Mechanics of Time-Dependent Materials最新文献

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.

Due to the unlimited usage and involvement of nanoparticles, researchers got much interest in their study. This research discusses the utilization of a hybrid nanofluid model mixed in water-based liquid in a rotating disk. The flow is considered with the involvement of Hall and ion slip effects in a rotating disk. Thermal transport is discussed by engaging quadratic thermal radiation phenomenon along with Joule heating. The boundary layer equations are generated in the form of coupled PDEs and are converted into a set of ODEs by engaging similarity variables. The derived converted ODEs are highly nonlinear and have been solved numerically via the finite element method. The involvement of numerous emerging parameters against velocity, temperature and concentration is plotted and tabulated and their insight physics is discussed in detail. The obtained results confirm the reliability of finite element scheme.

The study of nanofluids using a stretchy disc has lately gained importance in fluid mechanics. This work investigates the impacts of the Cattaneo-Christov model, heat radiation, and melting events on TiO₂–Al₂O₃/water and Ag–MoS₂/water hybrid nanofluids over a disc. The results show that hybrid nanofluids greatly increase the thermal conductivity and heat transfer capabilities of base fluids. Water-based hybrid nanofluids are used in military applications such as solar thermal energy, heating pumps, heat exchanger devices, ships, air cleaners, the automotive industry, electric chillers, nuclear-powered systems, turbines, and equipment. To explain the flow of hybrid nanofluids, the two-dimensional nonlinear governing equations, which include the continuity, momentum, and heat transfer rate equations, are expressed in a non-dimensional form. The bvp4c solver firing technique in MATLAB is used to solve these non-dimensional equations and investigate the physical effects of various parameters on velocity and temperature profiles. Increasing the magnetic parameter and nanoparticle volume fraction substantially affects the velocity profile in opposing flow. Greater values of the thermal radiation and heat source-sink parameters result in a greater temperature profile. In addition, raising the thermal relaxation and melting parameters improves the temperature profile. The study’s findings may be utilized in various sectors, including drainage, chemical engineering, solar panels, solar absorption and filtration, groundwater hydrology, solar cells, and other sheet flow applications.