Search Results (210)

This study investigates the cracking behavior of high-performance calcium oxide-activated concrete incorporating basalt and synthetic macro fibers under compressive and flexural loading. Acoustic emission (AE) monitoring was employed to capture real-time crack initiation and propagation, offering insights into damage evolution mechanisms. A comprehensive series of uniaxial compression and four-point bending tests were conducted on fiber-reinforced and plain specimens. AE parameters, including count, duration, risetime, amplitude, and signal energy, were analyzed to quantify crack intensity and classify fracture modes. The results showed that tensile cracking dominated even under compressive loading due to lateral stresses, while fiber inclusion significantly enhanced toughness by promoting distributed microcracking and reducing abrupt energy release. Basalt fibers were particularly effective under flexural loading, increasing the post-peak load-bearing capacity, whereas synthetic macro fibers excelled in minimizing tensile crack occurrence under compression. Full article

This study systematically investigates the degradation and failure prediction of pipeline materials in sulfur-containing environments, with a particular focus on X52 pipeline steel exposed to high-sulfur environments. Through uniaxial tensile tests to assess mechanical properties, it was found that despite surface corrosion and a reduction in overall structural load-bearing capacity, the intrinsic mechanical properties of X52 steel did not exhibit significant degradation and remained within standard ranges. The Johnson–Cook constitutive model was developed to accurately capture the material’s plastic behavior. Subsequently, a genetic algorithm-optimized backpropagation (GABP) neural network was employed to predict the failure pressure of defective pipelines and the corrosion rate in acidic environments, with prediction errors controlled within 5%. By integrating the GABP model with NACE standard methods, a framework for predicting the remaining service life for in-service pipelines operating in sour environments was established. This method provides a novel and reliable approach for pipeline integrity assessment, demonstrating significantly higher accuracy than traditional empirical models and finite element analysis. Full article

To investigate the degradation mechanisms of the surrounding rock in abandoned mine roadways used for oil storage, this study combined uniaxial compression tests with digital image correlation (DIC), scanning electron microscopy (SEM), and other techniques to analyze the evolution of the rock mechanical properties under the coupled effects of oil–water soaking and initial damage. The results indicate that oil–water soaking induces the loss of silicon elements and the deterioration of microstructure, leading to surface peeling, crack propagation, and increased porosity of the sample. The compressive strength decreases linearly with the soaking time. Acoustic emission (AE) monitoring showed that after 24 h of soaking, the maximum ringing count rate and cumulative count decreased by 81.7% and 80.4%, respectively, compared to the dry state. As the liquid saturation increases, the failure mode transitions from tension dominated to shear failure. The synergistic effect of initial damage and oil–water erosion weakens the rock’s energy storage capacity, with the energy storage limit decreasing by 45.6%, leading to reduced resistance to external forces. Full article

The instability of mine roadways is significantly influenced by the coupled effects of groundwater seepage and non-uniform loading. These interactions often induce localized plastic deformation and progressive failure, particularly in the roof and sidewall regions. Seepage elevates pore water pressure and deteriorates the mechanical properties of the rock mass, while non-uniform loading leads to stress concentration. The combined effect facilitates the propagation of microcracks and the formation of shear zones, ultimately resulting in localized instability. This initial damage disrupts the mechanical equilibrium and can evolve into severe geohazards, including roof collapse, water inrush, and rockburst. Therefore, understanding the damage and failure mechanisms of mine roadways at the mesoscale, under the combined influence of stress heterogeneity and hydraulic weakening, is of critical importance based on laboratory experiments and numerical simulations. However, the large scale of in situ roadway structures imposes significant constraints on full-scale physical modeling due to limitations in laboratory space and loading capacity. To address these challenges, a straight-wall circular arch roadway was adopted as the geometric prototype, with a total height of 4 m (2 m for the straight wall and 2 m for the arch), a base width of 4 m, and an arch radius of 2 m. Scaled physical models were fabricated based on geometric similarity principles, using defect-bearing sandstone specimens with dimensions of 100 mm × 30 mm × 100 mm (length × width × height) and pore-type defects measuring 40 mm × 20 mm × 20 mm (base × wall height × arch radius), to replicate the stress distribution and deformation behavior of the prototype. Uniaxial compression tests on water-saturated sandstone specimens were performed using a TAW-2000 electro-hydraulic servo testing system. The failure process was continuously monitored through acoustic emission (AE) techniques and static strain acquisition systems. Concurrently, FLAC^3D 6.0 numerical simulations were employed to analyze the evolution of internal stress fields and the spatial distribution of plastic zones in saturated sandstone containing pore defects. Experimental results indicate that under non-uniform loading, the stress–strain curves of saturated sandstone with pore-type defects typically exhibit four distinct deformation stages. The extent of crack initiation, propagation, and coalescence is strongly correlated with the magnitude and heterogeneity of localized stress concentrations. AE parameters, including ringing counts and peak frequencies, reveal pronounced spatial partitioning. The internal stress field exhibits an overall banded pattern, with localized variations induced by stress anisotropy. Numerical simulation results further show that shear failure zones tend to cluster regionally, while tensile failure zones are more evenly distributed. Additionally, the stress field configuration at the specimen crown significantly influences the dispersion characteristics of the stress–strain response. These findings offer valuable theoretical insights and practical guidance for surrounding rock control, early warning systems, and reinforcement strategies in water-infiltrated mine roadways subjected to non-uniform loading conditions. Full article

This article aims to clarify the applicability of He’s two-scale fractal dimension transform by replacing $t^{\mathsf{\alpha }}$ with $\mathsf{\tau }$. It demonstrates the potential to capture the influence of the fractal parameter on the system’s damping frequency, particularly when the viscoelastic term (damping) does not equal half of the fractional inertia force term. The analysis examines the elastomer materials’ dynamic fractal amplitude–time response, considering the viscohyperelastic effects related to the material’s energy dissipation capacity. To determine the amplitude of oscillations for the nonlinear equation of motion of a body supported by a viscohyperelastic elastomer subjected to uniaxial stretching, the harmonic balance perturbation method, combined with the two-scale fractal dimension transform and Ross’s formula, is employed. Numerical calculations demonstrate the effectiveness of He’s two-scale fractal transformation in capturing fractal phenomena associated with the fractional time derivative of deformation. This is due to a correlation between the fractional rate of viscoelasticity and the fractal structure of media in elastomer materials, which is reflected in the oscillation amplitude decay. Furthermore, the approach introduced by El-Dib to replace the original fractional equation of motion with an equivalent linear oscillator with integer derivatives is used to further assess the qualitative and quantitative performance of our derived solution. The proposed approach elucidates the applicability of He’s two-scale fractal calculus for determining the amplitude of oscillations in viscohyperelastic systems, where the fractal derivative order of the inertia and damping terms varies. Full article

This study explores the use of recycled brick powder (P_RB), derived from waste bricks, and calcined recycled slurry powder (P_CRS), sourced from waste cement blocks, as partial replacements for cement and fly ash in concrete. These materials can be utilized to produce concrete with favorable engineering properties. Five concrete mixtures with varying P_RB/P_CRS proportions were prepared. Uniaxial monotonic compression tests were conducted to generate stress-strain curves for each mixture. Corresponding physical superposed slabs were fabricated, and finite element (FE) models were developed for each slab. Both physical testing and explicit FE simulations were performed to evaluate the flexural performance of the slabs. The results demonstrated that the flexural performance of the P_RB/P_CRS recycled micro-powder concrete slabs was comparable to that of conventional concrete slabs. Notably, the slab incorporating a 1:1 mixture of P_RB and P_CRS instead of fly ash exhibited the highest yield and ultimate bearing capacities, reaching 99.3% and 98.4% of those of the conventional concrete slab, respectively. The FE simulations accurately predicted the flexural performance, with maximum deviations of 8.9% for the yield load and 6.5% for the ultimate load. Additionally, the simulation-based energy time-history curve provides valuable insights into the progression of slab cracking. This study contributes to the advancement of research on the engineering and mechanical performance of concrete members incorporated with P_RB/P_CRS. Full article

Bolted spherical joints (BSJs) are widely used in spatial grid structures owing to their clear force transmission paths and ease of on-site assembly. This study investigates the corrosion behavior and tensile performance of BSJs fabricated with #45 carbon steel joint spheres and 40Cr high-strength bolts (grade 10.9S) under chloride exposure under varying bolt screwing depths. Accelerated salt spray corrosion tests were conducted across different exposure cycles (20, 40, 60, and 80 cycles) and at screwing depths ranging from 0.8 d to 1.2 d, followed by uniaxial tensile testing. Results revealed that chloride-induced pitting corrosion was more pronounced on bolts than on joint spheres, with four distinct types of microscopic corrosion morphologies identified. Inadequate screwing depth (<1.0 d) led to pull-out failure, while greater depths (≥1.0 d) generally resulted in bolt fracture. Chloride exposure significantly reduced the ultimate tensile capacity of BSJs. For bolts with λ < 1.0, post-corrosion tensile strength dropped below the specification threshold, indicating a critical safety concern. Full article

Grouting is widely used in the treatment works of goaf, which can enhance the foundation bearing capacity, reduce deformation, and ensure the stability of the construction of goaf. As the goaf is located below the water table line, the mechanical properties and microscopic changes of the stone body in the water-rich environment have not been revealed, which leads to the effect of grouting treatment in water-rich goaf being difficult to achieve in terms of the expected goal. This paper used uniaxial compression, electron microscopy (SEM), and X-ray diffraction (XRD) to study the mechanical properties and microscopic changes of the nodular body under natural, pure water, and tap water curing and revealed the deterioration mechanism of the nodular body’s mechanical properties under water curing. The research results show that under identical material proportions and curing durations, compared to naturally cured specimens, the specimens cured in purified water and tap water exhibited a significant increase in the content of unreacted fly ash, a reduction in the amount of hydration products such as C-S-H gel and ettringite, and a looser microstructure, resulting in average decreases in uniaxial compressive strength of 35.7% and 49.9%, respectively. In addition, the presence of chloride ions and Friedel’s induced decalcification of the C-S-H gel under tap water curing conditions led to a significant deterioration in the physical strength of the grouted stones. Full article

Commercially pure aluminum (Al) was refined through the addition of the Al-5Ti-0.25C master alloy, resulting in the formation of Al₃Ti and TiC phases, which serve as refining agents. Open-cell metallic foams were successfully produced using the replication casting technique, with pore sizes ranging from 1.00 to 3.35 mm. For the infiltration process, refined aluminum was used, while unrefined aluminum served as a baseline reference. The resultant foams underwent multiple annealing cycles at 480 °C, with the most refined and homogeneous microstructure observed after 504 h. Comprehensive microstructural characterization was conducted utilizing scanning electron microscopy and optical microscopy. Additionally, uniaxial compression tests were performed to generate stress–strain profiles for the foams, facilitating an assessment of their energy absorption capacity. The findings indicated an enhancement in energy absorption capacity by a factor of 2.4 to 3, which can be attributed to the incorporation of Al-5Ti-0.25C and the subsequent annealing process. Full article

Traditional concrete has low tensile strength, is prone to cracking, and has poor durability, which limits its scope of application. Basalt Fiber Textile–Reinforced Concrete (BTRC), a new type of fiber-reinforced cement material, offers advantages such as light weight, increased strength, improved crack resistance, and high durability. It effectively addresses the limitations of traditional concrete. However, the tensile properties of BTRC have not been fully studied, especially with fine aggregate concrete as the matrix, and there are few reports on this topic. Therefore, this study conducted uniaxial tensile tests of Basalt Textile–Reinforced Fine Aggregate Concrete (BTRFAC) and systematically investigated the effects of two mesh sizes (5 mm × 5 mm and 10 mm × 10 mm) and two to four layers of fiber mesh on the tensile strength, strain hardening behavior, crack propagation, and ductile tensile mechanical properties of BTRFAC thin slabs. The tests revealed that an increase in the number of fiber mesh layers significantly reinforced the material’s tensile strength and ductility. The tensile strength of the 5 mm mesh specimen (four-layer mesh) reached 2.96 MPa, which is 193% higher than plain concrete, and the ultimate tensile strain increased by 413%. The tensile strength of the 10 mm mesh specimen (four-layer mesh) was 2.12 MPa, which is 109% higher than plain concrete, and the ultimate tensile strain increased by 298%. The strength utilization rate of the 5 mm and 10 mm mesh fibers was 41% and 54% respectively, mainly due to the weakening effect caused by interface slippage between the fiber mesh and the matrix. An excessively small mesh size may lead to premature debonding from the matrix, but its denser fiber distribution and larger bonding area exhibit better strain hardening characteristics. More than three layers of fiber mesh can significantly improve the uniformity of crack distribution and delay propagation of the main crack. A calculation formula for the tensile bearing capacity of BTRFAC thin slabs is proposed, and the error between the theoretical value and the experimental value was very small. This research provides a theoretical basis and reference data for the design and application of basalt fiber mesh–reinforced concrete thin slabs. Full article

This study develops a quantitative framework to assess performance degradation and damage evolution in CRTS I ballastless track slabs. Based on the impact-echo method, the internal void distribution characteristics of the new and old track slabs were obtained. The track slabs were sampled separately by drilling cores to verify the distribution of voids, and uniaxial compression tests were conducted simultaneously to quantify the attenuation of bearing capacity. The on-site wheel–rail force and temperature field data were monitored, based on the established three-dimensional finite element model of CRTS I ballastless track, and the damage distribution characteristics of the track slab under different load combinations after performance degradation were studied. The results show the following: (1) As the performance of the track slabs gradually deteriorated, it was reflected in the increasing internal void distribution area from 0.5% to 3.6%, corresponding to a 22.4% decrease in core strength. (2) The on-site monitoring results showed that the average wheel–rail force was 84.5 kN. The temperature gradient range varied from −50.4 °C/m to 100.0 °C/m, exceeding the allowable value of the design specifications. (3) The actual damage distribution of the track slab after performance degradation under different load combinations significantly increased at key stress locations such as near fasteners, convex abutments, and anchor holes of prestressed steel bars, which required special attention in actual maintenance and repair. Full article

Bimetallic-clad pipes demonstrate exceptional advantages in transporting corrosive oil and gas through the combination of the load-carrying capacity of the base material and the anti-corrosive function of the thin layer of corrosion-resistant alloy. This study investigates the mechanical properties of 24-inch X65 + Alloy625 metallurgically clad pipes through experimental tests and finite element analysis. Uniaxial tensile testing with digital image correlation reveals uniform deformation between the base and clad layers until interfacial failure initiates at an average strain threshold of 34.17%. Microstructural characterization shows continuous metallurgical bonding, with the X65 layer exhibiting polygonal ferrite and bainitic phases, contrasting with the austenitic equiaxed grain structure of Alloy625. In terms of numerical modeling, finite element analyses that consider both initial geometric imperfections and manufacturing-induced residual stresses are performed to evaluate the bending response of the clad pipe. The effect of initial ovality and residual stresses on its bending capacity is also studied. Full article

This paper presents the development of two solutions for sandwich panels composed of a thin-layer alkali-activated composite (AAc) layer and a thicker insulation layer, formed by extruded polystyrene foam or expanded cork agglomerate (panels named AP_XPS or AP_ICB, respectively). The AAc combined ceramic waste from clay bricks and roof tiles (75%) with ladle furnace slag (25%), activated with sodium silicate. The AAc layer was further reinforced with polyacrylonitrile (PAN) fibers (1% content). The mechanical behavior was assessed by measuring the uniaxial compressive strength of cubic AAc specimens, shear bond strength, pull-off strength between the AAc layer and the insulation material, and the flexural behavior of the sandwich panels. The thermal performance was characterized by heat flux, inner surface temperatures, the thermal transmission coefficient, thermal resistance, and thermal conductivity. Mechanical test results indicated clear differences between the two proposed solutions. Although AP_XPS panels exhibited higher tensile bond strength values, the AP_ICB panels demonstrated superior interlayer bond performance. Similar findings were observed for the shear bond strength, where the irregular surface of the ICB positively influenced the adhesion to the AAc layer. In terms of flexural behavior, after the initial peak load, the AP_XPS exhibited a deflection-hardening response, achieving greater load-bearing capacity and energy absorption capacity compared to the AP_ICB. Finally, thermal resistance values of 1.02 m² °C/W and 1.14 m² °C/W for AP_ICB and AP_XPS were estimated, respectively, showing promising results in comparison to currently available building materials. Full article

Fiber-reinforced polymer (FRP) composites demonstrate significant advantages in the reinforcement of timber structures, with basalt fiber-reinforced polymer (BFRP) and carbon fiber-reinforced polymer (CFRP) exhibiting distinct characteristics. This study systematically compares the mechanical performance differences between BFRP- and CFRP-reinforced Northeast larch timber columns. Uniaxial compression tests focused on the mechanical responses under different reinforcement conditions along the grain direction. The results indicate that BFRP-reinforced specimens exhibit superior cost-effectiveness, enhanced ductility, and improved damage tolerance, whereas CFRP-reinforced specimens demonstrate higher stiffness and ultimate load-bearing capacity. A damage constitutive model, developed based on Poisson distribution theory, accurately describes the damage evolution process of fully FRP-reinforced Northeast larch timber columns. Numerical simulations show excellent agreement with experimental results. The study provides critical guidance for FRP material selection and reinforcement strategies in timber structure engineering: BFRP is more suitable for general applications prioritizing cost efficiency and ductility, while CFRP is better suited for special structures requiring higher load-bearing capacity. Finite element models of CFRP- and BFRP-reinforced timber specimens under axial compression were established using ABAQUS 2020 software, with simulation results closely matching experimental data. The proposed constitutive model and finite element analysis method offer a reliable tool for predicting the mechanical behavior of FRP-wood composite structures. Full article

The objective of this study is to develop failure-limit material models for Aluminum 6061-T6, A36 Carbon Steel, 304 Stainless Steel, and Nitronic 60 metals, based on parameters of plastic equivalent strain (failure strain) and stress triaxiality. The research is conducted in two parts. This paper presents Part One of the study. In Part One, custom-designed test specimens undergo controlled uniaxial tension and compression testing at ambient temperature. These tests are performed at quasi-static speeds using Universal Testing Machines (UTMs) in accordance with ASTM E8 and ASTM E9 standards. Experimental data, specifically engineering stress–strain and force–displacement curves, are recorded from the onset of loading until specimen fracture, or in the case of compression tests, until the capacity of the testing machine is reached. In Part Two, the emphasis shifts to the calibration of Finite Element Analysis (FEA) models of the custom-designed test specimens. Plastic equivalent strain and the corresponding stress triaxiality values at failure are extracted from each test specimen for the given metal. These values are then systematically plotted onto a single graph to construct the failure-limit curve, which delineates the boundary conditions for material failure. This approach will facilitate the development of a comprehensive material property definition that correlates plastic equivalent strain with stress triaxiality at failure for Aluminum 6061-T6, A36 Carbon Steel, 304 Stainless Steel, and Nitronic 60 metals. Full article