Mechanics of Time-Dependent Materials最新文献

Coal, as a complex gas-bearing medium, exhibits unique rheological behavior under mining disturbance. However, with increasing mining depth, the creep and seepage mechanisms of low permeability coal remain unclear. Therefore, to investigate the coupled relationship between creep and gas seepage in low permeability coal, time-dependent triaxial experiments were conducted in this study. To consider the effects of gas, a modified creep model based on the Nishihara creep model was developed and validated by numerical simulations and experimental results. The correlation between coal creep and seepage was then analyzed under different gas pressure conditions, showing a significant reduction in Young’s modulus during creep. This reduction indicates a strong correlation between creep and gas seepage, which is supported by the agreement between creep strain and permeability curves. In addition, the results show a significant attenuation effect in the seepage process at different gas pressures due to pore pressure and adsorption. It is worth noting that unlike conventional soft coal, no permeability reduction was observed in the initial stage due to the low permeability and stiffness of the coal. And it was shown that the presence of methane accelerated the creep behavior of the coal, resulting in a decrease in permeability. Overall, this study provides important insights into the rheological behavior of low-permeability coal under mining disturbance and sheds light on the mechanisms governing gas seepage in coal.

The application of piezomagnetic layers on the external surfaces of passive sandwich shells has the potential to create multifunctional smart sandwich structures. This work introduces new, smart magnetoelectroelastic (MEE) shells and studies their geometrically nonlinear bending and transient behavior as a first endeavor. A High-order Shear Deformation Theory (HSDT) is adopted to develop the Finite-Element model of the smart MEE shells considering the multiphysics couplings, meanwhile the Lagrangian nonlinear strain–displacement relations are employed to account for the geometric nonlinearity. The developed FE is modeled with nodal degrees of freedom that include displacements, rotations, and electric and magnetic potentials. Moreover, the physical characteristics of aggregated CNTRC are evaluated based on a micromechanics model incorporating the two agglomeration parameters. Different agglomeration schemas are considered for CNTs in the nanocomposite core layer. The precision and reliability of the current FE model are confirmed through a comparison of the existing results in the open literature. The study explores the influence of parameters such as CNT volume fraction and their agglomeration phenomena and various geometrical parameters of the shell on the nonlinear bending and dynamic behavior of smart MEE sandwich structures. The findings provide valuable insights into the subject.

Thin-laminate composites with thicknesses below 200 μm hold significant promise for future, larger, and lighter deployable structures. This paper presents a study of the time-dependent failure behavior of thin carbon-fiber laminates under bending, focusing on establishing a fundamental material-level understanding of this type of failure. A novel test method was developed, enabling in-situ micro-CT imaging during long-term bending. Time-to-rupture experiments revealed the stochastic nature of failure, prompting a statistical approach to account for initial imperfections. The total probability of failure was calculated using separate Weibull functions for instantaneous and delayed time-dependent failures. The resulting function, dependent on curvature and aging time, is a design guideline for the design of future deployable space structures. Time-lapse micro-CT imaging identified kink bands and fiber–matrix debonding as primary failure mechanisms, providing essential insights for the design optimization of composite laminates.

Within the framework of fractional-order thermoelasticity, the propagation of elastic waves in non-local isotropic rotating medium has been considered. The frequency dispersion relation is derived by solving the governing equations in the (xy)-plane for the given problem. Three coupled quasi-waves have been seen to move through this kind of medium at different rates. The Helmholtz decomposition theorem has been used to decompose the system into longitudinal and transverse components. Analytical computations are made for the waves’ related amplitude ratios and their speed. The amplitude ratios for the reflected waves are computed with the help of suitable boundary conditions. The impact of fractional order, rotational frequency, and non-local parameters on propagation speed and amplitude ratios has been studied and the same has been plotted graphically. In the absence of rotation, the prior findings mentioned in the literature are obtained as a specific case.

In this investigation, we conducted graded creep cyclic loading and unloading testing to measure the viscoelastic-plastic rheological properties of red sandstone from Southern China under acidic conditions. We utilized an enhanced method to divide the strain into four components: instantaneous elastic strain, instantaneous plastic strain, viscoelastic strain, and viscoplastic strain. We analyzed the strain characteristics of the corroded samples in relation to the deformation modulus. Employing nonlinear rheological theory, we derived the constitutive equations for creep damage in rock under both one-dimensional and three-dimensional stress states. Our findings indicate that acid corrosion has a minimal impact on the resistance to elastic deformation in red sandstone, with the elastic deformation modulus remaining relatively unchanged at comparable stress levels. The relationships between instantaneous elastic strain and viscoelastic strain with deviatoric stress are nearly linear. Increased acidity enhances the plastic deformation of the sandstone, marked by a progressive increase in the instantaneous plastic modulus and a decrease in instantaneous plastic strain increments with successive loading and unloading cycles. The viscoplastic modulus decreases as stress levels rise, leading to increased viscoplastic strain. Incorporating a chemical damage variable that accounts for plastic deformation, we established a creep damage constitutive equation that separates viscoelastic-plastic strains. The validity and accuracy of our proposed model are confirmed through comparison with the traditional Nishihara model.

The recent availability of a wide range of additively manufactured materials has facilitated the translation from prototype-limited to application-ready 3D printed components. As such, additively manufactured materials deployed in dynamic environments require extensive characterization to elucidate and optimize performance. This research evaluates the dynamic response of fused filament fabrication and vat photopolymerization printed polymers as a function of temperature. Dynamic mechanical analysis is used to extract the viscoelastic properties of several generations of samples exhibiting a range of thermomechanical behavior, highlighting the stiffness and damping characteristics. A modified stiffness–temperature model supports the experimental characterization and provides additional insight concerning the molecular motion occurring over each thermal transition. The insights from the analysis were collated into a case study that leverages their dynamic characteristics in a multimaterial application. The outcomes from this research assimilate a framework that defines the temperature operating range and broadens the design envelope for these additive manufacturing materials.

This article explores the memory effects of a three-dimensional cylindrical panel with a void using the Three-Phase-Lag (3PL) theory. The study derives the governing equations for displacement, temperature, void volume fraction, and stress. These equations are solved using Fourier–Laplace transforms and eigenvalue methods. To obtain numerical solutions and generate graphical representations, the transformed equations were inverted. Material properties from Gauthier’s work were used, and graphical results were produced using Mathematica software. The influence of memory response is then demonstrated by comparing kernel functions and time delay parameters within the 3PL porous cylindrical panel. The results show significant changes in the behavior of the panel. The validity of the proposed model is confirmed by comparing its predictions with previously published findings. The authors believe these results can provide valuable insights for various engineering applications involving porous materials. The model allows for accurate prediction of material behavior under different loading conditions, leading to a deeper understanding of various kernel phenomena.

This paper attempts to evaluate the influence of strain rate on the debonding stress of the spherical nanoparticles using a closed form solution. A coherent model to correlate a relationship between the debonding stress of polymer-based nanocomposites and the strain rate was developed. A representative volume element (RVE) containing a spherical nanoparticle, an interphase material, and a pure polymer phase was regarded. A relationship between the debonding stress and the applied strain rate, the material, and geometrical properties of the RVE’s constituents was correlated. In addition to the strain rate, the role of some effective variables such as nanoparticles size, interphase thickness, and interphase stiffness on the debonding stress were investigated. To evaluate the model, three case studies based on the experimental studies performed on silica nanoparticles/epoxy, CaCO₃ nanoparticles/high-density polyethylene (HDPE), silica nanoparticles/photopolymer nanocomposites were conducted. For the nano-silica/epoxy system, the results revealed that by enhancing the strain rate, the normalized debonding stress decreases. Additionally, under a certain strain rate, the normalized debonding stress enhances as much as the stiffness of interphase material increases and the nanoparticle size decreases. In the case of CaCO₃/HDPE nanocomposites, it was observed that by increasing the size of nanoparticles, the normalized debonding stress was reduced significantly. For the nano-silica/photopolymer nanocomposites, it was found that the dependence of the normalized debonding stress on the strain rate is more remarkable for the thicker interphase region. The proposed model can be used to predict the mechanical properties of nanoparticles/polymer systems under high strain rate conditions.

This research formulates a nonlocal systemic model to integrate viscoelastic and thermal deformations in solid structures based on fractional thermo-viscoelasticity theory. This enhanced model offers a more comprehensive understanding by integrating several existing theories. We apply the model to a one-dimensional problem involving a micro-rod made of an electrically conductive polymer, heated by a moving heat source. The analysis employs Laplace transforms with numerical inversion to determine the effects of fractional order, nonlocal elasticity, and nonlocal thermal conduction on thermal dispersion and the thermoviscoelastic response. Comparative figures illustrate the impact of an applied magnetic field. Results show that nonlocal thermal and viscoelastic parameters significantly influence all measured field values, potentially providing guidelines for the design and analysis of thermal-mechanical features in nanoscale devices.

This study investigated the long-term creep behavior of concrete in drilled shafts using conventional and soft-cutting head techniques, focusing on their propensity for internal defects and crack propagation under sustained loading. Triaxial creep tests were performed on concrete specimens subjected to multistage loading to examine the axial- and radial-creep responses associated with each cutting-head method. The findings reveal that concrete prepared with conventional cutting heads exhibits a higher susceptibility to creep failure, attributed to an increased presence of internal defects. In contrast, specimens using soft-cutting heads demonstrated reduced axial- and radial-creep deformations. Concrete cured in laboratory conditions and those cut with soft-cutting heads at various elevations predominantly experienced shearing failures, whereas specimens with soft-cutting heads positioned at higher elevations were more prone to radial tension-shear failures. Considering the Burgers model and fractional-order theory, we introduce a one-dimensional nonlinear damage creep model, alongside a more comprehensive three-dimensional damage creep model. Validation of these models confirms their effectiveness in describing the creep behavior of concrete under different cutting-head disturbances. Importantly, our analysis suggests that the role of soft-cutting head methods on the integrity of cast-in-place concrete piles is comparatively minimal. This insight underscores the potential for optimizing pile-head breaking techniques to mitigate creep-related failures in concrete structures.