Search Results (1,667)

Aging and deterioration of urban underground drainage pipelines frequently trigger road collapses, urban waterlogging and groundwater contamination, posing critical challenges to the operation, maintenance and disaster prevention of urban underground infrastructure. Conventional rehabilitation solutions, including cement-based linings and traditional polymer liners, suffer from inherent limitations such as reduced effective flow cross-sections caused by excessive lining thickness, unsatisfactory corrosion resistance and durability, and high construction disturbance. In this study, a modified polyurea (MPU) material was applied to the trenchless rehabilitation of drainage pipelines via spray-applied pipe lining technology. The mechanical properties and interfacial bonding performance of MPU were systematically characterized at the material scale; full-scale external pressure tests were conducted to investigate the effects of 3–8 mm thick MPU linings on the bearing capacity and failure characteristics of structurally damaged concrete pipes; and the anti-seepage repair performance for local perforation defects was evaluated through void-crossing testing. The results demonstrate that MPU lining can meet the engineering performance requirements for pipeline rehabilitation when applied with matched interfacial primer following standard construction procedures. Even the baseline bond strength tested without primer remains sufficient to ensure stable cooperative load bearing between the lining and the host concrete pipe. The 3–8 mm thick linings increase the cracking load of damaged pipes by 61.7–145.7% and the ultimate load by up to 162.2%, while transforming the failure mode from brittle fracture to ductile failure. For local perforation repair, the 3 mm thick MPU lining achieves a critical hydrostatic failure pressure of 1.23 MPa, maintaining favorable structural integrity and interfacial bonding stability under the test conditions. With a well-balanced combination of thin lining thickness, rapid curing and high structural strengthening efficiency, as well as favorable inherent corrosion resistance, the MPU lining provides novel material alternatives and fundamental experimental evidence for the green trenchless rehabilitation of aged underground pipelines and offers technical support for the safe operation and maintenance of urban underground infrastructure. Full article

Prefabricated steel–concrete composite bridge decks are widely used in the construction of long-span bridges due to their excellent mechanical performance and rapid construction speed. However, the joints in these decks are prone to tensile failure under negative bending moments, which limits the overall mechanical behavior of the structure. To improve the flexural–tensile performance of joints in prefabricated steel–concrete composite bridge decks under negative bending moments, a novel prefabricated steel grid–hybrid fiber concrete (PSG-HFC) composite bridge deck with closed-loop steel bar joints is proposed. Basic unit specimens of the composite bridge deck with closed-loop steel bar joints were designed and fabricated. Both physical and numerical experiments, including finite element modeling and model refinement, were conducted to clarify the mechanical response and failure mode of closed-loop steel bar joints under negative bending moments and to identify their rational structural parameters. Theoretical formula for calculating the flexural capacity of the closed-loop steel bar joints based on the strut-and-tie model theory was derived and verified. The results indicate that the failure mode of the novel PSG-HFC composite bridge deck under negative bending moments is typical plastic failure, with the ultimate failure mode being flexural–tensile failure at the joint section. The loading process includes elastic, elastoplastic, and plastic stages. From the perspectives of improving flexural capacity and fully utilizing high-strength materials, the rational structural parameters for the closed-loop steel bar joints are as follows: lap length of closed-loop steel bars of 230~250 mm, spacing of closed-loop steel bars of 130~150 mm, and bending radius of closed-loop steel bars of 70~90 mm. The maximum deviation between the theoretical formula results and the experimental and finite element numerical simulation results is 8.21%, indicating that the proposed formula is suitable for calculating and analyzing the flexural capacity of the joints in this novel composite bridge deck. This study reveals that the proposed closed-loop steel bar joint enables a ductile flexural–tensile failure mode in PSG-HFC composite deck under negative bending moments, and provides a validated theoretical formula for advancing the understanding of joint design in fiber-reinforced concrete structures. Full article

Load-bearing prefabricated concrete sandwich wall panels (LBPCSW) offer potential for rapid construction and energy efficiency, yet their seismic performance requires systematic evaluation. In this study, quasi-static tests and finite element analysis were conducted on LBPCSW specimens with varying height-to-width ratios and embedded column configurations. The results indicate that the LBPCSW specimens exhibit satisfactory structural integrity, with all specimens achieving ductility coefficients greater than 3.0. Specifically, specimen W1 with a height-to-width ratio of 1:1 failed in shear, whereas specimens with a height-to-width ratio of 2:1 exhibited flexural failure. Compared with W1, specimen W2 with embedded columns at the wall ends demonstrated significantly enhanced load-bearing capacity and ductility. Parametric analysis revealed that concrete layer thickness is the dominant factor influencing load-bearing capacity: taking W1 as an example, as the single-side concrete layer thickness increased from 30 mm to 50 mm, the ultimate load-bearing capacity increased from 182 kN to 246 kN, representing a 35% improvement. In contrast, the effect of concrete strength was relatively minor: increasing the strength grade from C25 to C35 raised the ultimate load-bearing capacity from only 223 kN to 255 kN, an increase of merely 14%. It is concluded that the proposed LBPCSW combine favorable seismic performance with energy efficiency, representing a promising solution for shear wall systems in low-rise rural housing in earthquake-prone regions. Full article

The reliable joining of graphite and Cu holds significant promise for applications in electronic heat dissipation and sliding electrical contacts. However, the substantial differences in their physicochemical properties, poor wettability, and mismatch in coefficients of thermal expansion often result in low joint strength. In this study, a two-step joining strategy combines surface modification with low-temperature sintering, and this is proposed for fabrication of Cu/graphite joints. First, the graphite surface is modified using an AgCuTi active filler alloy under vacuum conditions. Ti preferentially segregates at and reacts with the graphite interface, leading to the formation of an Ag-Cu eutectic modified layer on the graphite surface. Subsequently, low-temperature joining of the modified graphite to a Cu substrate is achieved via a hot-pressing sintering process using a Ag paste. In the sintered joint, the Ag sintered layer forms sound metallurgical bonds with both the Cu substrate and the graphite-modified layer. When the sintering temperature is 250 °C, the joint exhibits a shear strength of 30 MPa, which is significantly higher than that of a directly brazed joint. This strategy effectively reduces thermal residual stress in the joint during cooling and shifts the failure location from the brittle graphite substrate to the ductile Ag sintered layer, thereby substantially enhancing the mechanical performance. Full article

The development of fully biodegradable poly(3-hydroxybutyrate) (PHB)-based materials with improved mechanical performance remains a major challenge due to the limited ductility and processability of this highly crystalline polymer. Blending and plasticisation are viable strategies to enhance PHB toughness; however, the interactions governing polymer–plasticiser compatibility and their impact on structure–property relationships remain not fully understood. In this work, the compatibility and plasticisation mechanisms of two citrate-based plasticisers, tributyl citrate (TBC) and acetyl tributyl citrate (ATBC), were systematically investigated in biodegradable blends based on PHB, polylactic acid (PLA), and poly(butylene adipate-co-terephthalate) (PBAT). Polymer–plasticiser affinity was evaluated through Hansen Solubility Parameters and interaction radius, which indicated good compatibility of PHB with both plasticisers and a stronger affinity for ATBC. Differential scanning calorimetry showed that citrate plasticisers reduced the glass transition temperature, modified crystallisation kinetics, and altered the crystalline morphology of the blends. Dynamic mechanical analysis confirmed the reduction in the glass transition temperature of PHB–PLA systems, which is in agreement with the DSC results. Migration experiments showed equilibrium after approximately 72 h, with PHB–PLA blends exhibiting better plasticiser retention than PHB–PBAT systems. TBC consistently showed higher migration than ATBC, in line with its lower molecular weight and higher volatility. Mechanical testing demonstrated that plasticisation efficiency strongly depended on blend composition: TBC was more effective in enhancing ductility in PHB–PLA blends, whereas ATBC performed better in PHB–PBAT systems. It was also highlighted that the plasticisers had a remarkable ability to substantially increase the ductility of the blends compared with their unplasticised counterparts, as reflected by the pronounced decrease in stiffness and the marked increase in elongation at break. SEM analysis of tensile fracture surfaces evidenced a brittle failure mode for PHB–PLA blends, whereas PHB–PBAT systems exhibited a ductile fracture mode with fibrillar features and clear signs of phase separation. Finally, thermogravimetric analysis showed no appreciable thermal degradation within the processing temperature window used for mixing and hot pressing, confirming the thermal stability of the materials under the selected conditions. These findings establish clear correlations between thermodynamic compatibility, migration behaviour, thermal properties, fracture mechanisms, and mechanical performance, providing useful guidelines for the design of citrate-plasticised PHB-based biodegradable materials. Full article

The effect of quenching rate combined with pre-tempering treatments on the mechanical properties of H13 steel was systematically investigated in this study. Tensile testing, electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and X-ray diffraction analysis (XRD) were employed to study the structure–property relationships associated with different heat treatment conditions. The results showed that the specimen subjected to pre-tempering at 680 °C exhibited optimal strength performance, and fractographic analysis revealed that the specimen exhibited characteristic ductile fracture features. Further analysis revealed that increasing the quenching cooling rate effectively refined the grain size of the matrix, thereby significantly enhancing the strength of the sample. Tensile tests demonstrated optimal comprehensive mechanical performance with a yield strength of ~1050.4 MPa and elongation after fracture of ~17.1% for the oil-quenched specimen subjected to 680 °C pre-tempering treatment. The findings provide valuable experimental evidence and theoretical guidance for optimizing the heat treatment process of H13 steel and improving its failure resistance. Full article

To investigate the stress evolution, deformation behavior, and failure characteristics of composite-reinforced prestressed concrete hollow square piles (PHSC piles) under bending, a four-point bending test was conducted on a full-scale PHSC500 (340) hollow square pile specimen with a length of 7000 mm, a square section of 500 mm × 500 mm, and a hollow core diameter of 340 mm. The test was used to obtain load–deflection curves, crack propagation patterns, deformation responses, sectional strain distributions, and failure modes. In addition, an ABAQUS finite element model was established to compare the bearing capacity, stiffness degradation, and ductility of different pile types with varying prestressed and non-prestressed reinforcement ratios. The results show that vertical cracks changed their propagation direction at the edge of the tensile zone in the flexural–shear region of the PHSC piles and developed into a critical diagonal crack with a width of 1.7 mm. The specimen ultimately exhibited a shear–compression failure mode. During the failure stage, the midspan deflection increased rapidly as the load rose from 710 to 740 kN, with the deflection increasing from 24.88 to 32.00 mm. The load–midspan deflection curve obtained from the finite element analysis was generally consistent with the experimental results. Moreover, the predicted damage concentration zones corresponded well to the experimentally observed crack locations, indicating that the model can be used to analyze relative variations under different parameter conditions. The combination of prestressed and non-prestressed reinforcement improved the flexural capacity and ductility of the PHSC piles. However, ductility did not increase monotonically with the prestressed reinforcement ratio. These findings provide a reference for evaluating the flexural performance of PHSC hollow square piles and optimizing their reinforcement parameters. Full article

Resins printed via stereolithography are increasingly common in digital dentistry, yet the impact of production parameters on their performance remains considerable. This study examined the mechanical, tribological, and antibacterial performance of two stereolithography resins intended for restoration (white) and denture (pink) applications, selecting three different exposure times (4.5, 6, and 7.5 s) as the fabrication parameter. Compression tests showed that the white resin lost ductility with increasing exposure time, presenting statistically significant decreases in failure strain and toughness. In contrast, the pink resin maintained a stable failure strain and reached its peak energy absorption capacity at 4.5 s. Statistical analysis confirmed that the two resins responded differently to UV exposure, demonstrating that the impact of exposure time varied depending on the resin type. Furthermore, increasing exposure time significantly reduced surface roughness without a statistically significant effect on hardness. Antibacterial assessment revealed contact-mediated growth-inhibitory effects depending on strain and resin type. Accordingly, optimal exposure time was resin- and property-dependent: 7.5 s favored white resin surface quality, whereas 4.5 s maximized pink resin strength and toughness. Tailoring exposure time to both the specific resin and targeted property is crucial for enhancing the clinical longevity and structural reliability of dental applications. Full article

High-strength low-alloy (HSLA) steels produced by thermomechanical controlled processing (TMCP) are widely used in structural applications because of their high strength and weldability. However, the performance of welded joints is strongly affected by welding thermal cycles. This study investigated the effects of heat input (0.6, 1.4, and 1.8 kJ/mm) and filler metal strength (matching and undermatching) on the microstructure and mechanical properties of S700MC steel joints produced by metal-cored arc welding (MCAW). Microstructural characterization, hardness measurements, tensile testing, Charpy impact testing, and analysis of variance (ANOVA) were performed. Heat input was identified as the dominant factor controlling heat-affected zone (HAZ) development and mechanical performance. Increasing heat input enlarged the HAZ and reduced hardness through enhanced microstructural recovery. Filler metal strength mainly influenced failure location and joint strength. The lowest heat input (0.6 kJ/mm) provided the highest strength retention, particularly with the matching consumable, but also produced localized hardness peaks approaching 400 HV_0.01 at the weld metal (WM)/HAZ interface, reducing ductility and impact toughness. An intermediate heat input (1.4 kJ/mm) produced the best balance between strength and toughness by promoting a more homogeneous microstructure and smoother hardness distribution. These results provide practical guidance for optimizing welding procedures for TMCP HSLA steels. Full article

The modification of cementitious binders using active mineral additives and nano-components represents a crucial pathway for developing high-performance, sustainable concrete composites. Nevertheless, unilateral modification of the matrix with highly reactive siliceous materials often leads to an undesirable increase in composite brittleness. This study investigates the synergistic effect of the concurrent application of nano-silica (NS), silica fume (SF), and Class F fly ash (FA) in ternary and quaternary binders, aimed at optimizing both load-bearing capacity and fracture toughness. The experimental program was conducted on seven concrete series, evaluating their mechanical parameters and non-linear fracture properties using the two-parameter fracture model (TPFM) on notched beams subjected to three-point bending. Additionally, a high-resolution energy partitioning framework was applied, decomposing the total fracture energy into four distinct components—fracture initiation energy in the elastic range (G_ini), pre-peak microcracking energy (G_pre), main material softening energy (G_soft), and residual tail energy dissipated at large crack openings (G_tail)—along with the determination of the characteristic length (l_ch). The results demonstrated that while purely siliceous systems (modified with NS and SF) generate high strength increments, they simultaneously trigger a “brittleness trap,” manifested by a 13.65% decrease in the l_ch parameter. The introduction of FA effectively mitigates this hazard, transforming the failure mode into a quasi-ductile behavior. The concrete series modified with the NS+FA hybrid (Mix-5) exhibited a spectacular 107% increase in G_f and an increase in l_ch of nearly 50%, while maintaining high fracture toughness. Energy decomposition analysis in quaternary concretes confirmed a desirable reduction in the initiation energy share in favor of the softening and tail phases (G_tail reaching a record 13.1% for Mix-7), suggesting the probable activation of macroscopic crack-bridging mechanisms driven by the delayed hydration of FA particles. The research indicates that precise design of multi-component binders allows for achieving an optimal technological equilibrium point—the “sweet spot”—combining high structural capacity with safe material ductility. Full article

Coal has abundant bedding and joint structures, and most of it exhibits obvious brittle characteristics, which leads to its easy cracking and failure under mining stress. This easily leads to slab cracking and roof collapse in coal mining faces, as well as large deformations in roadways. On-site grouting of fractured coal bodies can effectively prevent these disasters. To reveal this mechanism, this study has first developed a modified ultra-fine cement grouting material and high-pressure continuous grouting system, and then conducted grouting and uniaxial compression tests on post-peak coal samples. Test results indicate that the post-peak residual bearing capacity of grouted coal specimens can recover to 65~85% of the peak strength of intact raw coal. The pre-peak plastic deformation becomes significant, and the post-peak stage exhibits stable strain softening. Grouting is considered to serve to improve the internal stress state of coal samples, act as a ductile grid skeleton, coordinate their internal deformation, and enhance their post-peak bearing capacity. Full article

This study presents an integrated experimental methodology to determine the forming and fracture limits of welded thin-walled steel tubes, with emphasis on weld-line effects and manufacturing-induced anisotropy. The methodology combines longitudinal and transverse uniaxial tensile tests, using specimens extracted from different positions relative to the weld line, with elastomer-based tube expansion tests. Digital Image Correlation, combined with time-dependent strain analysis, was used to identify the onset of localized necking, while local strain and thickness measurements near the fracture regions supported the determination of fracture limits. This experimental work covered strain paths in the principal strain space ranging from uniaxial tension to near plane-strain expansion within the investigated conditions, enabling the experimental determination of both the Forming Limit Curve and the Fracture Forming Line for the welded tube material. Results reveal a pronounced directional dependence of mechanical response and formability. Transverse specimens exhibited higher yield and ultimate tensile strengths but lower ductility, whereas longitudinal specimens showed greater elongation and strain-hardening capacity. Strain localization and fracture were governed by the combined effects of local thickness variations, weld heterogeneity, and manufacturing-induced anisotropy. In longitudinal specimens, fracture occurred preferentially along the weld line, while in transverse specimens it developed away from the weld region, indicating distinct failure mechanisms depending on the loading direction. These findings highlight the need to account for weld-related heterogeneity and manufacturing history when assessing the formability of welded thin-walled tubes. The proposed methodology provides valuable experimental data for improving failure prediction and supporting the design, simulation, and optimization of welded tubular components. Full article

Timber is a natural and renewable construction material, so it is environmentally friendly. However, timber has natural defects and also deteriorates over time. These problems require structural reinforcement. The present study aims to systematically explore the compression performance of natural Larch circular columns reinforced with Carbon Fiber-Reinforced Polymer (CFRP) and Basalt Fiber-Reinforced Polymer (BFRP). Thirty specimens were tested in pure axial compression to investigate the influence of the number of wrapping layers (0–3 layers), the specimen height (150, 200 and 300 mm) and the type of FRP material. The strengthening mechanism primarily relies on the passive hoop confinement provided by the FRP, which restricts the transverse expansion of the timber under axial load. Because CFRP possesses a higher tensile strength and elastic modulus than BFRP, it activates confining stresses more rapidly and provides a stronger restraint, leading to distinct improvements in load-bearing performance. The experimental results show that the failure mode of the short columns changes from inherent brittle splitting to a more ductile failure pattern, characterized by FRP ruptures and crushing of the timber as a result of external FRP wrapping. The axial compressive performance of the timber columns has been improved with both FRP materials. Given the same conditions, the CFRP caused increases in load-bearing capacity and stiffness, as a result of its higher tensile strength and elastic modulus, which gave rise to peak loads that were 4.9% to 7.8% greater than the BFRP-strengthened groups. There was a tendency for the reinforcement efficiency to increase with the number of layers of CFRP wrapping, and 2–3 layers of CFRP was found to be the optimal number of layers based on the aspect of material efficiency. In addition, FRP confinement was able to prevent premature failure and improve the ultimate transverse strain by as much as 2.1 times, significantly increasing ductility and energy dissipation. Finally, a theoretical ultimate strength prediction model was developed based on the passive confinement theory with the introduction of a height correction factor to consider the slenderness effects. The proposed model showed an overall coefficient of determination R² of 0.8027, which was good for reference for designing the reinforcement and evaluation of the performance of sustainable timber structure. Full article

Beam–column joints are critical elements in reinforced concrete (RC) frame structures. They are subjected to complicated load mechanisms in the event of earthquakes, which often leads to non-ductile damage in the form of shear cracking failure and concrete spalling. With recent advances in computer vision techniques, an image-based methodology is implemented for effectively assessing the seismic damage of RC beam–column joints. Specifically, this study integrates digital image correlation (DIC)-derived strain fields with microplane damage theory to identify concrete surface damage, and subsequently, fractal dimension analysis is employed to quantitatively evaluate the damage metric. The proposed image-based analysis procedures are implemented to investigate the damage evolution of six full-scale RC beam–column joints subjected to quasi-static loading tests. The damage results derived using fractal dimension analysis are compared with those computed using conventional mechanics-based damage models. It is observed that the fractal-based damage index of the RC joints agrees reasonably well with the stiffness-based damage index. The damage curves reveal that the DIC-assisted fractal dimension analysis provides an effective means for automated identification of the surface damage pattern as well as damage progression of RC beam–column joints under seismic loading or other complex loading scenarios. Full article

In this paper, an innovative T-stub connection with square-neck one-side bolts (TS-SNUBC) is developed to improve the bearing capacity and construction reliability of the box column-H beam joint. Twelve T-stub specimens, considering variations in bolt type, flange thickness, and bolt hole orientation, were designed and tested under uniaxial tension. The failure modes, load–displacement responses, ultimate load-bearing capacities, and key quantitative mechanical indicators (initial stiffness, ductility index and cumulative energy dissipation) of the specimens were evaluated. The results indicate that all specimens failed due to the yielding of the thin flange. Specimens with conventional bolts demonstrated the highest load-bearing capacity, followed by those with TS-SNUBC and then slotted one-side bolts. Increasing the thin flange thickness significantly improved the ultimate bearing capacity of the TS-SNUBC specimens. Notably, TS-SNUBC specimens with thin flange thicknesses below 10 mm experienced tear-out failure. Furthermore, specimens with horizontally oriented bolt holes exhibited higher load-bearing capacity than those with vertically oriented holes. A thin flange thickness above 10 mm ensures high initial stiffness, and TF12H has a stiffness of 32.00 kN/mm. Ductility gradually reduces with the growth of thin flange thickness. Energy dissipation decreases sharply when the thin flange is thicker than 10 mm. The joint with 16 mm thick flange, 8 mm thin flange and horizontally arranged square-neck one-side bolts presents the best comprehensive performance. The proposed TS-SNUBC shows favorable bearing performance and initial stiffness, offering a promising solution for reliable and efficiently constructed connections between box columns and steel beams. Full article