-stage planetary gear system is difficult. In this paper, a dynamic model of multi-stage planetary gear system containing sun gear crack is proposed from the perspective of nonlinear dynamics to study the failure mechanism and dynamic characteristics of tooth root crack. The mesh stiffness with root crack is calculated by using the modified energy method. By means of global bifurcation diagram, RMS curve, phase diagram, Poincare map, time series diagram and FFT spectrum, the dynamic responses of the system with and without fault are analyzed and compared. The results show that there are differences in the impact of crack failure on the dynamic characteristics at different rotational speeds. The crack disturbance will cause an abrupt change in the vibration amplitude of the system, which can excite the system into chaos from a quasi-periodic state. The system tends to be unstable due to crack failure, which is manifested by irregular expansion of the attractor, divergence of the phase trajectory, periodic pulses in the time series diagram, and sideband frequencies with the sun gear fault characteristic frequency as interval appearing around the meshing frequency. The chaotic motion range should be avoided during crack fault diagnosis.
查看更多>>摘要：? 2022 Elsevier LtdElectroplating chromium coating is a common and critical surface coating technology for the artillery bore. In this study, the fracture behavior of interface cracks in the chromium coating-steel substrate system under transient convective cooling was studied by the finite element method. A two-dimensional model containing periodic segmented coatings was established, and the temperature dependence of material parameters was considered. The effects of convection strength, crack geometry and coating thickness on the delamination behavior of chromium coatings were discussed. It was found that the increase in crack density and coating thickness reduced the energy release rate. The shear mode dominates the fracture mode of the interface crack during the convection cooling period, and the crack closes once the convection stops. When the crack density and coating thickness reach a certain value, the proportion of the shear traction no longer changes. These results can provide references for artillery coating design.
查看更多>>摘要：? 2022The preload loss of high-strength bolts in friction connections was investigated considering the corrosion damage and fatigue loading. Double lap connections were assembled and the ultrasonic measurement method was employed to obtain the real-time preload of the bolts. Accelerated corrosion tests of specimens were used to achieve four corrosion levels and the and the corresponding weight loss ratio of the specimens varied from 0 to 10.1%. Fatigue test was then performed on eight corroded connections. The preload change of bolts after installation, corrosion tests, and certain number of load cycles was measured. It is found that the corrosion effects on the bolt preload loss was significant, and an average value of 41.2% preload loss was observed for specimens of 10% weight loss. The influence of fatigue load on the preload loss after unloading could be ignored, but the combination of tensile loading, fatigue loading, and corrosion damage could lead to an up to 11% preload loss.
查看更多>>摘要：? 2022 Elsevier LtdIn this study, the temperature evolution of the fracture toughness in single-crystal gallium arsenide (GaAs) was investigated on the (0 0 1) plane using Vickers indentation. The highest temperature considered was 95 °C, corresponding to the typical maximum operating temperature of common GaAs semiconductor devices. Experimental results showed a decrease in hardness and an increase in toughness between 25 and 95 °C. GaAs cleavage planes were mostly composed of {1 1 0} and {1 0 0}, and predominantly aligned with the indenter's diagonal. Measured crack lengths were used to calculate the fracture toughness. Interestingly, the size of the primary cracks on {1 1 0} was found to be unaffected by temperature, while higher temperatures led to an increased formation of secondary {0 0 1} cracks and 〈110〉 slip. An Arrhenius-type model was found to describe the observed temperature dependence of the fracture toughness. This improved understanding of the mechanism underlying the mechanical properties of GaAs during fracture is particularly useful for the failure analysis of GaAs semiconductor devices, and highlights the importance of selecting appropriate crystallographic orientations if failure in GaAs devices is to be avoided.
查看更多>>摘要：? 2022 Elsevier LtdThis paper presents the development of a modelling methodology in a finite element framework for the simulation of novel composite joints with delamination arresting features. The investigated composite joints employ the co-consolidation technique for the assembly of composite skins and stiffeners in a structural joint; in order to arrest and retard delamination damage evolution that may appear during service life, crack stopping features are included in the joint. Progressive damage modelling and cohesive zone modelling methodologies are employed for the analysis of intralaminar and interlaminar failure of laminate composite materials components. The modelling and simulation of experimental test cases available in the open literature are used for validation of the developed progressive damage and cohesive zone models through comparison of numerical results to respective experimental results for all test cases. The mechanical response of the butt-joint structural element is experimentally investigated and linear/nonlinear finite element models are developed to simulate its mechanical behaviour. The comparison between the experimental and numerical results demonstrates the applicability of the developed methodology in the simulation of novel composite structural joints with crack-stopping features.
查看更多>>摘要：? 2022 Elsevier LtdThis paper discusses the effect of elbows in the downstream region of pipe and pumps inlet flow conditions according to standards. Cavitation is a significant occurrence in such types of flow regimes that causes erosion and ultimately affects the pump's performance. Cavitation is also investigated using computational analysis using ANSYS Fluent. It is concluded that the elbow with 90° angle in pipe with some curvature produce eddies in the fluid flow. The variations in the velocity near the downstream were uneven. Moreover, it is also determined computationally that the effect of cavitation on pump inlet flow conditions is also high and in increasing trend. The effect of cavitation in an elbow pipe can be increased if the curvature of the elbow is reduced. This ultimately effect the performance of the pump.
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