Mechanics of Time-Dependent Materials最新文献

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.

Deep coal mining increasingly encounters complex geological conditions characterized by high ground stress, elevated gas pressure, and intensive mining activities. These factors interact through multi-field coupling mechanisms, intensifying dynamic disasters such as gas outbursts. To investigate the damage evolution of coal under such coupled conditions, this work develops an integrated numerical simulation framework. The approach incorporates three major components: (i) the Weibull statistical distribution to describe the heterogeneous mechanical properties of coal, (ii) the Mohr-Coulomb shear failure criterion and maximum tensile stress criterion to evaluate damage initiation and propagation, and (iii) coupled control equations for deformation mechanics, gas seepage, and adsorption-induced strain. The role of confining pressure on coal’s mechanical behavior is examined through uniaxial and biaxial compression tests, and the patterns of damage evolution under stress–seepage–adsorption coupling conditions are systematically analyzed. The results indicate that increasing confining pressure elevated peak stress and strain while inhibiting damage progression. In contrast, higher gas pressure differences accelerate coal failure, with coal showing greater sensitivity to changes in confining pressure. Moreover, unidirectional gas flow produces a decreasing stress and damage distribution along the flow direction, whereas bidirectional gas flow generates distinct damage patterns due to differing boundary conditions. This work provides new insights into the mechanisms of coal damage under multi-field coupling conditions, offering theoretical support for predicting and mitigating dynamic disasters in deep coal mining.

The nonlinear dynamic problem of an incompressible viscoelastic composite spherical shell under sudden constant loading on its inner and outer surfaces was studied. A mathematical model was established in this paper. Starting from the fundamental equations, the viscoelastic constitutive equation was expressed in the form of Stieltjes convolution. The governing equations for the displacement function were derived, and general solutions for displacement and stress expressions in the Laplace domain were obtained using Laplace transforms. The displacement and stress distributions were then solved via inverse Laplace transforms. Additionally, the variation rules of stress and displacement inside the spherical shell with increasing internal/external pressures and geometric parameters of the composite shell were discussed.

The nitrate ester plasticized polyether (NEPE) solid propellant incorporates three principal high-energy components: cyclotetramethylene tetranitramine (HMX), ammonium perchlorate (AP), and aluminum powder (Al), sharing compositional similarities with aluminized explosives. To characterize the detonation response and establish the equation of state (EOS) parameters for detonation products, two (Phi )50 mm cylinder tests were conducted on NEPE propellant. The radial expansion displacement-time profiles were derived through continuous monitoring of electric probes arrays, which measured the radial displacement differential induced by detonation products. The experimental results demonstrate close agreement between the two datasets, indicating that the electric probes methodology achieves measurement accuracy and exhibits excellent repeatability. A calibration method of Jones–Wilkins–Lee (JWL)-Miller EOS parameters of propellant detonation products considering the reaction of aluminum powder based on cylinder test data, Genetic Algorithm and numerical simulation was proposed. The calibrated JWL-Miller EOS parameters acquired through this methodology demonstrate enhanced fidelity in reproducing the copper cylinder expansion processes.

This work focuses on the assessment of the viscous dissipation and thermo-diffusion facets on buoyancy-driven heat-propagative unsteady magnetized flow of water based nanofluids (Cu-H₂O and TiO₂-H₂O) from a vertical moving penetrable channel with chemical reaction in the incidence of thermal radiation. Due to their excellent heat transfer properties, considered two different nanoparticles Cu and TiO₂ in this prevalent investigation and water as the base liquid. Non-dimensional variables are exploited to convert the structured dimensional partial derivative model for the flow fields into non-dimensional PDEs, which are subsequently solved using the computational scheme of semi-implicit finite difference. The convergence and stability test were performed to confirm the precision of the results. The work involved a detailed study of flow parameters and their ranges, including Eckert number (0.1 le Ec le 0.4), Soret number (0.1 le Sr le 0.4), nanoparticle volume fraction (0.01 le varphi le 0.04), heat source parameter (0.5 le Hs le 3.0), and radiation parameter (1.0 le N le 4.0). Relevant results on how the emerging parameters influence the flow fields as well the skin friction, temperature and mass gradients are explained in a tabular and graphical mode. The ultimate results visibly exposed for both nanofluids that the temperature and flow velocity significantly abridged by high Prandtl numbers and radiation, but amplified by viscous heating and heat source development of both fields. Increased thermo-diffusion stimulated to intensify the flow speed and species concentration, but both fields compressed by the chemical reaction. The temperature of both nanofluids boosted by the addition of nanoparticles to the base fluid, while the fluid flow velocity decreased. The skin-friction for both nanofluids raised by heat source and viscosity, but it was diminished by the magnetic field and chemical reactions. Heat transfer rate raised-up at plate surface for both nanofluids by heat source, radiation and viscous heating. Remarkably, when dissolving (4%) of Cu nanoparticles into the water, heat transfer rate improved to (7.1%) but when dispersing the same amount of TiO₂ nanoparticles into the water, heat transfer raised-up rate to (8.7% ). Further, the flow fields are superior for TiO₂-H₂O nanofluid, because of their hydrodynamic interaction properties compared to Cu-H₂O nanofluid.

A time-dependent Hoek-Brown strain-softening constitutive model was developed for underground coal-roof rock masses. The basic strain-softening model requires strength parameters ((m) and (s)) as functions of plastic strain and time. It is important to note that the material exhibits yielding before reaching peak strength at the crack/yield initiation point. The yielded elements show time-dependent (creep) behavior. During this process, the strength parameters decrease over time. Keeping this in mind, a mathematical exponential expression has been developed to estimate the peak strength parameter over time, considering an additional peak reduction parameter. The peak strength parameter at zero time is referred to as the ultimate peak strength parameter. The constitutive model comprises two sets of strength parameters: peak strength parameters ((m_{rm}) and (s_{rm})), residual parameters ((m_{mathit{rmt}}) and (s_{mathit{rmt}})), and the peak reduction parameter ((beta )). Deducing these parameters is practically impossible in the laboratory for large-scale coal masses. Therefore, instances of immediate failure, short-term stability, and long-term stability in field cases are used to deduce the strength parameters through a back analysis technique. In total, 34 Indian coal mine cases have been considered for assessing these parameters. The numerical models for all cases have been developed by incorporating the material properties, in-situ stress, and boundary conditions. This research introduces a novel method that employs numerical simulations using a viscoelastic-plastic model to capture the time-dependent behavior of rock, including the gradual reduction of its strength. The findings offer key insights into time-dependent roof rock behavior, supporting advanced stability strategies and collapse risk reduction.

This study examined shear thickening fluids (STFs) for soft armor composites. STFs, consisting of 55 wt.% silica nanoparticles in polyethylene glycol (PEG), have been used to boost the quasi-static and dynamic stab resistance of E-glass fabrics. To enhance the rheological properties of virgin STF (VSTF), we introduced modifications to the PEG chain structure through interactions with malonic and tartaric acid, resulting in the creation of MSTF and TSTF, respectively. Rheological analysis demonstrated that these modifications led to a substantial increase in viscosity, with MSTF and TSTF exhibiting approximately 25.92 and 5.92 times greater viscosity than VSTF, respectively. A series of quasi-static knife stab tests was conducted, revealing a significant improvement in peak force. Moreover, as stab loading speed increased, the energy absorption capacity of the materials demonstrated a direct correlation. Subsequently, we employed regression analysis with artificial intelligence techniques to predict knife stab resistance across various loading speeds. Our results established a robust relationship between force-displacement characteristics and knifing speed. Notably, the heightened viscosity of fabrics infused with TSTF, MSTF, and VSTF led to dynamic impact energy absorption values that were 1.74, 1.58, and 1.43 times higher, respectively, compared to the neat fabric.