Mechanics of Time-Dependent Materials最新文献

This study presents a comprehensive time-dependent electromechanical analysis of functionally graded piezoelectric (FGP) composite panels resting on concrete auxetic foundations, subjected to aerodynamic flow. The investigation integrates advanced theoretical, numerical, and machine learning methodologies to capture the coupled behavior of smart structures under transient loading. A refined higher-order shear deformation theory (HSDT) is employed to model the mechanical behavior of the FGP panel, ensuring an accurate representation of through-thickness deformation without requiring shear correction factors. The electromechanical coupling is governed by Maxwell’s equations, while Hamilton’s principle is utilized to derive the governing equations of motion. To discretize and solve the resulting time-dependent partial differential equations efficiently, a differential quadrature hierarchical finite element method (DQHFEM) is proposed, in conjunction with the Gauss-Lobatto-Legendre (GLL) quadrature rule to ensure numerical stability and precision. The effect of the auxetic foundation, characterized by negative Poisson’s ratio behavior, is incorporated through a modified elastic foundation model. Aerodynamic loads are modeled using first-order piston theory. To validate the proposed mathematical model and verify its predictive capabilities, a deep neural networks (DNN) is trained on simulation data, showing high accuracy in capturing nonlinear time-dependent responses. Parametric studies are conducted to examine the influence of material gradation, aerodynamic intensity, and foundation characteristics on the dynamic response. The results demonstrate the robustness and accuracy of the proposed framework, suggesting its potential for optimizing smart composite structures in aeronautical and civil engineering applications under complex loading environments.

Nickel–chromium (Ni–Cr) alloys offer high strength, wear resistance, shape-memory effect, and broad clinical applications. This study evaluates the effect of pre-annealing on their electrochemical corrosion behavior. Samples were annealed at 500 °C and 700 °C and compared with a non-annealed reference. Microstructure and composition were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX), while corrosion behavior was examined by open-circuit potential (OCP), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS). Annealing at 500 °C and 700 °C resulted in lattice expansion (from 3.551 Å to 3.561 Å) and a reduction in crystallite size (from 9.40 nm to 8.10 nm), accompanied by chemical inhomogeneity leading to degradation of the passive oxide layer. These changes accelerated corrosion: compared to the non-annealed alloy (0.0125 mm/year), the rate increased to 0.0356 mm/year at 500 °C and 0.313 mm/year at 700 °C. Concurrently, passive current density (I_pass) doubled from 20 to 40 (mu )A cm⁻², while the Pitting potential (E_pirs) shifted from +0.290 mV to –0.287 mV, indicating weaker passivation. EIS confirmed declining charge transfer resistance with temperature. Post-corrosion surface analysis confirmed these findings: SEM revealed increased roughness and defects, while EDX detected reduced oxygen content, consistent with thinning of the protective oxide film after annealing. Thus, high-temperature pre-annealing, therefore, markedly degrades corrosion resistance, underscoring the need for optimized heat treatment in dental applications.

Polyamide (PA) is a widely used semi-crystalline polymer that exhibits complex viscoelastic-viscoplastic behavior including the double-yielding (DY) phenomenon. Uniaxial tensile tests at different strain rates were performed using PA11 specimens obtained at different annealing temperatures to evaluate the effect of the strain rate on the DY phenomenon. The slope of the stress-strain curve after the first yield and the distance between the first and second yields increased with decreasing strain rate. In contrast, the maximum stress observed during the DY phenomenon was independent of the strain rate, and uniform deformation continued for a longer strain range at lower strain rates. The first yield stress was strain-rate dependent, whereas the second yielding stress was governed by the annealing temperature. These findings indicate that the first and second yielding events were characterized by the amorphous and crystalline phases, respectively. The viscoelastic-viscoplastic transient network model was generalized to reproduce the experimentally observed time-dependent DY phenomenon of PA11. Subsequently, a two-dimensional plane stress finite element model was established using the proposed method, and computational simulations of the uniaxial tensile tests were performed and compared with the experimental results. The simulation results reproduced the time-dependent characteristics of PA11, including changes in the first yielding stress, different degrees of hardening and softening during deformation between the first and second yields, and shifts in the strain at which the second yield occurred as a function of strain rate.

As a core component, the mechanical behavior and failure criterion of solid propellant grain are the key to environmental adaptability and safety of solid rocket motors. However, considering variable Poisson’s ratio with significant strain dependence as an elastic constant and failure behavior with loading time dependence as fixed limits are important factors in the current inaccuracy of motor structural integrity analyses. Here, a series of constant speed tensile and creep tests were carried out. The variable Poisson’s ratio phenomenon and time-dependent failure behavior of propellant were analyzed and discussed, and the microscopic mechanism was revealed. A model for predicting time-dependent failure behavior of composite materials is proposed, and each model parameter has a corresponding macroscopic and microscopic physical meaning. The validity of model prediction accuracy is verified in three working conditions, and the coefficient of determination R² is between 0.88 and 0.98. This work could provide theoretical and experimental guidance for long-term service life prediction and reliability evaluation of solid propellant, as well as other particle-reinforced materials.

Background: This research investigates the magnetohydrodynamic flow of a chemically reactive Casson hybrid nanofluid within a Sodium Alginate base, flowing over a curved stretching surface in a porous environment. The analysis accounts for internal heat sources, magnetic field influence, reactive diffusion, and thermophoretic effects to improve thermal performance. Methodology: The model considers transport effects, including Brownian motion, thermophoresis, internal heating, viscosity, and Arrhenius-type reactions. Similarity transformations reduce the governing PDEs to ODEs, which are solved using MATLAB’s BVP4c. The sensitivity of thermal and flow parameters is further evaluated using Multiple Linear Regression (MLR). Core findings: Results indicate that elevating the Biot number can boost the Nusselt number by approximately 42%, emphasizing improved heat transfer at the surface. The heat generation parameter exerts the strongest effect on thermal output, with a sensitivity index peaking at 2.8673. Furthermore, the curvature parameter plays a significant role in modulating surface shear. The sensitivity analysis pinpoints parameter combinations that yield optimal performance, reinforcing the utility of machine learning in fluid system optimization. Validation: Comparisons to previous studies demonstrate excellent agreement, as deviations remain under 1.6% for skin friction and 2.3% for the Nusselt number when the curvature parameter equals zero. These results affirm the robustness of the applied transformations and numerical approach. Furthermore, the MLR model perfectly matches numerical outputs, reaching an (R^{2}) score of 1.0, confirming predictive accuracy. Applications: The findings reference engineering applications, specifically solar thermal systems, HVAC equipment, and miniaturized heat exchangers. By combining numerical modeling with machine learning, this study offers a reliable approach for designing and controlling energy-efficient thermal systems under varying physical conditions.

Highly Modified Asphalt (HiMA) binders have garnered significant attention due to their superior resistance to rutting, fatigue cracking, and thermal distress under heavy traffic loads and extreme environmental conditions. While elastomeric polymers such as Styrene-Butadiene-Styrene (SBS) have been extensively used in HiMA applications, the potential of plastomeric polymers, including Polyethylene (PE) and Ethylene Vinyl Acetate (EVA), remains largely unexplored. This study aims to evaluate the performance of reference binder (RB) modified with plastomeric HiMA asphalt in comparison to SBS-modified binders and determine the optimal polymer dosage for achieving an optimal balance between rutting resistance and fatigue durability. The experimental program involved modifying a base asphalt binder with SBS, PE, and EVA at dosages of 6%, 7%, and 8% by weight of binder. A comprehensive evaluation was conducted, including conventional tests (penetration, softening point, viscosity, mass loss, storage stability, and specific gravity) and rheological characterization using the Dynamic Shear Rheometer (DSR). The Multiple Stress Creep Recovery (MSCR) test was employed to assess high-temperature performance, while the Linear Amplitude Sweep (LAS) test evaluated fatigue behavior. Additionally, an Overall Desirability (OD) analysis was performed to integrate multiple performance criteria and establish a ranking for each modification. The results demonstrated that SBS-modified binders exhibited the most balanced performance, with SBS8 achieving the highest elastic recovery (52.87%) and superior fatigue life, exceeding 1,017,904 cycles at 2.5% strain. PE8 exhibited exceptional rutting resistance, reaching the lowest J_nr 3.2 value (0.0078 kPa⁻¹); however, its limited elasticity (15.7% recovery) indicated reduced flexibility. EVA modifications demonstrated marginal improvements in fatigue resistance but failed to meet the AASHTO M332 criteria for high-traffic applications. The OD analysis ranked SBS8 as the most effective HiMA binder (OD score = 0.715), followed by SBS7 (0.588) and SBS6 (0.509). PE7 (0.354) and PE6 (0.337) demonstrated moderate performance, whereas EVA had the lowest desirability score (0.000). Based on these findings, SBS-modified binders are recommended for applications requiring a balance between fatigue and rutting resistance, whereas PE-based HiMA is more suitable for high-temperature regions where rutting is the primary concern. Further field studies are necessary to validate the long-term durability of plastomeric HiMA binders and optimize their use for specific pavement conditions.

Creep behavior of short glass fiber reinforced poly(butylene terephthalate) (SFRC PBT) composites was analyzed using plates processed by injection molding and push–pull processing, with fiber contents of 0, 20, and 30 wt%. Tensile test bars were extracted parallelly and perpendicularly to the flow direction to assess short-term mechanical properties, fiber length distribution, and orientation. An elementary volume approach was used to predict the longitudinal and transverse creep compliances, showing that the time dependencies were mainly governed by the PBT matrix. Given the minimal fiber orientation in the thickness direction, a transformation based on RM Jones’ mechanics of composite materials was applied to account for fiber misalignment. This led to the introduction of the unknown shear modulus (G_{12}), which was addressed by expressing it in terms of the transverse compliance (J_{22}) and shear correction factor. Comparison of predicted and measured creep compliances revealed an underestimation of 15–30% parallelly and 5–15% perpendicularly to the flow direction, attributed to imperfect fiber-matrix adhesion. SEM analysis of fracture surfaces indicated different failure behaviors based on the fiber orientation. This suggests that fiber-matrix adhesion is stress-direction dependent. The time range for accurate prediction of composite creep behavior, governed by matrix creep, is defined by the creep time limit, which decreases exponentially with increasing creep stress.

This study presents a comprehensive analytical investigation of linear viscoelastic behavior based on the classical Zener model and its generalized extension. Closed-form expressions are derived for key mechanical quantities, such as stress, tangent stiffness, hysteresis area, complex modulus, relaxation modulus, and creep modulus, under typical loading conditions, including constant strain rate, sinusoidal cyclic loading, stress relaxation, and creep. Particular attention is given to energy-dissipation phenomena, with formulations that elucidate the relationships between measurable mechanical responses and the underlying constitutive parameters. Notably, under cyclic loading, the analysis reveals linear correlations between the relaxation time and the time period corresponding to maximum energy dissipation. A linear extrapolation technique is also proposed to identify viscous parameters from stress-relaxation or creep data. These findings provide a practical reference for interpreting experimental results and support parameter estimation through analytical or computational approaches. Overall, this work offers a structured and interpretable framework for viscoelastic modeling, complementing numerical methods and enhancing the physical understanding of time-dependent behavior in polymers and time-dependent materials.

Existing models for the freeze-thaw damage of concrete consist mainly of discrete prediction models based on freeze-thaw test data from saturated or highly saturated concrete. These models have difficulty reflecting how temperature and saturation would affect hydraulic concrete’s performance loss from freeze-thaw cycles. To address this problem, this study first improved a formula of equivalent damage age to reflect the effects of freeze-thaw temperature and saturation. Next, the fractional-order freeze-thaw damage model of hydraulic concrete for sealed freeze-thaw and water-freeze-thaw concrete was established by using fractional calculus theory. Finally, freeze-thaw tests of hydraulic concrete under three freeze-thaw temperatures and three saturation conditions were designed and carried out. The loss rates of strength obtained by tests served as input to the GWO algorithm to predict the freeze-thaw damage of hydraulic concrete based on the freeze-thaw temperature and saturation, and the model’s applicability was verified. The results show that the loss rates of strength increase with increasing equivalent damage age. In addition, the loss rate of both types of strengths increases with decreasing freeze-thaw cycle temperature and increasing saturation, and the loss rate of splitting tensile strength exceeds the loss rate of compressive strength for a given freeze-thaw temperature and saturation level. The correlation coefficients between the fitted values and the test values of the sealed and water freeze-thaw concrete specimens are 0.950–0.958 and 0.903–0.924, respectively, which indicates that the fractional-order freeze-thaw damage model developed in this paper is reliable.

Polymer coatings with enhanced mechanical properties and deformation behavior, as well as energy dissipation capacity, have attracted increasing attention for broad functional applications. This work investigates the role of winding angles and diameter ratios on the tensile properties, damage behavior, and spatial Poisson’s ratio distribution of helical auxetic yarns (HAYs) and their polyurea-based composites. Optimal mechanical performance was observed for HAYs with a 5° winding angle and a 9:1 diameter ratio, resulting in a 1.6–2.4 fold increase in fracture energy and a maximum negative Poisson’s ratio of −11.18. When embedded in polyurea, HAYs increased the composite’s tensile strength by 1.50–2.46 times and energy dissipation by 2.65 times compared to pure polyurea. The composites also exhibited a significant negative Poisson’s ratio of −7.75. The deformation behavior was characterized by using digital speckle correlation method (DSCM) to determine strain and displacement fields in the elastic and plastic regimes. These findings establish a quantitative relationship between HAYs structural parameters and the mechanical response of such composite coatings.