Interfacial Slip Research Articles

Shallow Tectonic Stress Magnitudes at the Hikurangi Subduction Margin, New Zealand

AbstractQuantifying tectonic stress magnitudes is crucial in understanding crustal deformation processes, fault geomechanics, and variable plate interface slip behaviors in subduction zones. The Hikurangi Subduction Margin (HSM), New Zealand, is characterized by along‐strike variation in interface slip behavior, which may be linked to tectonic stress variations within the overriding plate. This study constrains in situ stress magnitudes of the shallow (<3 km) overriding plate of the HSM to better understand its tectonics and how they relate to larger scale subduction dynamics. Results reveal σ3: Sv ratios of 0.6–1 at depths above 650–700 m TVD and 0.92–1 below this depth interval along the entire HSM. Additionally, for depths below 650–700 m TVD, SHmax: Sv ratios of 0.95–1.81 in the central HSM and 0.95–2.3 in the southern HSM are estimated. These stress ratios suggest a prevalent thrust to strike‐slip (σ1 = SHmax) faulting regime across the central and southern HSM. In the central HSM, the presence of NNE‐NE striking reverse faults co‐existing with a modern σ1 (SHmax) aligned ENE‐WSW suggests that overtime the stress state here evolved from a contractional to a strike‐slip state, where the compressional direction changes from perpendicular (NW‐SE) to oblique (ENE‐WSW) to the Hikurangi margin. This temporal change in stress state may be explained by forearc rotation, likely combined with the development of upper plate overpressures. In the southern HSM, the modern WNW‐ESE/NW‐SE σ1 (SHmax) and pre‐existing NNE‐NE striking reverse faults indicate that stress state remains contractional and perpendicular (NW‐SE) to the Hikurangi margin overtime.

Analytical study of unsteady two-layer combined electroosmotic and pressure-driven flow through a cylindrical microchannel with slip-dependent zeta potential

For investigating dynamics of two-fluid co-flows at an arbitrary time, the unsteady two-layer pressure-driven electroosmotic flow in a cylindrical microchannel is studied. To propose a model of universal significance, the interfacial slip and slip-dependent zeta potential are incorporated. The momentum equations are analytically solved and the physical picture how the unsteady two-layer flow evolves into the steady state is provided by evaluating the transient velocities. The two-layer velocities or flow rates are computed at different slip coefficients, electrokinetic widths, viscosity ratios, density ratios, radius ratios and zeta potential ratios, thereby the resulting interactive influences are assessed. When considering slip-dependent zeta potential, the change in two-layer velocity with other parameters is more pronounced. The increasing rate of flow rate with slip coefficient augments with electrokinetic width and outer zeta potential, which decreases with radius ratio. This work establishes mechanisms for the enhancement of transporting efficiency in microdevices associated with multi-layer flows.

Experimental investigation on shear behavior of bamboo-concrete composite structure with perforated steel plate connection

In order to fully utilize the high tensile strength of bamboo while mitigating the drawbacks of its small elastic modulus and large deformation, a composite structure combining bamboo and concrete was employed. The transfer of longitudinal shear force between the two materials was accomplished by capitalizing on their respective advantages and minimizing the relative slip at the interface. This study proposed a bamboo-concrete composite (BCC) structure utilizing a perforated steel plate (PSP) as a shear connection. An experimental investigation was conducted, exploring different combinations of several parameters, including the aperture size of the PSP, the concrete strength, the presence of penetrating steel bars, and the diameter of the penetrating steel bar. Sixteen groups of BCC structure with PSP connection were tested, and the failure mode, ultimate bearing capacity, and relative interface slip of the structures were analyzed. The test results indicate that as the concrete strength increases, the stiffness and bearing capacity of the connection also increase. However, the corresponding slip at the ultimate load diminishes. Under the condition where the concrete strength and the diameter of the penetrating steel bar are the same, the larger the aperture size of the PSP, the lower the stiffness of the connection, and the greater the slip corresponding to the ultimate load. Furthermore, a larger diameter of the steel bar results in greater connection stiffness and decreased slip at the ultimate load. Drawing on the shear capacity calculation formulas proposed by scholars for PSP connections, this study integrates the experimental results into these formulas and compares them with the actual outcomes. Through a comprehensive assessment of the primary factors influencing load-bearing capacity, a shear capacity calculation formula specifically designed for the BCC structure with PSP connections is proposed and developed.

Numerical and experimental investigation on the flexural stiffness of RC beams strengthened with prestressed CFRP plate exposed to wetting/drying cycles

The load-deflection relationship is critical for the serviceability and structural durability of reinforced concrete (RC) structures strengthened with prestressed carbon fiber-reinforced polymer (CFRP) plates. This study aims to investigate the impact of prestressing levels and wetting/drying cycles (WDCs) on the flexural stiffness of prestressed CFRP-strengthened RC beams. A modified flexural stiffness prediction model was proposed by incorporating prestressing levels, interfacial bond slip, and softening after WDCs. Subsequently, four-point bending tests were conducted on 11 strengthened beams with different prestressing levels and WDCs to estimate flexural behavior. The results suggest that WDCs can adversely affect the flexural stiffness of the strengthened beams, particularly for the post-cracking stiffness of the non-prestressed specimens. However, prestressed strengthening can mitigate the stiffness degradation caused by WDCs. Moreover, a finite element (FE) model utilizing a traction separation model can accurately predict flexural stiffness. Finally, the flexural stiffness was computed using both the existing and proposed models and the proposed model provides the closest prediction of the flexural stiffness for CFRP-strengthened beams under WDC and prestressing.

Experimental Investigation on the Effect of Velocity Anisotropy on Oil Film State under Different Surface Wettability Interface

This study focuses on the utilization of surface modification technology to create glass disks with varying surface wettability. A measurement test bench for point contact lubrication film is employed to investigate the impact of changes in the angle between the velocities of the glass disk and steel ball on the state of the lubricating oil film at the interface. The results show that altering the surface wettability reduces the adhesive strength between the interface and the adjacent lubricant, leading to a decrease in the ultimate shear stress, and inducing interface slippage. When the rotational velocity of the disk matches the translational velocity of the ball and their trajectories are inclined at specific angles, the sliding velocity increases proportionally to the inclination angle, which contributes significantly to the thermal effect. Furthermore, when the velocity varies across the interface with differences in wettability, the contact zone forms a wedge-shaped gap and causes modifications in the oil film’s shape, including the formation of an inlet dimple and an inclined straight stripe. The dominant factor influencing the interface is the slip when the angle is acute, whereas the thermal effect plays a significant role when the angle is obtuse. This work is expected to provide a new strategy for elastohydrodynamic lubrication under surface wettability interfaces.

Effective width evaluation for HSS-UHPC composite beams with perfobond strip connectors

This paper investigates the design criteria for predicting the effective width in high strength steel (HSS)-to-Ultra-high performance concrete (UHPC) composite beams with perfobond strip connectors (PBLs). Twenty-eight HSS-UHPC composite beams with varying parameters of shear connection degree (C), span length (S), thickness (T) and width (W) of UHPC slab were numerically simulated and evaluated. The composite beams' strain distribution and shear lag effect were presented and analyzed. Results indicate that the shear lag of the HSS-UHPC composite beam under flexural loadings was significant, and the effective width coefficient (β) of the concrete slab was enlarged by the magnification of the C, T, and S. A comparison between the results obtained from the FE model and procedures for predicting the composite beams’ effective width was performed to assess the feasibility of design approaches. It reveals that existing codes provide good predictions for the HSS-UHPC composite beams with a W/S ratio below 0.3 but underestimate the effective width for those with W/S ratio beyond 0.3. Furthermore, an empirical model for predicting the effective width of HSS-UHPC composite beams, considering the shear lag and steel-to-UHPC interfacial slip, is derived and fitted by a data regression. The outcome of this study can provide a reference for HSS-UHPC composite beams in practical applications.

Experimental and numerical simulation of pull-out response in textile-reinforced concrete

Textile-reinforced concrete (TRC) is a construction material that uses continuous fibres such as carbon to create a lightweight and durable structural system. Even though TRC possesses vast possibilities in terms of its usage, identification of bond-slip behaviour at the material interface is one of the limitations that need to be addressed. Based on the literature, there are difficulties in determining the bond-slip relationship both experimentally and numerically, creating inconsistency in the results. This study aims to determine the bond-slip relation of TRC through pullout tests and validated through finite element analysis to replicate the actual bond-slip behaviour at the interface. The bond characteristics of TRC were assessed using a double-sided pullout test setup with different bond lengths of textile, namely 20 mm, 30 mm, 40 mm, 50 mm, and 60 mm. It was noticed that in short bond specimens (20 mm, 30 mm, and 40 mm), the phenomena of pullout failure were due to weakened bond at the interface until pre-peak, followed by complete loss of adhesive bond due to debonding of fibre. However, for the specimens with longer bond lengths (50 mm and 60 mm), rupture of the textile leading to a sudden loss of bond capacity was observed. Additionally, the general fibre pullout phenomenon curve was used to explain the debonding process. Using a calibrated tri-linear bond-slip interface relation, the numerical model was developed to simulate the pull-out response of fibre. The numerical model was able to reproduce experimental results, including maximum load, post-peak behaviour, and interfacial slip. The difference of maximum shear stress between pull-out tests and numerical modelling was within 2 % while the slip difference was between 4 and 31 % for different bond lengths. However, for longer bond lengths, the fibre failure mode was due to pullout instead of rupture, unlike the experimental results.

Integrating electric double layer time-varying and dual interface slip for predicting migration behavior of moisture and ions

Migration of moisture and chloride ions in calcium-silicate-hydrates (C-S-H) nanopores is important factor for controlling the durability of concrete and affecting the physical and chemical properties of cement-based binder. Quantitative analysis of experimental results indicates that the pore in C-S-H is mainly distributed on the nanometer scale. Due to the prominent interfacial effects at the nanoscale, moisture and ions in different regions within nanochannels exhibit distinct molecular structures and dynamic properties. Therefore, the wetting behavior of the synthesized C-S-H surface and its influence on microfluid dynamics analysis and boundary condition definition were systematically analyzed based on the contact angle experiment. Statistical thermodynamics were introduced to describe the time-varying characteristics of the electric double layer (EDL). With the interaction as the theoretical framework and interaction energy as an important parameter, the equilibrium behavior of interacting particles was studied to describe the stability of EDL system. The flow control equation and boundary conditions were modified considering the action of EDL. The transport model of moisture and chloride ions under the combined influence of electric double layer and dual interface slip was proposed. The results show that the existence of EDL impedes the movement of the fluid, while the dual slippage of water film and time-varying of EDL reduce the resistance. Quantitative analysis indicates the contribution ratios of water film slip and EDL time-varying can reach 85% and 29%, respectively. In addition, water film slip has a greater influence on water migration and EDL time-varying has a greater influence on ions. This research can provide new insights into the transport mechanism of water and chloride ions at micro-nanoscale.

Experimental and nonlinear-analytical studies of cross-laminated-timber concrete composite floors with interface shear resistance enhancement of plate-end

Cross-laminated-timber (CLT)-concrete composite system has drawn more attention as a new technology. This study investigated CLT-concrete composite (CCC) floor with shear resistance enhancement of plate-end experimentally and analytically. In order to obtain the shear performance of coach screw connectors, two groups of push-out tests were carried out. Based on the test results and failure modes, three characteristic slip moduli of the push-out specimen were calculated. Then, three groups of four-point bending tests were conducted to study the flexural behavior of CCC floor with different screw arrangements. One group of bending specimens was designed by shear resistance enhancement of plate-end and showed excellent performance in terms of bending stiffness and bearing capacity. Furthermore, the nonlinear analytical model for calculating the relative slip of composite floor was established, which took into account the stiffness reduction effect of the connectors. Finally, based on the generalized connection system model, the optimized γ-method for calculating effective bending stiffness was proposed, which considered the Interface slip modulus transformation. By comparing with the experiment results, the analytical methods presented in this study could predict interface relative slip and effective bending stiffness of composite floor well, which provided important references for the design of CCC floor.

Computational method for energy transport of MHD nanofluids flow near non-aligned stagnation point with non-linear thermal radiation and interface slip

Haemodialysis, nuclear reactors, cooling and heating systems, and heat exchangers are glimpses of applications where thermal problems are considered as a fundamental for flow over aligned stagnation points with heat and mass transfer components. The purpose of this study is to present steady dual solutions for non-aligned stagnation point flow of nanofluid over a linearly contracting/expanding surface under temperature and velocity slips. The mathematical model is established using boundary layer assumption. The authors acknowledge from prior investigations and studies that the non-aligned stagnation point flow across a contracting/expanding surface is highly rare in the field of engineering and fluid dynamics research. In the backdrop of non-linear thermal radiation, the problem of oblique hydromagnetic stagnation point flow of an electrically conducting optically dense viscous incompressible nanofluid across a convectively heated stretching sheet is formulated. The effects of Brownian motion and thermophoresis are incorporated into the nanofluid model. With the use of appropriate similarity transformations, the governing nonlinear partial differential equations for momentum, energy, and nanoparticle concentration are converted into a set of nonlinear ordinary differential equations. Using the BVP4c approach, the modified equations are numerically solved. It is discovered that when the strength of the magnetic field increases, the non-alignment of the re-attachment point on the sheet surface becomes less pronounced. The thickness of the thermal boundary layer grows as the magnetic and Biot parameters expand. The extent of the skin friction factor ascends with increasing magnetic field and suction variable inputs. The heat transfer rate detract with radiative parameter.

Experimental research on interfacial bonding performance of high‐strength steel pipe and surrounding concrete/grout for assembled composite columns

AbstractHigh‐strength steel pipe joints are proposed for assembled composite columns. The steel pipe extends into the upper and lower prefabricated columns and is anchored by poured concrete or grout to realize the connection of the prefabricated columns. Bonding performance of high‐strength steel pipe and surrounding concrete/grout is critical to the joint reliability. Steel pipe push‐out test was carried out, considering parameters of steel pipe section specification, bonding length, bonding material, and outer wall treatment of the steel pipe. Comparative analysis of measured load–displacement/slip curves and calculated bond strength were conducted. Bonding length of 600 mm could provide sufficient bond strength. Increasing bonding length could delay the slippage, but the bond strength decreased. High‐strength grout significantly increased the peak load size. The slenderness ratio and diameter–thickness ratio of the steel pipe had no obvious influence on the bonding performance. Steel pipe with D114*25 section obtained higher bonding strength with smaller ratio of bonding area to cross‐sectional area. Spiral ribs welded to the outer wall of the steel pipe could effectively improve the bonding strength and delay the interface slip. With easy construction and reliable performance, spiral ribs were recommended to be applied in prRactical projects.

Investigating the Mechanism of Continuous–Discrete Coupled Destabilization of Roadway-Surrounding Rocks in Weakly Cemented Strata under Varying Levels of Moisture Content

This study examines frequent disasters, including large-scale deformation and collapse, caused by underground mining in weakly cemented strata in Western China. The weakly cemented rock’s unique characteristics, including low strength and easy disintegration, demonstrate a different damage pattern than that traditionally seen in the central and eastern regions. Using Fast Lagrangian Analysis of Continua-Particle Flow Code (FLAC2D-PFC2D) coupling, we model the strata, focusing on the 3-1 coal seam roadway at Hongqinghe mine. This study investigates the damage–rupture–destabilization progression in the peripheral rock under varying levels of moisture content. Our findings indicate that a water content of ω = 5.5% is the threshold for roadway damage, and moisture content <5.5% yields minimal rock deformation. However, moisture content >5.5% abruptly increases cracks and shifts the rock’s force chain, causing significant deformation and affecting the ceiling the most. Moreover, higher levels of moisture content weaken the anchor solid’s performance, with two primary failure modes: anchor interface slippage (comprising five stages: elasticity, elasticity–shear hardening, elasticity–shear hardening–decohesion, shear hardening–decohesion, and decohesion) and shear damage. These insights are vital for improving numerical simulations of underground mining, obtaining a more accurate understanding of mineral pressure disasters in weakly cemented strata mining regions in Western China, and developing a solid foundation for the better control of such strata.

Theoretical analysis and numerical simulation of axial tensile behavior of pipe joints based on bi-linear cohesive bond-slip model

PurposeDue to its inexpensive production costs, low stress concentration and maintenance-friendliness, the adhesive bonded pipe joint is frequently utilized for pipe connection. However, further theoretical analysis is needed to understand the debonding failure mechanism of such bonded pipe joints under axial tension.Design/methodology/approachIn this study, based on the bi-linear cohesive zone model, the integrated closed-form solutions were derived by considering the axial stiffness ratio and failure stage to determine the relative interfacial slip, interfacial shear stress and relationship of tension–displacement in the bonded pipe joint.FindingsAdditionally, solutions for the critical bonded length and the ultimate load capacity were put forth. Besides, the numerical study was conducted to verify the theoretical solutions regarding the load–displacement relationship. The interfacial shear stress distribution at different failure stages was presented to understand the interfacial shear stress transmission and debonding process. The effect of bonded length on the ultimate load and ductility of pipe joints was also discussed.Originality/valueThe findings in this study can give a reference for the design of bonded pipe joints in their actual engineering applications.

Investigation on flexural behavior of steel-UHPC composite beams with steel shear keys

To investigate the flexural performance of steel-UHPC (ultra-high performance concrete) composite beams with welded steel shear keys (SSK), eight specimens were experimental studied by four-point bending test. The finite element (FE) models were established based on the experimental results, then, the failure mode, load, deflection, strain and relative interface slip were parametric analyzed. The influences of strength, dimensions and configuration of upper concrete slab, steel beams as well as SSK on flexural performance, in terms of load-deflection response, ductility and ultimate energy dissipation, were studied. The experimental results show that steel-UHPC composite beams have superior bearing capacity, deformation capacity, ductility and energy dissipation ability when compared with steel-NSC (normal strength concrete) composite counterparts. Increasing the height of upper concrete slab has a significant effect on improving bending capacity and flexural stiffness, while increasing the width has a significant effect on enhancing deformation, ductility and ultimate energy dissipation. Increasing the yield strength, thickness of web and flange of steel beams has significant effect on improving bending capacity. Reducing the SSK spacing or increasing the yield strength of SSK, height and thickness slightly improve the cracking, yield and ultimate loads, reduce deflections, enhance the flexural stiffness, slightly weakens the ductility and ultimate energy dissipation. Besides, four types of failure modes were defined, based on reasonable assumptions, formulae for bearing capacity were proposed, and the predicted results fit well with experimental results. The results can be taken as reference for the design and application of steel-UHPC composite beams in long-span and heavy-load structures.

Effect of helium bubbles on the interface shear strength of copper/niobium multilayer

The influence of the helium bubble on the interfacial shear strength of copper/niobium multilayers and the corresponding deformation mechanisms are studied through molecular dynamics. Strong anisotropy of the shear strength is demonstrated, and the ratio of the highest strength to the lowest is approximately 4.3. The interface bubble leads to the dislocation emission under the shear along the high-strength directions and results in the severe decrease of the interface bearing capability, while the loss of the interface bearing is negligible for the case along the weak/medium-strength directions. The contradictory effects of the bubble on the interface shear strength under different shear directions are explained by the competition between the bubble-related dislocation emission and propagation and the regular uniform interface slip. For the shear along the high-strength direction, the interface could bear relatively high shear stress which is large enough to activate the dislocation from the bubble. Consequently, the corresponding deformations are dominated by the mechanism of bubble-related dislocation emission and its propagation. For the shear along the weak/medium-strength direction, the interface itself is sheared under relatively low shear stress before the effective nucleation of dislocation. Therefore, the corresponding deformation mechanism is controlled by the regular interface shear.

Surfactant-influenced oil–water slip and flow in nanochannels studied by molecular dynamics and theoretical modeling

This work uses molecular dynamics (MD) methods to investigate oil–water two-phase flow in hydrophilic nanochannels with surfactants adsorbed at the oil–water interface. We reveal two new discontinuous effects of nanoscale fluid flow: (i) the velocity distribution in the water layer is not a univariate function of the pressure gradient, and (ii) the apparent viscosity in the oil–water interface region is a function of surfactant concentration and pressure gradient. Based on the MD results, a layered theoretical model describing the discontinuous effects at the nanoscale is developed. The theoretical model provides quantitative two-dimensional functions for oil–water interface slip and fluid mass flux with pressure gradient and surfactant concentration. Surfactants significantly inhibit oil–water slip and reduce fluid mass flux. This study thus provides important insights into the theoretical and numerical models for shale or tight oil production predictions.

Flexural behavior and crack width prediction of UHPC-steel strip composite decks under sagging moments

The UHPC-steel strip composite deck is a novel technique for strengthening in-service orthotropic steel decks with numerous fatigue cracks penetrating the steel deck plate. However, the anti-cracking behavior of the new composite decks under sagging moments is still unclear and formulas for prediction of the crack width at the bottom surface of the UHPC layer is unavailable. In this study, the flexural behavior of the UHPC-steel strip composite deck under sagging moments was investigated through a series of experimental tests. In the tests, the width of the steel strips and the thickness of the UHPC layer were considered as the two primary parameters. The responses of the UHPC-steel strip composite specimens, including the load–deflection curve, failure mode of the specimens, interfacial slippage, and nominal cracking stress of UHPC, were systematically analyzed and discussed. The test results indicate that the specimens with steel strips possessed a better anti-cracking performance compared to that of the specimens without steel strips. This phenomenon implies that the steel strips should impede the initiation and propagation of cracks in UHPC. Moreover, an increase to the width of the steel strips could reduce the average crack spacing and maximum crack width of UHPC. Further, theoretical formulas were proposed to calculate the maximum crack width at the bottom surface of the UHPC layer. The theoretical results obtained via the proposed formulas agreed well with the test results, confirming that the proposed analysis method should be suitable for the UHPC-steel strip composite deck. So the proposed method could be utilized to calculate the crack width at the bottom surface of the UHPC layer under sagging moments.

Mechanically robust all-hydrogel supercapacitor having seamless interfaces among components by rapid phase transition of physical gels

In a flexible energy storage device, the interface between the components not only degrades the electrochemical performance but also makes it mechanically vulnerable. Therefore, interface engineering is important to ensure device performance. Here, we propose a design strategy for the fabrication of seamless energy storage device that maximizes the structural integrity between all-components. Utilizing a rapid phase transition characteristic of agarose, a seamless device composed of carbon cloth, agarose/activated carbon electrode, and agarose electrolyte were prepared. The seamless interface improved areal capacitance and lap-shear strength by 35% (166.6 mF/cm2) and 1000% (12 kPa), respectively, compared to that of the conventional sandwich-type supercapacitor. In addition, the impedance of the seamless device was measured as 80% of that of the sandwich device demonstrating a decrease of interfacial resistance. While the areal capacitance of the seamless device was maintained even after 100 bending cycles, the device failure by interfacial slip for the sandwich device was observed. Considering that flexible electronic devices are subjected to repeated mechanical deformations, the device fabrication strategy using phase changing materials proved to be very effective which can be applied to versatile applications.

Bending performance of RC slabs strengthened by CFRP sheets using sprayed UHTCC as bonding layer: Experimental study and theoretical analysis

Debonding failure is one of the main drawbacks of reinforced concrete (RC) structures strengthened with externally bonded (EB) fiber reinforced polymer (FRP) systems. Due to the huge application potential of sprayed ultra-high toughness cementitious composite (UHTCC) in strengthening and retrofit, this study, with the aim of delaying or preventing intermediate crack-induced debonding of EB FRP sheets, experimentally and analytically investigated the flexural behavior of RC slabs strengthened by EB CFRP sheets with sprayed UHTCC as bonding layers, which has been rarely reported in previous research works. For this purpose, five RC slabs with low strength concrete and low reinforcement ratio, including one control specimen and four strengthened specimens repaired by EB CFRP sheets with sprayed UHTCC as bonding layers, were manufactured and tested under four-point bending load. Variable parameters in the four strengthened specimens included the thickness (10 mm, 20 mm, and 30 mm) and length (600 mm and 900 mm) of the sprayed UHTCC bonding layer. The experimental results indicated that the specimens strengthened by EB FRP sheets with sprayed UHTCC as bonding layers experienced higher load-bearing capacity (24.43 %–120.92 %) and toughness (43.15 %–166.14 %), compared to the control specimen. The thickness of the UHTCC bonding layer had a significant effect on the structural performance. By increasing the thickness from 10 mm to 20 mm and from 20 mm to 30 mm, the ultimate load was enhanced by 32.69 % and 33.81 %, while the ultimate deflection was decreased by 14.99 % and 41 %, respectively. The test findings also showed that sprayed UHTCC had a strong cracking-control ability and that no debonding failure occurred between the UHTCC layer and the CFRP sheet, while interface slip was observed between the concrete substrate and the UHTCC layer. The sectional analysis method was then used to propose an analytical model for analyzing the composite action between the concrete substrate and the strengthening material, as well as a model for predicting the load-bearing capacity of strengthened specimens. Comparing the analytical results to the experimental ones revealed that the proposed models can properly predict the flexural behavior of RC slabs strengthened by EB CFRP sheets with sprayed UHTCC as bonding layers under four-point bending load.

Theoretical and experimental study on multiscale coupled Mohr–Coulomb shear strength criterion of fibre-reinforced sand

Fibre-reinforced sand (FRS) is a multiphase and multiscale geo-material, which is widely used in geotechnical engineering as supporting structure of excavation of underground space and reinforcement of foundation of underground structures, and its strength is determined by the properties of the heterogeneous substances of the FRS and their coupling mechanical responses. In order to investigate the influence of fibre characteristics and mechanical properties on the shear strength of the FRS, according to the microscopic interface slip effect generated by the interaction between sand particles and the interaction between these particles and fibre, the material phase of the FRS is divided to conceptualize a micro cell element of the FRS that is capable of reflecting the internal material characteristic information of the FRS. Moreover, based on the coordinated deformation condition between fibres and sand particles at the microscale and the couple stress theory that is capable of effectively describing the discontinuous mechanical responses at the sand-fibre interface, a mesomechanism-based multiscale Mohr–Coulomb shear strength criterion of the FRS is derived, and the yield locus of the FRS is also drawn on the π plane. Furthermore, a series of FRS samples with different fibre content and fibre length were prepared by adopting the freezing method, and consolidated and drained triaxial compression tests were conducted on these samples to validate the proposed multiscale coupled Mohr–Coulomb shear strength criterion. Results show that the multiscale coupled Mohr–Coulomb shear strength criterion is capable of effectively reproducing and predicting the yield strength of the FRS. The yield locus of the FRS extends outwards as fibre content and fibre length increase. The yield stress of the FRS predicted by the proposed multiscale coupled Mohr–Coulomb shear strength criterion is in good agreement with that of the test result.