Mechanics of Time-Dependent Materials最新文献

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.

Highly cross-linked epoxy resins are ubiquitous in high-performance structural applications, particularly when used as matrices for fibre-reinforced composites. The optimisation of composites requires a quantitative and predictive description of the mechanical behaviour of the matrix. To explore master trends in the mechanical response as well as to guide first-order modelling, the complete stress-strain response of six epoxies is characterised under uniaxial compression up to large strain and fracture. A number of characteristic properties are analysed and rationalised mainly through establishing partly physical and partly empirical relationships with the ratio (T / T_{g}) of test over glass transition temperature. Among others, an enhanced Eyring-type model is identified for the yield stress and found valid for a wide range of temperatures and strain rates below (T_{g}). The yield stress of all six epoxies is related to (T_{g}) within 10% error without any other adjustment of parameters. A similar relationship for the modulus with (T / T_{g}) also accounts for strain rate. Lastly, the failure stress and strain are found to also correlate to (T / T_{g}) in subgroups of resins with similar molecular structure, while the re-hardening modulus does not.

The present study aims to implement regression modeling using Response Surface Methodology (RSM) for analyzing the heat transfer and prediction of skin-friction coefficients of a magnetohydrodynamic (MHD) nanofluid flow across a vertical wedge along with its applications in data prediction and response optimization. The differential equations arising after the similarity transformations were solved using bvp4c in MATLAB. The importance of the present study lies in its application in forging of hot exhaust-valve heads, manufacture of water heaters, extrusion processes, cooling processes, turbine blades, and medical industries, etc. Some of the insightful results noted were increasing heat-transfer rates by (0.74%) for nonaggregation modeling and by (0.78%) for aggregated model with increase in the magnetic parameter from 0.2 to 0.8 followed by the increase in skin-friction coefficient for transition from nonaggregation to the aggregation model. Augmented velocity profiles by (2.08%) were observed for the nonaggregation as compared to the aggregation model. A face-centerd central composite design was implemented in RSM for determining the Analysis of Variance (ANOVA) for our results using a quadratic fitting model with (R_{1}^{2}=Adj R_{1}^{2}=100%) for both the aggregation and nonaggregation models. The velocity-ratio parameter showed negative sensitivity to the response parameter. (Pred R_{1}^{2}=99.99%) represented very high predictability rate for new observations. The predicted values recorded a maximum absolute error of the order (10^{-4}) when compared to the actual numerical data along with a desirability of (100%) to attain the extremum values for both models.

In deep underground engineering, the synergistic effects of dike interfaces and initial damage significantly influence the brittle-fracture characteristics and rockburst tendency of rock masses. To investigate this phenomenon, a multiscale experimental approach was adopted to characterize the mesostructural evolution of veined granite specimens with varying levels of damage, particularly focusing on the coupled mechanisms governing their brittle-failure behavior and susceptibility to rockbursts. The research results indicate that the presence of rock veins increases the complexity of the pore structure, causing more large pores. The orientations of weak planes differ across the rock-vein interface, mica flake structure, and quartz-particle cementation zone. Granite with rock-vein interface-like characteristics exhibits a staircase increase in the rate of AE energy before reaching its peak value, featuring progressive failure. Specimens with rock veins generate more AE events and show more pronounced characteristics of concentrated energy release. As the initial damage intensifies, the cumulative ring-down count (RDC) and the rate of release of AE energy show a more significant staircase growth, with the values reducing successively, suggesting that initial damage weakens the brittle-failure characteristics of the rock. When the initial damage value (D leq ) 0.33, the rock is at risk of rockbursts, but the intensity thereof is lower than that under undamaged conditions. When (D geq ) 0.41, the rock no longer meets the conditions for the occurrence of a rockburst.