Mechanics of Time-Dependent Materials最新文献

One important strategy for increasing the strength and load-bearing capability of damaged tunnel linings is to reinforce them with steel plates. An important factor in determining the long-term performance of the restored tunnel is the bond interface’s longevity. This study focuses on the bond interface creep behavior in steel plate-reinforced shield tunnels through experimental investigation. Accelerated testing was used to investigate the long-term creep response of the bond contact using the creep equivalence and Boltzmann superposition principles. The key takeaways are as follows: The progression of creep at the bond interface – from the moment of initial loading to when it reaches a stable state – can be broadly broken down into four phases: an instantaneous deformation phase, a stage of decay creep, a period of steady–stable creep, and accelerated creep phase. The bond contact of the shear specimen experiences accelerated creep after 186 hours when it is subjected to 90% of its maximum stress, while the bond interface of the tensile specimen reaches this stage in just 96 hours. As the stress level rises, so does the quantity of creep at the bond interface. As the distance from the loading end increases for the shear specimens, the amount of creep at the bond contact progressively diminishes. A notable 1000-fold increase in creep time is seen when Time-Stress Superposition Principle (TSSP) is used to speed up the characterization of experimental creep curves for the bond contact.

Creep stresses are evaluated in a hemispherical shell made of functionally graded transversely isotropic materials under uniform external pressure. The concept of transition theory is applied to evaluate the creep stresses in the shell under external pressure. The strength and compatibility of the hemispherical shell composed of magnesium, zinc, and beryl are compared based on creep stresses. This physical problem is regulated by a non-linear differential equation obtained by substituting the derived relations in the equilibrium equation. For estimating the creep stresses in the shell, the transition function (R) is considered as the difference of radial stress (T_{rr}) and circumferential stress (T_{theta theta } ). Analytical method is applied to solve the equations by taking the critical point (Prightarrow -1) of the governing differential equation into consideration. This study examines the hemispherical shell composed of Functionally graded transversely isotropic material, which is more robust and biocompatible than homogenous transversely isotropic material. Based on all the numerical calculations and graphs it is concluded that the circumferential and radial creep stresses are minimum for a hemispherical shell composed of functionally graded transversely isotropic material magnesium in comparison to zinc and beryl, it implies that the shell composed of (FGM) magnesium is experiencing the most stable or optimal state of deformation under the conditions of external pressure. Therefore, the hemispherical shell of functionally graded transversely isotropic material magnesium might be useful in practical applications like pressure vessels, tanks, or any spherical shell structures exposed to high pressure over long durations.

This study proposes a modified cumulative damage model for GAP-based composite solid propellants, considering thermal aging effects. Accelerated thermal aging experiments were conducted at 333.15 and 343.15 K to analyse the variations in mechanical properties, including elastic modulus and maximum elongation. The results revealed an approximately 15% increase in elastic modulus and an approximately 25% decrease in maximum elongation during 333.15 K thermal aging. Based on the Arrhenius equation, a predictive model for mechanical parameter degradation was established, and the evolution of cumulative damage parameters was simplified using three assumptions. The modified model, accounting for aging effects on parameter (beta ), demonstrated good agreement with direct computational results. Numerical simulations indicated that aging substantially amplifies cumulative damage in solid rocket motors under thermal cycling loads. This research provides a theoretical framework for assessing the structural integrity of solid rocket motor during long-term storage.

In response to the growing demand for sustainable construction practices, this study evaluates the potential use of calcined bentonite (CB) and recycled glass powder (GP) as supplementary cementitious materials in self-compacting mortar (SCM). The environmental objective is to reduce the reliance on Portland cement, which is a major contributor to CO₂ emissions, by incorporating industrial and post-consumer waste materials. In mixtures, CB was introduced at replacement levels of 5, 10, 15, and 20%, while GP was added at levels ranging from 5 to 25% by weight in binary and ternary binders. A comprehensive assessment of the fresh properties, including mini-slump flow, V-funnel flow time, yield stress, and plastic viscosity, was conducted, alongside mechanical and durability tests such as compressive strength, water absorption, acid resistance (5% HCl) and sulfate attack (5% K₂SO₄). Results indicate that, CB decreases the flowability of SCM mixtures, necessitating a higher dosage of superplasticiser. However, when combined with GP, the flowability improves significantly, reducing the demand for superplasticiser. Optimal mechanical performance was observed in mixtures containing 15% CB and 0% GP, as well as 10% CB with 5% GP, which achieved compressive strength improvements of 12% and 13%, respectively, after 90 days. Moreover, the incorporation of higher GP contents (15–25%) enhanced the mortar’s resistance to hydrochloric acid and potassium sulfate solution, highlighting its contribution to long-term durability. These findings support the valorization of calcined clays and glass waste as viable alternatives for developing sustainable and cost-effective SCM, while reducing environmental impact in the construction industry.

Rejuvenators used for hot mix recycling can be classified broadly into recycled rejuvenators (RR) and commercial rejuvenators (CR). A comparative evaluation between two RR and two CR is done in this study. A series of tests on rejuvenators (Brookfield viscometer, rolling thin film oven and Fourier Transformed Infrared Radiation tests), recycled binder blends (zero shear viscosity, frequency sweep, multiple stress creep recovery) and recycled mixes (uniaxial cyclic compression test and Indirect tensile asphalt cracking test) are performed. FTIR spectra revealed that all rejuvenators comprise aliphatic and aromatic hydrocarbons, which are similar to the maltenes portion of asphalt. Test results showed that RR are thermally stable than CR and recycled binder blends with RR are softer than CR. Hence, RR have higher cracking resistance and cross-over frequency, but lower Zero Shear Viscosity and rutting resistance. Also, recycled mixes with RR showed higher irrecoverable strains than mixes with CR. On top of performing well in rutting, recycled mixes with CR also showed better or comparable fatigue performance at 40% recycled content. From the ranking analysis, it is concluded that RR outperformed CR, and weight change after RTFO test has the best correlation with the global total rank value (GTRV).

This study presents an analytical investigation of peristaltic pumping and coupled heat–mass transfer in an incompressible, electrically conducting Jeffrey viscoelastic fluid within tapered oblique channel geometries. The model incorporates buoyancy effects, reactive solute dynamics, Hall currents with linear dependence, a uniform transverse magnetic field, porous medium resistance via the Darcy–Brinkman formulation, and radiative heat transport under the gray approximation. Chemical reactions are assumed to be first-order. The governing nonlinear coupled equations are solved in closed form under long-wavelength and low-Reynolds-number approximations, which justify steady, creeping peristaltic motion. Validation against benchmark solutions reported by Ravi Rajesh and Rajasekhara Gowd demonstrates excellent agreement across varying Hall current parameters, confirming the robustness of the analysis. Results indicate that Hall currents enhance velocity by mitigating electromagnetic resistance, whereas higher Hartmann number suppress flow owing to Lorentz forces. An increasing Darcy number reduces drag from the porous matrix, thereby strengthening fluid transport. Both thermal and solutal Grashof numbers intensify buoyancy-driven convection, while Jeffrey fluid elasticity and thermal radiation contribute significantly to pumping efficiency. The Prandtl number regulates heat balance by promoting storage at higher values but supporting convective release near boundaries at lower ranges. Concentration profiles are sensitive to Biot, Soret, and Schmidt numbers as well as chemical reaction strength, underlining boundary-layer-controlled solutal modulation. Trends in pressure rise highlight viscoelastic effects in both forward and retrograde pumping regimes, whereas parametric variations in Nusselt and Sherwood numbers delineate pathways for optimizing thermal–solutal transport. This unified formulation of electromagnetic, porous, radiative, chemical, and viscoelastic effects provides benchmark-quality insights relevant to microfluidics, biomedical pumping technologies, and high-temperature industrial transport systems.

A novel analytical-mathematical formulation for the multi-physics thermo-elasto-visco-plastic (TEVP) behavior of materials with nonlinear combined hardening is proposed. New closed-form expressions for the incremental visco-plastic multiplier (IVPM) and the consistent tangent operator (CTO) were derived. Specifically, all stiffness, hardening, and viscous coefficients were treated as temperature-dependent, and their temperature derivatives were explicitly included in the analytical solution. A UMAT (User Material) subroutine was programmed and implemented to compute the IVPM, CTO, and isotropic, kinematic, and viscous stresses for TEVP modeling. Finite element (FE) models were created and compared for the Abaqus^® built-in material model and the developed UMAT subroutine. The IVPM and CTO equations were successfully validated and the influence of the initial IVPM value on the accuracy of the results and the run time of simulations was examined for the first time. It was found that, in the Newton-Raphson method, the initial IVPM value must not only be nonzero to avoid singularity issues, but also be less than or equal to (10^{-8}) to ensure accurate results. In addition, the initial IVPM value did not influence computational efficiency. Ultimately, based on a comparative study of analytical solutions, UMAT-driven simulations, and standard Abaqus simulations, the developed formulation enables accurate prediction of strains, stresses, and temperatures in TEVP problems, providing a solid foundation for modeling industrial manufacturing processes such as quenching.

This work investigates the effect of three-dimensional joint roughness coefficient ((mathit{JRC}^{3D})) on the nonlinear shear creep properties of granite structural planes. Four natural granite structural planes with distinct surface morphologies were prepared using the Brazilian splitting method, with (mathit{JRC}^{3D}) values controlled within the typical engineering range of 5-18. A self-developed laser three-dimensional scanner was employed to capture surface morphology, enabling three-dimensional visualization and quantification of morphological parameters. Shear creep tests were then conducted to examine the effect of (mathit{JRC}^{3D}) on the creep behavior of the structural planes. The results show that with increasing (mathit{JRC}^{3D}), creep deformation, steady-state creep rate, and accelerated creep rate gradually decrease, whereas failure shear stress, creep failure time, and long-term shear strength exhibit an increasing trend. Based on these findings, a shear creep model incorporating the influence of (mathit{JRC}^{3D}) was developed. Model parameters were identified and validated, confirming the model’s reliability. The model quantitatively links (mathit{JRC}^{3D}) to creep parameters of engineering rock joints, addressing limitations of traditional models that neglect surface morphology effects. By capturing the progressive damage evolution in rock masses, the model provides a mechanistic framework for predicting time-dependent instability and mitigating the risk of abrupt collapses induced by creep accumulation. These results offer valuable guidance for the prevention, control, and evaluation of geological engineering hazards.

Despite being at room temperature, thermoelastic damping (TED) plays an important role in energy loss in micro-scale structures. The micro-electro-mechanical system (MEMS) resonators are designed to have low energy dissipation, which is associated with high-quality factors. In couple stress theory, considering the size effect is necessary to explain the problem when plates have micro- or nano-scale thicknesses. This research aims to theoretically obtain an expression for the TED quality factor of size-dependency micro-plate resonators by employing the modified couple stress theory (MCST) with the condition of plane stress and heat conduction for the Quintanilla model. We consider thin silicon micro-plate resonators to explore how the parameter of length scale affects TED’s quality factor. The variation of TED has been examined in terms of the parameters of length-scale, micro-plate thickness, and normalized frequency, and also looked into the impact of phase lag parameters on TED. A comparative study of the proposed model and conventional continuum theory (CCT) has been explained. The present work states that the quality factor of resonators with an infinitesimal thickness may increase by considering small parameter values of phase lags under the modified couple stress theory.

Recently, with the increase in tunnel construction, mining, and other projects, it is of great significance to conduct research on rock-creep characteristics. This paper investigates the viscoelastic and viscoplastic strain characteristics of red sandstone under different stress levels by conducting cyclic loading and unloading creep tests. The study separates the viscoelastic and viscoplastic strains and establishes a damage-hardening creep constitutive model. The results show that rock creep is a dynamic process in which internal stress is continuously adjusted, and viscoelastic and viscoplastic strains continue to develop and transform into each other. As the stress level increases, the decelerated creep rate of viscoelastic strain in the rock sample increases, while the steady-state creep rate remains relatively unchanged; in contrast, both the decelerated creep rate and the steady-state creep rate of viscoplastic strain increase significantly. Under constant stress, the viscoelastic strain of the rock sample remains relatively stable over time, exhibiting characteristics of elastic stability; although viscoplastic strain continues to increase, its increment gradually decreases, reflecting the hardening characteristic in the plastic deformation process of the rock sample. To accurately describe this complex creep behavior, this paper introduces elastic damage and plastic hardening functions and constructs a nonlinear creep constitutive model based on the effective stress principle. Through the introduction of an equivalent nonlinear viscous element, the model was analytically investigated and compared with the traditional Nishihara model, thereby demonstrating its enhanced accuracy and superior performance. The model developed in this paper effectively describes this complex creep-deformation behavior at various stages, providing a theoretical basis for further understanding rock-creep behavior and its engineering applications.