Mechanics of Time-Dependent Materials最新文献

In this paper, we investigate the role of transverse isotropy on the creep behavior of bedded salt. We conducted a series of triaxial creep tests on prismatic specimens subjected to confining pressures ((sigma _{3})) of up to 24 MPa and a constant octahedral shear stress ((tau _{mathrm{o}})) of 9 MPa. The specimens were oriented with their bedding planes at various angles ((beta )) to the major principal axis to simulate transverse isotropic conditions. Our findings reveal that both instantaneous and creep deformations are most significant when (beta = 0^{circ }), decreasing progressively to a minimum at (beta = 90^{circ }) across all confining pressures. The discrepancy in deformations between these intrinsic angles narrows with increasing (sigma _{3}). Creep deformations for intermediate angles ((0^{circ} < beta < 90^{circ })) follow the elliptical equations. Utilizing the Burgers creep model, we observed that the instantaneous, viscoelastic moduli, and viscoplastic coefficients escalate with (beta ). The degree of anisotropy declines sharply as confining pressures increase, reaching an isotropic state under (tau _{mathrm{o}} = 9text{ MPa}) and (sigma _{3}) around 40 MPa, beyond which transient creep ceases, indicating a transition to Maxwell-material behavior. Employing linear viscoelastic theory, we derived an equation for time-dependent deformation under varying octahedral shear stresses. This enables the formulation of governing equations for Burgers-model parameters, considering bedding plane orientations, loading durations, and the interactions between shear and confining stresses.

In this study, a time-dependent constitutive model of a coal pillar was developed using the Hoek–Brown strain-softening model, which is useful for studying the strength deterioration of a coal pillar over time. A database of 32 failed cases of coal pillars of different ages from the Witbank Coalfield has been utilized to deduce the strength parameters of the coal seam through back analysis. A three-dimensional finite-difference method (FDM) has been chosen to simulate the failed cases. The simulation results have been obtained in terms of pillar strength and FOS of the pillar concerning time. Based on the simulation results the life of the pillar is considered when FOS is nearly equal to 1. The appropriate strength parameters have been derived as peak strength parameters: (m_{i} = 1.47) and (s_{i} = 0.01); residual parameters: (m_{r} = 0.125) and (s_{r} = 0.00001); strength-reduction parameters: (alpha = 0.04), (beta = 200) for a coal mass. 39 stable cases from the same coalfields (Witbank) have been considered to validate the strength parameters. The simulation results of all the stable cases were showing FOS > 1. The proposed constitutive model is suitable for assessing a pillar’s time-dependent strength deterioration and creep behavior. The deterioration/yielding of the pillar is observed to be initiated from the skin/side, extending deeper into the pillar’s core with time and ultimately forming an hourglass shape. It is also observed that the FOS of the pillar decreases with time.

This article investigates the influence of an electromagnetic field, angular velocity, and internal heat sources on two-dimensional thermoelasticity in a micropolar thermoelastic medium using a generalized model of higher-order (multi-phase-lag) heat conduction. The governing coupled partial differential equations are transformed through the normal mode analysis method. The eigenvalue approach is then applied to determine analytically the displacement components, stress components, couple stresses, and temperature distributions from the vector-matrix differential equation. The study’s findings are validated through boundary conditions, and graphical representations highlight the influence of angular velocity, magnetic field, and heat sources in this multi-phase-lag model. The graphical comparison of different thermoelastic models is presented, and the inclusion of tabular data enhances clarity, facilitating a comparative analysis of field variables.

Photothermal transport process and voids in solids are important phenomena in a variety of engineering approaches and scientific disciplines. For this purpose, the photothermal theory is being utilized to study the coupling between elastic waves and plasma waves in a semiconducting medium with voids. The basic governing equations for photothermal waves are derived in the framework of hyperbolic two-temperature theory and Green–Lindsay model. Normal mode analysis method is used to obtain the physical field distributions under investigation. A moving thermal load is applied at the outer free surface of the medium to obtain the complete solution. Expressions are calculated numerically for silicon (Si) material and presented to observe the variations of the field quantities. The effects of various key parameters on the physical fields are also shown graphically. Special cases that are consistent with the earlier findings have been obtained. Although, numerous studies do exist on the deformation analysis in a photothermoelastic medium under different thermoelasticity theories. However, no research emphasizing thermodynamical analysis of the photothermal transport process in a hyperbolic two-temperature semiconducting medium with voids under the influence of gravity and Hall current has been carried out. This provides us a motivation to study the current research. Chemical engineering, geophysics, earthquake engineering, soil dynamics, high-energy particle physics, nuclear fusion, aeronautic biomechanics, bone mechanics, and petroleum industry are the major application areas of the photothermolelasticity theory.

We investigate herein the thermo-mechanical behavior of nitrate ester plasticized polyether (NEPE) propellants under dynamic, nonshock loading scenarios, such as impacts and drops, which are vital for assessing the safety of solid rocket motors. Using a split Hopkinson pressure bar (SHPB) apparatus, we performed dynamic loading tests on NEPE propellant samples at high strain rates (4000, 5100, and 6000 s⁻¹) and various temperatures (228, 298, and 318 K). High-speed cameras captured the deformation, fracture, ignition, and combustion stages under these conditions. Results indicate that both the mechanical properties and ignition behavior of the propellant are significantly affected by strain rate and temperature. The propellant demonstrated nonlinear elastic deformation, with both ultimate stress and strain increasing with strain rate and decreasing with temperature. During dynamic loading, samples underwent stages of uniform and nonuniform deformation, fragmentation, and for some, ignition, which was more prompt and intense at higher strain rates and temperatures. High-speed footage, along with optical and scanning electron microscopy, revealed friction among ammonium perchlorate particles as the primary ignition catalyst, presenting as shear flow on a macroscopic level. This investigation underscores the complex interplay between strain rate, temperature, and mechanical integrity in the safety and performance of high-energy propellants.

Abstract

The main objective of this work is to introduce a new thermal conductivity model that can be utilized to solve the infinite thermal diffusion problem in the Green and Naghdi type III model. This proposed model incorporates two key concepts: the fourth-order Moore–Gibson–Thompson (MGT) concept and thermal relaxation. By incorporating higher-order terms, the fourth-order MGT model provides a more accurate representation of the thermal behavior of the material. The thermal behavior of a functionally graded (FG) infinite medium containing a spherical gap is then studied using this model. A rectified sine wave heating system is applied to the traction-free gap surface. Power functions are utilized to model the uniform radial variation of the physical properties of the FG medium. The physical variables under investigation were meticulously examined, considering the impacts of heterogeneity, relaxation duration, and thermal frequency. These variables were estimated numerically using a suitable technique for Laplace transformations. Through this work, the expected outcomes may be able to make a significant contribution to the field of thermoelastic analysis in advanced and FG materials, as well as to engineering applications.