查看更多>>摘要：In recent decades, the penetration depth, hit accuracy, and damage ability of earth-penetrating weapons have been greatly improved. High dams will thus face increasingly severe threats of penetration and explosion from such weapons. The nonlinear dynamic responses and failure processes of dams under the combined action of penetration and explosion are much more complicated than those under static or seismic loadings, and they are yet more complex than those under air blasts or underwater explosion loads. There have been various comprehensive numerical investigations of concrete gravity dams subjected to underwater explosions; however, there have been few such investigations considering penetration and explosion. In this study, the damage characteristics and failure modes of a concrete gravity dam subjected to the combined action of penetration and explosion are examined. A fully coupled Lagrangian-Eulerian approach is adopted to describe the nonlinear dynamic responses and damage processes of the dam, and this includes consideration of the dam-reservoir-foundation interactions. In this paper, the validities of the penetration model and internal explosion model are discussed by comparing results obtained from the proposed method with those obtained from empirical formulas and experimental tests. The penetration characteristics of the concrete gravity dam subjected to impact by high-velocity projectiles are presented. The damage development processes and nonlinear dynamic responses of the dam to an internal explosion with and without consideration of the initial penetration damage are compared. The failure modes of the dam resulting from different penetration and explosion conditions are categorized. The penetration depths of different explosives resulting in the greatest damage range are obtained. The results show that although the initial penetration increases the degree of damage to the dam, it has little impact on the failure mode of the dam. The failure modes can be divided into two categories: a blasting funnel at the surface and an internal ellipsoidal explosion. The adverse penetration depth resulting in the greatest damage range is found to increase nonlinearly with increasing explosive weight.
查看更多>>摘要：In order to prevent skid accidents of main cable of suspension bridge, dynamic contact behaviors between saddle materials and steel wires were explored in the present study. Dynamic contact tests of saddle materials were conducted employing the self-made dynamic contact test rig. Dynamic contact behaviors of the saddle material (transverse slip, longitudinal deformation, contact state, wear mechanism) in a friction cycle were investigated. Effects of transverse and longitudinal locations, friction cycles and saddle materials on the dynamic contact behaviors were presented. The results show that dynamic contact states between saddle specimen and steel wireexhibits the adhesion-gross slip-adhesion-gross slip state in a friction cycle. The transverse slip and longitudinal deformation of saddle specimen both decrease with increasing distance to the contact interface, decrease along the transverse sliding direction, and increase with increasing friction cycles. The ZG270-480 saddle material exhibits the largest average transverse slip and longitudinal deformation, while ZG275-485 saddle material shows the smaller values.
查看更多>>摘要：The Flip Chip (FC) technology has been widely used in microelectronic packaging, and the FC technology requires not only higher precision, but also higher reliability, which makes the defect detection of FC more challenging. In this paper, the SAM image of FC is segmented. Histogram of oriented gradient (HOG) as a feature extraction method and optimized support vector machines (SVM) are combined to design an intelligent diagnosis algorithm, which was called H-SVM. This method was used to realize the defect detection of solder bumps. In the same variable environment, it evaluates and compares with other machine learning algorithms. The results show that it is effective to combine HOG and optimized SVM for the diagnosis of convex defects with high detection accuracy.
查看更多>>摘要：In this paper, the effect of brick arrangement on structural behaviour of Persian brick masonry barrel vaults has been studied by the micro-modelling method using non-linear finite element analysis performed by the ANSYS code. Vaults have semi-circular, pointed and four-centred crosssectional shapes. Two different spans and three different lengths, with Roman brick arrangement and Persian brick arrangement have been considered. The vaults have been subjected to linear load at mid-span, linear load at one-third-span, support settlement, inward rotation of one support, inward rotation of two supports and outward rotation of two supports. In the cases of linear load at mid-span and support settlement, the Persian brick arrangement is more satisfactory in the semi-circular and pointed vaults, and the Roman brick arrangement is favoured in the fourcentred vault. In the case of linear load applied at one-third-span, the load-bearing capacity provided by the Persian brick arrangement is up to two times the Roman brick arrangement. When one support rotates inwards, the Roman brick arrangement is always better. For both cases of inward and outward rotation of two supports, the performance of the Persian brick arrangement is more satisfactory in pointed and four-centred vaults, and that of Roman brick arrangement is better in the semi-circular vault.
查看更多>>摘要：Tunnelling in ground fissure areas is prone to collapse even with reasonable reinforcement. Based on the collapse of a tunnel in Xi'an Metro Line 3 near a ground fissure, potential causes and corresponding mechanisms were analysed. Preliminary in-situ investigation indicates that the hydraulic erosion induced loose pressure and crack-rich soil below the unclosed initial support were mainly attributed to be the triggering force of the collapse. Compared with the two common failure modes in tunnels, this collapse is of unique characteristics, showing that special attention to the arch feet is required in similar strata. The collapse mechanisms were subsequently analysed in aspects of geology, soil meso-features and construction. In addition, The failure process was simulated based on discrete element method in MatDEM and stress chains have been observed, showing results consistent with the above analysis. To prevent a secondary disaster, necessary appropriate remedies with considerable resources were implemented at three sites: the tunnel, portal and surface. Combined with the monitoring data during the treatment, their effects and shortcomings were discussed. The result facilitates prevention and treatment of collapse induced by underground tunnelling near ground fissures.
查看更多>>摘要：The splitting phenomenon during drawing will cause the quality decline of wire. A clear understanding of formation mechanism of splitting can help to promote the development of engineering drawing. Therefore, the splitting fracture and microstructure are analyzed by SEM. The experimental results indicate that the main crack run through the core and surface of both sides of wire. Furthermore, multi-pass drawing of different material properties and die angles is simulated by using FEM with the developed damage modeling. The results show that after each drawing pass, the damage and section stress are formed near the center and surface of wire, respectively. Meanwhile, the damage will be enhanced with the increase of die angle, drawing strain and material properties. Among these influencing factors, the die angle has little effect on the section stress, but the increase of the other two factors will lead to the gradual increase of section stress. Moreover, wire core becomes the source of crack due to its larger damage, and then crack propagates to the surface of wire under the action of stress, thus forming splitting fracture.
查看更多>>摘要：Due to the harshness and unpredictability of the tidal site environment, the damage induced by an accidental impact should be considered in the certification of composite cylindrical structures intended to be used in the design of the composite MJM tidal turbine concept. The first part of this paper deals with the effect of different failure criteria based on quadratic stress functions on the low-velocity impact response of thick filament wound glass/epoxy cylindrical structures. A userdefined material model (VUMAT) applied to three-dimensional solid elements was implemented into the finite element software Abaqus-Explicit to explore the effect of failure criteria on the predicted dynamic response with intralaminar damage. The investigated failure criteria include the two-dimensional Hashin criteria presented by Hashin in 1973 and extended to the threedimensional case by including analytically the out-of-plane stress terms (criteria denoted "Hashin 3D"), the three-dimensional Hashin criteria described by Hashin in 1980 (criteria denoted "Hashin 3D 1980"), the Puck matrix transverse criterion coupled to Hashin criteria (criteria denoted "Hashin-Puck") and Chang-Chang criteria (criteria denoted "Chang & Chang 1987"). The intralaminar damage model includes damage onset based on quadratic failure criteria, damage evolution, and element deletion from the solid mesh. FEA analyses are carried out with different low-level impact energies. The numerical results show different impact responses as well as the damage characteristics particularly the matrix cracking through the thickness. In the second part the bilinear cohesive zone model (CZM) is employed for modelling the interlaminar damage. The combination of the intralaminar damage model with the interlaminar model is applied using an uncoupled methodology. By comparison with the experimental force-time curves, interface properties used in the cohesive model have been estimated numerically using a reverse methodology and a baseline FEA model. The modelling approach has proven to be capable of reproducing experimental results with good accuracy. The modelling outcomes and predicted damage are therefore intended to be applied in the design loop and development of the MJM tidal turbine prototype where thick filament wound glass/epoxy cylinders are subjected to low-velocity stones impact.
查看更多>>摘要：Failure analysis and lifetime assessment of drilling systems are very important to reduce maintenance costs. Of all the failure modes, coupled vibration due to the stick-slip phenomenon is the most common problem that can affect rotary drilling systems. The main objective of this study is to estimate the number of cycles before failure (useful life) of the lower part of rotary drilling system toolstring under axial and torsional vibrations. To achieve this goal, a complete procedure based on different methods and approaches, such as: finite element method (FEM), rainflow counting method (RFM), Goodman approach (GA), S-N diagram and Miner's rule, has been proposed. To this end, the FEM has been used to determine the loading cycles (equivalent stress); whereas, the number of stress cycles in the loading cycle diagram has been counted using RFM. The GA has been used to select the main cycles that can cause failure on the toolstring and to calculate their amplitudes. Then, S-N diagram has been used to determine the number of cycles to failure of the toolstring. Finally, Miner's rule has been applied to find the approximate time to failure of the drilling system. Regarding the estimation of the toolstring lifetime, the results obtained have shown a good agreement with real data recorded in an oil field in Algeria.
查看更多>>摘要：Variations in design parameters and methodology have a significant effect on the fracture char-acteristics of spur gear. Furthermore, the geometry and load acting on the spur gear affect the propagation of fractures and the bending fatigue life. In comparison with conventional gear design, the direct design strategy is a highly efficient method for improving fracture resistance. This study attempts to investigate the fracture properties of a direct designed asymmetric high contact ratio (AHCR-DD) spur gear subjected to the mix-mode of crack failures. The stress in-tensity factor (SIF) and the shape factor are compared to conventional normal and high contact ratio spur gears. In addition, the fracture properties of conventional design symmetric HCR (SHCR-CD), direct design symmetric HCR (SHCR-DD), and AHCR-DD spur gears are compared. When compared to other gears, the AHCR-DD spur gear has a higher fracture resistance. A parametric study of the fracture properties of the AHCR-DD spur gear is also carried out to provide useful information for designing such gears. Variations in the contact ratio, rim thickness, number of teeth, and addendum pressure angle are used to assess fracture performance. It is observed that using a direct design technique significantly reduces the SIF. This investigative study provides valuable guidelines in the future for developing non-standard spur gears such as AHCR-DD.
查看更多>>摘要：An innovative model of engineering failure analysis leading to a prospective model of sustainability and decarbonisation, supported by design-material-failure threads, emerge from two defective test inflatable seals (Seals; -2 m dia) subjected to laboratory investigations i.e. visual, dimensional, physico-mechanical, material fingerprinting and analysis of variation. The Seals of 500 MW(e) Prototype Fast Breeder Reactor (PFBR) design were industrially manufactured (year: 2007) by cold feed extrusion and continuous cure (CFECC) of a peroxide cured, Viton GBL 200S:600S blend compound, APA-1, 2007. Primary aim was to implement life maximization (global design thread) potential (>= 30 y) of advanced polymer architecture (APA) fluoroelastomer (FKM) in reactor inflatable seals (-6.3 m/-4.2 m dia) with repeatability and reproducibility by eliminating premature failure source from improper manufacture.
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Elsevier