Search Results (845)

Molybdenum disulfide is a 2D material with excellent lubricant properties, resulting from weak van der Waals forces between lattice layers and shear-induced crystal orientation. The low forces needed to shear the MoS₂ crystal layers grant the tribological system low coefficients of friction (COF). However, film oxidation harms its efficacy in humid atmospheres, leading to an increased COF and poor surface adhesion, making its use preferable in dry or vacuum conditions. To overcome these challenges, doping MoS₂ with elements such as Nb, Ti, C, and N emerges as a promising solution. Nevertheless, the adhesion of these coatings to a steel substrate presents challenges and strategies involving the reduction in residual stresses and increased chemical affinity to the substrate by using niobium-based materials as interlayers. In this study, Nb-doped MoS₂ films were deposited on H13 steel and silicon wafers using the pulsed direct current balanced magnetron sputtering technique. Different niobium-based interlayers (pure Nb and NbN) were deposited to evaluate the adhesion properties of Nb-doped MoS₂ coatings. Unlubricated scratch tests, conducted at room temperature and relative humidity under a progressive load, were performed to analyze the COF and adhesion of the coating. Instrumented indentation tests were conducted to assess the hardness and elastic modulus of the coatings. The microstructure of the coatings was obtained by Scanning Electron Microscopy (SEM), Scanning Transmission Electron Microscopy (STEM), and Transmission Electron Microscopy (TEM), with Energy-Dispersive X-Ray Spectroscopy (EDS). Results indicated that niobium doping on MoS₂ coatings changes the structure from crystalline to amorphous. Additionally, the Nb concentration of the Nb:MoS₂ coating changed the mechanical properties, leading to different cohesive failures by different loads during the scratch tests. Results have also indicated that an NbN interlayer optimally promoted the adhesion of the film. This result is justified by the increase in hardness led by higher Nb concentrations, enhancing the load-bearing capacity of the coating. It is concluded that niobium-based materials can be used to enhance the adhesion properties of Nb-doped MoS₂ films and improve their tribological performance. Full article

In the waterway construction projects of the upper reaches of the Yangtze River, crushed mudstone particles are widely used to backfill the foundations of rock-socketed concrete-filled steel tube (RSCFST) piles, a structure widely adopted in port constructions. In these projects, the steel–mudstone interfaces experience complex loading conditions, and the surface profile tends to vary within certain ranges during construction and operation. The changes in boundary conditions and material profile significantly impact the bearing performance of these piles when subjected to cyclic loads, such as ship impacts, water level fluctuations, and wave-induced loads. Therefore, it is necessary to investigate the shear characteristics of the RSCFST pile–soil interface under cyclic vertical loading, particularly in relation to varying deformation levels in the steel casing’s outer profile. In this study, a series of cyclic direct shear tests are carried out to investigate the influential mechanisms of roughness on the cyclic behavior of RSCFST pile–soil interfaces. The impacts of roughness on shear stress, shear stiffness, damping ratio, normal stress, and particle breakage ratio are discussed separately and can be summarized as follows: (1) During the initial phase of cyclic shearing, increased roughness correlates with higher interfacial shear strength and anisotropy, but also exacerbates interfacial particle breakage. Consequently, the sample undergoes more significant shear contraction, leading to reduced interfacial shear strength and anisotropy in the later stages. (2) The damping ratio of the rough interface exhibits an initial increase followed by a decrease, while the smooth interface demonstrates the exact opposite trend. The variation in damping ratio characteristics corresponds to the transition from soil–structure to soil–soil interfacial shearing. (3) Shear contraction is more pronounced in rough interface samples compared to the smooth interface, indicating that particle breakage has a greater impact on soil shear contraction compared to densification. Full article

Infilled joints or faults are often subjected to long-term stable shear forces, and nature surface processes of normal unloading can change the frictional balance. Therefore, it is essential to study the sliding behavior of such granular materials under such unloading conditions, since they are usually the filling matter. We conducted two groups of normal unloading direct shear tests considering two variables: unloading rate and the magnitude of constant shear force. Dry sands may slide discontinuously during normal unloading, and the slip velocity does not increase uniformly with unloading time. Due to horizontal particle interlacing and normal relaxation, there will be sliding velocity fluctuations and even temporary intermissions. At the stage of sliding acceleration, the normal force decreases with a higher unloading rate and increases with a larger shear force at the same sliding velocity. The normal forces obtained from the tests are less than those calculated by Coulomb’s theory in the conventional constant-rate shear test. Under the same unloading rate, the range of apparent friction coefficient variation is narrower under larger shear forces. This study has revealed the movement patterns of natural granular layers and is of enlightening significance in the prevention of corresponding geohazards. Full article

This study presents a comprehensive investigation into the cyclic shear behavior of sand–fly ash mixtures through experimental and data-driven modeling approaches. Cyclic direct shear tests were conducted on mixtures containing fly ash at 0%, 2.5%, 5%, 10%, 15%, and 20% by weight to examine the influence of fly ash content on the shear behavior under cyclic loading conditions. The tests were carried out under a constant stress of 100 kPa to simulate field-relevant stress conditions. Results revealed that the fly ash content initially reduces shear strength at lower additive contents, but shear strength increases and reaches a maximum at 20% fly ash content. The findings highlight the trade-offs in mechanical behavior associated with varying fly ash proportions. To enhance the understanding of cyclic shear behavior, a Nonlinear Autoregressive Model with External Input (NARX) model was employed. Using data from the loading cycles as input, the NARX model was trained to predict the final shear response under cyclic conditions. The model demonstrated exceptional predictive performance, achieving a coefficient of determination (R²) of 0.99, showcasing its robustness in forecasting the cyclic shear performance based on the composition of the mixtures. The insights derived from this research underscore the potential of incorporating fly ash in sand mixtures for soil stabilization in geotechnical engineering. Furthermore, the integration of advanced machine learning techniques such as NARX models offers a powerful tool for predicting the behavior of soil mixtures, facilitating more effective and data-driven decision-making in geotechnical applications. Evidently, this study not only advances the understanding of cyclic shear behavior in fly ash–sand mixtures but also provides a framework for employing data-driven methodologies to address complex geotechnical challenges. Full article

The development of a constitutive model for soil–structure contact surfaces remains a pivotal area of research within the field of soil–structure interaction. Drawing from the Gudehus–Bauer sand hypoplasticity model, this paper employs a technique that reduces the stress tensor and strain rate tensor components to formulate a hypoplastic model tailored for sand–structure interfaces. To capture the influence of initial anisotropy, a deposition direction peak stress coefficient is incorporated; meanwhile, a friction parameter is introduced to address the surface roughness of the contact. Consequently, a comprehensive hypoplastic constitutive model is developed that takes into account both initial anisotropy and roughness. Comparative analysis with experimental data from soils on contact surfaces with diverse boundary conditions and levels of roughness indicates that the proposed model accurately forecasts shear test outcomes across various contact surfaces. Utilizing the finite element software ABAQUS 2021, an FRIC subroutine was developed, which, through simulating direct shear tests on sand–structure contact surfaces, has proven its efficacy in predicting the shear behavior of these interfaces. Full article

Gravel layers are vital ecological barriers in Gobi Desert mining areas. However, open-pit activities increase wind and soil erosion. Thus, the effects of fly ash addition, water content, and compaction on the shear strength and wind erosion resistance of soil crusts were explored by compaction tests, direct shear tests, and wind tunnel experiments. (1) The results of the direct shear test and vane shear test show that the modified soil sample achieved the maximum shear strength under the conditions of 15% fly ash content, 13% water content, and 3 compaction cycles. (2) The results of the wind tunnel test indicate that the wind erosion resistance of the gravel layer soil crust was improved after fly ash treatment. Compared to the untreated soil crust, the wind erosion amount of the treated soil was reduced by 23%. (3) Microscopic analysis revealed that hydration products from fly ash filled the soil pores, enhancing particle bonding and soil structure, using a scanning electron microscope (SEM) and an X-ray fluorescence spectrometer (XRF). (4) Considering the water scarcity in the Eastern Junggar Coalfield of China, a revised rehabilitation scheme was selected, involving 11% water content and single compaction, offering a balance between performance and economic efficiency. This study provides a novel approach to gravel layer restoration in arid mining regions using fly ash as a soil stabilizer, offering a sustainable method to enhance wind erosion resistance and promote fly ash recycling. Full article

Energy piles are highly favored for their excellent, low energy consumption in providing heating for public residences. The temperature field changes the activity of the diffuse double electric layer (DEL) on the particle surface, thereby altering the distribution of the stress field in the soil and ultimately affecting the mechanical properties of the interface between the energy pile and the soil. Therefore, studying the influence of water content on the mechanical behavior of the soil–structure interface in the temperature field is crucial for energy pile safety. This study used a modified temperature-controlled direct shear apparatus to obtain the influence of water content and temperature on the shear behavior of the soil–structure interface. Then, the test results were analyzed and discussed. Finally, three results were obtained: (1) The water content of bentonite (w_bent) had a significant impact on the shear stress–shear displacement curve of the soil–structure interface; when the w_bent was less than the w_p of the bentonite, the τ-l curve exhibited a softening response, then displayed a hardening response. (2) The shear strength of the soil–structure interface gradually decreased with the increase of w_bent. (3) The shear strength of the soil–structure interface increased with increasing temperature under various w_bent and vertical loads. Full article

Vegetation concrete is one of the most widely used substrates in ecological slope protection, but its practical application often limits the growth and nutrient uptake of plant roots due to consolidation problems, which affects the effectiveness of slope protection. This paper proposed the use of a plant protein foaming agent as a porous modifier to create a porous, lightweight treatment for vegetation concrete. Physical performance tests, direct shear tests, plant growth tests, and scanning electron microscopy experiments were conducted to compare and analyze the physical, mechanical, microscopic characteristics, and phyto-capabilities of differently treated vegetation concrete. The results showed that the higher the foam content, the more significant the porous and lightweight properties of the vegetation concrete. When the foam volume was 50%, the porosity increased by 106.05% compared to the untreated sample, while the volume weight decreased by 20.53%. The shear strength, cohesion, and internal friction angle of vegetation concrete all showed a decreasing trend with increasing foaming agent content. Festuca arundinacea grew best under the 30% foaming agent treatment, with germinative energy, germinative percentage, plant height, root length, and underground biomass increasing by 6.31%, 13.22%, 8.57%, 18.71%, and 34.62%, respectively, compared to the untreated sample. The scanning electron microscope observation showed that the pore structure of vegetation concrete was optimized after foam incorporation. Adding plant protein foaming agents to modify the pore structure of vegetation concrete is appropriate, with an optimal foam volume ratio of 20–30%. This study provides new insights and references for slope ecological restoration engineering. Full article

In order to explore the influence of different layer treatment methods on the macro- and meso-mechanical properties of cemented sand and gravel (CSG), in this paper, the shear behavior of CSG material was simulated by a three-dimensional particle flow program (PFC3D) based on the results of direct shear test in the laboratory. In shear tests, untreated CSG samples with interface coating mortar and chiseling were used, and granular discrete element software (PDC3D 7.0) was used to establish mesoscopic numerical models of CSG samples with the above three interface treatment methods, in order to reveal the effects of interface treatment methods on the interface strength and damage mechanism of CSG samples. The results show that, with the increase in normal stress, the amount of aggregate falling off the shear failure surface increases, the bump and undulation are more obvious, and the failure mode of the test block is inferred to be extrusion friction failure. The shear strength of the mortar interface is 40% higher than that of the untreated interface, and the failure surface is smooth and flat under different normal stresses. The shear strength of the chiseled interface is 10% higher than that of the untreated interface, and the failure surface fluctuates significantly under different normal stresses. Through the analysis of the fracture evolution process in the numerical simulation, it is found that the fracture of the sample at the mortar interface mainly expands along the mortar–aggregate interface and the damage mode is shear slip. However, the cracks of the samples at the gouged interface are concentrated on the upper and lower sides of the interface, and the damage mode is tension–shear. The failure mode of the samples without surface treatment is mainly tensile and shear failure, and the failure mode gradually changes to extrusion friction failure. Full article

This research explores how temperature and relative humidity impact the mechanical properties of corrugated cardboard. Samples were treated under a range of controlled climate conditions in a climate chamber to simulate varying environmental exposures. Following this conditioning, we performed a series of mechanical tests: the Edge Crush Test (ECT) to assess compressive strength, four-point Bending Tests (BNTs) in both the Machine (MD) and Cross Directions (CD) to evaluate bending stiffness, Sample Torsion Tests (SSTs) for shear stiffness, and Transverse Shear Tests (TSTs) to measure torsional rigidity. By comparing results across these tests, we aim to determine which mechanical property shows the highest sensitivity to changes in humidity levels. Findings from this study are expected to offer valuable insights into the environmental adaptability of corrugated board, particularly for applications in packaging and storage, where climate variability can affect material performance and durability. Such insights will support the development of more robust and adaptable packaging solutions optimised for specific climate conditions. Full article

The shear-yielding bolt is a new type of anchoring structure, and its working mechanism in layered rocks is not yet well understood. To investigate its transverse shear characteristics, this paper takes the shear-yielding bolt as the research subject and uses different anchoring states of bolts as variables. A comparative study of shear-yielding bolts and traditional bolts is conducted using the Abaqus numerical simulation software and large-scale direct shear tests. The results show that (1) low-modulus material allows a slight displacement between the structural surface layers, which exerts the friction strength between rock mass layers and avoids stress concentration on the bolt. The shear-yielding bolts reach their peak shear stress in the case of greater displacement, averagely increased by 40% compared to traditional anchor bolts. (2) An increase in the moisture content has less influence on the shear-yielding bolt owing to the material properties. When the moisture content of the structural surface rises from 12% to 20%, for cases where the shear-yielding bolts are used, the peak shear stress decreases by 0.12 kPa, which only accounts for 12% of the original strength. (3) There is an optimum thickness of the low-modulus material in the shear-yielding bolt, considering its effect of releasing shear and the bonding effect between it and the bolt. According to the test results and numerical analysis, the optimum thickness is 15 mm. The results of this research provide a reference and basis for future study and engineering applications of shear-yielding bolts. Full article

Shear failure of non-persistent joints represents a significant contributing factor to rock mass instability. Since non-persistent joints have various parameter characteristics, it is of great practical importance to explore shear behavior with different parameters for preventing geological disasters and engineering construction. In this study, the effects of joint aperture, joint persistency, and normal stress on the shear behavior of non-persistent persistent joints were investigated by combining indoor tests with numerical simulations. Firstly, an indoor direct shear test was carried out to examine the shear stress, normal displacement, and failure patterns from a macroscopic perspective. Then, a numerical model was constructed using the FEM-CZM method to analyze the stress evolution process of non-persistent joint shear failure from a microscopic perspective. The results show that within the scope of the research, the peak shear strength of non-persistent joints is negatively correlated with joint aperture and joint persistency and positively correlated with normal stress. The residual shear strength is negatively correlated with joint persistency and positively correlated with normal stress. Peak normal displacement is negatively correlated with joint aperture and normal stress, and final normal displacement is negatively correlated with joint persistency and normal stress. The failure pattern of non-persistent joints is affected by internal stress. As joint aperture, joint persistency, and normal stress increase, stress concentration at the rock bridge intensifies, the width of the shear failure zone diminishes, and the specimen changes from tensile failure or mixed failure to shear failure. The research results may enrich the understanding of the shear behavior of non-persistent joints and provide some reference value for safe construction and geological hazard protection. Full article

Edge-oxidized graphene oxide (EOGO) is a nano-sized material that is chemically stable and easily mixed with water due to its hydrophilic properties; thus, it has been used in various engineering fields, particularly for the reinforcement of building and construction materials. In this study, the effect of EOGO in soil reinforcement was investigated. When mixed with soil, it affects the mechanical properties of the soil–GO mixture. Various amounts of the GO (0%, 0.02%, 0.06%, 0.1%) were added into the sand–clay mixture, and their geotechnical properties were evaluated via multiple laboratories testing methods, including a standard Proctor test, direct shear test, compressibility test, and contact angle measurement. The experimental results show that with the addition of EOGO in soil of up to 0.06% EOGO, the compressibility decreases, the shear strength increases, and the maximum dry density (after compaction) increases. Full article

The shear failure of rock masses is one of the primary causes of underground engineering instability. The shear mechanical behavior of rocks at different sizes is of great significance for studying the shear failure pattern of engineering rock masses. However, due to the presence of various joints and defects in natural rocks, the obtained rock specimens exhibit significant discreteness, making it difficult to customize specimen sizes for size effect studies. In recent years, 3D printing (3DP) technology has gained widespread application in rock mechanics tests due to its high printing precision and ability to form specimens in a single step with minimal discreteness. Among these, specimens prepared using sand-powder 3DP exhibit elastoplastic mechanical characteristics similar to those of natural rocks. Therefore, this study utilized sand-powder 3DP to prepare rock-like specimens of four different sizes and conducted compression shear tests under three different shear velocities. The shear strength, shear strain, and wear of the shear surfaces were analyzed as functions of specimen size and shear velocities. The results indicate that under the same shear velocity, the shear strength of the specimens is negatively correlated with specimen size. The peak shear strain is generally unaffected by shear velocities, but it increases initially and then decreases with increasing specimen size. As specimen size increases, the degree of specimen damage intensifies, and larger specimens are more prone to developing derived fractures. This study broadens the application of sand-powder 3DP technology in investigating the shear mechanical properties of soft rocks, offering novel insights into the study of size effects in rock mechanics. However, the current research does not encompass tests on 3D-printed rock specimens with varying printing directions, nor does it delve into the role of fractures in size effect analyses. Future investigations will aim to address these limitations, thereby advancing the applicability of 3D printing technology in rock mechanics research and enhancing its contributions to the field. Full article

The deterioration of the interlayer interface of a double-block ballastless track is affected by the environmental temperature and moisture conditions, which will have a negative effect on its service life. Composite specimens with interlayer interfaces of double-block ballastless track were fabricated and deteriorated by an accelerated method, i.e., immersed in saturated ammonium chloride solution with various temperatures for different times. Then, the deterioration condition and mechanical properties of the composite specimens were investigated experimentally by a universal material testing machine and acoustic emission technique. The automatic sensor test (AST) method is capable of assessing the deterioration condition of the interlayer interface based on the relative wave velocity. The deterioration depth of the interlayer interface tends to increase with increasing solution temperature and immersion time. Both the solution temperature and immersion time have a negative impact on the splitting tensile strength and direct shear strength. A linear relation is found between the splitting tensile strength (direct shear strength) and the cumulative AE energy released at the fracture moment. The damage factor defined by the cumulative AE energy for most composite specimens is no greater than 0.2 before they are going to be fractured but increases sharply to 1.0 at the fracture moment. Full article