查看更多>>摘要：This paper investigates graphite decohesion as the primary fracture mechanism of compacted graphite iron (CGI) subjected to thermal load. Despite CGI's extensive industrial use and considerable research on its mechanical behaviour, thermal debonding is not yet fully understood, nor is the influence of matrix phases on it. After thermal cycling to confirm the occurrence of the phenomenon, a numerical approach is developed: a 2D unit cell is constructed, with a single graphite particle, represented as an ellipse embedded in a metallic matrix. The inclusion is surrounded by an extra layer that accounts for either pearlite or ferrite, in order to study their effect on thermal debonding. An elastoplastic behaviour is assumed for all constituents, described with a classical J2 flow theory of plasticity, and the models are analysed employing a finiteelement approach. The proposed numerical strategy focuses on the influence of matrix phases on thermal debonding, identifying numerical schemes to assess it. The obtained results can provide significant knowledge on the response of CGI to thermal load at the microscale, contributing to the understanding of its macroscopic thermomechanical behaviour.
查看更多>>摘要：This paper proposes an improved critic method and establishes an operational safety assessment method for straddle-type monorail vehicle system based on cloud model and improved critic method. Firstly, according to the structure and function of straddle-type monorail vehicle system, the reliability index system of straddle-type monorail vehicle is established, and the weight value of reliability evaluation index is determined by improved critic method. Then, the cloud model expression of reliability evaluation index of straddle-type monorail vehicle system is obtained by virtual cloud. finally, similarity analysis is conducted between the new cloud of straddle-type monorail vehicle system reliability comprehensive index and the cloud model of reliability evaluation set, so as to judge that the comprehensive cloud model of straddle-type monorail vehicle system can be used to evaluate the operation status of "main functions " of the system. The analysis shows that the reliability evaluation method of straddle-type monorail vehicle system based on cloud model and improved critic method can correctly describe the daily operation of straddle-type monorail vehicle system in Chongqing, which provides a method reference for reliability evaluation of straddle-type monorail vehicle system.
Metcalfe, Roger G.Costanzi, RogerHorner, GarryVance, John...
16页
查看更多>>摘要：This paper presents the results of an examination of a single row tapered roller bearing from a 650 t Face shovel swing transmission gearbox that exhibited an unusual pattern of axial fracture. The bearing sustained multiple axial fractures around the inner ring (cone) many of which exhibited a fracture face with a two tone pattern, suggesting a two stage fracture, comprising a dark internal region of lubricant discolouration and a bright fresh fracture border. SEM examination indicated the discoloured region to have fractured following an intergranular path consistent with hydrogen embrittlement arising from lubricant breakdown, while the border region exhibited a cleavage fracture.
查看更多>>摘要：Fatigue test of steel tubular T-joint specimens was performed. A beach mark (BM) technique was employed to measure the crack size. Some rare fracture patterns were found. One of the specimens generated two major surface cracks around the weld toe. They were independently propagating at the initial stages and were coalesced into a single surface crack at a certain amount of cyclic loads. Subsequently, the crack was enlarged and became a doubly curved surface crack. Crack propagation (CP) simulation is performed to investigate the fracture behaviors. Extended finite element method (X-FEM) option in an open-source software Code_Aster is used. FEM CP simulation is also performed to validate the X-FEM results. The CP phenomena are carefully examined using the fracture mechanics parameters and crack front trajectories.
查看更多>>摘要：Flexible wires present wet occluded spaces where corrosion induces supersaturation of ferrous ions and precipitation of FeCO3. Localized corrosion is possible due to discontinuities of the precipitated FeCO3. This work aims to investigate the Stress Corrosion Cracking susceptibility of armour layer in FeCO3 supersaturated seawater, addressing the influence of CO2 partial pressure and strain rate, at 25 degrees C and at 40 degrees C, using the Slow Strain Rate Test. The results were expressed by ASTM G129 standard parameters. The material showed loss of ductility under all experimental conditions. The most aggressive conditions were at 25 degrees C, 10 bar, under 10(-7) s(-1) and 10(-6) s(1)strain rates, respectively. The results showed that fracture mechanism is related to hydrogen embrittlement, suggested by the presence of internal secondary cracks on the fracture surface. These secondary cracks suggest the interference of delamination. From the results it was possible to rank the severity of experimental conditions imposed.
查看更多>>摘要：Contact fatigue spalling failure ocurred in the M50 steel bearings during test due to the formation of white etching area (WEA). In this paper, characteristics, formation mechanism, influence on contact fatigue spalling failure and control methods of the WEA were obtained by examining loctaions and morphological characteristics, composition analysis, hardness test and microstructure analysis of the WEA in the two failure bearing and the other three bearing which are not failure. The results show that the WEAs origin from the boundary between matrix and primary carbides or inclusions which located in the subsurface of raceway, show irregular block shape morphologies, have length direction of about 30 degrees -50 degrees degrees to the rolling direction and microstructure of body centered cubic ferrite nanocrystalline. There is no obvious difference between the WEA and matrix in chemical compositions, while hardness of the WEA is higher than that of the matrix. Formation mechanism of WEA is phase transformation driven by accumulation of plastic deformation induced by high stress in micro region. The smaller the distance between WEA and the raceway surface, the faster of WEA growth rate are reached. And WEA is more likely to cause contact fatigue spalling of the bearing as the deformation coordination between WEA and matrix is poor. The initiation and propagation of WEA can be controlled by reducing the material defects and avoiding the bearing from high working stress.
查看更多>>摘要：The investigation pertains to the failure analysis of Fibre Reinforced Plastic rods used in overhead transmission line insulators using appropriate data acquisition and analysis. The leakage current data, over an experimental period is captured and time-frequency analysis is implemented for determining the in-service condition of the overhead transmission insulators. It is observed from the investigation that the signal displays various events like dry-band arcing, partial surface arcs and triple-point discharges at the electrodes. The study presents a simple time-frequency analysis used for presenting the phenomena, an algorithm is developed for the harmonic analysis, also Empirical Mode Decomposition is conducted to reinforce the analysis. The main focus of the study is to estimate the early failures with minimal time and with available data.
查看更多>>摘要：Here we examine the AC corrosion characteristics of the buffer layer in high voltage corrugated-aluminum sheathed power cables, and analyze the relationship between corrosion and cable failure. Penetration of moisture into the buffer layer, including dampness introduced during manufacture and direct water entry through mechanical damage to the cable sheath, results in AC corrosion and formation of hydrogen and Al(OH)(3). On the basis of AC current density spectroscopy, the influences of voltage, moisture content, and pressure on the threshold current density are investigated. The cable structure is considered, and a relationship between the AC corrosion and cable failure is determined. A large ripple depth of the corrugated aluminum promotes a non-uniform circular current distribution. The combination of high moisture content and non-uniform current density results in local high temperatures in the buffer layer that ultimately cause the failure of the power cables.
查看更多>>摘要：Strong blasting disturbances and excavation unloading effects may result in rib spalling and roof collapse of the near-field rocks surrounding the drift during longhole stope mining. An underground gold mine in Shandong Province, China, was selected as a case study to investigate the evolution of the damage to the near-field rocks surrounding the drift through theoretical analysis and field tests, and the relationship between the convergence deformation and damage zone radius of the rock surrounding the drift was established. The results of this study revealed that the convergent deformation of the near-field rocks surrounding the drift exhibited a stepwise increase with time. At the moment of stope blasting, the maximum increment of the convergent deformation of the rock surrounding the drift reached 30.90 mm. Moreover, the convergence deformation of the rock surrounding the drift exhibited exponential decay with increasing distance from the stope boundary. The area within the vicinity of the drift and 7.32 m from the stope boundary was defined as the strongly affected zone, and the area within 7.32-21.62 m of the stope boundary was defined as the moderately affected zone. In view of the functional relationship between the convergence deformation and the damage zone radius of the rock surrounding the drift, a method of calculating the damage zone depth of the rock surrounding the drift was established by considering the effects of the deformation relief before convergence monitoring and the disturbance caused by the extraction of the longhole stope based on the unified strength theory. The error between the damage zone depth obtained using the proposed method and the actual value was less than 3.00%. It was found that the increment of the damage zone depth reached 2.07 m in the strongly affected zone and the average increment was 1.76 m. The method developed in this study can be used to assess the depth of the damage zone in the near-field rocks surrounding the drift in the longhole stope in similar mines.
查看更多>>摘要：To realize the numerical analysis of rock bolt bearing-yield-fracture under tension-shear coupling and to provide an effective means for supporting the design of roadways or tunnels, a new numerical model was developed to analyse the tension-shear coupling fracture behaviour of rock bolts in engineering rock masses. Based on the study of the mechanical behaviour of rock bolts under tensile-shear coupling load, the mechanical criterion and constitutive model of the yield and fracture of rock bolts were proposed, and the secondary development of the FLAC3D platform was realized. At the same time, self-developed equipment was used to conduct the rock bolt tensile shear test. By comparing the numerical simulation results with the experimental results, we determine that the maximum difference in the shear displacement of the rock bolt does not exceed 2 mm during the yielding and breaking of the rock bolt, and the percent difference was approximately 3% and 10%, respectively. In the field of engineering, this result is generally considered acceptable. Using the numerical model we proposed, a numerical simulation experiment was conducted on the rock bolt support design of a coal mining roadway in engineering practice. The results show that under the original support scheme, a large amount of rock bolt tensile-shear failure occurs at the coal-rock interface, which makes the original support scheme unable to meet the engineering requirements with tensile-shear coupling failure tendency. In this regard, we adopted the support method of grouting anchorage at the interface of coal and rock. The results show that the deformation of the roadway surrounding rock has been effectively controlled.
NSTL
Elsevier