Search Results (1,443)

Classical soil mechanics models are inadequate for predicting the traction of wheeled vehicles under high-velocity off-road conditions due to the complex dynamic soil response. To address this, this study proposes a velocity-segmented dynamic compression-shear model for aeolian sandy soil, enhancing classical theories with velocity-dependent corrections for the 0–10 m/s range. A theoretical patterned wheel–soil interaction model is developed, incorporating lug effects via an equivalent radius. Furthermore, a comprehensive vehicle traction model is established by integrating the soil model with a dynamic equilibrium iteration method that couples suspension dynamics, pitch attitude, and axle load distribution. Validation results demonstrate that the single-wheel traction theoretical model achieves an error of less than 18%, while the full vehicle traction model reaches a 73% prediction accuracy for drawbar pull and sinkage, as verified through soil bin tests and full-vehicle experiments. This research provides theoretical framework for the real-time and accurate prediction of wheeled-vehicle traction performance on unprepared terrain, offering significant improvements for high-velocity off-road mobility analysis. Full article

Objective: The effects of fatigue on swimming propulsion are unclear. This study examined upper-limb propulsive force and bilateral coordination during constant-speed front crawl performed until exhaustion. Methods: Twelve competitive swimmers completed a visually paced front-crawl trial performed at a constant speed (95% of maximal speed) until volitional exhaustion. Upper-limb propulsion (pressure-derived) was quantified using wearable differential-pressure mini-paddles synchronized with high-speed video. Propulsive force and impulse were analyzed at ten standardized time points (10–100% of test duration), distinguishing the early (entry–catch–pull) phase and the push phase of the stroke cycle. Results: Total overall propulsive impulse (time-integral of propulsive force) and mean propulsive force decreased significantly as early as 30–40% of test duration, with the largest reductions occurring during the push phase. Interestingly, push-phase impulse declined earlier in the non-dominant left arm (from 20% of test duration) compared to the dominant right arm (from 40%), whereas force generated during the early phase did not change. Peak propulsive force decreased at later stages, while intra-cycle timing indices (peak timing and force centroid) and inter-limb asymmetry remained unchanged. Stroke frequency increased from mid-test onward and was strongly negatively associated with stroke efficiency (r = −0.79). Stroke efficiency correlated positively with push-phase impulse and peak force. Conclusions: During constant-speed front crawl performed to exhaustion, propulsion progressively declines, primarily through reduced force and impulse during the push phase rather than changes in the early (entry–catch–pull) phase or temporal and asymmetry-related variables. Increased stroke frequency initially compensates for declining propulsion but ultimately fails to maintain the imposed swimming velocity. Full article

Understanding how geometry governs interfacial contact and material removal is central to designing efficient bioinspired surface systems. Gastropod radular teeth form natural arrays of microscale cutting elements optimized for repeated interaction with compliant and semi-rigid substrates, yet experimentally validated shape–performance relationships remain limited. Here, we isolate geometric effects on interfacial mechanics using stereolithography-printed biomimetic tooth arrays inspired by the taenioglossan radula of the hard-substrate grazer Spekia zonata. Two morphologically distinct tooth types (central and marginal) were systematically varied in cusp and stylus geometry (four variants each), while array configuration, material, and boundary conditions were kept constant. Tooth stiffness was quantified in bending tests as load-induced height reduction. Interfacial performance was assessed using a controlled pull-through assay in agarose substrates of two stiffness levels (0.4% and 0.8%), with continuous force recording and measurement of removed mass. Marginal-tooth geometries were stiffer and consistently removed more substrate than central variants. Although work increased substantially in stiffer gels, removal did not scale proportionally and declined for central teeth, revealing a decoupling between mechanical input and yield. Performance correlated with active engagement rather than work alone, indicating geometry-limited contact regimes. These findings establish geometry-controlled stiffness and engagement as key parameters for efficient abrasive interfaces. Full article

Windsurfing (WS) and kitesurfing (KS) share the same environment but differ in biomechanics and equipment demands. This cross-sectional study compared physical performance between WS and KS athletes. Twenty-five male recreational athletes participated (WS n = 13, age 27.7 ± 7.0 years; KS n = 12, age 29.0 ± 7.5 years). Body composition, isometric strength (handgrip and back-and-leg dynamometer), dynamic balance (Y-Balance Test: YBT), functional movement quality (FMS), and drop-jump performance (ground contact time, reactive strength index, jump height, take-off time) were assessed. Groups were compared using the Mann–Whitney U test (p < 0.05), and Cliff’s δ was calculated for significant outcomes. Participant characteristics were similar, although surfing experience was greater in WS. KS showed higher leg strength (p = 0.041; δ = 0.481) with no difference in handgrip strength. KS also demonstrated higher FMS shoulder mobility (p = 0.022; δ = 0.532) and total FMS score (p = 0.014; δ = 0.577). No between-group differences were found for YBT metrics or drop-jump variables (p > 0.05). These findings indicate that KS athletes exhibit greater isometric pulling strength and movement proficiency, whereas balance and reactive jump performance are comparable, supporting discipline-specific conditioning priorities. Full article

To solve the problems of high-precision attitude control and vibration isolation of satellite payloads, this paper conducts in-depth research on satellite attitude dynamics and maglev active vibration isolation control technology. A dual-super collaborative control scheme is proposed, which consists of payload module ultra-high precision and ultra-high stability control, relative position control of two modules, and service module attitude control. The target attitude and angular velocity obtained by maneuver path planning and attitude guidance are transmitted to the attitude and orbit control management unit, and the total control command torque is formed by combining feedback control and feedforward control, which is then distributed to each maglev actuator to realize high-precision control of the payload module. The architecture of the maglev vibration isolation system is designed, and its dynamic model is established based on the Newton–Euler equation. Meanwhile, the dynamic model of the maglev actuator is constructed, and the active control strategy is designed by adopting PID control. The models of output force and torque are established, system parameters are set for simulation analysis of dynamic responses such as displacement, attitude and electromagnetic force, and a 20% pull-bias robustness test is carried out. Simulation results show that the system has high isolation accuracy, stability, and can effectively suppress the interference and shaking of the platform and load, with strong robustness. Full article

Three-edge bearing (TEB) tests and a crack-width-dependent load-carrying model were used to assess the combined effects of recycled glass fiber-reinforced polymer (rGFRP) short fibers and glass fiber-reinforced polymer (GFRP) bars in concrete pipes. Using the force method, a circumferential statically indeterminate ring analysis was formulated to obtain internal forces at critical sections and the neutral-axis position. Fiber distribution was simulated by means of Monte Carlo sampling, and single-filament pull-out tests were fitted to relate embedded length to pull-out force, enabling calculation of the fiber-bridging contribution at cracked sections. Ten specimen types with different bar/fiber schemes were tested under external pressure to validate the model. Predicted cracking and ultimate loads agreed with measurements, with most errors within ±20%. Adding 1% (vol.) rGFRP fibers increased the cracking load by 11.81% and the ultimate load by 0.45%. Without fibers, replacing steel bars with equal-area GFRP bars increased the cracking load by 1.35% but reduced the ultimate load by 35.45%. For all specimens, the load–maximum crack-width relation was strongly linear (R² > 0.93). The proposed approach and dataset support engineering use of recycled GFRP materials for crack control and load-carrying design of concrete pipes. Full article

Active rotors with trailing-edge flaps (TEFs) are a promising method applied to the main-rotor blades of the helicopter for vibration suppression. For active rotors, both the TEF actuator and the corresponding deflection control law determine their overall performance and effectiveness for vibration reduction. In this study, a double-acting piezoelectric actuator is designed to actuate the TEFs, where bidirectional push/pull output is achieved by two groups of piezoelectric stacks operating in opposite directions. Benchtop tests indicate that the TEF deflection angle of the active rotor equipped with this actuator can reach ±4.3°. Subsequently, based on the controlled autoregressive moving average (CARMA) model, an adaptive controller is developed to reduce vibrations in the active rotor by using a minimum variance direct self-tuning regulator (MVSTDR). Finally, an unmanned helicopter is retrofitted with the active rotor, and vibration control experiments are performed under tethered hover conditions with vertical cabin vibration as the control target. Experimental results demonstrate the effectiveness of the designed actuator and the MVSTDR for vibration reduction on the helicopter equipped with an active rotor, which also validates the feasibility of active rotors for practical engineering applications in helicopter vibration control. Full article

To improve the blasting performance of tunnel wedge cutting while mitigating vibration effects, this study proposes a precise delayed blasting method and evaluates its effectiveness through a three-dimensional numerical simulation, similarity model test, and field application. The proposed method divides the cut holes into initial and secondary groups and uses electronic detonators to control the delay time. The numerical results show that delayed blasting reduces the peak stress in the surrounding rock, accelerates stress-wave attenuation, improves cavity integrity, and lowers the peak particle velocity (PPV), while maintaining sufficient rock breaking capacity. Model tests conducted under different delay times indicate that the delayed scheme increases the pull efficiency, decreases the ratio of large fragments, and reduces the PPV, with an optimal delay time range of 4~8 ms for moderately weathered limestone. Field tests in the Da Balai Tunnel further verify the effectiveness of the proposed method. Compared with conventional blasting, delayed blasting increases the pull efficiency from 77.8% to 97.3%, reduces the large fragment ratio from 30.6% to 11.4%, decreases the PPV by 52.5%, and increases the dominant vibration frequency by 48.7%. These results demonstrate that the proposed method can simultaneously enhance the rock-breaking quality and vibration control, providing practical guidance for tunnel blasting excavation under complex geological conditions. Full article

Post-installed rebars are extensively used in the strengthening and rehabilitation of concrete structures, where compressive stresses in the anchorage zone provide transverse pressure and significantly affect bond behavior. However, it remains unclear how different transverse pressure conditions, particularly one-way and two-way transverse pressure, influence the bonding behavior of post-installed rebars and how their effects differ. To address this gap, this study investigates the effects of one-way and two-way transverse pressure on the bond mechanism and failure mode of post-installed rebars. To achieve this, 22 pull-out tests were carried out under two transverse pressure configurations, namely one-way and two-way transverse pressure, with pressure levels ranging from 0 to 12 MPa. The results show that, without confinement, concrete splitting was the dominant failure mode, whereas under transverse pressure, failure shifted to adhesive failure or adhesive–rebar interface failure. Transverse pressure significantly improved bond strength, with maximum increases of 49.9% under one-way transverse pressure and 82.9% under two-way transverse pressure. Both the transverse pressure configuration and pressure level had a significant influence on failure evolution and bond performance. In general, increasing the pressure level enhanced the interfacial bonding capacity; however, one-way transverse pressure tended to induce stress concentration in the adhesive layer, thereby promoting adhesive-related failure. These findings clarify the role of transverse pressure conditions in the anchorage behavior of post-installed rebars and provide a basis for the design and analysis of post-installed rebar anchorage systems. Full article

Strength training (ST) is commonly implemented to enhance soccer-related fitness qualities such as sprinting, jumping, and changes-of-direction while also contributing to injury risk reduction. It is traditionally emphasized in the pre-season period. In-season ST may confer these benefits, but it can also induce muscle damage and inflammation. To examine the effects of a 12-week in-season ST program on maximal dynamic strength, muscle damage biomarkers, and inflammatory biomarkers, 24 elite young female soccer players (Tier 4 according to the McKay et al. classification) aged 14.9 ± 0.8 years and a maturity offset of +2.6 ± 1.1 years were randomly allocated to an ST group (STG, n = 12) or an active control group (CG, n = 12). Both groups followed the same soccer training program. However, in the STG, two weekly soccer sessions were replaced with ST. Overall training volume was comparable between groups. Maximal dynamic strength (1-RM tests for bench press, lat pull-down, and leg press), blood biomarkers of muscle damage (creatine phosphokinase [CPK], lactate dehydrogenase [LDH]), and inflammation (interleukin-6 [IL-6], tumor necrosis factor-α [TNF-α]) were assessed before (T1) and after (T2) the interventions. Analyses showed significant increases for STG for the 1-RM bench press, the 1-RM lat pull-down, and the 1-RM leg press (p < 0.001). No significant interactions were detected for any blood marker of muscle damage (LDH and CPK) or inflammation (IL-6 and TNF-α) (all p > 0.05). Results support a 12-week in-season ST program improved maximal dynamic strength in elite young female soccer players without altering resting levels of muscle damage or inflammatory markers measured 48 h after training compared to regular soccer training. These findings suggest that ST can be safely implemented during the competitive season in young female soccer players without overreaching or overtraining. Full article

In the present study, the influence of the parameters of the bonding process, namely the applied pressure during curing, as well as the duration and temperature of curing, on the tensile strength of the bonded joints was investigated. Pull-off tests were conducted in accordance with the ASTM C633 standard. The samples were bonded using a single-component thermosetting adhesive, HTK Ultra Bond 100. On the basis of the results obtained, it was concluded that the tensile strength of the bonded joint, and thus its overall quality, is strongly influenced by the curing parameters of the thermosetting adhesive. The most effective bonding conditions were identified. Full article

Resin and interlayer properties play significant roles in the resistance to impact of fibre-reinforced polymer composites (FRPCs). To investigate the contribution of each factor within the coupled variables to the impact resistance ability of FRPCs, in this work, waterborne polyurethane (WPU) with different tensile elastic modulus, tear strength and bonding strength was obtained. To systematically evaluate the impact resistance and failure mechanisms of the composite materials under varying external loads, impact resistance tests, numerical simulations, and relative weight analysis were conducted. The relative weight analysis results quantified the individual contributions of these three factors to the overall energy absorption capacity across diverse loading conditions. The results indicated that with the increasing rate of the external loading, the resin modulus consistently contributed more significantly to energy absorption than tear strength of resin and interlayer strength, reaching up to 44.3%. In ballistic penetration tests, with the increase in resin modulus, the ballistic performance of PE/WPU laminates demonstrated an S-shaped downward trend. Composites prepared with more rigid matrix could lead to unsatisfactory interlayer damage. A more robust structure could result in fibre pull-out and breakage to a greater extent at the point of forced impact while less in the secondary affected area, presenting comparatively lower impact resistant performance. Full article

To address the challenges of winter pavement icing and the disposal of organic waste, this study developed a sustained-release deicing filler utilizing biochar derived from spent coffee grounds (SCGs). The material was synthesized through high-temperature carbonization, followed by physical adsorption of chloride salts and surface hydrophobic modification to control release rates. The study made asphalt mixtures and replaced normal mineral filler with the SCG material by volume at ratios of 0%, 50%, 75%, and 100% to test road and deicing performance. Wheel-tracking tests showed that the additive improved high-temperature stability and dynamic stability went up by 27.04% at the 75% replacement level. Salt dissolving created voids and slightly lowered water stability at high dosages, but all performance numbers still met the current engineering rules. Rutting slab tests at −5 °C showed the 100% replacement mix cut snow coverage to 11.43% in 60 min and proved it works for deicing. Pull-out tests measure the bond strength between ice and pavement at −5 °C, −7 °C, and −9 °C. The SCG deicing material weakens ice sticking and the bond strength for the 100% group at −5 °C was 0.35 kN, which is about 57.8% lower than the control asphalt. The bond strength of the deicing mix at −9 °C was still lower than the normal mix at −5 °C. This big drop in stickiness means the pavement stops ice from packing hard and makes mechanical removal easier. This study shows that the prepared deicing materials exhibit excellent sustained-release performance and snow-melting efficiency while ensuring satisfactory road performance. SCG deicing materials can effectively reduce snow accumulation on road surfaces in winter, lower the difficulty of ice-layer removal, and realize the sustainable utilization of SCGs. Full article

This study evaluated eleven resin cements used as core build-up materials by examining the following properties: (a) push-out force between root dentin and the fiber post; (b) pull-out force between the fiber post and the core build-up material; (c) shear bond strength of the resin cement to root dentin; (d) flexural strength of the resin cement; and (e) flexural modulus of elasticity of the resin cement. The purpose of this investigation was to clarify the relationships between recently available universal adhesives, core build-up materials, resin cements, and fiber posts. All experiments were performed at two evaluation periods: after 1 day of water storage (Base) and after 20,000 thermocycles (TC 20k). For the push-out test, simulated post spaces were prepared in single-rooted human premolars. The specimens were sectioned perpendicular to the long axis into 2 mm-thick slices and then subjected to push-out testing to assess the bond strength of the dentin–resin cement–fiber post complex. No significant differences in bonding performance were found between Base and TC 20k. These findings suggest that universal adhesives used for pretreatment of multiple substrates in fiber post cementation can provide not only strong but also durable adhesion over time. Full article

This study develops a multi-scale fiber-reinforced cementitious composite (MFRC) by hybridizing calcium carbonate whisker (CW), polyvinyl alcohol (PVA) fiber, and steel fiber. The interfacial micromechanical properties between steel fiber/matrix and PVA fiber/matrix under the influence of CW were systematically examined through single-fiber pull-out tests. The two-dimensional and three-dimensional distribution characteristics of fibers in the MFRC were analyzed using backscattered electron imaging (BSE) and X-ray computed tomography (X-CT), respectively. Based on the fiber distribution characteristics, flexural strength prediction models were developed with R² values of 0.79 (2D) and 0.82 (3D). Experimental validation via splitting tensile tests and three-point bending tests confirmed the model’s effectiveness in simultaneously predicting splitting tensile strength (R² = 0.89) and flexural strength (R² = 0.93). These findings demonstrate the reliability and universality of the proposed model for predicting flexural–tensile strength in an MFRC. Full article