Search Results (608)

In this study, free vibration analysis of three-layer sandwich panels with cores based on a triply periodic minimum surface (TPMS) and graphene platelet-reinforced composite (GPLRC) faces is performed. Four different geometries including cylindrical, spherical, saddle and flat panels were investigated and the governing equations were solved using higher-order shear deformation theory (HSDT) extracted from Hamilton’s principle. The accuracy and precision of the presented analytical method is verified by comparing the dimensionless natural frequencies with reference studies. Then, the effect of various parameters including panel geometry, core topology type and graphene weight percentage on the vibration response was investigated. The results show that adding graphene to the face layers significantly increases the natural frequencies and improves the overall stiffness of the structure. In addition, the frequencies of the panel may be controlled through different patterns and topologies. Also, double-curved panels, especially spherical geometries, present the highest fundamental natural frequency. The findings of this research could play an important role in the design and performance evaluation of advanced structures with TPMS cores and nanoscale reinforcement. Full article

Accurate prediction of the load–settlement response of axially loaded piles remains challenging because the pile–soil interface undergoes progressive elastoplastic shear deformation accompanied by stress-dependent volumetric changes. Conventional one-dimensional load-transfer models are computationally efficient but usually rely on empirical or hyperbolic fitting functions, making it difficult to explicitly describe the coupled evolution of interface shear hardening, volumetric hardening, and radial effective stress. Although three-dimensional elastoplastic models provide a more rigorous mechanical representation, their high computational cost limits routine engineering application. To address this gap, this study develops a double-hardening elastoplastic load-transfer model for axially loaded piles based on a physically interpretable pile–soil interface constitutive formulation. In the proposed model, the Hardening Soil model is used to characterize interface shear hardening, while the Modified Cam-clay model is introduced to describe volumetric hardening. These two mechanisms are coupled through a stress–dilatancy relationship. According to the loading direction and the position of the current stress point relative to the shear and volumetric yield surfaces, the p′–q stress plane is divided into elastic, shear-hardening, volumetric-hardening, and coupled double-hardening regions. The corresponding incremental constitutive equations are derived and embedded into a conventional load-transfer framework. The model is validated using interface direct shear tests and field-scale static pile load tests. The predicted shear stress–displacement curves and pile-head load–settlement responses agree well with the measured data. Quantitative evaluation shows that the MAPE values are lower than 5%, the maximum relative errors are below 7.6%, and the R² values exceed 0.96 for all validation cases. Full article

The discharge behavior of granular materials from double-orifice silos is strongly affected by the inter-orifice spacing, yet the mechanical role of the inter-orifice region remains unclear. In this study, discrete element method (DEM) simulations are combined with experiments to investigate the formation, stability, and collapse of an inter-orifice quasi-solid region and its impact on the discharge rate. The results show that increasing the inter-orifice spacing progressively weakens shear transmission between adjacent outlets, promoting the development of a low-velocity, load-bearing quasi-solid region. Based on μ(I) rheology and a nonlocal granular fluidity framework, the quasi-solid region is shown to be controlled by local shear activation rather than by geometric separation alone. Once the inter-orifice quasi-solid region is formed, this region restricts the spatial extension of shear bands near the outlets, leading to a reduction in the effective shear area and a corresponding decrease in the discharge rate. A critical inter-orifice spacing is identified, beyond which the two outlets discharge independently. These findings provide a mechanistic understanding of flow-rate regulation in multi-orifice silos, offering guidance for the design of granular discharge systems. Full article

Roof stability plays a crucial role in maintaining the overall stability of surrounding rocks to ensure safety of tunnel construction and operation. In this work, tension cut-off (TC) technique is introduced to modify the Hoek–Brown (HB) criterion to describe the tensile failure of rock strata. Thereafter, stability analysis of anchor bolt-reinforced tunnel roofs in rock strata subjected to a hybrid tensile-shear fracture is performed. The work balance equation is established by equating the external work rates of the falling block and the anchor bolts to the internal energy dissipation rate. Two stability indicators, that is the stability number (N) and the factor of safety (FoS) are proposed to quantitatively analyze the stability of tunnel roofs. Optimization algorithms combining genetic algorithm and particle swarm optimization are programmed to capture the optimal upper bound solutions. The influences of TC, strength criterion parameters, and anchor bolt-reinforcement strength on roof stability are explored in this work. It was found that increasing the anchor tension T improves the FoS of reinforced tunnel roofs, with an increase of up to 68% observed for rectangular tunnel roofs under the selected representative case, while the improvement is relatively less pronounced for circular tunnel roofs. Regarding anchor support, as ξ increases, the N for rectangular tunnels nearly doubles. This work provides a theoretical basis for preliminary designing of tunnels in reinforced rock strata. Full article

Resistance spot welding was performed to join 2 mm thick TA2 titanium plate and Q235 steel plate using an Nb-Ni bi-interlayer. The microstructure of the interfacial zone was observed and analyzed, and the tensile shear load of the joint was evaluated. The joints obtained display double-nugget-type and penetration-type joints. For the double-nugget-type joint, Ni₆Nb₇ and Ni₃Nb layers have been formed in the region between the residual Nb layer and the steel, while for the penetration-type joint, a mixed nugget composed of Ti-Fe intermetallic compounds was formed at the center zone of the weld. As the welding current increased or welding time extended, the tensile shear load of the joint exhibited a trend of initially increasing and subsequently decreasing. When a bi-interlayer consisting of 0.05 mm-Nb and 0.04 mm-Ni is utilized, the tensile shear load of the joint reached the maximum value of approximately 8.7 kN under the condition of 11 kA welding current, 300 ms welding time, and 3 kN electrode pressure. The results indicate that the Nb layer can effectively impede the cross-interface diffusion of Ti atoms and Ni-Nb intermetallic compound layers are formed in the interface region in the case that the interlayer thickness and the welding parameters are well-matched when resistance spot welding of Ti/steel is performed with a bi-interlayer of Nb-Ni. Full article

Variational principles and variationally consistent boundary conditions are presented for double-layer graphene nanoribbons undergoing time-dependent and free vibrations. The van der Waals forces acting in the core region are modelled as shear and tensile–compressive effects. The nonlocal constitutive formulation of the problem is based on the sandwich beam model in order to represent the graphene nanoribbon layers as faces and van der Waals forces acting in the core region. The constitutive equations which govern the vibrations of the nanoribbons are in the form of four coupled partial differential equations involving the in-plane and out-of-plane deflections. The first part of the study involves the derivation of the variational principle for the system undergoing time-dependent vibrations. Hamilton’s principle is formulated based on the kinetic and potential energies of the system. The next section involves the freely vibrating nanoribbon system and the formulation of the variational principle for this case is given. Based on this formulation, the expressions for the Rayleigh quotients are obtained for the longitudinal natural frequency and the transverse natural frequency. The last section involves the derivation of the variationally consistent boundary conditions and the expressions for the shear force and moment at the boundaries. Full article

Heterostructured metals and alloys are designed with spatial variations in strength and hardening that produce synergy beyond the rule of mixtures. This review surveys face-centered cubic (FCC), body-centered cubic (BCC), and hexagonal close-packed (HCP) systems, including architectures formed or modified by rolling and related severe plastic deformation routes, and examines them under tension, compression, and shear. Across material classes, mechanical incompatibility between hetero-zones drives stress partitioning and plastic strain gradients that store geometrically necessary dislocations near zone boundaries. The associated internal back and forward stresses sustain work hardening, delay instability, and influence localization and damage initiation. We evaluate continuum, crystal plasticity, dislocation-based mesoscale, and atomistic approaches by whether they predict these internal fields and whether they are validated against internal-field measurements. Key observations are that predictive models require physically identifiable intrinsic length scales, experimentally constrained interface laws, and careful separation of mechanisms to avoid double-counting when gradient and kinematic terms coexist. Major gaps remain in parameter identifiability for multi-zone and nonlocal formulations, in transferability across processing routes and loading modes, and in community benchmarks that couple well-characterized microstructures with multimodal measurements. Recommendations are provided for validation targets and benchmark campaigns to accelerate predictive design. Full article

Four-point bending tests were conducted on precast ultra-high-performance concrete (UHPC) segmental beams reinforced with unbonded prestressing tendons. A nonlinear finite element model was established and rigorously validated against the experimental data to simulate their flexural behavior. The experimental results show that compared with monolithic beams, the segmental beams experience a slight reduction in flexural capacity of 9.22% and 12.44% for the double-joint and triple-joint configurations, respectively. Nevertheless, the segmental beams possess greater ductility reserves; specifically, their average peak displacements increased from 9.83 mm for the monolithic beams to 11.60 mm and 14.78 mm for the double-joint and triple-joint beams, respectively, demonstrating substantially improved ductility. Based on the validated finite element model, extensive parametric analyses were performed. The numerical results indicate that concrete strength and steel strand reinforcement ratio significantly enhance the load-carrying capacity. Furthermore, shifting the joint positions away from the loading points increases the beam’s bending capacity, though this enhancement aggressively flattens out beyond a critical distance threshold of 0.25 L (L is the effective span). Finally, segmental beams with shear-resistant keyed joints exhibit higher overall stiffness and ultimate load-carrying capacity compared to those with plain flat joints. Full article

Interlaminar fracture toughness (ILFT) is a key factor governing the damage tolerance and service reliability of carbon fiber-reinforced polymer (CFRP) laminates. This study aims to clarify how the deformation capability of epoxy resin affects the Mode I and Mode II ILFT of carbon fiber/epoxy laminates under comparable fiber, resin-content, and laminate-configuration conditions. Two epoxy systems were compared: a high-strength/high-modulus (HSHM) resin system, designated as Group B, and a high-toughness (HT) resin system, designated as Group T. Neat resin castings were characterized by tensile and flexural tests, and the corresponding CFRP laminates were evaluated using double cantilever beam (DCB) and end-notched flexure (ENF) tests. Although Group T showed slightly lower tensile strength and modulus than Group B, its elongation at break increased from 4.0% to 6.5%, corresponding to an increase of approximately 62.5%. The Mode I ILFT (GIC) increased from approximately 279 J/m² for Group B to 487 J/m² for Group T, while the Mode II ILFT (GIIC) increased from approximately 530 J/m² to 708 J/m², corresponding to improvements of approximately 74.6% and 33.6%, respectively. Scanning electron microscopy (SEM) observations indicated that Group T promoted more resin-covered fibers, resin tearing, crack-tip blunting, crack deflection, shear deformation features, and crack-path reconstruction. These results indicate that, within the present two-system comparison, resin ductility-related deformation capability and local crack-tip deformability should be considered together with strength and modulus when evaluating interlaminar crack resistance. The toughening effect also showed loading-mode dependence, with Mode I improvement mainly related to crack-tip blunting and resin tearing, whereas Mode II improvement was mainly associated with matrix shear deformation, resistance to interfacial sliding, and crack-path deflection. Full article

The use of computational fluid dynamics provides an important tool for the design of supersonic ejectors. Within Reynolds/Favre-averaged simulations, the turbulence model plays an essential role in determining results’ reliability. Existing validation studies show general accuracy problems, whose relevance, partially masked in the double-choked regime, becomes fully evident for the single-choked regime. For this flow regime, errors reported in the literature are strongly erratic, reaching magnitudes higher than 50% in terms of global performance. The absence of clear, unified conclusions by different authors motivates the present work, focused on single-choked ejectors. In the first part, the main ejector flow features are discussed, highlighting the importance of adequately reproducing the turbulence response to different shear intensities. To properly address this point, an original analysis is conducted, exploiting data from previous studies on jets and basic shear flows. The developed analysis explains how the prediction of an ejector jet is influenced by the constitutive relationship of eddy viscosity models and by the modelled balance of the turbulent-dissipation rate. The modelling failures of these two elements are discussed for existing models in common use and addressed through the development of a new Consistent Realizable K − ε model. In Part 2, the analyzed models are used to simulate two test cases, with detailed measurements available. Full article

This study evaluates the corrosion evolution of N80 steel in H₂S/CO₂ environments simulating Carbon Capture, Utilization, and Storage-Enhanced Gas Recovery (CCUS-EGR) processes. High-pressure autoclave experiments were conducted to analyze the impacts of CO₂/H₂S partial pressure ratios (2.9–67.4), temperature (40–80 °C), and flow rate. Grey relational analysis indicates that the CO₂/H₂S partial pressure ratio dominates uniform corrosion (γ = 0.880), while flow rate and temperature primarily govern pitting behavior (γ > 0.85). Increasing the ratio from 2.9 (H₂S-dominated) to 67.4 (CO₂-dominated) doubled the uniform corrosion rate to 1.042 mm/y but reduced pitting by 46%. Mechanistically, the semiconductor conductivity of FeS (∼10⁻¹ S/cm) drives deep pitting via “large cathode–small anode” galvanic effects. Additionally, fluid shear stress selectively erodes porous FeCO₃, enriching surface FeS and creating differential corrosion patterns. A comprehensive evolution model describing the transition from a H₂S-dominated regime to mixed control and finally to a CO₂-dominated regime is established, providing a theoretical foundation for wellbore integrity management throughout the CCUS-EGR lifecycle. Full article

Heritage rammed earth is a special soil material formed by manually selecting and ramming locally available Quaternary surface deposits layer by layer. However, the quantitative influence of material sourcing and rammed technology on the compressive properties of heritage rammed earth remains insufficiently understood, which limits the mechanical assessment and conservation planning of rammed earth sites. In this study, undisturbed rammed earth from 15 Ming Great Wall sites in Northwest China was investigated. Field 3D scanning, particle-size analysis, uniaxial compression testing, mesoscopic structural observation, and DEM analysis were combined to evaluate the effects of material characteristics and rammed technology on the compressive properties of heritage rammed earth. The results show clear regional differences in material characteristics and rammed technology parameters across the 15 sites. Across the five occurrence regions from the Extremely Arid Area to the Semi-Humid Area, dry density, silt fraction, curvature coefficient, and ramming pit distribution area ratio generally decreased, whereas clay and colloidal particle fraction, $d_{60}$, $C_u$, and rammed modulus generally increased. These variations were accompanied by changes in internal fabric, including aggregate proportion, coordination-number difference, high-stress particle proportion, and force-chain particle proportion. The peak stress and failure strain ranged from 0.48 to 1.01 MPa and from 0.03 to 0.07, respectively. Both parameters showed a decreasing regional trend from the extremely arid area to the semi-humid area, following the sequence: extremely arid area, arid area, semi-arid area, cold and humid area, and semi-humid area. From the Extremely Arid Area to the Semi-Humid Area, the shear failure mode changed from single-fork to mixed double-fork and then to intersecting double-fork. Regression analysis further showed that material and rammed technology parameters were closely related to mesoscopic structural parameters, with R² values generally greater than 0.75. These findings suggest that the regional differences in compressive behavior were closely associated with variations in material sourcing, rammed technology, internal fabric, and the load-bearing structure of rammed earth. Full article

To reveal the long-term anti-aging mechanisms of rubber–plastic elastomer-modified asphalt in complex service environments and overcome the inherent defects of single polymer modifiers—namely their susceptibility to degradation or phase separation—this study prepared styrene-butadiene-styrene (SBS), low Mooney rubber (LMMR), and low-density polyethylene (LDPE)-modified asphalts. Simultaneously, an LMMR-LDPE rubber–plastic thermoplastic elastomer (TPE) was fabricated utilizing twin-screw extrusion technology and subsequently used to prepare a composite-modified asphalt. Three aging protocols were simulated: short-term thermo-oxidative aging (RTFOT), long-term pressure aging (PAV), and ultraviolet light aging (UV). A multi-scale quantitative characterization was conducted using a dynamic shear rheometer, Fourier transform infrared spectroscopy, and atomic force microscopy to evaluate the rutting factor, carbonyl index, and surface microroughness of each system before and after aging. The experimental results indicate that the coupled effect of long-term stress and thermal oxidation causes the most severe damage to the colloidal structure of modified asphalt. Conventional SBS-modified asphalt, due to its abundance of unsaturated double bonds, exhibits a sharp increase in the carbonyl index and aging index of the rutting factor after aging, making it highly susceptible to oxidative chain scission. Although LDPE-modified asphalt possesses chemical inertness, it is prone to crystalline phase separation under aging conditions, resulting in a microroughness distortion rate of up to 86.36%. In contrast, the LMMR-LDPE composite system, leveraging the high chemical stability of the saturated aliphatic carbon chain and the flexibility-enhancing and crystallization-inhibiting effects of LMMR, effectively reduces active oxidation sites and improves interfacial compatibility. This composite system exhibits the lowest carbonyl increment and rheological attenuation under all aging conditions, while effectively inhibiting the free migration and agglomeration of macromolecular components. The LMMR-LDPE composite modification technology effectively overcomes the inherent drawbacks of single polymers, such as susceptibility to degradation or segregation, demonstrating excellent long-term macroscopic rheological stability and microscopic phase morphology anti-aging capability. The present findings provide laboratory-scale mechanistic support for the design of durable rubber–plastic-modified asphalt systems, while further pilot-scale, economic, and field validation is still required before practical engineering application can be fully assessed. Full article

In a seepage control system composed of geomembranes, the mechanical properties of the geomembrane welds directly determine the overall safety and durability of the system. To clarify the influence of welding parameters on the mechanical properties of the welds, this paper prepares weld specimens using different welding processes and systematically investigates the effects of welding temperature, welding pressure, and welding speed on the mechanical properties of double wedge welds in HDPE geomembranes through peel tests, shear tests, and DIC deformation measurement technology. The results indicate that the peel strength of HDPE welds has no linear correlation with welding pressure but there exists a threshold effect. The peel strength exhibits an exponential relationship with welding temperature and a Gaussian relationship with welding speed. The shear strength of the welds can be fitted by an exponential function for all three welding parameters. The coefficient of determination (R²) for each of the above fitting equations is higher than 0.9. Under different welding parameters, the yield strength of the double welds is slightly lower than that of the base material (approximately 89–94% of the base material), while the yield strain decreases more significantly (to 62–81% of the base material). Observations of the weld deformation distribution using DIC show that when the specimen elongation is below 11%, strain is concentrated near the weld; after reaching the yield strain, necking occurs; and the strain concentration shifts to the necking region. As the elongation further increases, significant plastic yield deformation occurs in the necking region, with a maximum strain of 500%. Full article

Fine-grained dredged clay is difficult to reuse without treatment due to its high water content and weak soil structure. From a sustainability perspective, this limitation poses challenges for the beneficial reuse of dredged materials and often leads to disposal and increased demand for natural resources. In this study, the 28-day mechanical behavior of stabilized dredged clay, treated with cement or lime and modified with coir fiber, polypropylene (PP) fiber, and styrene–butadiene rubber (SBR) latex, was systematically investigated through experimental measurements, with an emphasis on resource-efficient and sustainable ground improvement. The unconfined compressive strength (UCS) results showed that the UCS of dredged clay stabilized with 4% cement was 374 kPa, and this value increased linearly with increasing cement content, reaching 2487 kPa at 16% cement. In contrast, the UCS of dredged clay stabilized with 16% lime was approximately 30% of that achieved with cement at the same dosage, at only 780 kPa, indicating the need to balance mechanical performance with the environmental impact associated with high cement usage and its carbon footprint. In addition, the inclusion of fibers significantly enhanced the UCS of the stabilized soil samples. The experimental results indicate that the UCS of specimens stabilized with 16% cement could be doubled with the addition of fibers, suggesting the potential to achieve target strength with reduced binder content, thereby contributing to a low-carbon and material-efficient design. Among the fibers tested, coir fiber exhibited better performance than PP fiber in improving UCS, highlighting the effectiveness of natural, renewable, and biodegradable materials in sustainable soil stabilization. Furthermore, fiber length also influenced the UCS of the stabilized soil samples. Additionally, the direct shear test results indicated that both fiber content and length played important roles in determining the internal friction angle of the stabilized soil. It was observed that stabilized soil reinforced with 6 mm fibers exhibited a higher internal friction angle compared to that reinforced with 12 mm fibers. These findings provide insights into optimizing material composition for improved mechanical performance while supporting environmentally sustainable and resource-efficient geotechnical practices. Full article