Search Results (125)

Composites are widely used in the building sector for high-rise building load-bearing components, bridge decks, prefabricated structural panels, and seismic-resistant members, where excellent mechanical performance and structural durability are critical. As specialized advanced composites, variable stiffness composites (VSCs) have gained increasing engineering applications due to their excellent overall performance. Nevertheless, exploring the fracture characteristics of composite materials, especially VSCs, remains a significant challenge. In particular, cracks in composite components can adversely affect structural integrity and durability. In this study, a dynamic fracture phase-field model for VSCs is developed within the framework of elastic dynamics to investigate crack propagation behavior of VSCs under dynamic loads. The proposed model is first validated by experimental results of fracture behavior of single-edge cracked FRC laminae. Then, the proposed model is employed to systematically study the effects of three fiber orientation design variables and internal defects on the fracture behavior of VSCs. Additionally, fiber trajectories are optimized for different pore distribution configurations. The results demonstrate that the model effectively captures the fracture behavior of VSCs and that optimizing these three design parameters enables the fabrication of high-performance VSCs with enhanced crack propagation resistance. This work provides fundamental insights for the design of curvilinearly fiber-reinforced composites and lays a solid theoretical foundation for the practical application of VSCs in building engineering. Full article

Bone tissue exhibits viscoelastic behavior, and stress relaxation analysis provides valuable insight into its time-dependent mechanical performance. This study aimed to evaluate the effects of allicin supplementation on the mechanical and viscoelastic properties of tibial bone in Bovans Brown laying hens. Tibiae of 68-week-old hens were subjected to three-point bending tests to determine quasi-static mechanical properties, as well as stress relaxation tests conducted at three deformation velocities (0.1, 1, and 10 mm/s). Stress relaxation behavior was described using a five-parameter generalized Maxwell model. Allicin supplementation resulted in significantly greater bone stiffness and work to fracture compared with the control group. Stress relaxation tests demonstrated a rate-dependent viscoelastic response in all samples. Bones from allicin-supplemented hens exhibited higher force levels during the relaxation period and reduced stress decay, indicating enhanced elastic behavior and decreased viscous deformation. Model analysis revealed a tendency toward higher equilibrium modulus values and longer relaxation times in the supplemented group, particularly at low deformation velocities. However, no statistically significant differences were observed for E₀, τ₁, and τ₂ between the tested groups. These findings suggest that allicin supplementation may improve bone mechanical and viscoelastic properties in laying hens. Full article

Thermally induced frequency shift (FS) and energy dissipation are key factors limiting the quality factor (Q-factor) of resonators. This study combines nonlocal elasticity theory (NET) with the nonlocal dual-phase-lag (NDPL) heat-conduction model to establish a theoretical framework for evaluating thermoelastic damping (TED) in micro/nano cylindrical shells with size-dependent effects. The equation of motion of the cylindrical shell is simplified using the Donnell–Mushtari–Vlasov (DMV) approximation. The resonant frequency of the cylindrical shell with size-dependent effects is obtained by combining the compatibility equation with the equation of motion and applying the Galerkin method. Additionally, an analytical solution for the TED of cylindrical shells considering size effect under classical boundary conditions is derived using the complex frequency method. The proposed formulation is validated by comparing its predictions with available numerical results. Numerical results indicate that size effects have a significant impact on the TED of cylindrical shells, particularly as mechanical nonlocal effects increase TED, thereby reducing the Q factor of micro/nano cylindrical shells. Moreover, the impact of size effects on the FS and frequency attenuation (FA) is examined. This study lays crucial theoretical groundwork for the design of resonators utilizing micro/nano cylindrical shell materials. Full article

In high-speed train traction power supply systems, compensation ropes serve as critical transmission components to ensure system stability. These ropes are specially designed as right-hand alternating lay wire ropes. During tension compensation of the contact wire, the compensation rope undergoes repeated bending around the ratchet device, making it susceptible to fatigue fracture. This study conducted bending fatigue tests on compensation ropes with complete structural configurations in accordance with GB/T 12347-2008. The stress distribution and deformation evolution induced by bending were simulated using the finite element method, enabling fatigue life prediction under cyclic bending conditions. Given the significant convergence difficulties encountered in large-deformation bending simulations of the full structural model, this study innovatively adopts Love’s elastic thin-rod theory as an alternative approach, which avoids the computational prohibitions of full-scale helical modeling while preserving critical bending stiffness characteristics. The results demonstrate that the equivalent elastic modulus derived from Love’s elastic thin-rod theory closely matches the modulus obtained through stress–strain curve fitting from strand tensile tests. Furthermore, under identical axial tensile loads, the equivalent diameter model and the full-structure finite element model exhibit nearly identical end elongations. The predicted bending fatigue life using the equivalent diameter model agrees well with experimental results, and the fatigue fracture mechanisms are further revealed through microscopic morphology analysis, collectively confirming that the proposed equivalent modeling strategy provides an efficient and reliable solution for fatigue life prediction of complex wire rope structures under coupled tension–bending conditions. Full article

In goafs formed by underground mineral resource extraction, the remaining pillars are often subjected to uniaxial loading at different loading rates, and their mechanical responses and failure mechanisms directly affect the long-term stability of the goafs. This study uses rock-like materials to conduct uniaxial compression tests at loading rates ranging from 0.001 mm/min to 0.05 mm/min, combined with acoustic emission (AE) monitoring, to systematically investigate the effects of loading rate on the mechanical properties, energy distribution, constitutive model, and AE characteristics of the material. The results show that an increase in loading rate significantly enhances the stiffness and strength of the material, promotes a transition in failure mode from a shear–tension composite to tension-dominated, intensifies brittle characteristics, and simultaneously inhibits full crack development and fragments generation. In terms of energy evolution, an increased loading rate enhances the pre-peak total strain energy and elastic strain energy storage but reduces the efficiency of energy dissipation, leading to an intensified mismatch between energy storage and dissipation capacities at peak stress. A damage variable induced by loading rate was proposed, and a damage constitutive model considering the loading rate was established, with the theoretical curves showing good agreement with the experimental data. AE characteristic analysis further reveals that an increase in loading rate causes the crack type to transition from shear-dominated to tension-dominated, and the fluctuating increase in the b-value reflects a reduction in pre-peak fracture scale and a decrease in the degree of material fragmentation. The research findings are expected to deepen the understanding of the damage and failure mechanisms of rock materials under different loading rates, thereby laying a research foundation for the stability assessment of goaf pillars and disaster warning. Full article

Classical contact mechanics typically relies on simplifying assumptions such as linear elasticity and frictionless interfaces. A notable example is the Westergaard model, a rigorous theoretical solution for the contact between a rigid sinusoidal surface and an elastic half-space with a flat surface. This configuration captures the features of surface roughness at a single characteristic scale. Such modeling is particularly relevant since most natural and engineered surfaces exhibit roughness, significantly influencing their contact behavior. In this work, we present a nonlinear analytical contact model, which overcomes the main limitations of the Westergaard solution. Specifically, we formulate the contact problem within a finite elasticity framework and include interfacial friction. The analytical model is derived from the results of dedicated finite element simulations and subsequently validated against experimental data from the literature, demonstrating improved predictive accuracy in estimating the contact area as a function of the applied mean pressure. This work lays the foundation for the development of weakly nonlinear multiscale models, where solutions for single-scale roughness can be superimposed to approximate the behavior of more complex, fractal surface geometries. Such an approach holds promise for applications in areas such as tactile human–device interactions, soft robotics, and the design of bioinspired surfaces. Full article

The development of lightweight, high-strength structural systems is a persistent pursuit in modern civil engineering. This paper presents an experimental study on a novel hybrid beam concept in which a sawn timber core is fully bonded with an externally applied Carbon Fiber-Reinforced Polymer (CFRP) laminate, fabricated through a controlled hand lay-up process. The design seeks to exploit the complementary characteristics of the two materials: timber provides compressive resistance and serves as a permanent formwork, while the CFRP carries tensile stresses with high efficiency. Fourteen hybrid beams, with variations in the number of longitudinal CFRP layers (one, two or, three), the presence or absence of longitudinal CFRP layers bonded along the top and bottom surfaces, and the presence or absence of circumferential wrapping in the pure bending region, were tested under four-point bending alongside two solid timber control beams. The results demonstrate that circumferential wrapping is a critical design detail. Wrapped beams consistently failed by tensile rupture of the CFRP—the intended failure mode—and exhibited ultimate moments 15–20% higher than their unwrapped counterparts. Beams with two longitudinal CFRP layers offered the most favorable balance between strength enhancement and material efficiency; adding a third layer shifted the failure mode to crushing of the timber core, indicating a core-limited condition. All hybrid beams showed pronounced linear-elastic behavior up to sudden brittle failure, with performance variability attributable to the inherent inhomogeneity of wood and the sensitivity of the hand lay-up process. The study provides quantitative data and mechanistic insights that support the design and application of bonded CFRP–timber hybrid beams as efficient structural members. Full article

Elliptical fractures are often used to characterize the deformation of real fractures; however, their deformation responses do not accurately align with those of actual fractures. Nonelliptical fractures shorten by closing near the fracture tips under compression, demonstrating significant advantages in accurately capturing fracture closure characteristics. This warrants investigation of the elastic response of rocks containing nonelliptical fractures. Focusing on single-fracture closure, this study verifies the accuracy of the numerical simulations for elliptical and nonelliptical fractures. A dynamic numerical simulation for crack deformation under compression is proposed to simulate crack closure. The stress-dependent fracture parameters are collected for models consisting of the two fracture types. Then, the pressure-dependence of wave velocities is fitted using an empirical relationship. Under initial compression (<10 MPa), the velocity increase in the elliptical fracture model is just 14.45% of that in the nonelliptical fracture model, displaying a three-stage stress-dependent behavior. The nonelliptical model follows a more realistic two-stage trend, which is more consistent with empirical observations. Moreover, the differences between microscopic parameters are negligible for the models containing elliptical and nonelliptical fractures with a small aspect ratio (≈0.003). This research lays a theoretical foundation for future inversion of fracture distributions using nonelliptical fracture models. Full article

Against the backdrop of sustainable development and global climate governance, this study focuses on the evaluation and trend prediction of provincial carbon emission efficiency and constructs a multi-model integrated analytical framework featuring “data preprocessing—efficiency decomposition—dynamic forecasting—policy deduction”. First, economic, energy consumption and carbon emission data for 30 provinces in China from 2009 to 2019 are collected. Data cleaning is performed through outlier identification and Lagrange interpolation, and a cross-regionally comparable quantification system is established based on a unified carbon emission standard, laying a foundation for subsequent analysis. Second, data envelopment analysis (DEA) is adopted to decompose carbon emission efficiency. It is found that approximately 23% of provinces lie on the technical efficiency frontier, with the average variance share of technical inefficiency being 0.62; 6% of provinces have the potential for scale expansion; and 10% suffer from diseconomies of scale, reflecting significant structural efficiency losses in regions concentrated with high-carbon industries. Third, the long short-term memory (LSTM) neural network is employed for dynamic forecasting and scenario simulation of carbon emissions by 2025. The model’s prediction error in 2019 is controlled within 8.7%. Simulation results show that when the share of clean energy rises to 35%, China’s national carbon emission growth rate can be reduced to 1.2% by 2025. However, multi-scenario sensitivity analysis indicates that the achievement of this target highly depends on policy enforcement intensity and power grid accommodation capacity. In addition, stochastic frontier analysis (SFA) reveals the heterogeneous contributions of different energy types to economic and social outputs. The consumption elasticities of electricity, liquefied petroleum gas and gasoline are significantly positive, whereas the negative elasticities of oil, fuel oil and coal deeply reflect the low energy utilization efficiency and rigid lock-in of high-carbon industries in some regions. Finally, combined with efficiency evaluation, trend prediction and mechanism analysis, differentiated emission reduction strategies are proposed for technologically backward provinces, scale-imbalanced provinces and clean energy base provinces, forming a complete closed loop from “efficiency diagnosis” to “future deduction” and then to “policy feedback”. This study breaks through the limitations of a single model. Through the coupling of parametric and non-parametric methods, as well as the integration of dynamic forecasting and scenario simulation, it effectively addresses issues such as data heterogeneity. It provides scientific support for local governments to formulate emission reduction policies and optimize energy structures, establishes a methodological foundation for industrial efficiency analysis and international carbon responsibility allocation research, and helps to promote regional clean, low-carbon, and sustainable development. Full article

The mechanical behavior of carbon-fiber-reinforced polymer (CFRP) laminates manufactured using plasma-assisted solvolysis recycled fibers was evaluated experimentally through a comprehensive mechanical testing campaign. The plasma-assisted solvolysis parameters were selected based on an earlier sensitivity analysis. Prepregs made from both virgin and recycled carbon fibers were fabricated via a hand lay-up process and manually stacked to produce unidirectional laminates. Longitudinal tension tests, longitudinal compression tests, and interlaminar shear strength (ILSS) tests were performed to assess the fundamental mechanical response of the recycled laminates and quantify the retention of mechanical properties relative to the virgin-reference material. Prior to mechanical testing, all laminates underwent ultrasonic C-scan inspection to assess manufacturing quality. While both laminate types exhibited generally satisfactory quality, the recycled-fiber laminates showed a higher density of defects. The recycled laminates preserved around 80% of their original tensile strength and maintained an essentially unchanged elastic modulus. Compressive strength was more susceptible to imperfections introduced during remanufacturing, with the recycled laminates exhibiting roughly a 14% decrease compared with the virgin material. On the contrary, the compressive modulus was largely retained. The most substantial reduction occurred in ILSS, which dropped by 58%. Overall, the results demonstrate that plasma-assisted solvolysis enables the recovery of carbon fibers suitable for remanufacturing CFRP laminates, while the observed reduction in mechanical properties of recycled CFRPs is mainly attributed to defects in manufacturing quality rather than to intrinsic degradation of the recycled carbon fibers. Full article

The growing need for intelligent educational systems calls for architectures supporting adaptive instruction, while enabling more permanent, long-term personalization and cognitive alignment in the long run. While we have seen progress in adaptive learning technologies at the intersection of Self-Regulated Learning (SRL), Continual Learning (CL), and Meta-Learning, these are generally employed in isolation to provide piecemeal solutions. In this paper, we propose CAMEL, a unified architecture for (1) cognitive modelling based on SRL, (2) continual learning functionalities, and (3) meta-learning to provide adaptive, personalized, and cognitively consistent learning environments. CAMEL includes the following components: (1) A Cognitive State Estimator that estimates learner motivation, attention, and persistence from behavioral traces, (2) A Meta-Learning Engine that allows it rapid adaptation through Model-Agnostic Meta-Learning (MAML), (3) A Continual Learning Memory that preserves knowledge across sessions using Elastic Weight Consolidation (EWC) and Replay, (4) A Pedagogical Decision Engine that makes real-time efficient adjustments of instructional strategies, and (5) A closed-loop that continuously reconciles misalignments between pedagogical actions and predicted cognitive states. Experiments conducted on the xAPI-Edu-Data dataset evaluate the system’s few-shot adaptation capability, knowledge retention, cognitive-state prediction accuracy, and knowledge, as well as cognitive responsiveness to the impending questions. It offers competitive performance in learner-state prediction and long-term performance compared to the baselines, and the improvements are consistent across the different baselines. This paper lays the groundwork for next-generation adaptive and cognition-driven AI-based learning systems. Full article

The advancement of polymeric materials for orthopedic applications has enabled the development of lightweight, adaptable structures that support patient-specific solutions. This study focuses on the design, fabrication, and mechanical characterization of additively manufactured (AM) polymeric polylactic acid (PLA) components produced via Material Extrusion (MEX), commonly known as Fused Filament Fabrication (FFF). By optimizing geometric configurations and process parameters, these structures demonstrate enhanced flexibility, energy absorption, and load distribution, making them well-suited for orthopedic products and assistive devices. A comprehensive mechanical testing campaign was conducted to evaluate the elasticity, ductility, and strength of FFF-fabricated samples under tensile and three-point bending loads. Key process parameters, including nozzle diameter, layer thickness, and printing orientation, were systematically varied, and their influence on mechanical performance was recorded. The results reveal that these parameters affect mechanical properties in a complex, interdependent manner. To better understand these relationships, an automated routine was developed to calculate the experimental mechanical response, specifically, stiffness and strength. This methodology enables an automated evaluation of the output, considering parameter ranges for future applications. The outcome of the analysis of variance (ANOVA) of the experimental investigation reveals that the printing orientation has a strong impact on the mechanical anisotropy in FFF, while layer thickness and nozzle diameter demonstrate moderate-to-weak importance. Thereafter, the experimental findings were applied on an innovative orthopedic wrist splint design to be fabricated by means of FFF. The most suitable mechanical properties were selected to test the mechanical response of the designed components under operational bending loading by means of linear elastic finite element (FE) analysis. The computational results indicated the importance of employing the actual mechanical properties derived from the applied printing process parameters compared to data sheet values. Hereby, an additional parameter to adjust the mechanical response is the product’s design topology. Finally, this framework lays the foundation for future training of neural networks to optimize specific mechanical responses, reducing reliance on conventional trial-and-error processes and improving the balance between orthopedic product quality and manufacturing efficiency. Full article

The anti-pillow effect of mesh antennas has adverse effects on satellite communication. The curvature isotropy of a negative Poisson’s ratio material is expected to be applied and solved for the anti-pillow effect of mesh deployable antennas. Based on the tension characteristics of mesh antennas, our research group has proposed a novel pre-wound six-ligament chiral material, and provided the analytical solutions of Poisson’s ratio and Young’s modulus under the assumption of a small deformation. Following on from the above work, this paper takes into account the variable curvature deformation of pre-wound ligaments and the bending deformation of straight ligaments. The analytical solutions of Poisson’s ratio and Young’s modulus under large deformations are derived, and verified by finite element simulation combined for both small and large deformations. The results show that theoretical solutions considering large deformation of the ligament are more consistent with the simulation results in the large-strain range of anisotropy in the material plane. The analytical solution of Young’s modulus derived from the energy equivalent principle of elastic deformation with a curved beam and a straight beam is consistent with the simulation results under large tensile strain. It has been verified that the existence of a pre-wound ligament can slow down the deformation of the node and reduce the loss of in-plane isotropy to a certain extent, so it is easier to maintain the negative Poisson’s ratio characteristic and maintain an excellent in-plane isotropic deformation mechanism over a larger strain range under tensile load. This characteristic proves the reliability of the prospects applying the pre-wound six-ligament chiral structure in deployable mesh antennas, which lays a theoretical foundation for the subsequent prototype. Full article

Piston pair is a key friction pair of the axial piston pump, but the influence of elastic deformation and the structure design method is not clear. To reveal the real performance of piston pair, a new fluid–solid coupling calculation method is proposed. With the method, the oil film pressure and thickness field, elastic deformation, axial viscous friction and leakage of the piston pair are studied. The influences of the elastic deformation of the piston pair on oil film pressure, axial viscous friction, and leakage were revealed. To reduce the impact brought by deformation, a new piston with hollow piston structure (piston B) is designed. Compared with the traditional structure (piston A), piston B is featured with small elastic deformation, small leakage, large peak pressure, and large viscous friction force. The new fluid–solid coupling calculation method and hollow piston structure of this paper lay the foundation for the piston pair design of the axial piston pump. Full article

Accurate determination of elastic properties, especially Poisson’s ratio, is crucial for the design and modeling of composite materials. Traditional methods often struggle with low strain measurements and non-uniform strain distributions inherent in these anisotropic materials. This research work introduces a novel methodology that integrates Digital Image Correlation (DIC) with frequency analysis techniques to improve the precision of Poisson’s ratio determination during tensile tests, particularly at low strain ranges. The focus is on the evaluation of two distinct frequency-based approaches: Phase-Based Motion Magnification (PBMM) and Lock-in filtering. DIC + PBMM, while promising for motion amplification, encountered specific challenges in this application, particularly at very low strain amplitudes, leading to increased variability and computational demands. In contrast, the DIC + Lock-in filtering method proved highly effective. It provided stable, filtered strain distributions, significantly reducing measurement uncertainty compared to traditional DIC and other conventional methods like strain gauges and Video Extensometers. This study demonstrates the robust potential of Lock-in filtering for characterizing subtle periodic mechanical behaviors leading to a reduction of approximately 70% in the standard deviation of the measurement. This work lays a strong foundation for more precise and reliable material characterization, crucial for advancing composite design and engineering applications. Full article