Search Results (1,082)

Mixed structures with lightweight steel added stories are particularly vulnerable to damage and failure at the joints during seismic events. To evaluate the secondary seismic behavior of the joints in lightweight steel added stories after seismic damage repair, a low-cycle load test was conducted in this study. Following the initial damage, carbon fiber-reinforced polymer (CFRP) was applied for reinforcement, along with epoxy resin for the repair of concrete cracks. The experimental analysis focused on the structural deformation, failure characteristics, and energy dissipation capacity in both the original and repaired joint states. On the basis of the experimental findings, finite element analysis was carried out to examine the influence of varying CFRP layer configurations on the seismic performance of the repaired joints. The results revealed a significant change in the damage pattern of the repaired specimen, shifting from secondary surface damage to significant concrete deterioration localized at the bottom of the column. The failure mechanism was characterized by the CFRP-induced tensile forces acting on the concrete at the column base, following considerable deformation at the beam’s end. When compared to the original joint, the repaired joints exhibited markedly improved performance, with a 33% increase in horizontal ultimate strength and an 85% increase in energy dissipation capacity at failure. Additionally, the rotation angle between the beams and columns was effectively controlled. Joints repaired with two layers of CFRP demonstrated superior performance in contrast to those with a single layer. However, once the repaired joints met the required strength, further increasing the number of CFRP layers had a minimal influence on the mechanical properties of the joints. The proposed CFRP-based seismic retrofit method, which accounts for the strength degradation of concrete in damaged joints due to earthquake-induced damage, has proven to be both feasible and straightforward, offering an easily implementable solution to improve the seismic behavior of structures. Full article

In saline soil and alpine regions of northwest China, fiber-reinforced recycled aggregate concrete (FR-RAC) beams are subjected to coupled degradation from a chloride–sulfate composite salt attack and freeze–thaw cycling. Existing studies predominantly focus on natural aggregate concrete in freshwater environments or single-salt solutions, with limited documentation on the shear performance of FR-RAC beams after freeze–thaw exposure in chloride–sulfate composite salt solutions. To investigate the durability degradation patterns of FR-RAC beams in Xinjiang’s saline soil regions, two exposure environments (pure water and 5% NaCl + 2.0% Na₂SO₄ composite salt solution) were established. Shear performance tests were conducted on nine groups of FR-RAC beams after 0–175 freeze–thaw cycles, with measurements focusing on failure modes, cracking loads, and ultimate shear capacities. The results revealed that under composite salt freeze–thaw conditions: after 100 cycles, the cracking load and shear capacity of tested beams decreased by 39.8% and 22.2%, respectively, compared to unfrozen specimens representing reductions 29.6% and 82.0% greater than those in freshwater environments; at 175 cycles, cumulative damage intensified, with total reductions reaching 56.8% (cracking load) and 36.1% (shear capacity). A shear capacity degradation prediction model for FR-RAC beams under composite salt freeze–thaw coupling was developed, accounting for concrete strength attenuation and interfacial bond degradation. Model validation demonstrated excellent agreement between predicted and experimental values, confirming its robust applicability. Full article

This study focuses on the performance evolution of Engineering Geopolymer Composites (EGCs) in long-term thermal environments, investigating the mechanical properties and microstructural evolution of alkali-activated fly ash–slag composites under sustained 60 °C thermal conditions. The research results indicate that sustained exposure to 60 °C significantly enhances the static and impact loading compressive strength of EGCs; however, single-slag or high-alkalinity systems exhibit strength retrogression due to insufficient long-term thermal stability. After exposure to elevated temperatures, the tensile strain-hardening curve of EGCs becomes smoother, with a reduced number of cracks but increased crack width, leading to a transition from a distributed multicrack propagation pattern to rapid widening of primary cracks. Due to the bridging effect of PVA fibers, sustained elevated temperature significantly enhances the peak impact load stress of the S50-6 sample. Microscopic analysis attributes this improvement to the matrix-strengthening effect caused by accelerated C-(A)-S-H gel polymerization and refined pore structure under continuous heat, as well as the energy dissipation role of the fiber system. The study recommends an optimal EGC system formulation with a fly ash–slag mass ratio of 1:1 and a Na₂O concentration of 4–6%. This research provides a theoretical foundation for understanding the performance evolution and strength stability of EGC materials under sustained elevated temperature. Full article

The shale oil reservoir in Block Y of the Ordos Basin exhibits low porosity and low permeability, yet it features distinct stratification and developed micro-fractures. During the development process using “horizontal wells + volume fracturing”, the differential in geostress exerts a certain influence on the initiation and propagation of fractures. This paper employs the Cohesive element simulation method to investigate the formation patterns of fracture networks in fractured formations. By prefabricating natural fractures, the study explores the impact of natural fractures on the direction of hydraulic fractures during the hydraulic fracturing process. The study considers the fracture initiation and propagation patterns as well as the interaction between hydraulic fractures and natural fractures under differential geostress conditions of 0 MPa, 1 MPa, and 5 MPa. The numerical simulation results reveal that the presence of natural fractures significantly affects the direction of hydraulic fractures, with the tip of the hydraulic fracture deflecting towards the natural fracture. The smaller the geostress difference, the more complex the fractures become with more branching fractures. Conversely, a larger geostress difference leads to the formation of a single double-wing fracture perpendicular to the minimum principal stress, resulting in a simpler fracture morphology. The pore pressure variation at the injection point generally experiences a rapid increase followed by a slight decrease, subsequently undergoing wavy changes. The occurrence of wavy pressure variations indicates the continuous generation of micro-fractures. The fracture width at the injection point generally exhibits an increasing trend followed by a decreasing trend. When the stress difference is 0 MPa, 1 MPa, and 5 MPa, the peak rupture pressures are 12.63 MPa, 13.42 MPa, and 18.33 MPa, respectively; the maximum crack openings are 0.797 cm, 0.779 cm, and 0.771 cm, respectively. The study on fracture initiation and propagation in shale reservoirs provides guidance for the field application of multi-cluster fracturing in horizontal well sections. Full article

Salt rock, owing to its excellent rheological and self-healing properties, has been widely applied in underground gas storage. However, a numerical method capable of systematically simulating the entire damage–healing process of salt rock is still lacking, which limits the in-depth understanding of fracture evolution mechanisms and the long-term stability of storage caverns. To overcome this limitation, this study improves the parallel bond model within the framework of the Discrete Element Method (DEM) by incorporating a stress-driven healing criterion and a healing-equivalent stress coupling algorithm, thereby enabling the complete simulation of crack initiation, propagation, and closure in salt rock. The results show that the proposed method effectively captures healing effects: under uniaxial compression and tension, the number of cracks decreased by approximately 27% and 23%, with strength recovery of 110.7% and 7%, respectively. Moreover, the reconstruction of particle contact chains closely corresponds to the crystal-bridge phenomena observed in experiments, verifying the model’s reliability in reproducing macroscopic mechanical responses. In addition, the healing process exhibits a temporal characteristic in which crack closure occurs earlier than volumetric strain reduction, indicating an evolution pattern of “structural closure first, macroscopic densification later.” This study not only fills the gap in DEM-based simulation of salt rock damage–healing processes but also provides theoretical support for long-term stability evaluation and operational optimization of underground salt cavern storage. Full article

The freezing method is widely employed in the construction of a vertical shaft in soft soil and water-rich strata. As the construction depth increases, investigating the water–heat–force coupling effects induced by the hydration heat (internal heat source) of concrete is crucial for the safety of the lining structure and its resistance to cracking and seepage. A three-dimensional coupled thermal–hydraulic–mechanical analysis model was developed, incorporating temperature and soil relative saturation as unknown variables based on heat transfer in porous media, unsaturated soil seepage, and frost heave theory. The coefficient type PDE module in COMSOL was used for secondary development to solve the coupling equation, and the on-site temperature and pressure monitoring data of the frozen construction process were compared. This study obtained the model-related parameters and elucidated the evolution mechanism of freeze–thaw and freeze–swelling pressures of a frozen wall under the influence of hydration heat. The resulting model shows that the maximum thaw depth of the frozen wall reaches 0.3576 m after 160 h of pouring, with an error rate of 4.64% compared to actual measurements. The peak temperature of the shaft wall is 73.62 °C, with an error rate of 3.76%. The maximum influence range of hydration heat on the frozen temperature field is 1.763 m. The peak freezing pressure is 4.72 MPa, which exhibits a 5.03% deviation from the actual measurements, thereby confirming the reliability of the resulting model. According to the strength growth pattern of concrete and the freezing pressure bearing requirements, it can provide a theoretical basis for quality control of the lining structure and a safety assessment of the freezing wall. Full article

To clarify the influence of reinforcement corrosion on the mechanical performance of road tunnel linings, localized tests on reinforcement-induced concrete expansion are conducted to identify cracking patterns and their effects on load-bearing behavior. Refined three-dimensional finite element models of localized concrete and the entire tunnel are developed using the concrete damaged plasticity model and the extended finite element method and validated against experimental results. The mechanical response and crack evolution of the lining under corrosion are analyzed. Results show that in single-reinforcement specimens, cracks propagate perpendicular to the reinforcement axis, whereas in multiple-reinforcement specimens, interacting cracks coalesce to form a π-shaped pattern. The cover-layer crack width exhibits a linear relationship with the corrosion rate. Corrosion leads to a reduction in the stiffness and load-bearing capacity of the local concrete. At the tunnel scale, however, its influence remains highly localized, and the additional deflection exhibits little correlation with the initial deflection. Local corrosion causes a decrease in bending moment and an increase in axial force in adjacent linings; when the corrosion rate exceeds about 15%, stiffness damage and internal force distribution tend to stabilize. Damage and cracks initiate around corroded reinforcement holes, extend toward the cover layer, and connect longitudinally, forming potential spalling zones. Full article

Understanding the combined effects of water and dynamic disturbance on rock behavior is essential for deep underground engineering, where groundwater and blasting often coexist. Existing studies have mainly emphasized static weakening by water or the strength characteristics under impact, while the energy evolution process remains insufficiently addressed. To fill this gap, uniaxial impact compression tests were conducted on dry and water-saturated skarn specimens using a separated Split Hopkinson Pressure Bar system. The relationship between peak stress and impact pressure was analyzed, and the total input energy, releasable elastic strain energy, and dissipated energy were quantified to examine their evolution with strain. The results indicate that water saturation significantly reduces dynamic strength and modifies the damage process. During the compaction and elastic stages, dissipated energy is low but slightly higher in water-saturated specimens due to microcrack initiation. In the plastic stage, dry specimens exhibit faster energy dissipation, while water-saturated specimens show reduced capacity for crack propagation dissipation. Damage–strain curves follow an S-shaped pattern, with water-saturated specimens presenting higher damage growth rates in the plastic stage. These findings clarify the energy-based damage mechanisms of skarn under impact loading and provide theoretical support for evaluating stability in water-rich underground environments. Full article

The synergistic preparation of geopolymer from lithium slag, fly ash, and slag for underground construction can facilitate the extensive recycling of lithium slag. The effects of different activator moduli and water–binder ratios on the mechanical properties and damage mechanisms of the lithium-slag-based geopolymer were investigated by uniaxial compression tests and acoustic emission (AE) monitoring. The results show that, based on a comprehensive evaluation of peak stress, crack closure stress, plastic deformation stress, and elastic modulus, the optimal activator modulus is determined to be 1.0, and the optimal water-to-binder ratio is 0.42. At low modulus values (0.8 and 1.0) and low water–binder ratio (0.42), the AE events exhibit a steady pattern, indicating slow crack initiation and propagation within the geopolymer; with the increasing activator modulus and water-to-binder ratios, the frequency of AE events increases significantly, indicating more-frequent crack propagation and stress mutation within the geopolymer. Similarly, when the modulus is 0.8 or 1.0 and the water–binder ratio is 0.42, the sample presents a macroscopic tensile failure mode; as the modulus and water–binder ratio increase, the sample presents a tensile–shear composite failure mode. The energy evolution laws of geopolymer specimens with different activator moduli and water-to-binder ratios were analyzed, and a damage constitutive model was established. The results indicate that, with optimized mix proportions, the material can be used as a supporting material for underground spaces. Full article

Basin insulator is a critical component of gas-insulated transmission line (GIL) systems. Air gap defects and surface crack defects may form in basin insulators due to casting, installation, or transport processes. This phenomenon poses a significant threat to long-term safety and stability and may even lead to partial discharges. This study establishes a simulation model of a GIL system-incorporating insulator to systematically analyze the influence patterns of various defects on the insulation characteristics of the basin insulator. Meanwhile, an equation predicting the relationship between defect size and maximum electric field strength is derived. The research revealed the following: For short air gap defects near the conductor, increasing length reduces their impact on the surrounding electric field, with the radius having minimal effect; for long air gap defects near the conductor, increasing length amplifies their influence. Smooth air gap defects distant from the conductor show negligible variation in maximum electric field strength with increasing length, while unsmooth air gap defects exhibit more pronounced effects at shorter lengths. Under identical conditions, unsmooth air gap defects demonstrate greater influence on the electric field than smooth ones. For elliptical surface defects, variations in radius show the strongest distortion. The degree of influence from surface crack defects correlates directly with their proximity to the conductor. These findings provide critical diagnostic criteria for assessing the insulation performance of basin insulator under damaged conditions. Full article

Many studies have examined normal impacts on glass, but data on oblique impacts are limited, and, in particular, there is very limited experimental data on oblique impacts at various angles under consistent experimental conditions. Therefore, this study investigated fracture patterns of 5 mm thick low-emissivity (low-e) glass impacted by a 10 mm steel ball at velocities of 40 to 50 m/s at various oblique impact angles from 0° to 80°. Results showed that fracture patterns varied clearly with impact angle. Truncated cone fractures occurred in all specimens at 0° to 60°, while three of six specimens did not fracture at 80° because the normal energy dropped to below damage limit energy. Damage parameters normalized by kinetic energy showed that C_max/KE and C_min/KE remained stable at 5.7–6.4 and 4.9–5.3 mm/J from 0° to 45°, but dropped sharply to 0.7 and 0.6 mm/J at 80°. The aspect ratio of cone cracks remained relatively constant (1.2–1.3) regardless of oblique impact angle, while the aspect ratio of perforated holes increased from 1.0 (0°) to 1.6 (60°) before decreasing at 80°. Steel ball size comparison confirmed that normalized damage patterns are not significantly affected by projectile size variations. Mechanism-based analysis revealed that cone cracks and perforated holes are governed by fundamentally different physical processes. Cone cracks form through axisymmetric stress fields following Hertzian contact theory, showing limited angular sensitivity (15.4% maximum eccentricity change). In contrast, perforated holes result from trajectory-dependent mechanical penetration, exhibiting extreme angular sensitivity with 338.9% eccentricity increase from 0° to 60°. This 22-fold difference demonstrates a dual damage mechanism framework that explains the pronounced angular dependence of hole geometry versus the relative stability of cone crack patterns. These findings provide essential data for forensic glass analysis and impact-resistant glazing design, while the dual mechanism concept offers new insights into angle-dependent fracture behavior of brittle materials. Full article

A polyethylene pipe reinforced with winding steel wires (PSP) is a new composite pipe in which steel wires are effectively bonded with high-density polyethylene (HDPE) through hot-melt adhesive, ensuring the mechanical properties and structural integrity of the pipe. One of the main failure modes at the PSP joint is the interfacial debonding between the steel wire and the hot-melt adhesive. To find a good method to overcome this debonding failure mode, the first priority is to be able to quantitatively characterize the interface performance. Thus, in this study, double cantilever beam (DCB) tests are used to investigate the interfacial properties between steel and hot-melt adhesive, and a finite element model with cohesive element representing the adhesive interface is established to analyze the interfacial properties and the interfacial failure process. However, the interfacial parameters, including interface strength and fracture energy, cannot be obtained directly; thus, based on the inverse optimization calculation concept, an ABAQUS–Python–MATLAB interactive program is developed to continuously optimize and adjust the key parameters of the interface during iterative calculations so that the load–displacement simulation curve is close to the experimental curve, thereby determining the solution set of interface strength and fracture energy. With the inversion parameters substituted into the DCB model, the simulated reaction force–displacement curve is obtained, and it is consistent with the experimental one. Furthermore, this paper compares the pattern of simulated crack tip propagation during the loading process with the experimental results, and it is found that the simulated curve agrees well with the trends of the experimental ones. This proves the effectiveness of the DCB finite element model and the inversion calculation method from a new perspective, indicating that the simulation results of the DCB model were consistent with the experiment. This method can provide guidance and reference for the mechanical behavior analysis of the bonding interface of other materials or structures. Full article

Long bone fractures are breaks or cracks in a long bone of the body typically caused by trauma like a fall, sport injury, accidents etc. This study investigates the effectiveness of experimental methods for fast and safe healing of long bone fractures in humans, highlighting both their advantages and disadvantages, respectively finding the most effective and safe methods for evaluating the types of fixators that can be used in the consolidation of fractured long bones. As for the preliminary data, numerical methods and applied mathematics were used to address this problem. After collecting of preliminary data there were performed a series of experimental analysis as follows: Electrical Strain Gauges (ESGs); the Moiré Fringes method; Photo-Elasticity, with the particular technique thereof, the so-called Photo-Stress method; Holographic Interferometry (HI); Speckle Pattern Interferometry (ESPI) and Shearography; and Video Image Correlation (VIC), which is also called Digital Image Correlation (DIC). By analyzing different methods, the following two methods resulted to be widely applicable, namely, ESG and DIC/VIC. The findings highlight the net advantages regarding the objective choice of these types of fixators, thereby contributing to a possible extension of these approaches for the benefit of medical surgical practice Full article

This study investigates the mechanical behavior of a new type of link slab through experimental testing and numerical simulation. A full-scale segmental specimen of an I-shaped steel–concrete composite beam was designed, and a vertical active plus horizontal follow-up loading system was employed to realistically simulate the stress state of the link slab. In parallel, a nonlinear finite element model was established in ABAQUS to validate and extend the experimental findings. Test results indicate that the link slab exhibits favorable static performance with a ductile flexural tensile failure mode. At ultimate load, tensile reinforcement yielded while compressive concrete remained uncrushed, demonstrating high safety reserves. Cracks propagated primarily in the transverse direction, showing a typical flexural tensile cracking pattern. The maximum crack width was limited to 0.4 mm and remained confined within the link slab region, which is beneficial for long-term durability, maintenance, and repair. The FE model successfully reproduced the experimental process, accurately capturing both the crack development and the ultimate bending capacity of the slab. The findings highlight the reliability of the proposed structural system, demonstrate that maximum crack width can be evaluated as an eccentric tension member, and confirm that bending capacity may be assessed using existing design specifications. Full article

The objective of this study was to propose a correlation model of the damage class and deformation of reinforced concrete (RC) beams damaged by earthquakes with a focus on columns and walls. For this purpose, a series of full-scale RC beam specimens with different shear strength margins were tested under cyclic lateral loading to examine their deformation performance and damage states. Then, the damage class and seismic capacity reduction factor of RC beams were evaluated based on the test results. The results showed that the tendency of shear failure, such as shear crack pattern and shear deformation component, of specimens with small shear strength margins was more remarkable, and its maximum residual crack widths tended to be slightly larger and dominated by shear cracks. The results also indicated that the effect of the shear strength margin on the seismic capacity reduction factor which represents the residual seismic performance of RC beams was limited, whereas the specimen with a smaller shear strength margin exhibited lower ultimate deformation capacity. In addition, there was a difference in the boundary value of the lateral drift angle which classifies the damage class of specimens with different shear strength margins. Finally, correlation models between the damage class and deformation of RC beams with different deformation capacities were proposed. Full article