Search

Considering the advantages of hybrid steel I-section beams in reducing engineering costs and fully utilizing the mechanical properties of steel, and the lack of research on their ductility, hybrid steel I-section beams were tested to analyze the effects of the plate width–thickness ratio and steel strength matching on the flexural bearing capacity and ductility. The steel strength matching of the hybrid steel I-section beam with a high steel strength utilization rate and good ductility was related closely to the section size. Additionally, a parametric analysis based on the finite- element method was performed for further study. The steel strength ratio φ of the web to the flange with the best ductility was less than 1, and φ decreased with an increase in flange steel strength. The steel strength utilization rate and ductility decreased with an increase in φ. Based on the parametric analysis results, the optimal range of φ in hybrid-steel I-section beams with flange steel strength of 460–690 MPa was 0.56–1. The plate width–thickness ratio limit of the ductile section decreased with the decrease of φ. Considering the plate interaction and steel strength matching, a sectional ductility design method is proposed that is more applicable to hybrid steel I-section beams than existing methods. [ABSTRACT FROM AUTHOR]

Assembly deviations of wheelsets cause differential wheelset misalignments and change the wheel-rail contact relationship in railway turnouts. In this paper, the motion conditions of wheelsets under the same bogie are analysed with differential wheelset misalignment based on the mechanical equilibrium condition. A rigid-flexible coupling model of vehicle-turnout dynamic interaction that fully considering different misalignment conditions is established to evaluate the wheel and turnout rails dynamic interaction and vehicle dynamic characteristics. The results show that wheelset misalignment can change wheel load transition position and affect wheel-rail contact conditions, especially when the misalignment direction is toward the switch rail. The larger misalignment angle will increase flange contact range and keep the normal contact stress at a higher level. Both misalignment angle and form determine the wheel-rail vertical force. The lateral force is mainly affected by the superposition effect of the eccentric load and the lateral impact of the wheel load transition. [ABSTRACT FROM AUTHOR]

Abstract: Nanosintering behaviour of MgAl2O4 ultra-fine powder was investigated under high pressure. We found that the nanosintering mechanism under high pressure was quite different from that under ambient pressure. To shed light on the mechanism, the residual stress, grain size, and boundary situation were investigated using HRTEM and XRD, respectively. Our results show high pressure can restrain grain growth and initiate plastic deformation to eliminate pores and/or additional phases existing in triple junctions of the grains. However, the conventional sintering process is controlled by grain growth to avoid imperfections between grain boundaries when preparing transparent ceramics. [Copyright &y& Elsevier]

• The resistance values of ballast beds with concrete sleepers and composite sleepers were tested. • The resistance variation laws of ballast beds with the 2 types of sleepers were studied. • The 'rebounding' of ballast particles in the ballast bed with composite sleepers was discovered. • The moving differences of the ballast around the 2 types of sleepers were explained. A composite sleeper has a similar shape, stiffness, and weight to that of an existing wood sleeper with additional benefits including excellent durability, extended design life like a prestressed concrete sleeper, environmentally friendliness, and cost effectiveness. Therefore, in some cases, composite sleepers are considered as an alternative for wooden or concrete sleepers. In this study, the longitudinal- and lateral-displacement resistance changes of the fiber reinforced foamed urethane (FFU) composite sleepers and the concrete sleepers in ballast beds were tested. The application conditions of the composite sleeper in a ballast bed were analyzed. The results show that the resistance of the composite sleeper changed more sharply, and its value was greater than that of the concrete sleeper during the initial stage of their displacements. The longitudinal and lateral resistance of the composite sleeper was lower than that of the concrete sleeper with an increase in displacement (at 2 mm, longitudinal: 41.35% of the concrete sleeper, lateral: 35.64% of the concrete sleeper). Using the discrete element method (DEM), it was found that when the composite sleeper moves, the ballast around it may 'rebound.' The force and its transfer of the ballast near the displacement end of the concrete sleeper was an upward arc, while that of the composite sleeper was a downward arc. The ballast on the side of the concrete sleeper moved upward (tending to be horizontal) along the lateral-displacement direction of the sleeper, while that of the composite sleeper moved downward (tending to be vertical). [ABSTRACT FROM AUTHOR]

Film of Fe3O4 was prepared with laser molecular beam epitaxy deposition on a Si substrate with a native SiO2 layer. When the temperature is increased above 250 K, the resistance drops rapidly because the conduction path starts to switch from the Fe3O4 film to the inversion layer underneath the SiO2 via thermally assisted tunneling. A greatly magnified low field negative magnetoresistance of Fe3O4 is observed at 280 K. The effect is similar to a metal-oxide-semiconductor field-effect transistor. The magnetoresistance becomes positive with further increase in the magnetic field due to the Lorentz force and other effects on the carriers in the inversion layer. [ABSTRACT FROM AUTHOR]