Search Results (8,969)

SMA bars, particularly those based on NiTi, exhibit superelastic and self-centering properties, providing damage-resistant, self-centering structural systems. However, their natural smoothness and low machinability pose a significant challenge to adequate mechanical anchorage. This paper experimentally measures the efficiency of two feasible wedge-type anchorage systems, wedge-and-barrel (WB) and spring anchor (SA), which are typically used in post-tensioning systems, and assesses their applicability for anchoring smooth-surfaced NiTi SMA bars. A total of 24 testing configurations were examined in this study. A complete monotonic tensile test regime was performed at steady loads with desired strain levels. The findings validate that both wedge-type anchorage systems were able to effectively anchor the SMA bars, although some performance differences were observed. The WB anchorage system showed increased stress capacity, improved load transfer efficiency, and less scatter across repeated tests, which can be attributed to its greater mechanical confinement and frictional interlock, exhibiting an increase of approximately 27% in stress capacity compared to the SA anchorage system. On the other hand, the SA system exhibited good anchorage performance. It showed a slightly lower stress response and greater variation at higher levels of deformation due to the spring’s compression mechanism. The results demonstrate the feasibility of using wedge-type anchorage systems to anchor SMA rebars for seismic applications and provide guidance for future anchorage design. Full article

To investigate the distribution pattern and magnitude of residual stress at the weld toe of pipe-sphere connections in welded hollow sphere joints, the blind-hole method was employed to measure welding residual stress at both the spherical weld toe and pipe weld toe, yielding the magnitude and distribution characteristics of the residual stress. Additionally, the VISUAL-Environment finite element simulation software was utilized to obtain the temperature field, residual stress field, and residual stress distribution curves at the weld seam. The results indicate that welding residual stress in the entire welded hollow sphere joint exhibits both periodic and stochastic characteristics, with these two patterns showing good consistency. Meanwhile, finite element analysis results reveal the presence of both residual tensile and compressive stresses on the spherical surface and the connected pipe, with the welding residual stress maintaining a self-equilibrated state across the entire specimen. This study provides a foundational basis for subsequent research on the fatigue performance of grid structures with welded hollow sphere joints. Full article

This study investigates the influence of adhesive type on the bond performance between CFRP plates and steel interfaces through static tensile double-shear tests. Three types of adhesives (Araldite 420A/B, 2015-1, Sikadur-30CN) were tested under four bond lengths. The results indicate that adhesive strength significantly affects failure characteristics, with distinct material performance differences observed. Bond length influences the stress distribution, enhancing dispersion while potentially altering damage progression. High-performance adhesives exhibit superior shear resistance and fracture energy due to improved viscous properties, whereas moderately plastic adhesives achieve adaptive deformation and durable bonding by enhancing the flow and substrate contact. These findings provide a theoretical basis for material selection in CFRP-strengthened steel structures and offer actionable guidance for structural repair engineering applications. Full article

In this study, a polyethylene glycol (PEG)-based solid electrolyte composite (PEG)₁₀LiClO₄/NaAlOSiO suitable for anodic bonding packaging was successfully fabricated via a combined ball milling and hot pressing process. The micromorphology, ion transport characteristics, and mechanical packaging properties of the composite were systematically investigated using characterization techniques including electrochemical impedance spectroscopy, X-ray diffraction, scanning electron microscopy, and anodic bonding performance tests. The results demonstrate that doping with NaAlOSiO molecular sieve can effectively reduce the crystallinity of the polymer matrix, construct more efficient carrier transport pathways, and simultaneously enhance the ionic conductivity and mechanical properties of the material. When the mass fraction of NaAlOSiO doping is 8 wt.%, the composite exhibits a room temperature ionic conductivity of up to 1.31 × 10⁻⁵ S·cm⁻¹. Under room temperature and a bonding voltage of 800 V, the sample with this doping ratio achieves the optimal anodic bonding with metallic Al, and the tensile strength of the bonding interface reaches 5.93 MPa, showing excellent application prospects in micro–nano-packaging. Full article

The focus of this work was to investigate the mechanical properties of additively manufactured (AM) discontinuous carbon fibre-reinforced polymer (DCFRP) composites. Towards the specimen’s fabrication, the Fused Filament Fabrication (FFF) additive manufacturing technique was employed. A number of input printing parameters were varied, such as the infill pattern, infill density, layer height, shell configuration, and raster orientation, in a systematic way. The role of these paraments on the mechanical properties, such as tensile, flexural, and impact strength were investigated. The data was analysed in-depth and the “main effect method” was employed for their comparative ranking. The results of this study showed that tensile and bending strengths were strongly correlated with material content and structural reinforcement. The specimens attained up to 76.7 MPa of tensile strength, while the flexural strength was up to 159.4 MPa, with a deflection of up to 8 mm and 16 mm, respectively. Solid infills, higher densities, finer layer heights, and added shells significantly improved the strength and stiffness. Grid-patterned and low-density specimens caused poor load-bearing capacities, while hexagonal and gyroid infills offered a more balanced performance. Full article

Tunnels excavated in non-coal oil- and gas-bearing strata may experience the seepage and intermittent ingress of an oil–gas–water mixture during construction, creating aggressive corrosive conditions that can compromise the integrity of primary support and the safety margin of the final lining. However, the coupled degradation mechanism of primary support and its cascading effect on lining safety under such conditions remain poorly understood. Based on the Huaying Mountain Tunnel project, this study investigates the corrosion-driven damage evolution of primary support and its implications for the structural safety of the secondary lining under wet–dry cycling exposure. Accelerated wet–dry cycling tests were performed on concrete specimens using an on-site crude-oil–formation-water mixture collected during tunnelling, with exposure levels ranging from 0 to 120 cycles. Laboratory observations were then combined with inverse identification of degradation-dependent material parameters to establish a corrosion-informed mechanical description, which was implemented in numerical simulations for structural response assessment. Results show a staged evolution of mechanical properties, with an initial increase followed by progressive deterioration. After 120 cycles, compressive strength, tensile strength, and elastic modulus decreased by approximately 18.9%, 23.1%, and 17.4%, respectively. Degradation is more pronounced in the corroded zone, with tensile capacity and stiffness deteriorating earlier than compressive resistance. Numerical results indicate that corrosion leads to significant stress redistribution and damage development. The sidewall tensile stress reaches 2.80 MPa after 120 cycles, exceeding the post-corrosion capacity, while the safety factor drops below the code threshold at 90 cycles. The overall safety probability decreases from 1.0 to 0.4, accompanied by a degradation in safety grade from Level I to Level IV. These findings provide a quantitative basis for deterioration assessment, safety verification, and maintenance planning for tunnels subjected to oil–gas corrosive environments. Full article

Cement stabilized macadam (CSM) bases are prone to cracking and void damage under long-term traffic loading and environmental actions, which accelerates structural deterioration. Although grouting is an effective method for treating such concealed defects, laboratory-based evaluation of repair effectiveness remains limited. In this study, field-cored CSM specimens were recombined in a cylindrical mold to simulate four void conditions (1/4, 2/4, 3/4, and 4/4), and repaired using an inorganic cementitious composite grouting material based on ultra-fine cement and high-belite sulphoaluminate cement (HBSAC), and modified with ethylene-vinyl acetate (EVA) latex, wollastonite (WO) whiskers, and polyvinyl alcohol (PVA) fibers. The repair effectiveness was evaluated through ultrasonic testing, capacitance measurement, uniaxial compression with acoustic emission (AE) monitoring, and computed tomography (CT). The results show that the longitudinal wave velocity of all repaired groups increases continuously with curing time, with a maximum increase of 21.98% at 28 days. The normalized capacitance response exhibits clear time- and layer-dependent variation, with the 4/4 group showing the most pronounced spatial heterogeneity. In the uniaxial compression tests, the peak load increases from 181 kN in the control group to 201–286 kN in the repaired groups, while the tensile-related AE event proportion increases from 77.35% in the 1/4 group to 89.38% in the 4/4 group. CT analysis shows that the proportion of micropores smaller than 1 mm³ increases from 66.3% to 82.7%, whereas the proportion of pores larger than 100 mm³ decreases from 46.5% to 21.6% after repair. These results demonstrate that the composite grouting material provides effective filling, structural reconstruction, and mechanical enhancement for void-damaged CSM, and that the proposed multi-source characterization framework is suitable for evaluating grouting repair performance. Full article

Wire arc additive manufacturing (WAAM) is an efficient, low-cost technique for fabricating large-scale metallic components and, in particular, functionally graded materials (FGMs). This review focuses on the fabrication of 316L stainless steel–Inconel 625 FGMs by arc-based WAAM processes, examining Gas Metal Arc Welding (GMAW), Gas Tungsten Arc Welding (GTAW) and Plasma Arc Welding (PAW) in terms of their microstructural outcomes, compositional control strategies, residual stress development and mechanical performance. A critical finding emerging from the reviewed literature is that direct compositional interfaces between 316L and Inconel 625 can yield superior tensile strength and ductility and lower residual stresses compared to smooth gradient strategies, owing to the formation of detrimental secondary phases such as δ-phase, Laves phase and MC carbides at intermediate iron–nickel compositions encountered only during graded builds. The potential of Submerged Arc Additive Manufacturing (SAAM) as a future high-deposition-rate alternative for large-scale FGM fabrication is also discussed. Key challenges, including dilution control, Laves phase formation, residual stress management and the corrosion characterization of the graded region, are identified, together with priority research directions for advancing the industrial adoption of arc-based FGM components. Full article

Welded joints are widely recognized as the most critical point in structures made of armour steels due to pronounced thermal effects, microstructural heterogeneity, and the degradation of mechanical and fatigue properties. This study investigates the mechanical properties and fatigue crack growth resistance of a welded joint produced on SA 500 armour steel, with the aim of preserving the properties of the base material as much as possible. To achieve this, a welding procedure incorporating a high-strength filler wire and optimized welding parameters was applied. Hardness and tensile testing was conducted to evaluate the extent of property degradation caused by welding. The results demonstrate that the applied welding process effectively limited the reduction in hardness and tensile strength, achieving values reasonably close to those of the base material. In addition, fatigue crack growth behaviour was investigated in accordance with ASTM E647, using both the Paris law and the McEvily law. The obtained fatigue crack growth curves and threshold stress intensity factor (ΔK_th) values indicate the nearly identical fatigue behaviour of the base material and the heat-affected zone, confirming the successful preservation of base material fatigue behaviour in the thermally affected zone. Moreover, the weld metal exhibited superior resistance to fatigue crack initiation and growth. Overall, the results confirm that the proposed welding approach provides favourable mechanical and fatigue performance for welded joints in armour steel applications. Full article

The production of fiber-reinforced polymer composites using 3D printing technology offers significant potential and opportunities for industrial applications. However, current dimensional limitations in 3D printing necessitate the use of joining techniques to obtain larger components. Recently, innovative strategies such as friction stir spot welding (FSSW) have attracted considerable attention for joining polymer composites due to their ability to produce strong joints with relatively low heat input (solid-state welding). Nevertheless, it is important to understand how the fibers present in fiber-reinforced polymer composites influence material flow and welding performance during the FSSW process. In this study, glass fiber-reinforced polylactic acid (PLA-GF) composite samples produced using a 3D printer were joined by means of FSSW. Five different tool rotational speeds (900, 1200, 1500, 1800, and 2100 rpm) and three different plunge rates (10, 20, and 30 mm/min) were employed during the welding process. Mechanical tests were performed on the welded joints to investigate the relationship between the welding parameters and the resulting mechanical properties. In addition, microstructural analyses were conducted to examine the formation of welding defects. The results revealed that three distinct zones were formed in the material after the FSSW process: the stir zone, mixed zone, and shoulder zone. Defects were observed in the mixed zone of the samples exhibiting relatively lower mechanical properties. The highest tensile force was achieved at a plunge rate of 20 mm/min and a rotational speed of 900 rpm. The highest bending force, on the other hand, was obtained at a plunge rate of 30 mm/min and a tool rotational speed of 2100 rpm. Full article

Polyester resin biocomposites containing biochar have attracted attention for improving mechanical strength and thermal stability while promoting sustainability. The pyrolysis temperature of biochar and its proportion in the polymer matrix are key factors affecting biocomposite performance. This study examined how biochar pyrolysis temperatures (400, 600, 800 °C) and incorporation levels (10, 20, 30 wt.%) influence the physical, chemical, mechanical, flammability, and morphological properties of polyester-based biocomposites. The samples were analyzed for density, water absorption, FTIR, XRD, flexural and tensile strength, ignition time, structural degradation, volumetric loss, and SEM microstructure. Biocomposites with 30 wt.% biochar produced at 800 °C showed the best mechanical properties, with a flexural strength of 95.3 MPa and an elastic modulus of 4417.4 MPa, representing increases of 14.5% and 45.7%, respectively, over the control. FTIR and XRD results revealed decreased aliphatic groups and increased aromaticity at higher pyrolysis temperatures, improving interactions between the matrix and biochar. These biocomposites also demonstrated enhanced thermal stability, with an ignition time of approximately 963 s, delayed structural degradation, and reduced volumetric loss (~19.3%). Overall, pyrolysis temperature and biochar content significantly influence the structural, mechanical, and thermal properties of polyester biocomposites, showing that biochar serves as a sustainable, performance-enhancing component in thermoset polymer matrices. Full article

Fibroin-based films represent a promising platform for sustainable and bio-derived materials. Existing literature has mainly focused on isolated molecules, plasticizers, or chemical cross-linkers, and the function of complex, multi-component natural extracts as structure-modulating agents in fibroin films remains poorly understood. In this study, edible films containing mulberry leaf extract (MLE; 2–8 wt%) and fibroin (8 wt%) were prepared by solution casting, and their structures were investigated using spectroscopic, morphological, thermal, mechanical, and barrier property analyses. The results reveal that MLE induces concentration-dependent changes in film performance through multicomponent, non-covalent interactions with the fibroin. An approximately 187% increase in tensile strength was achieved at high MLE concentration, confirming effective physical reinforcement. The water vapor transmission rate decreased markedly from 0.888 to 0.170 g·h⁻¹·m⁻², indicating an enhanced moisture barrier, whereas oxygen permeability increased at higher extract loadings, suggesting localized chain rearrangements. High optical transparency in the visible region was maintained (79.95–83.77%), while UV response was selectively altered with extract concentration. Overall, the 8MLE formulation exhibited the most balanced performance. This study demonstrates that plant-derived extracts can serve as effective natural modifiers for tailoring fibroin film properties without inducing crystallization, offering a sustainable strategy for designing bio-based and edible protein film systems. Full article

Operando mechanical behavior of lithium-ion batteries under aggressive conditions remains insufficiently quantified, especially under combined high-rate and deep-discharge operation. This study investigated strain evolution in a commercial 18650 NMC lithium-ion cell using surface-mounted fiber Bragg grating sensors across 20 sequential conditions combining five discharge rates (1–4.5 C) and four cutoff voltages (2.5–1.0 V). All tests were performed on a single cell using identical 0.5 C constant-current constant-voltage charging, followed by a 2 h rest period and controlled discharge, to systematically evaluate mechanochemical evolution with increasing electrochemical severity. Maximum tensile strain during charging ranged from 45 to 59 µε and showed limited sensitivity to discharge severity. In contrast, discharge behavior exhibited clear rate- and cutoff-dependent transitions from tensile to compressive deformation; the most severe condition (4.5 C, 1.0 V cutoff) produced a peak compressive strain of about −27 µε and the most negative residual strain after relaxation. Although temperature increased monotonically with C-rate, strain evolution was nonlinear and non-monotonic, indicating that electrochemically induced stress dominated over thermal expansion alone. These findings reveal progressive amplification of irreversible deformation under severe discharge and demonstrate the value of fiber Bragg grating sensing for operando assessment of electrochemical–mechanical coupling in cylindrical lithium-ion cells. Full article

The global expansion of wind energy increases the need for sustainable recycling strategies for glass fiber-reinforced plastic (GFRP) from end-of-life wind turbine blades (WTB). Mechanical recycling is currently the most economically and ecologically viable technology. This study compares post-industrial (PI) waste from laminate cutoffs and post-consumer (PC) GFRP waste from end-of-life WTBs to investigate the influence of waste origin, pretreatment of shredded GFRP, different particle sizes and various matrix formulations on the tensile modulus and tensile strength of pressed bulk molding compounds produced with virgin epoxy resin. Thermogravimetric analysis showed a fiber content of up to 70 wt.%, but the resin residues on the embedded glass fibers dimmish a sufficient bonding of the new matrix system. Finer GFRP fractions consistently yielded higher tensile modulus and strength, with PI and pretreated PC materials performing best. The findings of this study demonstrate that controlled particle size distribution, impurity removal and optimized resin viscosity are key factors to achieve reliable mechanical performance and enable high-value recycling routes for glass fiber composite waste. Full article

This study investigates the development of sustainable composite materials using recycled low-density polyethylene (rLDPE) and high-density polyethylene (rHDPE) in an 80/20 mass ratio, incorporating kraft lignin as a bio-derived additive and polyethylene-graft-maleic anhydride (PE-g-MA) as a compatibilizer. Reactive melt mixing was employed to produce composites with varying lignin loadings (1, 3, 5, and 10 wt%). The structural, thermal, and mechanical properties and segmental dynamics of the materials were thoroughly examined using differential scanning calorimetry (DSC), infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS), tensile testing, scanning electron microscopy (SEM), and dielectric relaxation spectroscopy (DRS). The incorporation of lignin exhibited minimal disruption to the polymeric thermal transitions, while it boosted thermal stability, as confirmed by the TGA curves. According to the segmental dynamics findings, the glass transition temperature of the polymeric blend (−35 °C) was increased systematically with the addition of lignin by ~1–20 K. Tensile tests showed that the 1 wt% additive ratio demonstrated the optimal balance of strength and ductility. Morphological observations supported these findings, revealing uniform dispersion at low additive ratio and increased agglomeration at higher ratios. Based on its superior performance, the composite containing 1 wt% lignin was successfully extruded into filament suitable for 3D-printing. This study highlights the synergy of bio-based additives and recycled polymers in engineering high-performance materials, promoting circular economy principles and reduced environmental footprint through upcycling post-consumer waste into functional, valuable products. Full article