Bond–Slip Law Between Steel Bar and Different Cement-Based Materials Considering Anchorage Position Function

The bond performance between steel bar and cement-based materials was the prerequisite for the two materials to work together, and previous studies showed that the bond behavior of the steel bars and cement-based materials will vary with the kinds of cement-based materials. For this reason, this paper adopted 12 direct pullout test specimens including three types of concrete and two types of steel bars. The strain of the steel bar at six measuring points was measured with a strain gauge. Based on the measured strain and free end slip of the steel bars, the distribution of steel stress, bond stress, and relative slip and the bond slip relation along the anchorage length were obtained and analyzed for different concrete and different steel bars. Based on these test results of steel strain and relative slip at six measuring points, the anchorage position function could be established in consideration of anchorage position, which was conducive to the establishment of an accurate bond–slip relationship. In addition, the anchorage length of the steel bar in Engineered Cementitious Composites (ECC) calculated from the equilibrium equation of critical limit state is only half of the anchorage length calculated in the current Code for Design of Concrete Structures (GB 50010-2010) in China. It is suggested to establish the critical anchorage length formula suitable for ECC in future studies.

A calculation methodology of fault relative displacement used to study the mechanical characteristic of fault slip

Fault slip caused by mining disturbance is a crucial issue that can pose considerable threats to the mine safety. This paper proposes a point-by-point integration calculated methodology of fault relative slip and studies fault instability behavior induced by coal seam mining. A physical model with the existence of a fault and an extra-thick rock stratum is constructed to simulate the fault movement and calculate relative slip using the methodology. The results indicate that the fault relative slip can be regarded as a dynamic evolution process from local slip to global slip on the fault surface. The movement of surrounding rock masses near the fault experiences three stages, including along vertical downward, parallel to the fault and then approximately perpendicular to the fault. There will be an undamaged zone in the extra-thick rock strata when the mining face is near the fault structure. The collapse and instability of this undamaged zone could induce a violent fault relative slip. In addition, the influence of dip angles on the fault relative slip is also discussed. A formula for risk of fault relative slip is further proposed by fitting the relative displacement curves with different fault dip angles.

Analysis of Rail Corrugation Characteristics on High-Speed Rail Based on Transient Finite Element Method

By using the transient finite element method, a three-dimensional wheelset-track coupled rolling contact model for high-speed rail is established, and the rationality and effectiveness of the model are verified by field measurements. Next, the wheel-rail contact stress states and relative slip characteristics are calculated and analyzed to reveal the cause of inner rail corrugation. Then, the vertical vibration acceleration of the rail/wheel is taken as the output variable to study the dynamic responses of the wheelset-track system. Finally, the parameter sensitivity analysis is carried out. The results show that the maximum normal/tangential contact stress between the inner wheel and inner rail is greater than that between outer wheel and outer rail due to the unbalanced load of inner rail caused by the excess superelevation of track structure, which indicates that the unbalanced load of the inner rail may aggravate the development of rail wear, and the rationality of the model established in this paper is verified. The wheel-rail relative slip region on the inner rail side appears periodically, and the distance between the two adjacent slip regions is close to the characteristic wavelength of the measured inner rail corrugation, which illustrates that the periodic variation of slip regions on the inner rail surface plays an important role in the formation of rail corrugation, and the validity of the model is verified. The periodic distribution of wheel-rail relative slip regions on the outer rail surface is not obvious, demonstrating that the outer rail tends to form uniform wear, which is consistent with the fact that the outer rail corrugation is slight in the measured section. The wheelset-track system has been in the process of unstable continuous oscillation in the analysis interval, combined with the analysis results of the wheel-rail relative slip characteristics, it can be concluded that the unstable self-excited vibration of wheelset-track system under the condition of tangential contact force reaching saturation is the main cause of rail corrugation. The dominant characteristic frequencies of vertical vibration accelerations of rail and wheel are all 561 Hz, the corresponding characteristic wavelength (148 mm) is close to the distance (150 mm) between the calculated adjacent slip regions, and is also close to the characteristic wavelengths (125 mm and 160 mm) of inner rail corrugation, which shows that the resonance phenomenon occurs in the wheelset-track system at the above frequency, thus leading to the increase of dynamic responses of wheelset-track system. The fastener vertical stiffness and wheel-rail coefficient of friction have significant effect on the development of rail corrugation, and the running speed determines the occurrence probability of inner/outer rail corrugation by affecting the track superelevation state.

Performance Features of Tooth Gearing in Gear Hydraulic Machines

The paper presented determines that the rotation velocities of gears and radii connecting the axes of rotation of the gears with the point of their teeth gearing are not equal with each other. It is explained by the relative slip of involute gear profiles during their rolling. This phenomenon will become a prerequisite for further development of creation of mathematical models in the context of theory of gear hydraulic machines. The models can explain a number of specific phenomena in the operation of gear hydraulic machines, such as pressure and input pulsations, dynamics of hydraulic oil in the cut-off plane, combined torque pulsations in gear hydraulic motors and others.

A Three-Section-Settlement Calculation Method for Composite Foundation Reinforced by Geogrid-Encased Stone Columns

The analysis of the bearing characteristics and deformation mechanism of composite foundation reinforced with geogrid-encased stone columns is presented in order to obtain its settlement calculation method. The settlement of composite foundation is divided into three sections which are the reinforced section, unreinforced section, and underlying stratum. Based on Hooke’s law of space problem and the thoughts of the layer-wise summation method, the relative slip displacement between pile and soil of reinforced section without plastic zone is analyzed. The settlement of reinforced section is calculated by the layered iteration method based on the pile element model. The compatibility of vertical and radial deformations of unreinforced section is analyzed based on the pile-soil element model. The settlement of underlying stratum is still calculated by the layer-wise summation method. Finally, two engineering examples are analyzed and the results show that the settlement calculated by the presented method is close to the measured one. The method overcomes the defect that the calculated results by the other existing methods are more dangerous and it is more feasible and can be applied in engineering practice.

Friction mechanism and characteristics of reticle based on contact theory

With the development of integrated circuits, the structure of chips becomes more and more complex, and the processing cost increases accordingly. In order to improve the productivity of lithography, the acceleration of reticle stage should be increased to reduce the positioning time. However, the increase of acceleration will cause the relative slip between reticle and vacuum chuck, which seriously affects the accuracy and product yield of lithography. In order to suppress the slippage, the friction mechanism and characteristics between reticle and chuck are studied in this paper. Firstly, based on KE contact model and MB fractal contact model, the maximum static friction coefficient model between nano-scale surfaces was established. Then, the surface morphology parameters of reticle and chuck adsorption surface was obtained by atomic force microscopy (AFM) scanning. Finally, the maximum static friction force experiments show that the MB model is more suitable for the study of friction mechanism between reticle and vacuum chuck, and the model is more instructive for the suppression of reticle slip.

Walking–sliding experimental analysis of frictional characteristics socked feet

Simulation experiments and in-vivo experiments were widely employed for investigating sock-skin frictional characteristics. The simulation experiments usually was a type of sliding experiment which described the relative slip between fabric and artificial skin. The in-vivo approaches typically involved subjects adopting a variety of postures and friction between their clothing and the skin was estimated. However, simulation and in-vivo experiments were reported only separately. The connection between the two types of experiments was scarcely reported. To reveal the connection, we synchronously carried out two interrelated experiments, a natural walking experiment and sliding experiment, using the same sock fabric. In the natural walking experiment, the subject wearing socks walked on the force platform. Then the soles of these socks were cut out and were used in the soles-artificial skin sliding experiment. The coefficients of friction in the two types of experiments reflected some correlative frictional characteristics. We found the effect of the walking speed or sliding speed on the friction coefficient was not significant. While, water content increased the friction coefficient in the two experiment. Additionally, the friction in the coronal direction was smaller than that in the sagittal direction during walking. Through our efforts, we hope to bridge the simulation and in-vivo experiments and elucidate the frictional characteristics between the sock and insole.

A Sliding-Mode Control Algorithm to Enhance In-Hand Motion Capabilities

This paper reports a method for regulating the internal forces during in hand manipulation of an unknown shaped object with soft robotic fingers. The internal forces ensure that the object does not move between the robotic fingers, thus improving the grip. It is shown that if soft fingers show bounded conformity and the finger-object interface have bounded relative slip, then the relative angular velocity between the object and the fingertip coordinate frame in contact is bounded. Detailed derivation of the proof is presented. The proof is used to define a new metric of relative slip. The metric is used to design a sliding mode control algorithm that results in an efficient grip which is robust towards uncertainty in object shape. The robotic fingers are assumed to be under virtual rigidity constraint, that is, the distance between the fingertips do not change. The control algorithm is attractive as it skirts the requirement of information of the shape of the object or to solve optimization problems. The grip with the robust control algorithm is shown to be finite-time stable through Lyapunov's method. The methodology is demonstrated using simulations.

Dynamics Modeling and Simulation of a Net Closing Mechanism for Tether-Net Capture

Tether-net is a promising active debris removal technique, and a closing mechanism can ensure the reliable wrapping of space debris by using tether-net. This study focuses on the dynamics model of the split closing mechanism and the sliding joint between thread and ring. First, a new kind of closing mechanism is proposed, which drives the closing thread to close the net mouth through the split masses, and the mass-spring-damper method is used to model tether-net. Thereafter, for the first time, the model of thread-ring sliding joint is proposed based on the mass-spring-damper method, which can be used to simulate the closing process of tether-net. Finally, one-edge closure experiment of the net is carried out and the experimental results are compared with the simulation results, and the closing process of the tether-net is simulated by using the thread-ring sliding joint. Results reveal that the thread-ring sliding joint can be used to simulate the relative slip between the thread and the ring, and the tether-net can wrap the target reliably in a short time by using the split closing system. The split closing mechanism can make it possible for the tether-net to close successfully, whether it starts to work before or after the net contacts with the target.

Quantitative Demonstration of Wear Rate and Dissipation Energy during Tension–Torsion Cyclic Loading of Steel Wires with Fretting Contact in Different Environmental Media

The wear rate and dissipation energy during tension–torsion cyclic loading of steel wires with fretting contact in different environmental media were explored in this study. Hysteresis loops of tangential force versus displacement amplitude (Ft-D) and torque versus torsion angle (T-θ), and their dissipation energies were obtained employing the self-made test rig. Morphologies of wear scars of steel wires were observed employing the white light interference surface morphology. The quantitative demonstration of the coefficient of cyclic wear of steel wire was carried out combining polynomial fitting, reconstruction of three-dimensional geometric model of wear scar and Archard’s equation. The results show that Ft-D curves reveal both decreases of the relative slip and dissipation energy in the order: corrosive media, deionized water and air. Increases of contact load and crossing angle caused overall decreases in the relative slip and dissipation energy, while the relative slip and dissipation energy both increased with increasing torsion angle. T-θ curves indicated the largest and smallest dissipation energies in cases of acid solution and deionized water, respectively. Increases of contact load, crossing angle and torsion angle caused increases in relative slip and dissipation energy due to cyclic torsional loading with fretting contact. The wear coefficient in cases of distinct environmental media decreased in this order: air, corrosive media and deionized water. Increases of the contact load, torsion angle and crossing angle all induced increases in the wear coefficient.