Large Slippage Research Articles

Grouped rubber-sleeved studs–UHPC pocket connections in prefabricated steel–UHPC composite beams: Shear performance under monotonic and cyclic loadings

Prefabricated steel–ultra-high-performance concrete (UHPC) composite beams (PSUCBs) with grouped stud–UHPC pocket connections (GSUPCs) are a successful attempt of UHPC in bridge engineering, which offers significant advantages in accelerating on-site construction, enhancing structural performance, and improving environmental benefits. However, the uneven steel–concrete interfacial shear stresses distribution caused by the insufficient deformability of ordinary studs (OSs) in UHPC may result in the premature stud failure in large interfacial slippage regions. To address this issue, rubber-sleeved studs (RSSs) that wrapped rubber-sleeves around the stud roots were introduced to improve ductility and reduce the stiffness of connectors. However, the shear performance of grouped RSSs embedded in UHPC remains unclear, which hinders their application in practices. Against this background, systematic experimental and numerical studies were conducted to investigate the monotonic and cyclic shear performance of grouped RSSs–UHPC pocket connections. The results indicated that wrapping rubber-sleeve could increase the ultimate slip capacity and remained sufficient shear resistance, demonstrating great potentials of grouped RSSs–UHPC pocket connections in PSUCBs. Increasing the rubber-sleeve thicknesses and height effectively improved the ultimate slip capacity and deformation recovery, but led to the significant plastic deformation accumulation and cyclic stiffness degradation. Finally, design recommendation on rubber-sleeve configuration rationalization, ultimate shear resistance and load–slip relationship predictive models were provided.

Structural performance of speed-lock joints with split bolts in steel storage racks

This paper aims to experimentally and numerically investigate the structural performance of speed-lock joints with split bolts in steel storage racks. There are no bolts in the typical speed-lock joint for its ease of installation, and the joint transmits and bears force through interactions of the tabs and upright beam holes. However, the joint under seismic loading shows large looseness and slippage with low stiffness. Also, the energy dissipation capacity is insufficient and the failure of tabs in the joints might lead to brittle behavior. In this study, new detail of the speed-lock joint with bolts is proposed by adding a pair of split bolts in the beam end plate while still preserving its merit of ease of installation. A double-cantilever beam test was designed to test this speed-lock joint with split bolts along with the typical speed-lock joint. Low cyclic loading tests were performed on both types of joints: with split bolts and without split bolts. The results revealed the benefits that the split bolts could bring to significantly enhance the performance of the joint in terms of the maximum bending moment, the initial stiffness, the displacement ductility coefficient, the equivalent viscous damping coefficient, and the energy consumption. In addition, a two-step analysis method was proposed for the high-fidelity finite element model of the joints to overcome the complex contact nonlinearity. The numerical model was then validated with the tests for further numerical studies on the performance of speed lock joints with/without bolts.

Breakdown of classical bunch length and energy spread formula in a quasi-isochronous electron storage ring

Originating from the stochastic nature of the photon emission process, the longitudinal coordinates of electrons diffuse even if the global phase slippage of a storage ring is zero, as we cannot zero all the local phase slippages simultaneously. This quantum diffusion is viewed as the most fundamental effect limiting the lowest bunch length realizable in an electron storage ring from single-particle dynamics perspective. Energy spread diverges when bunch length is pushed to the limit given by this diffusion. Here we report the first experimental evidence supporting the existence of this effect. The measurements confirm the breakdown of the classical formula of bunch length and energy spread in an electron storage ring with globally small and locally large phase slippage.

Modified Lucas-Washburn theory for fluid filling in nanotubes.

Ultrafast water transport in carbon nanotubes (CNTs) has drawn a great deal of attention in a number of applications, such as water desalination, power generation, and biomolecule detection. With the recent experimental advances in water filling of isolated CNTs, the Lucas-Washburn theory for capillary rise in tubes needs to be revisited for a better understanding of the physics and dynamics of water filling in CNTs. Here, the Lucas-Washburn theory is corrected for the hydrodynamic entrance effects as well as the variation of capillary pressure and hydrodynamic properties with the radius and length of CNTs. Due to the large slippage in CNTs, inclusion of the entrance effects is important particularly for the initial stages of filling where a L∝t scaling, as opposed to L^{2}∝t, is observed in our molecular dynamics (MD) simulations. The corrected Lucas-Washburn theory is shown to predict the water filling dynamics in CNTs as observed in MD simulations. With the corrected theory, we achieve a better understanding of capillary rise and water filling dynamics in CNTs.

The Effect of Connections on The Global Response of Built-up Cold-formed Steel Beams with Corrugated Webs

The objective of this paper is to quantify the slippage and rotation in the connections of a double fixed corrugated web beam. Two types of connections between the component parts of the built-up beam were used, i.e. MIG brazing and spot welding, which offer different rigidities and bearing capacities for the built-up beams. Experimental tests were conducted on three MIG brazed and two spot welded specimens, respectively. The test setup consisted of a six-point bending configuration which is equivalent to a uniform distributed load applied to the beam. The load was applied from a 500kN actuator through a leverage system that allowed the distribution of the force. An out-of-plane structure prevented the beam from lateral torsional buckling. The testing exhibited relatively large slippage and deformation in the bolted connections and in the supporting device, respectively. However, the high rigidity of the beam maintained the mid-span deflection in the serviceability limit state limits. The built-up corrugated web beams made of cold-formed steel profiles represent an efficient and suitable structural solution for buildings. Nevertheless, experimental research due to inevitable slippage and the endplate deformation must be performed to characterize the connection.

Multiscale calculation results of the flow behavior in micro/nano porous filtration membrane with the adsorbed layer-fluid interfacial slippage

The paper presents the multiscale calculation results for the multiscale flow in micro/nano porous filtration membranes where the adsorbed layer effect is involved, by considering the adsorbed layer-fluid interfacial slippage. The analysis consists of the molecular scale analysis for the adsorbed layer flow and the continuum analysis for the intermediate fluid flow. The calculation results are respectively compared with the classical flow theory calculations and those based on the solid layer assumption. The adsorbed layer flow rate is also compared with the flow rate of the intermediate continuum fluid. It is shown that for a strong fluid-pore wall interaction or for a large adsorbed layer-fluid interfacial slippage the adsorbed layer can be treated as a solid layer; otherwise it should be treated as a flowing layer. The large interfacial slippage results in the flow rate through the pore far greater than the classical Hagen-Poiseuille equation calculation; it largely propels the flow of the intermediate continuum fluid and makes the adsorbed layer flow negligible particularly for the medium and strong fluid-pore wall interactions. The increasing fluid-pore wall interaction strength significantly reduces the flow rate through the pore.

Experimental study on seismic performance of shear wall with precast concrete hollow molds

AbstractA new type of connection between shear walls is proposed for the shear wall with precast concrete hollow molds (PCHM). The overlapping reinforcements are inserted into the PCHM before pouring concrete into the hollow in this method. Full‐scale test specimens are tested under low cyclic loading test to analyze their seismic performance, such as failure modes, hysteretic characters, stiffness degradation, energy dissipation, and ductility. For the precast specimen, although the penetrating crack appears at the horizontal connection, there is no large slippage leading to anchorage failure and disengagement of interfaces. Generally, compared with cast‐in‐situ shear walls, shear walls with PCHM have no large difference in bearing capacity, failure mode, stiffness degradation, energy dissipation and ductility. Therefore, the proposed shear wall with the new type of connection method is worth popularizing and utilizing in practical engineering projects with similar design procedure to cast‐in‐situ structures.

Dynamic modeling of bedding-plane slip during hydraulic fracturing

Whether the tip stresses around a dynamically propagating hydraulic fracture (HF) could activate a bedding plane (BP) or not is an important question for HF propagation and microseismicity generation. BP slip has been proposed to be one main source of microseismicity during HF treatments in unconventional reservoirs. However, a BP perpendicular to a principal stress direction is unlikely to be activated in a simple geomechanical model. We have applied a dynamic finite-element geomechanics method to examine the induced dynamic shear stress and the activation of BPs that are perpendicular to the HF based on the Cotton-Valley tight-sand reservoir properties. We work in a 2D vertical-plane framework. The induced dynamic stresses around a HF tip could be significant. We explore three different scenarios for the BP activation. In the first scenario, an HF is dynamically propagating toward two symmetric BPs, but has not touched them yet. We find that only low-strength BPs can be activated in this scenario. In the second scenario, an HF dynamically propagates toward two symmetric BPs and then it crosses them by a short distance. The BPs could be more easily activated in this scenario compared with the first scenario. The slip length and maximum slip decrease with cohesion, critical slip distance, or maximum principal stress. In the third scenario, an HF dynamically propagates toward two symmetric BPs, and then fluid invasion into the BPs occurs after the HF touches them. Large shear slippage and slip length happen in this scenario because fluid invasion weakens the BPs. In all of the scenarios, different senses of shear could occur along the BPs and a rupture typically propagates bilaterally from the initiation point on the BPs.

Large slippage and depletion layer at the polyelectrolyte/solid interface.

The slippage of polymer solutions on solid surfaces is often attributed to a depletion layer whose origin, thickness, and interaction with the flow are poorly understood. Using a Dynamic Surface Force Apparatus we report a structural and nanorheological study of the interface between hydrolyzed poly-acrylamide solutions and platinum surfaces. Polyelectrolyte chains adsorb on the surfaces in a thin charged layer, acting as a nonattractive wall for the bulk solution. We investigate the flow of the visco-elastic solution on the adsorbed layer from the nanometer to 10 micrometers, bridging microscopic to macroscopic properties. At distances larger than 200 nanometers, the flow is well described by an apparent slip boundary condition. At smaller distance the apparent slip is found to decrease with the gap. In contrast to the apparent slip model, we show that a 2-fluids model taking into account the finite thickness of depletion layers at the non-attractive wall describes accurately the dynamic forces over 4 spatial decades of confinement. Depletion layers are found to be an equilibrium property of the interface, independent on the flow and on the confinement. Their thickness is phenomenologically described by ξ + 2lD with ξ the correlation length of the semi-dilute solutions and lD the Debye length. We interpret this result in terms of screened repulsion between the charged adsorbed layer and the bulk polyions.

Ghana

Ghana’s macroeconomic performance has been mixed, as over the years recurrent policy slippages have amplified the impact of external and domestic shocks, created persistent imbalances, and contributed to high inflation, exchange rate volatility, and unfavorable debt dynamics. The new government thus faces significant challenges, including a large fiscal slippage that occurred in 2016. Addressing these challenges calls for an ambitious adjustment and reform agenda.

Super-harmonic resonance of gear transmission system under stick-slip vibration in high-speed train

This work deals with super-harmonic responses and the stabilities of a gear transmission system of a high-speed train under the stick-slip oscillation of the wheel-set. The dynamic model of the system is developed with consideration on the factors including the time-varying system stiffness, the transmission error, the tooth backlash and the self-excited excitation of the wheel-set. The frequency-response equation of the system at super-harmonic resonance is obtained by the multiple scales method, and the stabilities of the system are analyzed using the perturbation theory. Complex nonlinear behaviors of the system including multi-valued solutions, jump phenomenon, hardening stiffness are found. The effects of the equivalent damping and the loads of the system under the stick-slip oscillation are analyzed. It shows that the change of the load can obviously influence the resonance frequency of the system and have little effect on the steady-state response amplitude of the system. The damping of the system has a negative effect, opposite to the load. The synthetic damping of the system composed of meshing damping and equivalent damping may be less than zero when the wheel-set has a large slippage, and the system loses its stability owing to the Hopf bifurcation. Analytical results are validated by numerical simulations.

Defining the effects of cutting parameters on burr formation and minimization in ultra-precision grooving of amorphous alloy

Amorphous nickel phosphorus (Ni-P) alloy is a suitable mold material for fabricating micropatterns on optical elements for enhancing their performances. Ultra-precision cutting is preferred to be used to machine the mold material for high precision in a large workpiece. However, burrs and chippings always form and are detrimental especially when fabricating micropatterns. The formation mechanisms of burrs and chippings have not yet been revealed precisely in the cutting processes of amorphous alloys, because their cutting behavior is more complex and less discussed in existing researches than that of crystalline metals. In the present study, the burr formation process of amorphous Ni-P is defined and a three-dimensional cutting model using energy method is proposed to predict and minimize burrs and chippings. Microgrooving experiments were conducted with different undeformed chip geometries using three types of cutting tools to observe burr formation processes. Large burrs and chippings were formed when cutting with a tapered square tool and a tilted triangle tool. These large burrs and chippings were found to be induced by large slippages that are unique to amorphous alloys. It was revealed that burrs and chippings appear when the angle between the chip flow direction and the groove edge is less than a critical value. Energy method was used to predict the chip flow directions and the calculated results agree with the experimental ones, which proved that the energy method is valid for designing an appropriate undeformed chip geometry to reduce burrs and chippings in ultra-precision grooving.

Modelling the development of defects during composite reinforcements and prepreg forming.

Defects in composite materials are created during manufacture to a large extent. To avoid them as much as possible, it is important that process simulations model the onset and the development of these defects. It is then possible to determine the manufacturing conditions that lead to the absence or to the controlled presence of such defects. Three types of defects that may appear during textile composite reinforcement or prepreg forming are analysed and modelled in this paper. Wrinkling is one of the most common flaws that occur during textile composite reinforcement forming processes. The influence of the different rigidities of the textile reinforcement is studied. The concept of 'locking angle' is questioned. A second type of unusual behaviour of fibrous composite reinforcements that can be seen as a flaw during their forming process is the onset of peculiar 'transition zones' that are directly related to the bending stiffness of the fibres. The 'transition zones' are due to the bending stiffness of fibres. The standard continuum mechanics of Cauchy is not sufficient to model these defects. A second gradient approach is presented that allows one to account for such unusual behaviours and to master their onset and development during forming process simulations. Finally, the large slippages that may occur during a preform forming are discussed and simulated with meso finite-element models used for macroscopic forming. This article is part of the themed issue 'Multiscale modelling of the structural integrity of composite materials'.

Monotonic and cyclic response of speed-lock connections with bolts in storage racks

The purpose of this paper is to explore the bearing capacity and energy dissipation of several variations of speed-lock connections of cold-formed steel storage racks. Commonly used speed-lock connection exists large slippage and low energy dissipation capacity, new speed-lock connections with additional bolts (and welds) are investigated in order to enhance its performance. Their monotonic behavior and hysteretic response under cyclic loading were studied experimentally using a cantilever test method. The tests were conducted using both the EN 15512 monotonic protocol and AISC seismic provisions’ cyclic-test protocol for each specimen. The failure modes, moment–rotation response, and associated stiffnesses, bearing capacities, and energy dissipation capabilities were fully investigated. Both monotonic and cyclic responses showed that the additional bolts (and welds) significantly enhanced the bearing capacities and deformability of the connections, though the initial stiffness and equivalent stiffness (i.e., according to the EN 15512 specification) showed little improvement. The hysteretic responses of all connection variations investigated demonstrated pinching behaviors. The energy dissipation capability has been greatly improved with additional bolts (and welds) except of the one with only lower bolts, which could also be corroborated through the analyses of the calculated equivalent viscous damping coefficient and the displacement ductility factor. In addition, the stiffness degradation has been observed for both positive loading and negative loading, and adding bolts and welds could effectively reduce this effect.

Trends in the Happiness of Single Mothers: Evidence from the General Social Survey

We study the subjective well being (SWB) of single mothers from 1972 to 2008 using data from the General Social Survey. While past literature has examined the outcomes of single mothers, an investigation of SWB is warranted, since it has been shown that there are potentially large slippages between economic indicators and SWB. Our results indicate that (i) single mothers report being significantly less happy than non-single-mothers, and (ii) this “happiness gap” shrank between 1972 and 2008.

Influence of cup-center-edge angle on micro-motion at the interface between the cup and host bone in cementless total hip arthroplasty: three-dimensional finite element analysis.

We verified the index cup position required for bulk bone grafting instead of morcellized grafting immediately after cementless total hip arthroplasty. Three-dimensional finite element analysis was used to evaluate changes in the volume of the slippage of the cup-host bone interface as micro-motion of the cup at the acetabular bone defect site depending on the cup-center-edge (CE) angle. The conditions of bulk bone grafts were similar to those of cortical bone. Slippage increased with decreasing cup-CE angle. A bulk bone graft tightly fixed to the host bone prevented considerably larger slippage between the cup and host bone. A smaller cup-CE angle increased the impact of the bulk bone graft on slippage. When the cup-CE angle was 0° or -10°, the criterion for slippage in favorable initial fixation in all conditions was <40 μm. Even if transplanted bulk bone is used, unless good fixation is obtained between the host bone, and the cup and bone graft, it is impossible to obtain reliable fixation of the cup with a cup-CE angle <-10° and slippage exceeding 40 μm. Bulk bone grafting tightly fixed to the host bone improves initial the cup-host bone fixation, especially when the cup-CE angle is small, such as <-10°. In clinical practice, negative factors are implicated in the initial fixation of various cups, and sufficient fixation between the host bone and cup or bulk bone graft using a screw is effective when the cup-CE angle is extremely small.

The Effects of Various Slippage Loads on the Response Modification Factor of Steel Structures Equipped with Frictional Dampers

A common and successful way of structural control is to dissipate the seismic kinetic energy via frictional dampers. Response of a friction damped frame during an earthquake excitation is heavily dependent to the slippage limit of the frictional dampers. Low values of slippage load may lead to excessive deformations while large slippage loads may prevent sliding. Therefore, selecting appropriate values for slippages loads of the dampers is very important in order to have optimum energy dissipating system. Utilizing a response modification factor, the standard seismic design code procedure can be applied to the frames equipped with frictional dampers to determine the value of slippage loads. In this investigation, the response modification factor of steel moment resisting frames equipped with frictional dampers is evaluated considering the effects of various slippage loads. The response modification factor is calculated for two bay widths of 5 m and 7 m in length. It is shown that the optimum slippage load that results in the maximum response modification factor is in the range of 8% to 20% of the total weight of the structure. The taller the structure is, the less the optimum slippage load will be. Finally, an equation is proposed for the response modification factor as a function of the slippage load.

Selected papers from the third European Conference on Microfluidics: µFlu’12

The third European Conference on Microfluidics (lFlu’12) was held in Heidelberg in December 2012, under the sponsorship of the Hydrotechnic Society of France (SHF), the Alma Mater Studiorum University of Bologna, the University of Toulouse and the Karlsruhe Institute of Technology. This event has gathered 252 participants from 33 countries. During 3 days, 174 communications have been presented in 16 thematic sessions including Liquid Microflows, Gas Microflows, Microsensors and In-Situ Analytics, Fluidic Microactuators and Micromixing, Microfabrication Techniques for Microfluidic Systems, Convective Micro Heat Transfer, Micro Chemical Engineering, Lab-on-a-Chip, Electrokinetic Microflows, Microdroplets Management, Microflows in Biological Systems and Bioengineering, Multi-Phase Flows in Microsystems, Microflow Visualization, and other topics. Two special sessions have been devoted to Industrial Applications of Microfluidics and to Nanofluidics. The multi-disciplinarity of Microfluidics is highlighted by the variety of works presented in this Conference which confirms also that Microfluidics nowadays finds applications in every industrial sector like biology, medicine, chemical and process engineering, transports, environment, microelectronics. This year the Scientific Committee has selected four papers presented to the Conference for publication in Microfluidics and Nanofluidics; the common topic of these selected papers is the detailed analysis of the interactions at micrometric scale between the fluid and the solid walls of a microdevice by highlighting what happens when the solid surface either presents microgrooves, or gathers electrical charges, or has been submitted to a surface chemical treatment or is simply oscillating. More in detail, the paper of Gopalan and Kandlikar is devoted to the experimental analysis of the wettability of micro-patterned surfaces. Their results show that the wettability is strongly influenced by the spacing factor of a grooved surface, defined as the ratio between the channel depth and the channel width: The spacing factor influences the contact angle, the contact angle hysteresis, and the transition characteristics between the Cassie and Wenzel states. The authors demonstrate that their experimental results can be useful for the design of the gas channels of a Proton Exchange Membrane Fuel Cell (PEMFC) in order to optimize the water drainage. The paper presented by Gentili et al. is focused on the analysis of the combined effect of nanoscale roughness and surface chemistry modification in order to achieve large liquid slippage due to entrapment of air pockets in the surface asperities. In the paper, a numerical simulation campaign based on full atoms Molecular Dynamics aimed at reproducing a realistic superhydrophobic system comprising water, solid walls, and hydrophobic coating with octadecyltrichlorosilane (OTS) is described and compared with the results obtained by following a continuum S. Colin INSA, Institut Clement Ader (ICA), Universite de Toulouse, 135, Avenue de Rangueil, 31077 Toulouse, France e-mail: stephane.colin@insa-toulouse.fr

Pressure effects on water slippage over silane-coated rough surfaces: pillars and holes

Nanoscale roughness in combination with surface chemistry modification can achieve large liquid slippage due to entrapment of air pockets in the surface asperities (superhydrophobic Cassie state). However, pressure increase may result in the collapse of the gaseous enclaves into the fully wet Wenzel state, and in the irreversible loss of the desirable superhydrophobic features. In order to explain the subtle effects of pressure, an extensive simulative campaign based on full-atoms molecular dynamics and aimed at reproducing a realistic superhydrophobic system comprising water, solid walls, and hydrophobic coating with octadecyltrichlorosilane is addressed in comparison with a continuum approach. The dramatic impact of pressure on slippage is twofold: on the one hand, it influences the shape of the liquid/vapor interface, thus indirectly affecting the flow. This is a purely geometrical effect well captured in principle by the continuum description. On the other hand, pressure controls the complex interplay between water and hydrophobic chains close to the triple line where it significantly alters the liquid structure, thus modifying apparent slippage. This is an intrinsically atomistic phenomenology that cannot be predicted at the continuum level. The combination of the two effects is found to explain the peculiar response of slippage to the applied pressure at the nanoscale, that may look at first sight in contradiction with most microscale literature results.

Stability control of surrounding rocks for a coal roadway in a deep tectonic region

In order to effectively control the deformation and failure of surrounding rocks in a coal roadway in a deep tectonic region, the deformation and failure mechanism and stability control mechanism were studied. With such methods as numerical simulation and field testing, the distribution law of the displacement, stress and plastic zone in the surrounding rocks was analyzed. The deformation and failure mechanisms of coal roadways in deep tectonic areas were revealed: under high tectonic stress, two sides will slide along the roof or floor; while the plastic zone of the two sides will extend along the roof or floor, leading to more serious deformation and failure in the corner of two sides and the bolt supporting the corners is readily cut off by the shear force or tension force. Aimed at controlling the large slippage deformation of the two sides, serious deformation and failure in the corners of the two sides and massive bolt breakage, a “controlling and yielding coupling support” control technology is proposed. Firstly, bolts which do not pass through the bedding plane should be used in the corners of the roadway, allowing the two sides to have some degree of sliding to achieve the purpose of “yielding” support, and which avoid breakage of the bolts in the corner. After yielding support, bolts in the corner of the roadway and which pass through the bedding plane should be used to control the deformation and failure of the coal in the corner. “Controlling and yielding coupling support” technology has been successfully applied in engineering practice, and the stability of deep coal roadway has been greatly improved.