Search Results (26)

Currently, silicone is a common material used in medical research and biomedical applications. This research aims to characterize extra-soft platinum silicone (shore A 00 50) and compare its mechanical behavior with that of the human thoracic aorta. By developing molds to get samples, for tensile testing according to ISO 37 and ASTM D412, and for compression testing according to ISO 7743 and ASTM D575, using a universal testing machine for tensile and compression tests, and applying digital image correlation (DIC) algorithms, the mechanical properties were characterized in a total of 10 tensile samples and 6 compression samples. The results show an ultimate tensile strength up to 1.77 ± 0.12 MPa in the ASTM samples and 2.10 ± 0.14 MPa in the ISO samples; alongside an incremental elastic module of 80.08 ± 7.94 kPa and 117.98 ± 11.39 kPa; finally, an elongation at break of 1114.49 ± 76.77% and 936.08 ± 63.56%, corresponding to the values of a healthy thoracic aorta. The replica of the thoracic aorta in this material was developed by a brush method, with a thickness of 1.82 mm, a length from the aortic arch to the descending aorta of 200.49 mm, and diameters of 20.45 and 16.05 mm for the ascending and descending aorta, respectively. Full article

The service behavior of polyurea used for joint sealing and seepage control in concrete arch dams is governed by complex material, geometric, and interfacial nonlinearities. This study developed a generalized interface element model incorporating damage evolution based on the nonlinear Ogden constitutive theory of polyurea materials. Using the Xiaowan Arch Dam as the engineering case, a multiple-nonlinearity coupled numerical model was established, covering the construction period, impoundment period, and temperature cycles during the operation period. The mechanical responses of surface polyurea at different locations and under varying material parameters were systematically investigated. Results show that the proposed coupled model accurately captures nonlinear contact behavior. Governed by the structural stress pattern of the arch dam, the impermeable coating is predominantly subjected to compression, while regions of high tensile stress are confined to the bottom joint areas. In seepage-control design, the coating’s restraining effect on macroscopic dam deformation can be neglected; however, dam deformation must be treated as the primary boundary condition. It is recommended that polyurea with an elastic modulus of 50 MPa and a 3 mm thickness be adopted. Blindly increasing coating thickness or stiffness may instead significantly elevate the risk of internal tensile stress. Full article

Longwall top coal caving is one of the most effective methods for extracting steeply inclined and ultra-thick coal seams. To investigate the influence of caving ratio (the proportion between mining height and top coal thickness) on top coal recovery behavior and ground pressure characteristics, this study employs both the Particle Flow Code (PFC) discrete element method and a coupled FLAC^3D–PFC^3D numerical simulation approach. The effects of different caving ratios (1:3, 1:3.2, and 1:3.4) on the top coal recovery ratio, stress distribution, and gangue accumulation characteristics were analyzed. The results show that the caving ratio has a significant impact on top coal recovery. At a caving ratio of 1:3.2, adopting a two-cut-one-cave interval resulted in a top coal recovery ratio as high as 94.8%. A stress-relief zone with an arch-like distribution formed above the goaf, while a stress concentration zone developed ahead of the coal wall, where the coal–rock mass underwent compression and failure. The roof displacement exhibited an arch-shaped distribution, while the floor displacement was asymmetrical, with greater heaving observed at the lower end. As the working face advanced, the horizontal development of the plastic zone expanded rapidly, while the vertical extent changed only slightly. Throughout the caving process, the top coal demonstrated favorable caving behavior with good flowability and accumulation characteristics. These findings provide theoretical support for achieving high mining recovery in thick coal seam operations and offer practical guidance for optimizing caving process parameters in practice. Full article

This study proposes an arc-circular lightweight honeycomb structure. Three different configurations of honeycomb specimens, namely arched honeycombs (AHs), arc-circular honeycombs with a first-order hierarchical configuration (ACH-1), and arc-circular honeycombs with a second-order hierarchical configuration (ACH-2), are prepared using metal additive manufacturing technology, and quasi-static compression tests are conducted. The results show that all configurations exhibit significant multi-stage load responses, with the ACH-2 configuration, which incorporates smaller sub-cells, demonstrating higher compressive stress and energy absorption potential. The specific energy absorption (SEA) of ACH-2 is enhanced by 210% compared to the baseline AH. The effectiveness of the finite element analysis is validated against experimental results. Further parametric analysis of the wall thickness parameters, cell number, and macroscopic dimensions of ACH-2 reveals significant variations in how wall thickness at different local locations affects the mechanical properties. Additionally, although increasing the macroscopic dimension significantly enhances the energy absorption capacity, the effect of increasing the number of cells on the overall energy absorption performance at the same relative density is limited. Finally, a reverse design framework for ACH-2 with multi-stage plateau stress is established. The effectiveness of this performance design framework is validated through experiments, providing a feasible technical approach for the design of honeycomb structures with multi-stage plateau stress characteristics. Full article

Research on the configuration and mechanical performance of arch-column-tie beam joints, which combine features of arch-tie beam joints and tubular joints, remains limited, particularly for long-span structures subjected to heavy loads at high building stories. This study focuses on a joint in an engineering structure comprising a circular arch beam, a square-section inclined column, and a tie beam, where both the arch and the inclined column are concrete-filled steel tube (CFST) members. A novel joint configuration was proposed, then a refined finite element model was established. The joint’s mechanical mechanism and failure mode under axial compression in the arch beam were investigated, considering two conditions: the presence of prestressed high-strength rods and the failure of the rods. Subsequently, a parametric study was conducted to investigate the influence of variations in the web thickness of the tie beam, the steel tube wall thickness of the arched beam, the steel tube wall thickness of the supporting inclined column, and the strength grades of steel and concrete on the bearing capacity behavior and failure modes. Numerical simulation results indicate that the joint remains elastic under the design load for both conditions, meeting the design requirements. The joint reaches its ultimate capacity when extensive yielding occurs in the tie beam along the junction region with the circular arch beam, as well as in the steel tube of the arch beam. At this stage, the steel plates and concrete within the joint zone remain elastic, ensuring reliable load transfer. The maximum computed load of the model with prestressed rods was 2.28 times the design load. The absence of prestressed rods could lead to a significant increase in the high-stress area within the web of the tie beam, decreasing the joint’s stiffness by 12.4% at yielding, but have a limited effect on its maximum bearing capacity. Gradually increasing the wall thickness of the arch beam’s steel tube shifts the failure mode from arch-beam-dominated yielding to tie-beam-dominated yielding along the junction region. Increasing the steel strength grade is more efficient in enhancing the bearing capacity than increasing the concrete strength grade. Finally, a design methodology for the joint zone was established based on three aspects: local stress transfer at the bottom of the arch beam, force equilibrium between the arch beam and the tie beam, and the biaxial compression state of the concrete in the joint zone. Furthermore, the construction process and mechanical analysis methods for various construction stages were proposed. Full article

Fractures in straight-wall linings is a common disease that seriously affects the integrity and service life of tunnels. The presence of insufficient lining thickness can be regarded as one of the most important factors causing fractures. In this study, the fracture behaviors of straight-wall tunnels with insufficient lining thickness under progressive compressive loading were investigated. First, the fracture characteristics and failure mode were explored. Subsequently, the deformation behaviors were investigated by digital image correlation (DIC) technology. Finally, the fracture pattern was systematically discussed. The results show that the deformation intensifies in the areas with insufficient lining thickness, which is prone to induce cracks. As the ratio or range of insufficient thickness increases, the severity of fractures intensifies and the failure mode tends to be more complex. In addition, whether the lining comes into contact with the surrounding rock in the area with insufficient thickness has a significant impact on the failure mode. Furthermore, the more serious the defect is, the more obvious the spalling phenomenon will be. Moreover, the failure mode of straight-wall tunnels can basically be attributed to the combined effect of the fractures of defect zones, arch feet and tunnel floor. Full article

As a critical element within the prefabricated structural system, the prefabricated shear wall connected by sleeve grouting is renowned for its superior mechanical performance and high construction efficiency. It is widely applied in mid- and high-rise buildings. However, under fire conditions, not only do the material properties degrade, but the structural connections may also fail, significantly compromising the structural stability and safety. Therefore, this study delves into the fire resistance performance of such prefabricated shear walls. The research primarily focuses on analyzing fire resistance characteristics, including deformation patterns, lateral and axial deformations, fire resistance limits, and other performance metrics, for both prefabricated and cast-in-place shear walls subjected to three hours of single-sided fire exposure. Additionally, a parametric analysis is performed. The results reveal that, after three hours of single-sided fire exposure, the temperature distribution patterns at the mid-width and mid-height sections of the prefabricated shear wall generally resemble those of the cast-in-place wall, displaying arch-shaped and strip-shaped distributions, respectively. However, due to the presence of sleeves, higher temperatures are observed near the sleeve areas in the prefabricated wall, along with a more extensive high-temperature zone. Throughout the three-hour fire exposure, both types of shear walls demonstrated satisfactory structural stability and thermal insulation performance, meeting the requirements for a first-level fire resistance rating (3 h). Nevertheless, greater axial and lateral deformations were noted in the prefabricated shear wall. Key factors influencing the fire resistance performance of the sleeve-connected prefabricated shear wall include the axial compression ratio, longitudinal reinforcement diameter, protective layer thickness, and height-to-thickness ratio. Specifically, axial deformation is found to be directly proportional to the axial compression ratio and height-to-thickness ratio, while inversely proportional to the longitudinal reinforcement diameter and protective layer thickness. Lateral deformation is directly proportional to the axial compression ratio and longitudinal reinforcement diameter, and exhibits a trend of initially increasing and then decreasing with an increase in protective layer thickness, and initially decreasing and then increasing with an increase in the height-to-thickness ratio. Full article

Tunnel excavation typically induces disturbance to the surrounding soil. Advance grouting using small-diameter pipes can effectively mitigate surface settlement. Taking the mine-method tunnel at the southern end of Xiancun Station on Guangzhou Rail Transit Line 18 as the research object, this paper uses the Midas GTS NX three-dimensional finite element (FE) software and adopts the upper-lower excavation method that prioritizes the formation of an upper support closed loop to simulate and analyze the impact of the CRD method on tunnel excavation under different grouting layer thicknesses. The research indicates that the surface settlement curve exhibits a “U”-shape. The settlement value decreases as the thickness of the grouting layer increases; when the thickness increases from 1.2 m to 2.0 m, the maximum surface settlement decreases from 12.87 mm to 9.09 mm, with successive reductions of 1.30 mm, 1.11 mm, 0.81 mm, and 0.56 mm, corresponding to rates of 10.10%, 9.59%, 7.67%, and 5.6%. Increasing the thickness of the grouting layer can effectively control surface settlement; however, when the thickness reaches 2.0 m, the stress distribution undergoes a change. Specifically, the compressive stress at the arch waist increases to 1683.01 kPa, and plastic failure occurs in the surrounding rock. By comparing the numerical results with field monitoring data, it is determined that when the grouting layer thickness is 1.4 m and the elastic modulus is increased by 30% based on that of the upper-soft soil, the model prediction shows the highest consistency with the actual effect. Furthermore, it is suggested that the grouting layer thickness be increased to 1.6 m. This study delivers a scientific foundation for the design of grouting parameters and the optimization of construction schemes for tunnels in composite strata and is of importance to improving tunnel construction technology in underground rail transit. Full article

To evaluate the feasibility of a virtual overlay tester (OT), a modeling approach was proposed based on the discrete element method (DEM). Simulations were conducted on three types of asphalt mixtures across three different thickness conditions. Through the analysis of the load/displacement curves, crack propagation paths, force chains, and contact force characteristics, it was observed that the peak loads decrease with increasing thicknesses, indicating a notable size effect. The complexity of the crack path was positively correlated with the particle size along the path and the fractal dimension. Coarse aggregates can inhibit crack propagation to some extent. Prior to reaching the peak load, compressive force chains in asphalt concrete-13 (AC13) and large stone porous asphalt mixture-30 (LSPM30) exhibited a symmetrical and divergent distribution along the crack, while tensile force chains formed an arch-like pattern. After the peak load, compressive force chains were symmetrically distributed in an arch shape along the crack. In stone mastic asphalt-13 (SMA13), compressive forces were transmitted along coarse aggregates, forming several continuous vertical paths. The proportion of strong compressive force chains to total compressive force chains across the three gradations ranged from 0.74 to 0.83, while the corresponding proportion for tensile force chains ranged from 0.72 to 0.78. Full article

Corrugated steel–concrete (CSC) composite arches, an innovative structural system with simplified construction and enhanced stiffness, are widely used in bridge and tunnel modular engineering. However, insufficient research on their shear performance limits prefabricated applications. Similarly to beams, their shear behavior is significantly affected by loading location. Specifically, as a parameter significantly affected by the loading location, the shear–compression ratio exerts a notable influence on the shear bearing capacity of CSC arches by altering the development pattern of cracks and the inclination angle of shear cracks. To investigate the influence mechanism of the loading location, this study is the first to systematically link shear–compression ratio variation to load location in CSC arches. In this context, shear performance tests were conducted on two CSC specimens with different loading locations (mid-span and quarter-point) to investigate the influence of loading locations on the shear behavior of CSC arches. To further investigate the impact of key parameters on the shear bearing capacity of CSC arches, a validated finite element model was employed to support the parametric analysis. The parameters involved include the span-to-rise ratio, shear connector spacing, strength and thickness of corrugated steel, as well as strength and thickness of concrete. Theoretical calculations for internal forces under varying rise-to-span ratios and loading methods are conducted, proposing an analytical solution method. Validation using 2 experiments and 96 finite element results show that a modified method is applicable, with a mean value of 1.066, corresponding to a standard deviation of 0.071, and all relative errors within 15%. By introducing the shear–compression ratio, this study extends existing methods to make them applicable under single-point loading, thereby enabling their use for guiding engineering. Similarly, the internal force analysis method proposed herein can serve as a theoretical foundation, providing a valuable reference for future research on shear capacity calculation methods for CSC arches with varying cross-sectional configurations and those where bending moments play a more significant role. Full article

The layered composite roof of a coal mine roadway exhibits heterogeneity, with pronounced variations in layer thickness and strength. Fully grouted rock bolts installed in such layered roofs usually penetrate two or more strata and bond with them to form an integrated anchorage system. Roof failure typically initiates in the shallow strata and progressively propagates to deeper layers; thus, the mechanical properties of the rock at the free surface critically influence the overall stability of the layered roof and the load-transfer behavior of the bolts. In this study, a layered rock mass model was developed using three-dimensional particle flow code (PFC3D), and a triaxial loading scheme with a single free surface was applied to investigate the effects of free-surface rock properties, support parameters, and confining pressure on the load-bearing performance of the layered rock mass. The main findings are as follows: (1) Without support, the ultimate bearing capacity of a hard-rock-free-surface specimen is about 1.2 times that of a soft-rock-free-surface specimen. Applying support strengths of 0.2 MPa and 0.4 MPa enhanced the bearing capacity by 29–38% and 46–75%, respectively. (2) The evolution of axial stress in the bolts reflects the migration of the load-bearing core of the anchored body. Enhancing support strength improves the stress state of bolts and effectively mitigates the effects of high-stress conditions. (3) Under loading, soft rock layers exhibit greater deformation than hard layers. A hard-rock free surface effectively resists extrusion deformation from deeper soft rocks and provides higher bearing capacity. Shallow free-surface failure is significantly suppressed in anchored bodies, and “compression arch” zones are formed within multiple layers due to bolt support. Full article

The burgeoning electromagnetic pollution from 5G/6G technologies demands lightweight, broadband, and mechanically robust electromagnetic microwave absorbers (EMWAs). Conventional carbon aerogels suffer from structural fragility and inadequate electromagnetic dissipation. Herein, we propose a defect-engineering strategy through precise optimization of the chitosan (CS)/cellulose nanocrystal (CNC) ratio to fabricate elastic boron nitride nanosheet (BNNS)-embedded carbon aerogels. By fixing BNNS content for optimal impedance matching and modulating the CS/CNC ratio of the aerogel, we achieve synergistic control over hierarchical microstructure, defect topology, and electromagnetic response. The aerogel exhibits a wide effective absorption bandwidth (EAB) of 8.3 GHz at a thickness of 3.6 mm and an excellent reflection loss of −52.79 dB (>99.999% attenuation), surpassing most biomass-derived EMWAs. The performance stems from CNC-derived topological defects enabling novel polarization pathways and BNNS-triggered interfacial polarization, while optimal graphitization (I_D/I_G = 1.08) balances conductive loss. Simultaneously, the optimal CS/CNC ratio facilitates the formation of a stable and flexible framework. The long-range ordered micro-arch lamellar structure endows the aerogel with promising elasticity, which retains 82% height after 1000 cyclic compression at 50% strain. This work paves the way for biomass-derived carbon aerogels as next-generation wearable and conformal EMWAs with broadband absorption. Full article

Red-layer soft rock has characteristics such as softening when encountering water, loose structure, and significant rheological properties. In tunnel engineering, it is necessary to sort out and analyze the stress characteristics of its support structure. This paper focuses on the mechanical behavior and support effect during the construction of Neogene red-layer soft rock tunnels. Through field monitoring, it explores the mechanical characteristics of Huizhou Tunnel under complex geological conditions in depth. This study adopted a remote wireless monitoring system to conduct real-time monitoring of key indicators including tunnel surrounding rock pressure, support structure stress, and deformation, obtaining a large amount of detailed data. An analysis revealed that the stress experienced by rock bolts is complex and varies widely, with stress values between 105 and 330.5 MPa. The peak axial force at a depth of 2.5 m reflects that the thickness of the loosened zone in the surrounding rock is approximately 2.5 m. The compressive stress in the steel arches of the primary support does not exceed 305.3 MPa. Shotcrete effectively controls the surrounding rock deformation, but the timing of support installation needs careful selection. The stress in the secondary lining is closely related to the primary support. The research findings provide an important theoretical basis and practical guidance for optimizing the support design of red-bed soft rock tunnels and enhancing construction safety and reliability. Full article

Due to the impact of disordered mining activities in previous years, numerous abandoned roadways exist in the second mining district of the 13# coal seam in Chejiazhuang Coal Mine. The stability of the new roadway roof was analyzed under various distributions of abandoned roadways above. It was determined that the ultimate stable thickness of the coal layer between the new and abandoned roadways is 4.0 m. When the thickness between the two is less than 4.0 m, the roof becomes unstable after excavation, posing a risk of collapse. Advanced grouting reinforcement is required to enhance roof stability before installing U-shaped steel arches. Mechanical experiments were conducted on the polymer grouting consolidation of fractured coal, showing a significant increase in residual strength compared to intact coal. Furthermore, the uniaxial compressive strength of the polymer grouting consolidation partially recovered. On average, the consolidation coefficient and recovery coefficient were 5.28 and 85.51%, respectively. Grouting increased the ductility of the fractured surrounding rock, enhancing its resistance to deformation and plasticity. A polymer grouting consolidation technology for supporting fractured surrounding rock under the unstable roof of abandoned roadways is proposed, along with the design of corresponding support schemes and parameters. Monitoring the results of mine pressure indicated that the surrounding rock remained stable after roadway excavation, validating the effectiveness of the support schemes and parameters. Full article

Increasingly, research indicates that steel fibers can significantly enhance the engineering properties of mortar and concrete; however, few studies have examined their impact on the reinforcement of in-service tunnel linings within sleeve arch structures. In this study, a series of 1:2 scale experiments were conducted using a specialized loading device to compare the reinforcement performance of steel fiber-reinforced concrete sleeve arches and traditional reinforced concrete sleeve arches on prefabricated cracks with depths of 1/3 and 2/3 of the lining thickness. The experimental results were validated using numerical simulations. The results indicate that under the same load, when reinforcing components with 2/3 prefabricated cracks, the maximum compressive strains for steel fiber-reinforced and reinforced concrete sleeve arches were −852 με and −985 με, respectively, and the maximum deflections were 3.57 mm and 5.48 mm. Composite sleeve arches of both materials provide a certain degree of reinforcement to linings with varying damage. The reinforcement performance of steel fiber-reinforced concrete sleeve arches is superior to that of traditional reinforced concrete sleeve arches, with particularly significant reinforcement for linings with 2/3 prefabricated cracks. Numerical simulations have shown that the stress in reinforced concrete at the concentrated stress regions is 16.15%, 6.01%, 12.68%, 36.62%, and 4.82% higher than that in steel fiber-reinforced concrete, respectively, thereby validating the reliability of the experimental results. Therefore, this study recommends the application of steel fiber materials in sleeve arches to achieve superior maintenance and reinforcement, addressing cracking issues in in-service tunnel linings and thereby improving the safety and durability of these structures. Full article