Mechanics of Time-Dependent Materials最新文献

In this paper, we investigate the creep-deformation behavior of Fe-Cr-Ni single-crystal alloys, a crucial factor in the longevity and safety of materials in high-temperature applications. Using molecular-dynamics (MD) simulations, we generate the creep-strain data on the creep behavior of Fe-Cr-Ni single-crystal alloy. To predict creep curves under various temperatures and stress conditions, we employ random forest (RF) and convolutional neural network (CNN) models. These models are trained, tested, and validated on creep data at 300 K, 750 K, 950 K, and 1150 K, achieving deviations within 20% of simulation values. The RF model demonstrates strong predictive capabilities, with correlation coefficients of 0.96, 0.96, 0.94, and 0.98 at the respective temperatures. In contrast, the CNN model shows correlation coefficients of 0.92, 0.99, 0.99, and 0.99. The results of this investigation show that both models are capable of accurately predicting creep behavior. As compared to the CNN model, which performs better at higher temperatures and with larger datasets, the RF model works better at lower temperatures and with smaller datasets. These results enhance our understanding of creep properties and improve predictive modeling under varying conditions.

The characteristics of creep deformation and time to failure of deep hard rock are important for predict time-dependent disasters. Based on the short-term compression and long-term single-stage creep tests under true triaxial stresses, the characteristics of creep deformation and time to failure of Beishan granite subjected to different intermediate principal stress ((sigma _{2})) and deviatoric stress ((sigma _{1})-(sigma _{3})) were studied. The prediction formula of time to failure was established for hard rock, considering the effect of (sigma _{2}). The test results show that the time to failure of rock samples increases with the decrease of the stress-strength ratio (SSR = ((sigma _{1})-(sigma _{3}))/((sigma _{mathrm{p}})-(sigma _{3}))) under the same (sigma _{2}) and (sigma _{3}) conditions. In addition, the steady creep rate of rock sample is affected by the stress-strength ratio of the over-stress ((Delta)SSR = ((sigma _{1})-(sigma )_cd)/((sigma _{mathrm{p}})-(sigma _{3}))). With the increase of the (Delta )SSR, the steady creep rate of rock samples increases. With the increase of (sigma _{2}), the (Delta )SSR of rock samples decreases under the same SSR, therefore, high (sigma _{2}) increases the time to failure of rock samples. Based on the scientific understanding of the characteristics of small deformation and time to failure of Beishan granite, a 3D Nonlinear Creep Model of Beishan Granite under true triaxial stress is proposed. The model can reflect the viscoelastic-plastic characteristic and damage-accelerated creep process of Beishan granite under true triaxial stress. The applicability of the proposed model is verified by comparing with the creep test data.

The development of a robust constitutive model to accurately describe the creep behavior of rock is critical for predicting the time-dependent performance of rock engineering structures. To capture the instantaneous deformation of sandstone post-loading, an elastoplastic component that accounts for the compaction of internal microdefects was formulated. Additionally, a viscoelastic component incorporating a creep initiation stress threshold was proposed based on the Kelvin model, whereas a viscoplastic component was defined with dual stress and strain thresholds. These elements were integrated using a combination element method to develop a nonlinear visco-elasto-plastic (NVEP) model. The model creep equations were derived via Laplace transformation. Subsequently, uniaxial and triaxial creep experiments were conducted to determine the deformation characteristics, creep initiation stress threshold, and long-term strength (LTS) of sandstone. A systematic approach for determining the creep parameters of the NVEP model was also implemented. Validation through experimental results confirmed that the NVEP model provides a detailed and accurate representation of each creep phase, effectively capturing the deformation behavior of sandstone under varying stress conditions.

The effect of time-delayed stress response, typical for viscoelastic materials, on the evolution of damage in porous soft materials and fiber-reinforced soft-matrix composites is studied by employing the material-sink gradual damage evolution theory and the micromechanical finite strain high-fidelity generalized method of cells (HFGMC). In the material-sink approach, damage and crack locations are not postulated in advance, but are instead predicted by the solution of a two-way coupled system of mechanistically derived differential equations, which include the intact-material balance law, in addition to stress equilibrium. The viscoelastic response is based on a rheological model of the generalized Maxwell type, typical for biological tissues. The viscoelastic constitutive relation is generalized to incorporate evolving damage, resulting in loading-rate sensitive time-dependent response. The finite strain HFGMC micromechanics analyzes composite materials that possess periodic microstructure and are comprised of constituents characterized by complex response, with a viscous part, a hyperelastic part and a degradation part, described by a phase-field like approach, albeit derived mechanistically. In the framework of HFGMC micromechanics, the repeating unit cell of the periodic composite is divided into numerous subcells. The resulting coupled system of equations is enforced in the subcell in strong form in the volume-averaged sense and the internal (continuity) and global (periodic) boundary conditions are imposed in the surface-averaged sense. Subcell equilibrium is algorithmically attained prior to fields continuity. Applications are presented for the prediction of the stress response and damage evolution history in porous soft viscoelastic materials and fiber-reinforced viscoelastic composites.

Advanced technological applications of hybrid nanofluid flow over a Riga surface are vital because of their diversified physical properties. In particular, there are applications like lubrication processes and aerospace engineering, and the combined effect of more than one nanoparticle with various surface conditions affecting the flow properties is important. The melting heat conditions, along with the role of thermal radiation, viscous dissipation, and nonuniform heat source/sink for the time-dependent flow hybrid nanofluid over a Riga surface, are considered in this article. Along with the melting heat surface condition, the impact of velocity slip overshoots the flow phenomena. The contributing factors embedded within the system with their dimensional form are distorted into their corresponding dimensionless form by the utility of suitable similarity functions. Afterward, numerical methodology is employed to handle the set of equations. In particular, “shooting-based Runge-Kutta method” is proposed to solve the set transformed equations. The significant properties of various constraints are presented graphically, followed by the validation with earlier studies in particular cases. The key conclusions of the suggested study are as follows: the heat transfer rate is influenced by the squeezing parameter and growth of the Eckert number. In each of these scenarios, hybrid nanofluids again favor higher heat transfer rates.

This study examines the hydrothermal characteristics of hybrid nanofluid flow over a sheet in the presence of thermal radiation, chemical reaction, and waste discharge concentration to develop effective waste treatment and pollution control methods. The partial differential equations (PDEs) governing the conservation of mass, momentum, energy, and concentration, which are nonlinear, are transformed into ordinary differential equations (ODEs) using similarity transformations. The next stage in the process is to solve these differential equations using the bvp4c technique available in MATLAB. The study thoroughly explores several nondimensional parameters, including suction/blowing, Darcy number, stretching/shrinking parameter, local pollutant external source parameter, and chemical reaction parameter, visually illustrating their impacts on flow patterns, thermal distribution, and concentration profiles. The scrutiny focuses on key engineering parameters such as skin friction coefficient, heat transfer rate, and mass transfer rate, supported by tabular data that enhances the quantitative evaluation of these parameters. It is found that the velocity of hybrid nanofluid upsurges with the increment in the stretching/shrinking parameter and Darcy number. Also, results obtained reveal that the concentration profiles experience an upward shift with an increase in unsteadiness parameter and local pollutant external source parameter. Moreover, the Sherwood number decreases by 10.65% as the local pollutant external source parameter, ranging from 0.03 to 0.09, is increased.

To investigate the mechanical properties and energy evolution characteristics of freeze-thawed (F-T) red sandstone subjected to repeated impact loads, a series of repeated impacts were conducted on F-T red sandstone specimens using a split Hopkinson pressure bar (SHPB) device. The results demonstrate that with an increase in F-T cycle numbers, there is a continuous decrease in P-wave velocity accompanied by an increase in porosity and the number of cracks, leading to significant alterations in the microstructure. Both peak stress and modulus of elasticity show negative correlations with both the repeated impact times and F-T cycle numbers, whereas the peak strain and average strain rate exhibit positive correlations with these parameters. Moreover, the absorption energy per unit volume increases with both impact times and F-T cycle numbers, whereas the cumulative absorption energy per unit volume follows a linear increment trend. The established dynamic constitutive model can accurately describe the dynamic stress–strain characteristics of specimens under the repeated impact, demonstrating its high precision in forecasting. Furthermore, the observed failure mode of the specimen was characterized by tensile behavior, with a transition from intergranular fractures to transgranular fractures evident in the microcracks.

In concrete engineering, high temperatures at varying heating rates significantly affect the stability of concrete structures. In this paper, the dynamic tensile characteristics were investigated on concrete specimens subjected to heating rates ranging from 2 to 40 °C/min, using the digital image correlation (DIC) method. The results reveal a critical heating rate threshold, between 5 and 10 °C/min, which marks a shift in the influence of heating rates on both physical and dynamic tensile properties. Below this threshold, changes are minimal, but beyond it, significant effects are observed. As the heating rate increases, longitudinal wave velocity, density, and mass decrease, while porosity increases. Both wave velocity and dynamic tensile strength exhibit a linear decline with increasing heating rates, whereas porosity increases linearly. Additionally, when the heating rate surpasses the threshold, the angle between the failure surface and the loading bar increases, and the maximum principal strain in the direction perpendicular to the loading direction, measured on the specimen’s plane, decreases. Initial failure occurs at the location of highest strain, typically along the central axis of the specimen. These findings suggest that rapid heating should be avoided in concrete engineering to maintain structural integrity. However, rapid heating could be used to break and reuse concrete materials.

The study of fluid flow and heat transfer within a rectangular frame domain has diverse applications across various engineering fields, including energy and power, cooling technology, and nuclear reactors. Motivated by these applications, the current research examines the steady incompressible flow of two different mononanofluids: copper/ethylene glycol–water and titanium dioxide/ethylene glycol–water, within a rectangular frame. The dynamics of the flow, influenced by magnetohydrodynamics (MHD) effects and thermal radiation, are presented. The analysis includes the effects of suction and dual stretching behavior. Additionally, statistical analysis has been conducted to highlight skin-friction characteristics. The dimensionless system of equations has been solved numerically with the help of a numerical shooting scheme. Additionally, experimental design (response surface methodology) and sensitivity are performed for skin frictions. The rheological effects of the relevant parameters against subjective fields are analyzed through graphical representation.