查看更多>>摘要：? 2022 Elsevier LtdThe service safety problem of steel crane beams in metallurgical industrial buildings has been attracting increasing attention recently. The fatigue failure problem of the steel crane beam with variable-section supports becomes particularly severe. Therefore, the present study focuses on exploring the reason for such fatigue failure in terms of the design method, actual service load, and reliability of existing structural components of the steel crane beams. First, the study clarifies the “Z class” of various variable-section supports based on fracture mechanics theory to design fatigue strength parameters for steel crane beams. Then, it explores the indeterminant design parameters of fatigue load through numerous load tests and analyses, discussing the applicability of current approaches on selecting appropriate parameters. At last, this paper carries out a statistical analysis of fatigue reliability of existing steel crane beams with variable-section supports. This study concludes the main reasons for frequent fatigue failures of steel crane beams with variable-section supports, which provides a basis for solving such fatigue failure problems in practice.
查看更多>>摘要：? 2022 Elsevier LtdA three-dimensional finite element model of wheel-rail that contains an initial crack in rail subsurface was established, the influences of initial crack angle, depth and size on mixed fatigue crack growth behaviour under actual load were evaluated. The results showed that the initial crack propagated with II + III mixed mode, and the slip propagation of mode II was dominant. Different initial crack angle, depth and size lead to variable proportions of mode II and mode III because of the load mixity at the crack tip, which further affects the equivalent stress intensity factor (SIF) range ΔKeq and residual fatigue lifetime. 45° was the most dangerous angle of initial crack, which leads to the highest ΔKeq and the fastest crack growth initial crack depth increased, the ΔKeq and crack growth rate decreased sharply. With the increase of initial crack size, the ΔKeq increased and crack propagation was accelerated.
查看更多>>摘要：? 2022 Elsevier LtdThe failure accidents of the pipeline caused by girth weld problems occur frequently in recent years. However, the fracture mechanism and behavior of girth weld in pipeline are not clear at present. Accordingly, based on Gurson-Tvergaard-Needleman (GTN) damage model, a three-dimensional full-scale model of the X80 pipeline with girth weld was established in this paper, in which the differences of material properties in base, weld, and heat-affected zone (HAZ) were considered. Subsequently, the fracture process of the pipeline with girth weld under uniaxial tensile load was obtained. On this basis, the fracture behavior and the causes of failure of the pipeline were analyzed. The elongation and fracture strain were respectively defined to quantitatively describe the fracture toughness of the pipeline. The results showed that the crack initiated at the junction of the weld and HAZ in the inner wall of the pipeline due to material softening of HAZ, and then the crack propagated from the inner wall to the outer wall until forming a penetrated crack. Lastly, the crack grew rapidly along the circumferential direction, resulting in the overall failure of the pipe. Compared to the pipeline without weld, there was a smaller value of the elongation and fracture strain in the pipeline with girth weld. The elongation and fracture strain of the pipeline without weld was 26.49% and 0.78, and that of the pipeline with girth weld was 4.73% and 0.18, which was reduced by 82% and 77% respectively.
查看更多>>摘要：? 2022 Elsevier LtdPerforation in oil and gas wells can cause severe impact vibration of perforating string systems, which can even lead to the buckling of tubing, breaking of joints, and damage of packers. This study focuses on the dynamic behavior and failure analysis of perforated strings. A dynamic analysis model of perforating strings that couples transverse, longitudinal, and torsional vibrations was first established. The finite element method was used to discretize the perforating string into beam elements, and the Newmark-β method was used to solve the model. A field well was used as an example to prove the correctness of the model. The dynamic behavior of the perforating string at actual scale under the action of the explosive load was discussed. The effects of perforating parameters and string structure on the safety performance of the perforating string were analyzed. The results obtained can provide scientific guidance for the field perforating operation.
查看更多>>摘要：? 2022 Elsevier LtdFloor heaves threaten the safety of tunnels and pose major difficulties in tunnel engineering. This paper describes a case study on the floor heave mechanisms and corresponding control measures for highway tunnels in gently inclined coal seam in Guizhou Province, China. There are many factors behind floor heave in a highway tunnel, such as excavation method, high in-situ stress, weak rock, groundwater seepage, and quality of the floor. The displacement and stress of the tunnel were monitored during the tunnel construction to clearly illustrate the deformation, stress, and crack evolution characteristics. The stress in the tunnel structure indicated that horizontal stress was the main factor behind floor heave. It squeezed the layered coal rock mass along the beddings, causing fracturing of the rock mass under the floor. Meanwhile, water seeping through rocks further decreased the strength of the cracked rock mass. Subsequently, the failed rock mass squeezed the inverted arch upward. The secondary lining of concrete resulted in the inverted arch being subject to eccentric load, further causing buckling floor heave. Finally, the corresponding countermeasures were proposed and then verified by monitoring after implementation. The results of this study are significant for the optimization of tunnel design and can be used to ensure safety during construction in gently inclined coal seam.
查看更多>>摘要：? 2022 Elsevier LtdIn order to identify and quantitatively diagnose the dynamic unbalance of the cardan shaft equipped in high-speed trains, firstly, a numerical simulation model of the vehicle considering the cardan shaft dynamic unbalance is established. Secondly, the vibration and acceleration response of the motor and gearbox under different cardan shaft offset conditions are calculated. In order to better extract the feature signal related to the shaft unbalance, a novel algorithm based on the improved tunable Q-factor wavelet transform (TQWT) method is proposed. On this basis, in order to build the relationship between the unbalance and the characteristic frequency amplitude intensity (AI) index, radial basis function neural network (RBFNN) is used. In addition, non-dominated sorting genetic algorithm II (NSGA-II) is used to find the optimum Pareto solution of a combination of offsets to quantitatively analyze the cardan shaft dynamic unbalance. The results show that the proposed method can identify dynamic unbalance effectively and its magnitude quantitatively with an error of less than 15 %.
查看更多>>摘要：? 2022Natural fiber reinforced polymer composites are increasingly used in composites industry to propel towards sustainable and environmentally friendly materials. Basalt fibers have superior mechanical and thermal properties, but are brittle by nature. However, appropriate filler materials were ingeniously utilized to subdue this impediment. Moreover, optimizing the content and appropriating the combination of micro and nano size filler particle addition has significant effects on the final mechanical properties of the composite. The failure pattern of bidirectional basalt fiber mat (67 wt%) vinyl ester composite with SiC filler of micro and nano size added independently as well as in combination at various proportion ranging from 2 wt% to 10 wt% was analysed using fractographic images. Highest tensile strength, flexural strength, impact strength, hardness and specific wear rate of 204.33 MPa, 525.33 MPa, 3.55 J/mm, 43.87 VHN and 5 × 10–7 mm3/Nm respectively was obtained for the optimized composite sample. The fractured scanning electron microscopy (SEM) images taken at different stress conditions reveal failure patterns, such as fiber–matrix delamination, matrix cracking, matrix deformation, matrix pores, fiber breakage, etc to correlate with the mechanical strength and wear resistance. The degree of damage is very well associated to the percentage content, size and combination of the filler material in the composite along with the fiber mat.
查看更多>>摘要：? 2022 Elsevier LtdMost of the buildings in Saudi Arabia were constructed using reinforced concrete (RC) ordinary moment frames (OMFs), which, in most cases, had discontinuous bottom beam rebars across the beam-column joints. Consequently, they may be susceptible to the potential of progressive collapse owing to accidental loss of one (or more) exterior column(s) in an extreme event. Therefore, it is imperative to examine the progressive collapse robustness of RC OMF buildings. In this paper, 16 half-scale RC OMF assemblies (skeletal frames comprising of multi-span beams and two-story columns) were investigated using validated FE modeling for progressive collapse potential in the event of middle column removal. The analysis was carried out with the help of LS-DYNA software. It incorporated nonlinear constitutive modeling of concrete and steel rebars considering the effect of strain rate, and modeling of bond-slip behavior at the interaction of steel rebars with concrete. Out of the 16 assemblies, 12 specimens represented the actual detailing of an existing 8-story building. The studied variables included axial load on columns, percentage of continuous bottom beam rebars across the beam-column joint (with respect to the total number of bottom rebars), and number of beam spans. The performance of the 12 assemblies was evaluated in accordance with mode of failure and characteristics of load–displacement envelope. A simple approach was suggested to assess the progressive collapse risk level of RC OMFs. Five risk levels were proposed, ranging from very low to very high. Very high to high risk was predicted for the 12 studied assemblies. The last four assemblies of the analysis matrix were newly designed to reduce the progressive collapse risk to a moderate (or low) level.
查看更多>>摘要：? 2022 Elsevier LtdThis work reports investigation of the premature corrosion of power connectors made of silver plated ASTM 356 cast aluminum alloy from a Brazilian substation. Both the 500 kV and neutral terminals underwent severe oxidation and plating delamination, causing their electrical failure. The corrosion mechanism and failure root cause were investigated through visual inspection, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. The analysis revealed several defects in the plating, which exposed both the aluminum substrate and silver coating to electrolytes (humidity/rainwater), forming a galvanic couple. Moreover, the preferential dissolution of the aluminum rich areas, due to micro-galvanic corrosion, resulted in loss of loose aluminum particles that left the plating without mechanical support. Therefore, the electrical failure of the connectors occurred due to the existence of defects in the plating, causing severe galvanic corrosion of the substrate, aggravated by the micro-galvanic corrosion of the aluminum rich regions.
查看更多>>摘要：? 2022 Elsevier LtdIn this article, the vital operational characteristics such as reliability, performance and remaining useful life (RUL), pertaining to the electromagnetic solenoid valves (SVs), which govern their successful functioning and safe operation during service, are taken into account via a thorough review of the literature. Significance of the coil insulation on the SV reliability and performance is also focused upon. A brief description on the classification of SVs and, more importantly, a summary of the existing research efforts towards automotive and other industrial applications of SVs is included in this review. SVs are also used extensively in the rapidly growing electric and hybrid vehicle industry. The primary aim of this work is to assist the present and future research investigators in realizing the existing research gaps through communicating to them both the past developments and the present status with respect to the above factors associated with the solenoid valve.
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