查看更多>>摘要：High geometric precision of the machined surface after Wire Electrical Discharge Machining (WEDM) is in present one of the key quality parameters placed on machine parts manufactured for a wide range of industries. Despite the fact that WEDM belongs to the most precise finishing technologies, the deviations from the required geometric shape occur in the production of parts with rotary surfaces. These geometric deviations subsequently manifest in practice not only in the assembly of individual parts of the final product, but also in the operation. Another not the less important criterion considered at WEDM is the productivity of the WEDM process itself. WEDM productivity, in turn, is associated with the low overall productivity due to the need to apply multiple finishing cuts to achieve the desired quality of the machined surface in terms of geometric accuracy. Based on the already performed research, it is clear that the deviations of the geometric accuracy of the machined surface after WEDM are mainly caused by the vibrations of the wire tool electrode. Therefore, by eliminating these vibrations, it would be possible to achieve a substantial increase of the quality of the eroded surface, and thus reduce the number of finishing cuts. Ideally, the required quality level of the machined surface would be achieved right at the first cut. This would significantly increase productivity, enabling the WEDM technology to compete with other technologies in terms of productivity. In order to eliminate these undesirable vibrations of the wire tool electrode and to increase the quality of the machined surface after WEDM in terms of its geometric accuracy, the technical solution was proposed that applies the method of acoustic emission or laser beam vibration sensing in order to dynamically adjust the current values of technological parameters by the control system of the electroerosion machine. This way the given solution will increase the production accuracy of the circular holes, save the production time, increase the productivity, and ultimately bring the overall increase of the WEDM process economic efficiency.
查看更多>>摘要：This paper presents the determination of a suitable probability function for fatigue-related reliability assessment of automotive coil springs under various road excitations using maximum likelihood estimation (MLE). The fatigue-related reliability assessment is a critical element for determining the component warranty period. The fatigue lives of the coil spring under various road excitations were obtained from experimental analysis using strain life approaches. The parameters for various distribution approach were estimated through maximum likelihood estimation (MLE). The Akaike information criterion (AIC) was used to determine the most suitable approach for fitting. As the outcome, the Nakagami distribution has shown the lowest AIC value at 330 which indicating as the most suitable fitting among other distributions. For reliability assessment, the mean time to failure (MTTF), reliability function and hazard rate was analysed. Based on these results, the suitable distribution for fatigue-related reliability characterisation were determined for improving spring life cycle assessment.
查看更多>>摘要：This paper proposes a universal analytical method for the seismic performance assessment of concrete bridges with initial fatigue damage caused by traffic loads. Load modeling is firstly performed, and random models of traffic load and seismic loads are established using stochastic processes. Subsequently, the theoretical approach for deterministic seismic response analysis of concrete bridges with initial traffic-induced fatigue damage is established by a combination of the micro-meso stochastic damage constitutive models and the finite element numerical method. In this manner, the seismic damage and failure mechanism of concrete bridges with initial fatigue damage can be elucidated. Further, considering the randomness of loads, the stochastic seismic analytical framework of concrete bridges damaged by traffic loads is put forward, in accordance with the probability space partition-based random load combination method and the probability density evolution theory. In such a way, the seismic reliability and safety of existing damaged concrete bridges can be well evaluated. Finally, a railway concrete bridge, as a practical engineering application, is investigated to validate the applicability of the proposed method.
Ji, DongdongZhang, JiwangYi, KejianHuang, Yichang...
15页
查看更多>>摘要：High-speed railway axles may be damaged during service or maintenance. Therefore, to ensure axle service safety, the residual life of damaged axles is necessary for an accurate assessment. In this study, a small-sized specimen was analyzed and the effectiveness of the extended finite element method (XFEM) was verified by comparing the simulation and test results. Subsequently, the residual life of the EA4T axle with an initial crack was evaluated using the XFEM, which is based on fracture mechanics, and the actual axle service load spectrum. The results show that the critical failure sizes for the residual life of the power axle and non-power axle were 7 and 4 mm, respectively, for a crack located in the middle of the axle body; in contrast, for a crack located in the arc transition of the wheel seat, the critical failure dimensions were 9 and 5 mm, respectively. Based on the NASGRO equation and considering the damage tolerance safety factor, the residual lives of the power axle for the two crack locations were estimated to be 1.3953 x 10(6) and 9.636 x 10(5) km, respectively, while those of the non-power axle were 2.095 x 10(6) and 1.2583 x 10(6) km, respectively. The results of this study can provide a reference for the axle non-destructive testing (NDT) period.
查看更多>>摘要：Hydrogen embrittlement (HE) behavior of E690 high-strength steel as a weld joint was investigated in artificial seawater. The most vulnerable location and microstructure to HE was verified, and the underlying mechanism was clarified. Results showed that the weld metal with granular bainitic microstructure leads to premature fracture of the entire weld joint under slow strain rate tensile testing with in-situ hydrogen charging. Dislocation slip bands (DSBs) could be preferentially developed in this zone, and HE initiation was induced via dislocation-hydrogen interaction because the weld metal had the lowest local strength among the weld joint. Martensite/austenite (M/A) constituents and carbides could also contribute to crack initiation and propagation through microvoid coalescence and decohesion.
Bakhshayesh, M. MoshkbarFarzadi, A.Doustahadi, A.Nouripour, M....
11页
查看更多>>摘要：In this paper, the susceptibility to intergranular corrosion (IGC) of 13Cr-4Ni martensitic stainless steel clad deposited by submerged arc welding was studied in the as-welded condition and after post-weld heat treats (PWHT) at 420, 500, 540, and 580 degrees C. Microstructural studies showed a martensitic matrix, about 20% delta-ferrite and carbide precipitates in the microstructure under the as-welded condition. The results of the double loop electrochemical potentiokinetic technique revealed that the PWHT process significantly increased the degree of sensitization (DOS). The highest DOS corresponded was 87.9% in the sample treated at 500 degrees C. PWHT at temperatures higher than 500 degrees C returned the DOS to lower values. PWHT at 500 degrees C and below promoted the decomposition of delta-ferrite, and hence some new chromium carbides precipitated at delta-ferrite and martensite interfaces, whereas tempering at temperatures higher than 500 degrees C accounted for carbides precipitation at martensite lath boundaries owing to the formation of tempered martensite. The DOS value decreased with increasing PWHT time due to chromium diffusion to chromium-depleted regions. Also, the potentiodynamic studies showed an inverse relationship between the DOS and pitting potential; the higher DOS, the lower the pitting potential.
查看更多>>摘要：Non-destructive testing methods for detection of steel surfaces have become very popular to check the quality of surface finish in the steel and iron industries. Vision based approach which uses image processing has advanced with good accuracy for the surface inspection and classifications. This paper presents a review of some techniques based on vision system for detection surface defects. The purpose of this paper is to check the status of research progress in the field of vision inspection system. In this regard, hardware system, software system, lighting method and its selection, image processing and control system have been discussed. Development in vision based defect detection techniques and classifiers for classification of the defects have been presented in this paper.
查看更多>>摘要：The main objective of this short communication is to show the fracture progression in each loading case and complement knowledge about fracture mechanisms underpinning the tensile and fatigue performance of thin-walled tubes. For this purpose, the fracture surface topography analysis (FRASTA) method was used in the thin-walled tubular austenitic stainless-steel specimens. Two cases were analyzed: monotonic tension, and uniaxial fully-reversed fatigue. Furthermore, the fractures topographies were quantified through the profiles over their entire surfaces with the support of an optical confocal measurement system. The results showed the usefulness of the FRASTA method in identifying characteristic zones in the cracking process for the analyzed cases and motivates its development for other materials and complex loading cases.
Lai, Van QuiBanyong, RungkhunKeawsawasvong, Suraparb
20页
查看更多>>摘要：New average FELA solutions for the problem of the limiting pressure behind soil gaps and the lateral force acting on a pile per unit length of a contiguous pile wall in anisotropic clay are investigated in this paper. The anisotropic undrained shear (AUS) model is utilized to determine anisotropic soil behaviour. The limiting pressure factor (N) is derived by varying dimensionless parameters such as the anisotropic ratio (re), the adhesion factor (alpha), and soil gap ratios (S/D) which are presented in the form of sample charts and tables. The failure patterns of the soil gaps are also conducted and explained in light of the impacting factors. A closed-form equation of the limiting pressure factor is presented in order to efficiently and precisely establish and evaluate an undrained limiting pressure behind soil gaps and the lateral force operating on a pile wall in practice.
查看更多>>摘要：Train derailments in low-speed railway turnout areas are very common due to poor track alignment and rail failures, and in extreme cases can lead to casualties and damage to infrastructure and railway vehicles. This study aims to explore the dynamic derailment behaviour caused by rail joint failures before the railway switch panel, and to understand the effects of crucial parameters on the operating safety of trains. To this end, a 3D dynamic coupled freight train-track simulation model is developed based on the MBS-FEM method. The model takes into consideration the lateral difference between rail joint sections that directly cause the wheel to rise. Flexible deformations of the rail and wheelset are modelled, and the derailment mechanism of wheel jumping and climbing in the railway switch panel is revealed. Results show that increasing the curve radius and distance between the rail joint and switch toe can effectively improve passing safety. When a sharp curve has to be placed before the switch panel due to site limitations, reducing the wheel-rail coefficient can also ensure better operating safety. This study indicates that the proposed MBS-FEM dynamic coupled derailment simulation model is able to efficiently evaluate the operating safety as a result of various wheel and track defects, and thus form a basis for providing a cost-effective platform for the future parameter optimization of railway tracks and vehicles.
NSTL
Elsevier