Search Results (311)

The study of the strain rate effects on the PA6 glass fiber-reinforced polyamide, in this specific case, PA6 GF30 (30% reinforced glass fiber), is critical due to composites widely used in automotive applications where the velocity of loading can vary significantly. Some insights into material safety under high quasistatic strain rate regime are given by understanding tensile behavior with focus on strain and stress at break. For this, using injection molding, dog bone samples were subjected to tensile tests at different strain rates, using a precise displacement control and extensometer to record the engineering stress–strain. The results demonstrate that higher strain rates increased the stiffness and strength of the specimen, shifting the stress–strain behavior to higher stress at break due to the reduced time for the polymer relaxation. However, the strain at break decreases under rapid movement, indicating the fact that the specimens exhibited reduced ductility. The results indicate a pronounced strain rate sensitivity that needs to be evaluated and considered for the design and failure mechanism of the components made of PA6 GF30, highlighting the necessity of strain rate specific mechanical characterization for accurate evaluation of performance under high quasistatic strain rate load cases, leading to a more safe and reliable design. Full article

Joint connections are critical to the overall performance of prefabricated structures. This paper proposes a novel reverse-rotation locking sleeve connection method, designed to ensure the safety of joint engineering while optimizing construction processes, improving operational efficiency, and endowing the joints with excellent seismic energy dissipation performance. To evaluate the performance of this connection method, quasi-static tests under displacement-controlled lateral loading were designed and conducted on three reinforced concrete column specimens (Specimen A: conventional reinforcement–cast-in-place monolithic; Specimen B: conventional reinforcement–reverse-rotation locking sleeve connected; Specimen C: enhanced reinforcement–reverse-rotation locking sleeve connected). The failure modes, hysteretic characteristics, skeleton curves, ductility, energy dissipation capacity, load-bearing capacity, and stiffness degradation patterns of the specimens were systematically examined. The results indicate that Specimen B exhibited the most severe damage extent, while Specimen A demonstrated the best integrity; in contrast, Specimen B showed significant and rapid degradation in energy dissipation capacity during the intermediate-to-late stages of testing; the hysteretic curves of Specimens B and C were full in shape, without obvious yield plateaus; the skeleton curves of all specimens exhibited S-shaped characteristics, and the peak loads of Specimens A and C corresponded to a lateral displacement of 21 mm, while that of Specimen B corresponded to a lateral displacement of 28 mm; compared to the cast-in-place monolithic Specimen A, the reverse-rotation locking sleeve–connected Specimens B and C showed increases in ultimate load under positive cyclic loading by 18.7% and 5.5%, respectively, and under negative cyclic loading by 40.8% and 2.0%, respectively; the ductility coefficients of all three specimens met the code requirement, being greater than 3.0 (Specimen A: 5.13; Specimen B: 3.56; Specimen C: 5.66), with Specimen C exhibiting a 10.3% improvement over Specimen A, indicating that the reverse-rotation locking sleeve–connected specimens possess favorable ductile performance; analysis revealed that the equivalent viscous damping coefficient of Specimen C was approximately 0.06 higher than that of Specimen A, meaning Specimen C had superior energy dissipation capacity compared to Specimen A, confirming that the reverse-rotation locking sleeve connection can effectively absorb seismic energy and enhance the seismic and energy dissipation characteristics of the specimens. The load-bearing capacity degradation coefficients of all specimens fluctuated between 0.83 and 1.01, showing an initial stable phase followed by a gradual declining trend; the stiffness degradation coefficients exhibited rapid initial decline, followed by a deceleration in the attenuation rate, and eventual stabilization. This indicates that the reverse-rotation locking sleeve-connected specimens can maintain relatively stable strength levels and favorable seismic performance during the plastic deformation stage. 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

This study investigates the microscale mechanisms underlying the compressibility of biochar-amended soils through combined discrete element method (DEM) simulations and laboratory consolidation tests. A three-dimensional discrete element model was established based on the MatDEM platform, accounting for the particle crushing process of biochar particles and its impact on soil mechanical properties. The biochar agglomerate particles generated in the simulation exhibit irregular morphology, and particles within different size ranges were selected for investigation. According to the model and experimental results, the average relative error is about 7%. Results demonstrate that moderate biochar content effectively reduces soil compressibility by enhancing load transfer through stable force chains formed by biochar particles, which exhibit larger contact areas and higher stiffness compared to native soil particles. However, when the biochar content exceeds approximately 40%, particle crushing intensifies, particularly under high initial void ratios, leading to increased soil compressibility. Furthermore, a larger initial void ratio weakens interparticle confinement, promotes microcrack propagation, and thereby exacerbates compressive deformation. Biochar fragmentation progresses through three stress-dependent stages: initial compaction (<100 kPa), skeletal damage (100–800 kPa), and crushing saturation (>800 kPa). Increased biochar particle size correlates with higher fragmentation rates, refined particle gradation, and reduced coordination numbers, collectively weakening the soil skeleton and promoting deformation. These findings underscore the importance of optimizing biochar content and applying graded loading strategies to balance enhanced soil performance with material integrity. These findings emphasize the necessity of optimizing biochar application rates to balance enhanced soil performance with resource efficiency, providing critical insights for sustainable geotechnical practices. Full article

Optimizing the neuromechanical determinants of explosive performance remains a key objective in sports science. This study compared the effects of an eight-week movement-pattern-based training program (MPT) with an isometric strength training protocol (ITG) on countermovement jump (CMJ) mechanics in competitive track and field athletes. Thirty-four athletes (19 men, 15 women) with ≥7 years of training experience were randomly allocated to the MPT or ITG. Pre- and post-intervention assessments were conducted using dual force plates to evaluate jump height, musculotendinous stiffness, concentric and eccentric impulses, contraction time, eccentric-to-concentric force ratio, and rate of force development (RFD). The MPT elicited significant gains in stiffness (Δ = +840.94 ± 1302.21 N/m; p = 0.002), maintained concentric peak force, and reduced contraction time (Δ = –64.53 ± 190.32 ms; p = 0.01), suggesting improved elastic efficiency and neuromuscular timing. Conversely, ITG was associated with reductions in concentric peak force (Δ = –66.18 ± 77.45 N; p = 0.003) and stiffness (Δ = –691.94 ± 1414.41 N/m) and an increase in the eccentric-to-concentric force ratio (Δ = +1.99%; p = 0.006). The RFD changes were inconsistent across both groups. These findings indicate that dynamic multi-joint training confers superior neuromechanical adaptations compared to isolated isometric loading. From a performance perspective, programming strategies should prioritize movement-specific dynamic tasks to enhance the explosive qualities critical for sprinting, jumping, and multidirectional field sports. Full article

Spread-tow woven fabrics (STWs) have attracted considerable attention owing to their thin-layered characteristics, high fiber strength utilization rate and superior designability, finding wide application in the aerospace field. To meet the application requirements for materials with high specific strength/specific modulus in the aerospace field, this study designed an anti-sandwich structured composite with high specific load-bearing capacity. Herein, the core layer was a load-bearing structure composed of STW, while the surface layers were hybrid lightweight structures made of STW and nonwoven (NW) felt. Repeated impact test results showed that increasing the thickness ratio of the core layer enhanced the impact resistant stiffness of the overall structure, whereas increasing the proportion of NW felt in the surface layers improved the energy absorption of the composites but reduced their load-bearing stiffness and strength. The composite exhibited superior repeated impact resistance, achieving a peak impact load of 17.43 kN when the thickness ratio of the core layer to the surface layers was 2:1 and the hybrid ratio of the surface layers was 3:1. No penetration occurred after 20 repeated impacts at the 50 J or 3 repeated impacts at 100 J. Meanwhile, both the maximum displacement and impact duration increased, whereas the bending stiffness declined as the number of impacts increased. The failure mode was mainly characterized by progressive interfacial cracking in the surface layers and fracture in the core layer. Full article

In traditional scallion cultivation, the bare-root transplanting method—which involves direct seeding, seedling raising in the field, and lifting—is commonly adopted to minimize seedling production costs. However, during the mechanized transplanting of bare-root scallion seedlings, practical problems such as severe seedling damage and poor planting uprightness exist. In this paper, the Hertz–Mindlin with Bonding contact model was used to establish the scallion seedling model. Combined with the Plackett–Burman experiment, steepest ascent experiment, and Box–Behnken experiment, the bonding parameters of scallion seedlings were calibrated. Furthermore, the accuracy of the scallion seedling model parameters was verified through the stress–strain characteristics observed during the actual loading and compression process of the scallion seedlings. The results indicate that the scallion seedling normal/tangential contact stiffness, scallion seedling normal/tangential ultimate stress, and scallion Poisson’s ratio significantly influence the mechanical properties of scallion seedlings. Through optimization experiments, the optimal combination of the above parameters was determined to be 4.84 × 10⁹ N/m, 5.64 × 10⁷ Pa, and 0.38. In this paper, the flexible planting components of scallion seedlings were taken as the research object. Flexible protrusions were added to the planting disc to reduce the damage rate of scallion seedlings, and an EDEM-ADAMS coupling interaction model between the planting components and scallion seedlings was established. Based on this model, optimization and verification were carried out on the key components of the planting components. Orthogonal experiments were conducted with the contact area between scallion seedlings and the disc, rotational speed of the flexible disc, furrow depth, and clamping force on scallion seedlings as experimental factors, and with the uprightness and damage status of scallion seedlings as evaluation criteria. The experimental results showed that when the contact area between scallion seedlings and the disc was 255 mm², the angular velocity was 0.278 rad/s, and the furrow depth was 102.15 mm, the performance of the scallion planting mechanism was optimal. At this point, the uprightness of the scallion seedlings was 94.80% and the damage rate was 3%. Field experiments were carried out based on the above parameters. The results indicated that the average uprightness of transplanted scallion seedlings was 93.86% and the damage rate was 2.76%, with an error of less than 2% compared with the simulation prediction values. Therefore, the parameter model constructed in this paper is reliable and effective, and the designed and improved transplanting mechanism can realize the upright and low-damage planting of scallion seedlings, providing a reference for the low-damage and high-uprightness transplanting operation of scallions. Full article

This paper presents a compact dynamic optical frequency domain reflectometry (D-OFDR) platform enabling millimeter-scale, distributed strain sensing for real-time structural health monitoring (SHM) of reinforced concrete subjected to seismic loading. The proposed D-OFDR interrogator employs a dual-interferometer architecture: a main interferometer for strain sensing and an auxiliary interferometer for nonlinear frequency sweep compensation. Both signals are detected by photodetectors and digitized via a dual-channel FPGA-based DAQ board, enabling high-speed embedded signal processing. A dual-edge triggering scheme exploits both the up-chirp and down-chirp of a 50 Hz bidirectional sweep to achieve a 100 Hz interrogation rate without increasing the sweep speed. Laboratory validation tests on stainless steel cantilever beams showed sub-hertz frequency fidelity (an error of 0.09 Hz) relative to conventional strain gauges. Shake-table tests on a 2 m RC column under incremental seismic excitations (scaled 10–130%, peak acceleration 0.864 g) revealed distinct damage regimes. Distributed strain data and frequency-domain analysis revealed a clear frequency reduction from approximately 3.82 Hz to 1.48 Hz, signifying progressive stiffness degradation and structural yielding prior to visible cracking. These findings demonstrate that the bidirectional sweep-triggered D-OFDR method offers enhanced real-time monitoring capabilities, substantially outperforming traditional point sensors in the early and precise detection of seismic-induced structural damage. Full article

The classical definition of mechanical work, W = F × D, assumes that work depends solely on force magnitude and displacement, independent of loading rate. However, biological tissues exhibit inherent rate sensitivity—muscles demonstrate velocity-dependent force generation governed by Hill’s force–velocity relationship, while connective tissues and joints show load-rate-dependent stiffness and injury thresholds. These rate effects profoundly influence mechanical work, energy dissipation, and functional outcomes. In this work, we revisit the work–energy framework within biomechanics and biomaterials contexts, combining theoretical models, simulations, and a proposed rate-matched nano–bio indentation experiment to quantify how loading rate modulates energy partitioning between recoverable elastic storage and irreversible viscous dissipation. Our analyses span muscle contraction, viscoelastic tissue mechanics, and nanoparticle–membrane interactions, revealing that rapid loading markedly increases viscous dissipation and total mechanical work, even when peak force and displacement remain constant. We demonstrate that classical quasi-static formulations underestimate energy costs and tissue stresses by neglecting temporal dynamics and nonlinear material responses. Our multi-physics experimental–simulation platform bridges this gap, enabling controlled investigation of rate-dependent biomechanical phenomena at the nano–bio interface. These insights inform biomaterials design by emphasizing rate-matching viscoelastic properties to native tissues and guide experimental biomechanics toward capturing full dynamic histories. This unified framework advances understanding of rate-dependent mechanical work, improving predictive modeling, optimizing therapeutic delivery, and enhancing design in sports science, orthopedics, rehabilitation, and nanomedicine. Full article

This study developed a natural rubber composite reinforced with selenol-functionalized carbon nanotubes, demonstrating significant mechanical enhancement. The composite exhibited remarkable improvements in elastic modulus, with 300% and 500% modulus increasing by 2.23 MPa and 2.68 MPa, respectively, along with a 1.22 MPa boost in tensile strength compared to conventional counterparts. Material characterization was successfully performed using a polynomial hyperelastic constitutive model. The optimized composite was applied to the tread of a Bridgestone 1270 × 455 R aircraft tire for performance evaluation. Finite element analysis in ABAQUS revealed that under 2.5 MPa inflation pressure, the tire achieved specified dimensional requirements with a cross-sectional width of 459.55 mm and a diameter of 1270.50 mm. Three-dimensional static load simulations showed characteristic elliptical contact patches that expanded with increasing load, while maintaining rectangular normal contact stress distribution. Critical performance evaluation demonstrated excellent radial stiffness stability of 22.9 kN/mm within the operational pressure range of 1.5–2.0 MPa under rated load conditions. These findings validate the composite’s potential for enhancing aircraft tire performance. Full article

As traffic load continuously rises and climatic conditions increasingly vary, the performance of conventional base asphalt can no longer satisfy the needs of modern road engineering in low-temperature cracking resistance, high-temperature stability, and long-term durability. Therefore, the development of novel and efficient asphalt modifiers holds significant engineering value and practical importance. In this study, modified asphalt was prepared using varying dosages of ZM modifier (direct-injection asphalt mixture modified polymer additive). A series of experiments was executed to assess its influence on asphalt properties. First, fundamental property tests were implemented to determine the regulating effect of the ZM modifier on basic physical performances, like the softening point and penetration of the base asphalt. Penetration tests at different temperatures were performed to calculate the penetration index, thereby assessing the material’s temperature sensitivity. Subsequently, focusing on temperature as a key factor, tests on temperature sweep, and multiple stress creep recovery (MSCR) were implemented to delve into the deformation resistance and creep recovery behavior of the modified asphalt under high-temperature conditions. In addition, bending beam rheometer (BBR) experiments were introduced to attain stiffness modulus and creep rate indices, which were applied to appraise the low-temperature rheological performance. Aside from Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) was utilized to explore the mechanism by which the ZM modifier influences the asphalt’s functional group composition and microstructure. Our findings reveal that the ZM modifier significantly increases the asphalt’s softening point and penetration index, reduces penetration and temperature sensitivity, and enhances high-temperature stability. Under high-temperature conditions, the ZM modifier adjusts the viscoelastic balance of asphalt, hence enhancing its resistance to flow deformation and its capacity for creep recovery. In low-temperature environments, the modifier increases the stiffness modulus of asphalt and improves its crack resistance. FTIR analyses reveal that the ZM modifier does not introduce new functional groups, indicating a physical modification process. However, by enhancing the cross-linked structure and increasing the hydrocarbon content within the asphalt, it strengthens the adhesion between the asphalt and aggregates. Overall, the asphalt’s performance improvement positively relates to the dosage of the ZM modifier, providing both theoretical basis and experimental support for its application in road engineering. Full article

Arch structure is a crucial interface between the human body and the ground during landing tasks, but the biomechanical effects of arch support stiffness remain insufficiently explored. This study examines the effects of arch supports with different stiffnesses on lower-limb biomechanics during landing. Twelve male participants (six normal arches, six flat feet) performed a single-leg drop landing from a 45 cm height under four arch support conditions: no arch support pad (NAP), soft-stiffness arch support pad (SAP), medium-stiffness arch support pad (MAP), and high-stiffness arch support pad (HAP). Dominant lower-limb joint angles and moments in the sagittal plane and vertical ground reaction force (vGRF)-related parameters—time to peak vGRF, peak vGRF, and max loading rate—were recorded using a motion capture system and force plate. Data were analyzed using one-way repeated measures analysis of variance (ANOVA). Arch pad stiffness significantly affected ankle and knee kinematics. The NAP condition exhibited significantly higher ankle plantarflexion at initial contact (p ≤ 0.01), as well as larger range of motion (ROM) of the knee (p = 0.03) and hip (p < 0.01), compared to the use of a SAP or MAP. The use of a HAP resulted in a significantly lower peak ankle dorsiflexion moment and larger peak knee flexion angle than the other conditions (p ≤ 0.04). The peak knee extension moment was the highest when using a NAP, and was significantly higher than that shown with the use of a MAP or HAP (p ≤ 0.02). No significant differences were observed in hip joint moments or vGRF-related parameters across conditions (p ≥ 0.52). These results indicate that hard-stiffness arch support pads modulate lower-limb mechanics during landing, potentially enhancing shock absorption and reducing knee loading. Full article

With decreasing production costs, carbon nanomaterials have become common, scalable, and cost-effective additives in high-performance composites due to the potentially significant increases in mechanical, thermal, and electrical properties. The mechanical performance of carbon nanomaterial-reinforced matrix materials under high-strain-rate compressive conditions was investigated. This study compares neat epoxy-amine with 0.1 wt.% loadings of graphene or graphite dispersed in epoxy-amine. Quasi-static and high-rate testing was conducted using an Instron load frame and Split Hopkinson Pressure Bar (SHPB), respectively, to assess the material’s response to increasing strain rates via compressive loadings. No significant change in compressive strength was observed at quasi-static strain rates, with the 0.1 wt.% graphene sample showing no significant deviation from the neat resin at high strain rates. In contrast, the 0.1 wt.% graphite sample exhibited a substantial reduction in comparative compressive strength, decreasing by ~43% at 10² s⁻¹ strain rate and ~42% at 10³ s⁻¹ strain rate. While graphene may not significantly enhance stiffness at high strain rates, its ability to preserve ductility without introducing failure-prone features makes it a more effective additive for dynamic applications. Full article

Biomechanical strategies of running gait were compared among healthy and recently injured pediatric and adult runners (N = 207). Spatiotemporal, kinematic, and kinetic parameters (ground reaction force [GRF], vertical average loading rate [VALR]) and leg stiffness (K_vert) were obtained during running on an instrumented treadmill with simultaneous 3D-motion capture. Significant age X injury interactions existed for cadence, peak GRF, and peak joint angles in stance. Cadence was fastest in healthy adults and 2–3% lower in other groups (p = 0.049). Injured adults exhibited higher variance in stance and swing time, whereas injured pediatric runners had lower variance in these measures (p < 0.05). Peak GRF was highest in non-injured adults (2.6–2.7 BW) and lowest in injured adults (2.4 BW; p < 0.05). VALRs (BW/s) were higher among pediatric groups, irrespective of injury (p < 0.05). The interaction for ankle dorsiflexion/plantarflexion moment was significant (p = 0.05). Healthy pediatric runners produced more plantarflexion than all other groups (p = 0.026). Pelvis rotation was highest in healthy pediatric runners and lowest in healthy adults (17.3° versus 12.0°; p = 0.036). Pediatric runners did not leverage force-dampening strategies, but reduced gait cycle time variance and controlled pelvic rotation. Injured adults had lower GRF and longer stance time, indicating a shift toward force mitigation during stance. Age-specific rehabilitation and gait retraining approaches may be warranted. Full article

This study systematically investigates the influence of varying corrosion severity on the bearing capacity of K-shaped circular-section joints, with explicit consideration of weld line positioning. Four full-scale circular-section joint specimens with clearance gaps were designed to simulate localized corrosion through artificially introduced perforations, and axial static loading tests were performed to assess the degradation of structural performance. Experimental results indicate that the predominant failure mode of corroded K-joints manifests as brittle fracture in the weld-affected zone, attributable to the combined effects of material weakening and stress concentration. The enlargement of corrosion pit dimensions induces progressive deterioration in joint stiffness and ultimate bearing capacity, accompanied by increased displacement at failure. A refined finite element model was established using ABAQUS. The obtained load–displacement curve from the simulation was compared with the experimental data to verify the validity of the model. Subsequently, a parametric analysis was conducted to investigate the influence of multiple variables on the residual bearing capacity of the nodes. Numerical investigations indicate that the severity of corrosion exhibits a positive correlation with the reduction in bearing capacity, whereas web-chord members with smaller inclination angles demonstrate enhanced corrosion resistance, when θ is equal to 30 degrees, K_s decreases from approximately 0.983 to around 0.894. Thin-walled joints exhibit accelerated performance deterioration compared to thick-walled configurations under equivalent corrosion conditions. Furthermore, increased pipe diameter ratios exacerbate corrosion-induced reductions in structural efficiency, when the corrosion rate is 0.10, β = 0.4 corresponds to K_s = 0.98, and when β = 0.7, it is approximately 0.965. and distributed micro-pitting results in less severe capacity degradation than concentrated macro-pitting over the same corrosion areas. Full article