Search Results (321)

To investigate the synthesis route and electromagnetic wave absorption performance of SiC nanowires (SiC-NWs), boron was simultaneously employed as both a catalyst and a dopant, and the doped nanowires were embedded into a silicone matrix to fabricate SiC-NW/silicone composites with enhanced mechanical properties and microwave attenuation. Boric acid significantly increased the yield of SiC-NWs, while boron doping enhanced both conductive and relaxation losses. The subsequent nanowire pull-out mechanism improved the tensile strength of the composites by 185%, reaching 5.7 MPa at a filler loading of 5 wt%. The three-dimensional SiC-NW network provided synergistic dielectric and conductive losses, along with good impedance matching, achieving a minimum reflection loss of −35 dB at a thickness of 3.5 mm and an effective absorption bandwidth of 4.2 GHz within the 8.2–12.4 GHz range, with a nanowire content of only 5 wt%. Full article

This study investigates the effectiveness of combining helical piles (HPs) with geogrid reinforcement compared to conventional piles in improving pullout performance in dense sand, addressing a key challenge in reinforced foundation design. A comprehensive experimental program was conducted to evaluate the pullout behavior of HPs embedded in Shahriyar sand reinforced with geogrid layers. The research focused on quantifying the effects of critical parameters—pile configuration, helix pitch, and geogrid placement depth—on ultimate pullout capacity and displacement response to better understand hybrid reinforcement mechanisms. Pullout tests were performed using a Zwick/Roell Z150 universal testing machine with automated data acquisition via TestXpert11 V3.2 software. The experimental program assessed the following influences: (1) pile configurations—plain, single-helix, and double-helix; (2) helix pitch ratios of 1.00, 1.54, and 1.92 (pitch-to-shaft diameter); and (3) geogrid placement depths of 7.69, 11.54, and 15.38 (depth-to-shaft diameter) on pullout behavior. Results demonstrate that geogrid reinforcement substantially enhances pullout resistance, with single-helix HPs achieving up to a 518% increase over plain piles. Pullout resistance is highly sensitive to geogrid spacing, with optimal performance at a non-dimensional distance of 0.47 from the pile–soil interface. Additionally, double-blade HPs with geogrid placed at 0.35 exhibit a 62% reduction in displacement ratio, underscoring the role of geogrid in improving pile stiffness and load-bearing capacity. These findings provide new insights into the synergistic effects of helical pile geometry and geogrid placement for designing efficient reinforced granular foundations. Full article

This study aimed to assess, using finite element analysis (FEA), the mechanical effects of cortical bone thickness and cancellous bone density on the pull-out strength of suture anchors. A PEEK anchor was modeled and embedded in synthetic bone blocks with cortical thicknesses ranging from 1 to 5 mm and cancellous densities of 10 PCF, 20 PCF, and 30 PCF. Axial tensile loading simulations were conducted for all combinations, and selected cases were validated through experimental pull-out tests using commercial synthetic bone, demonstrating agreement within ±6%. Both cortical thickness and cancellous density were found to enhance pull-out resistance, though the magnitude and pattern varied with density. At 10 PCF, pull-out strength increased linearly with cortical thickness. At 20 PCF, substantial gains were observed between 2 and 4 mm, followed by a plateau. At 30 PCF, most of the increase was confined between 2 and 3 mm, with minimal improvement thereafter. These findings suggest that fixation strategies should be adapted on the basis of bone quality and provide biomechanical insights to inform patient-specific implant design and surgical planning. Full article

Drilling-induced damage in fiber-reinforced polymer composite materials was measured excavating four laminates, basalt (B₁₄), glass (G₁₄) and their two sandwich type hybrids (B₄G₆B₄, G₄B₆G₄), with 6 mm twist drills at 1520 revolutions per minute and 0.10 mm rev⁻¹ under dry running with an uncoated high-speed steel (HSS-R), grind-coated high-speed steel (HSS-G) or physical vapor deposition-coated (high-speed steel coated with Titanium Nitride (TiN) and Titanium Aluminum Nitride (TiAlN)) drill bits. The hybrid sheets were deliberately incorporated to clarify how alternating basalt–glass architectures redistribute interlaminar stresses during drilling, while the hard, low-friction TiN and TiAlN ceramic coatings enhance cutting performance by forming a heat-resistant tribological barrier that lowers tool–workpiece adhesion, reduces interface temperature, and thereby suppresses thrust-induced delamination. Replacement of an uncoated, grind-coated, high-speed-steel drill (HSS-G) with the latter coats lowered the mechanical and thermal loads substantially: mean thrust fell from 79–94 N to 24–30 N, and peak workpiece temperatures from 112 °C to 74 °C. Accordingly, entry/exit oversize fell from 2.5–4.7% to under 0.6% and, from the surface, the SEM image displayed clean fiber severance rather than pull-out and matrix smear. By analysis of variance (ANOVA), 92.7% of the variance of thrust and 86.6% of that of temperature could be accounted for by the drill-bit factor, thus confirming that the coatings overwhelm the laminate structure and hybrid stacking simply redistribute, but cannot overcome, the former influence. Regression models and an artificial neural network optimized via meta-heuristic optimization foretold thrust, temperature and delamination with an R² value of 0.94 or higher, providing an instant-screening device with which to explore industrial application. The work reveals TiAlN- and TiN-coated drills as financially competitive alternatives with which to achieve ±1% dimensional accuracy and minimum subsurface damage during multi-material composite machining. Full article

Short fiber-reinforced polymer (SFRP) has been extensively applied in structural engineering due to its exceptional specific strength and superior mechanical properties. Its mechanical behavior under medium strain rate conditions has become a key focus of ongoing research. A comprehensive understanding of the response characteristics and underlying mechanisms under such conditions is of critical importance for both theoretical development and practical engineering applications. This study proposes an innovative three-dimensional (3D) multiscale constitutive model that comprehensively integrates mesoscopic fiber–matrix interface effects and pore characteristics. To systematically investigate the dynamic response and damage evolution of SFRP under medium strain rate conditions, 3D-printed SFRP porous structures with volume fractions of 25%, 35%, and 45% are designed and subjected to drop hammer impact experiments combined with multiscale numerical simulations. The experimental and simulation results demonstrate that, for specimens with a 25% volume fraction, the strain rate strengthening effect is the primary contributor to the increase in peak stress. In contrast, for specimens with a 45% volume fraction, the interaction between damage evolution and strain rate strengthening leads to a more complex stress–strain response. The specific energy absorption (SEA) of 25% volume fraction specimens increases markedly with increasing strain rate. However, for specimens with 35% and 45% volume fractions, the competition between these two mechanisms results in non-monotonic variations in energy absorption efficiency (EAE). The dominant failure mode under impact loading is shear-dominated compression, with damage evolution becoming increasingly complex as the fiber volume fraction increases. Furthermore, the damage characteristics transition from fiber pullout and matrix folding at lower volume fractions to the coexistence of brittle and ductile behaviors at higher volume fractions. The numerical simulations exhibit strong agreement with the experimental data. Multi-directional cross-sectional analysis further indicates that the initiation and propagation of shear bands are the principal drivers of structural instability. This study offers a robust theoretical foundation for the impact-resistant design and dynamic performance optimization of 3D-printed short fiber-reinforced polymer (SFRP) porous structures. Full article

Geogrids are frequently utilized in engineering for reinforcement; yet, they are vulnerable to construction damage when employed on coarse-grained soil subgrades. In contrast, waste tire grids are more appropriate for subgrade reinforcement owing to their rough surfaces, integrated steel meshes, robust transverse ribs, extended degradation cycles, and superior durability. Based on the limit equilibrium theory, this study developed formulae for calculating the internal and external frictional resistance, as well as the end resistance of waste tires, to ascertain the interface bearing properties and calculation techniques of waste tire grids. Based on this, a mechanical model for the ultimate pull-out resistance of waste-tire-reinforced soil was developed, and its validity was confirmed through a series of pull-out tests on single-sided strips, double-sided strips, and tire grids. The results indicated that the tensile strength of one side of the strip was approximately 43% of that of both sides, and the rough outer surface of the tire significantly enhanced the tensile performance of the strip; under identical normal stress, the tensile strength of the single-sided tire grid was roughly nine times and four times greater than that of the single-sided and double-sided strips, respectively, and the grid structure exhibited superior anti-deformation capabilities compared to the strip structure. The average discrepancy between the calculated values of the established model and the theoretical values was merely 2.38% (maximum error < 5%). Overall, this research offers technical assistance for ensuring the safety of subgrade design and promoting environmental sustainability in engineering, enabling the effective utilization of waste tire grids in sustainable reinforcement applications. Full article

Helical piles are widely used in geotechnical engineering, and their rapid installation and service reliability have attracted significant interest from the offshore wind industry. These piles are frequently subjected to cyclic loading in complex marine environments. Although the cyclic bearing behavior of helical piles has been studied, most research has focused on soil properties and loading conditions, with a limited systematic analysis of plate parameters. Moreover, the selection of plate parameters is not explicitly defined. As a crucial preliminary step in the capacity calculation, it is vital for the design of helical piles. To address this gap, the present study combines physical modeling tests and finite element simulations to systematically evaluate the influence of plate parameters on their cyclic bearing behavior. The parameters investigated include the plate depth, the plate diameter, plate spacing, and the number of plates. The results indicate that, under the same embedment conditions, cumulative displacement increases with the plate depth, with a critical embedment depth ratio of H_cr/D = 6 under cyclic loading conditions, but decreases with the number of plates. Axial stiffness increases with the plate depth, diameter, and number of plates, with an increase ranging from 0.5 to 3.0. However, the normalized axial stiffness decreases with these parameters, reaching a minimum value of 1.63. The plate spacing has a minimal influence on cyclic bearing behavior. Additionally, this study examines the evolution of displacement and stiffness parameters over repeated cycles in numerical simulations, as well as the post-cyclic pullout capacity of the helical pile foundation, which varies between −5% and +12%. Full article

Continuous SiC fiber-reinforced SiC matrix composites (SiC/SiC), as structural heat protection integrated materials, are often used in parts for large-area heat protection and sharp leading edges, and there are a variety of low-velocity impact events in their service. In this paper, a drop hammer impact test was conducted using narrow strip samples to simulate the low-velocity impact damage process of sharp-edged components. During the test, different impact energies and impact times were set to focus on investigating the low-velocity impact damage characteristics of 2.5D SiC/SiC composites. To further analyze the damage mechanism, computed tomography (CT) was used to observe the crack propagation paths and distribution states of the composites before and after impact, while scanning electron microscopy (SEM) was employed to characterize the differences in the micro-morphology of their fracture surfaces. The results show that the in-plane impact behavior of a 2.5D needled SiC/SiC composite strip samples differs from the conventional three-stage pattern. In addition to the three stages observed in the energy–time curve—namely in the quasi-linear elastic region, the severe load drop region, and the rebound stage after peak impact energy—a plateau stage appears when the impact energy is 1 J. During the impact process, interlayer load transfer is achieved through the connection of needled fibers, which continuously provide significant structural support, with obvious fiber pull-out and debonding phenomena. When the samples are subjected to two impacts, damage accumulation occurs inside the material. Under conditions with the same total energy, multiple impacts cause more severe damage to the material compared to a single impact. Full article

Pedicle screw fixation is a common spinal surgery technique, but concerns remain about stability when screws are malpositioned. Traditional in vitro pull-out tests assess anchorage but lack physiological accuracy. This study examined the stability of correctly placed and intentionally malpositioned pedicle screws on forty vertebrae from five cadavers. Optimal screw paths were planned via CT scans and applied using 3D-printed guides. Four malposition types—medial, lateral, superior, and superior-lateral—were created by shifting the original trajectory. A custom setup applied three consecutive cycles of tensile and compressive load from 50 N to 200 N. Screw inclination under load was measured with a 3D optical system. The results showed increasing screw inclination with higher forces, reaching about 1° at 50 N and 2° at 100 N, similar in both load directions. Significant differences in inclination were only found at 100 N tensile load, where malpositioned screws showed a lower inclination. Overall, malpositioning had no major effect on screw loosening. These findings suggest that minor deviations in screw placement do not significantly compromise mechanical stability. Clinically, the main concern with malpositioning lies in the potential for injury to nearby structures rather than reduced screw fixation strength. Full article

In recent years, there has been a growing interest in the frictional anisotropy of snake scale-inspired surfaces, especially its potential applications in enhancing the bearing capacity of foundations (piles, anchor elements, and suction caissons) and reducing materials consumption and installation energy. This study first investigated the frictional properties and surface morphologies of the ventral scales of Cantor’s rat snakes (Ptyas dhumnades). Based on the findings on the snake scales, a novel snakeskin-inspired geosynthetic reinforcement (SIGR) is developed using 3D-printed polylactic acid (PLA). A series of pullout tests under different normal loads (25 kPa, 50 kPa, and 75 kPa) were performed to analyze the pullout behavior of SIGR in sandy soil. Soil deformation and shear band thickness were measured using Particle Image Velocimetry (PIV). The results revealed that the ventral scales of Ptyas dhumnades have distinct thorn-like micro-protrusions pointing towards the tail, which exhibit frictional anisotropy. A SIGR with a unilateral (one-sided) layout scales (each scale 1 mm in height and 12 mm in length) could increase the peak pullout force relative to a smooth-surface reinforcement by 29% to 67%. Moreover, the peak pullout force in the cranial direction (soil moving against the scales) was found to be 13% to 20% greater than that in the caudal direction (soil moving along the scales). The pullout resistance, cohesion, and friction angle of SIGR all showed significant anisotropy. The soil deformation around the SIGR during pullout was more pronounced than that observed with smooth-surface reinforcement, which suggests that SIGR can mobilize a larger volume of soil to resist external loads. This study demonstrates that SIGR is able to enhance the pullout resistance of reinforcements, thereby improving the stability of reinforced soil structures, reducing materials and energy consumption, and is important for the sustainability of geotechnical engineering. Full article

This paper outlines a structural qualification process to assess the use of newly developed high-modulus (HM) glass fiber-reinforced polymer (GFRP) bars with headed ends in the joint between concrete bridge barriers and decks. The main goals of the study are to evaluate the structural performance of GFRP-reinforced TL-5 barrier–deck systems under transverse loading and to determine the pullout capacity of GFRP anchorage systems for both new construction and retrofit applications. The research is divided into two phases. In the first phase, six full-scale Test-Level 5 (TL-5) barrier wall–deck specimens, divided into three systems, were constructed and tested up to failure. The first system used headed-end GFRP bars to connect the barrier wall to a non-deformable thick deck slab. The second system was similar to the first but had a deck slab overhang for improved anchorage. The third system utilized postinstalled GFRP bars in a non-deformable thick deck slab, bonded with a commercial epoxy adhesive as a solution for deteriorated barrier replacement. The second phase involves an experimental program to evaluate the pullout strength of the GFRP bar anchorage in normal-strength concrete. The experimental results from the tested specimens were then compared to the factored applied moments in existing literature based on traffic loads in the Canadian Highway Bridge Design Code. Experimental results confirmed that GFRP-reinforced TL-5 barrier–deck systems exceeded factored design moments, with capacity-to-demand ratios above 1.38 (above 1.17 with the inclusion of an environmental reduction factor of 0.85). A 195 mm embedment length proved sufficient for both pre- and postinstalled bars. Headed-end GFRP bars improved pullout strength compared to straight-end bars, especially when bonded. Failure modes occurred at high loads, demonstrating structural integrity. Postinstalled bars bonded with epoxy performed comparably to preinstalled bars. A design equation for the barrier resistance due to a diagonal concrete crack at the barrier–deck corner was developed and validated using experimental findings. This equation offers a conservative and safe design approach for evaluating barrier–deck anchorage. Full article

Aiming at the problem of the insufficient sealing performance of the solenoid valve poppet under a high working load and inspired by the multilevel groove structure of the octopus sucker and the adaptive sealing mechanism, a bionics-based design scheme for an annular groove sealing structure is proposed. By extracting the microscopic groove morphology features of the octopus sucker, we designed a multilayer rectangular cross-section groove structure at the annular interface, combined the designed structure with the Abaqus cohesive model to simulate the interface stripping behavior, and verified its mechanical properties by the pull-out test. The results show that the bionic groove structure significantly improves the bearing capacity of the sealing ring by enhancing the interface contact stress distribution and delaying the crack extension. Under the same working condition, the bionic structure increases the pull-out force by 46.1% compared with the traditional planar sealing ring. This study provides bionic theoretical support and an engineering practice reference for the design of sealing structures in complex working conditions, such as the solenoid valve poppet. Full article

To investigate the anchorage performance of an innovative assembled joint with large-diameter steel bar grout lapping in a concrete reserved hole, the effects of anchorage length and high-strength grouting material types on the failure mode, load–displacement curve, ultimate bond strength and strain variation were analyzed through the pull-out tests of 15 specimens. On this basis, the calculation formulae of critical and ultimate anchorage length were established and the applicability was verified, and then the recommended value of minimum anchorage length was provided. The results showed that the failure modes included splitting-steel bar pull-out failure and UHPC-concrete interface failure. With the increase in anchorage length, the bond strength showed a trend of increasing first and then decreasing. Increasing the grouting material strength can effectively improve the bond performance. When the anchored steel bar is HRB400 with a diameter not less than 20 mm, the recommended minimum anchorage length is 15.0d~18.3d. When the grouting material strength is larger than or equal to 100 MPa, the anchorage length should not be less than 15.0d. Full article

Conventional bolts frequently fail under large deformations due to stress concentration in soft rock tunnels. In contrast, yielding bolts incorporate energy-absorbing mechanisms to sustain controlled plastic deformation. This study employed FLAC3D to numerically investigate the pull-out, shear, and bending behaviors of yielding bolts, evaluating their support effectiveness in soft rock tunnels. Three-dimensional finite difference models incorporating nonlinear coupling springs and the Mohr–Coulomb criterion were developed to simulate bolt–rock interactions under multifactorial loading. Validation against experimental pull-out tests and field measurements confirmed the model accuracy. Under pull-out loading, the axial forces in yielding bolts decreased more rapidly along the bolt length, reducing stress concentration at the head. The central position of the maximum load-bearing capacity in conventional bolts fractured under tension, resulting in an hourglass-shaped axial force distribution. Conversely, the yielding bolts maintained yield strength for an extended period after reaching it, exhibiting a spindle-shaped axial force distribution. Parametric analyses reveal that bolt spacing exerts a greater influence on support effectiveness than length. This study bridges critical gaps in understanding yielding bolt behavior under combined loading and provides a validated framework for optimizing energy-absorbing support systems in soft rock tunnels. Full article

This study aimed to develop a novel modular pedicle screw system incorporating an elliptical sleeve to conform the pedicle’s elliptical cross-section and enhance fixation strength with mechanical stability. The biomechanical evaluation was conducted based on fundamental mechanics principles, followed by a finite element (FE) analysis to assess stress distribution under compressive and torsional loads. Subsequently, mechanical testing was performed to evaluate static and fatigue bending performance and in vitro biomechanical fatigue in porcine vertebrae by pull-out testing after 5000 and 100,000 cycles to assess fixation stability. The FE analysis demonstrated that the elliptical sleeve design improved bending resistance by 1.21× and torsional resistance by 1.91× compared to conventional cylindrical screws. Mechanical testing revealed greater bending/torsion stiffness and fatigue resistance, with the elliptical sleeve screw withstanding 5 million cycles at 235.4 N, compared to 175.46 N for cylindrical screws. Biomechanical pull-out testing further confirmed significantly higher retention strength after 100,000 cycles (1229.75 N vs. 867.83 N, p = 0.0101), whereas cylindrical screws failed prematurely at 10,663 cycles due to excessive displacement (>2 mm). The elliptical sleeve pedicle screw system demonstrated enhanced fixation strength, reduced micromotion, and superior fatigue resistance, making it a promising alternative to conventional pedicle screws for improving long-term spinal fixation stability. Full article