Mechanics of Time-Dependent Materials最新文献

This paper aims to model the primary creep regeneration (PCR) phenomenon, which is observed at variable loadings applied during the creep of engineering alloys such as 316H stainless steel, 10% Cr martensitic steel, nickel-based alloy, etc. Since PCR is a multifactorial problem, this research addresses a partial case: deriving relationships between the extent of PCR and the value of plastic strain occurring on reversal loading. Model results are compared with the PCR phenomenon for 316H stainless steel in uniaxial tension/compression for various plastic strains on reversal stresses at equal creep dwell times and zero durations of reversal stress actions.

In this study, a three-dimensional split Hopkinson pressure bar (SHPB) impact numerical model was established through the FDM–DEM coupling method to explore the mesoscopic damage accumulation and dynamic mechanical response of fractured sandstone under freeze–thaw cycles. Based on the volume-expansion theory, a discrete-element model of the phase-change expansion of pore-water–ice was constructed. Combined with the parameter calibration optimized by the genetic algorithm, the damage evolution of the rock during the freeze–thaw process was simulated. The research results show that: (1) The discrete-element simulation results show high consistency with experimental data. Taking the 40-mm rock bridge as an example, the maximum relative errors of peak strength and elastic modulus under different freeze–thaw (FT) cycles are 8.54% and 3.49%, respectively, meeting accuracy requirements. This validates the reliability of the particle expansion model and FT damage analysis method. (2) Under uniaxial compression, rock-bridge length significantly influences the mechanical properties of FT sandstone. Specimens with 50-mm rock bridges exhibit the highest elastic modulus and peak strength. However, FT cycles induce nonlinear degradation in compressive strength. (3) Dynamic impact tests reveal that FT cycles exacerbate rock fragmentation. With increasing impact velocity and FT cycles, strain rate rises, leading to nonlinear attenuation of dynamic strength and decelerated growth of the dynamic increase factor (DIF). The presence of rock bridges further causes multistage evolution characteristics in dynamic stress–strain responses.

Hybrid nanofluids have been utilized in various thermal engineering applications, including heat exchangers, materials science research, and industrial domains like solar trough collectors, food processing, and aerospace engineering. This study’s ultimate objective is to examine a Casson hybrid nanofluid’s hydrodynamic and thermal behavior in a porous medium subjected to a bilinear stretching surface. The effects of thermal radiation, chemical reactions, volumetric heat source/sink, Joule heating, and viscous dissipation are all included in the mathematical model. When a magnetic field with inclination is present, the fluid is electrically conducting. By means of similarity transformations, the governing nonlinear coupled partial differential equations (PDEs) that characterize the flow phenomena are transformed into a system of coupled ordinary differential equations (ODEs). The MATLAB bvp4c solver in conjunction with a shooting technique yields numerical solutions. The outcomes, which show how different dimensionless parameters affect the flow field, temperature distribution, and concentration profiles, are displayed graphically and tabularly. The skin friction coefficient, Sherwood number, and Nusselt number at the stretching surface are among the derived quantities that are calculated and examined. As the Casson parameter rises, the momentum barrier layer becomes thinner. The Lorentz force causes the temperature to exhibit the inverse trend as the magnetic parameter increases, causing a drop in fluid velocity. The chemical reaction parameter and the Schmidt number tend to drop as the concentration profile rises, whereas the Soret effect demonstrates the exact reverse. According to statistical analysis using modified R-squared and R-squared metrics, this model matches the skin friction coefficient exceptionally well, with an average accuracy of 99.87%. The Nusselt number is noticeably more sensitive to thermal radiation and heat sources than the Dufour effect.

The overburden stress and water environment for seepage in mines significantly affect the load-bearing capacity and deformation of gangue backfill materials (GBMs). A self-developed stress–seepage test system for backfill materials was used to conduct creep compression tests on GBMs during loading. Test results show that GBMs with a large particle size are significantly deformed, rotated, and broken, while those with a minute particle size appear to argillize under the combined action of axial stress and seepage pressure. The compressive creep deformation of GBM samples includes instantaneous deformation, attenuated creep deformation, and steady creep deformation. As the axial stress and seepage pressure increase, the instantaneous strain and creep strain of GBMs both enlarge. For instance, at a seepage pressure of 3 MPa, the instantaneous and creep strains of GBMs at axial stress of 10, 15, and 20 MPa are 1.18, 1.26, and 1.30 times as large as those at axial stress of 5 MPa, and 1.20, 1.39, and 1.56 times as large as those at axial stress of 5 MPa, respectively. The instantaneous strain and creep strain constantly increase, while the strain increments both decrease under increasing axial stress and seepage pressure. The seepage pressure degrades the mechanical properties of GBMs, which exhibit significant viscoelastic effects and nonlinear characteristics. Based on the theory of fractional-order calculus, a damaged Abel dashpot is constructed to optimize the conventional Burgers model, thus establishing a fractional-order creep constitutive model of GBMs under seepage and stress action to describe the creep properties. The model parameters were identified and verified using the creep compression test results during step-wise loading under the combined actions of seepage and stress. The parameter identification accuracy, as measured by (R^{2}), exceeded 0.997, indicating that the data were well-fitted.

Researchers have been studying self-healing in concrete for many years as a potential solution for self-repairing concrete structures. Bacterial concrete is one of the concrete types with self-healing characteristics. However, introducing and maintaining the required environment for bacteria is a challenging task. This study used biochar from the agricultural and food waste industries as an immobilizing agent for self-healing concrete containing Bacillus subtilis bacteria. As the self-healing due to bacteria is an alkaliphilic reaction, three cement types were used to investigate the self-healing characteristics. Three different methods, which included compressive strength recovery (M1), damage cycles using ultrasonic pulse velocity (M2), and the semicircular bending (SCB) test (M3), were used to quantify self-healing potential. In M1, control and bacterial concrete were loaded to a certain damage level, and self-healing was quantified based on strength recovery up to 84 days, while in M2, UPV was measured until the specimens were found to be intact. In M3, self-healing was quantified for concrete specimens subjected to tensile load. The M1 method indicated that ordinary Portland cement (OPC) exhibited on average 56.52% self-healing due to bacterial activity, while Portland Pozzolana and slag cement exhibited 20.82% and 49.67%, respectively. Further, the M2 method indicated that the degree of recovery in bacterial concrete was better than that of the control concrete. In addition, the M3 method, which is a first-of-its-kind test to quantify self-healing, showed that bacterial concrete was able to sustain a higher number of loading cycles compared to control specimens. The statistical analysis also indicated a significant effect of treatment and cement type on the self-healing potential.

Oxidative aging increases the stiffness and brittleness of asphalt pavements, reducing resistance to fracture and fatigue cracking. This study introduces a coupled aging–viscoelastic–viscodamage constitutive model to capture the effects of oxidative aging on the mechanical behavior of asphalt pavements. The model integrates oxygen diffusion, aging time, and temperature into a state variable that modifies viscoelastic compliance, relaxation times, and damage properties. Using a continuum damage mechanics framework, the model effectively couples aging, fatigue damage, and viscoelastic behavior. The proposed model was implemented in a finite-element framework to simulate a 2D axisymmetric asphalt pavement subjected to mechanical pulse loading and oxygen diffusion over ten years. Results show that the simulated unaged pavement exhibits a bottom-to-top cracking pattern, while surface-down cracking dominates in the aged pavement due to oxygen-induced material degradation. Validation against laboratory data demonstrates the model’s ability to predict fatigue life, stiffness evolution, and damage density under various aging conditions. The findings highlight the importance of incorporating oxidative aging effects in pavement performance models to improve design and maintenance strategies for long-term durability.

Uniaxial tensile creep tests were conducted at various stress levels to investigate the creep properties of hydroxy-terminated polybutadiene (HTPB) propellant. Due to the limitations of the classical time-hardening model and the Burgers model in predicting the nonlinear creep behavior of HTPB propellant, a new creep damage model was developed. This model combines linear viscoelasticity theory with continuum damage theory. Utilizing the user material subroutine UMAT provided by ABAQUS for the secondary development of the models, simulation calculations were performed on dumbbell specimens. A comparative analysis was conducted with the results from the time-hardening model and the Burgers model, and the simulation results were validated through experimental testing. The findings indicate that HTPB propellant exhibits a distinct three-stage process characterized by decay creep, stable creep, and accelerated creep. The creep damage model effectively describes the accelerated creep stage, with the simulation results demonstrating an error margin of less than 5%. This confirms the feasibility of the creep damage model for creep analysis of HTPB propellant.

This research aims to explore the creep behavior of the AZ31B alloy under various temperature and stress conditions using the impression technique. The experimental studies were carried out at temperatures ranging from 150 °C to 250 °C and stress levels ranging from 121 to 401 MPa. The results showed that the stress exponent and activation energy of this alloy varied depending on the test conditions, resulting in different creep mechanisms. The stress exponents obtained at high-stress values were 7.2, 4.44, 9.59, and 11.35 at 150, 175, 200, and 250 °C, respectively. In low-stress regimes, the values were 1.12, 3.25, 4.77, and 4.91, respectively. Results highlighted that at lower stress levels, grain boundary diffusion, dislocation viscous glide, and dislocation climb were the dominant creep mechanisms, while at high stress levels, dislocation climb and a combination of dislocation climb, glide, and cross-slip mechanisms governed the material’s deformation behavior. The activation energy was determined to be 87.61 kJ/mol at low-stress conditions, indicating grain boundary diffusion and pipe diffusion as the rate-controlling mechanisms. Under high-stress conditions, it reached 103.7 kJ/mol, suggesting pipe diffusion or Mg lattice self-diffusion. The upper-bound analysis results were also used to establish the correlation between creep properties obtained from impression ((P) and (dot{U}), which are punch pressure and velocity, respectively) and conventional ((sigma ) and (dot{varepsilon } ), representing stress and strain rate, respectively) tests. Conversion factors of (P)/(sigma ) = 3.72 and (dot{varepsilon } )/(dot{U}) = 2.23 were calculated to relate these parameters. These findings provide valuable insights for guiding design decisions in the industrial applications of magnesium alloys.

This paper aims to investigate the mathematical modeling of Casson hybrid nanofluid flow, which uses pure blood as the base fluid and incorporates the impacts of titanium dioxide (TiO₂) and silver (Ag) nanoparticles on a Riga plate that helps to stabilize and disperse drug molecules efficiently through a drug-delivery system. The bottom plate is assumed to be implemented with thermal-source effects where the fluid flow has time-dependent attributes. The squeezing characteristics are considered to be induced on the surface of the upper Riga plate that is moving with some speed. A set of suitable variables are incorporated to convert modeled equations to dimensionless form. The problem was initially solved through homotopy analysis method (HAM) and then the artificial neural network (ANN) is used on the basis of HAM. Medical diagnostics could benefit from this model, particularly in the process of drug delivery and the flow dynamics of the microcirculatory mechanism. It has been observed in this study that, with growth in the modified Hartman number, as well as the volumetric fraction of titanium dioxide nanoparticles, the velocity distribution was retarded for both Ag/blood nanofluid and Ag+TiO_2/ blood hybrid nanofluid. For an increase in the volumetric fraction of silver nanoparticles and thermal-source factor there is a corresponding progression in thermal distribution both for Ag/blood nanofluid and Ag+TiO_2/ blood hybrid nanofluid. The heat-transfer rate determines the sustainability of drug delivery by ensuring its safe administration. It is observed that using the 5% nanoparticle volume fraction the obtained results show that a 10.06% increase has been achieved using the hybrid nanofluid in comparison with Ag nanofluid that has increased the heat-transfer rate up to 7.79%. With an increase in the squeezing factor (S) such that (S = 0.0, - 0.2, - 0.4, - 0.6, - 0.8, - 1.0, - 1.2) there is a reduction in the thermal distribution. The optimal model performance is observed at epochs 211, 179, 115, 181, and 168, as indicated in the data displayed at these stated epochs throughout the training. For all five scenarios gradient values are linked at (9.94 times 10^{ - 8}), (9.88 times 10^{ - 9}), (9.90 times 10^{ - 8}), (9.90 times 10^{ - 8}), and (9.93 times 10^{ - 8}). Medical diagnostics could benefit from this model, particularly in the process of drug delivery and the flow dynamics of the microcirculatory mechanism.

Discrepancies between laboratory-based predictions and field performance of asphalt mixes in terms of fatigue life can be reduced by taking into account the self-healing characteristics of asphalt in experimental protocols. In this study, an unmodified binder and a polymer-modified binder are used to compare their relative performance in terms of healing both in the presence and absence of a warm mix additive (WMA). During the test, rest periods of varied durations (10, 15, and 30 minutes) are introduced at 25%, 50%, and 75% of damage levels prior to reaching failure to examine their influence on the further evolution of damage. The addition of the WMA resulted in an improved healing index of both unmodified and modified binders at all the damage levels pre-failure. The results suggest the potential of WMA additives to enhance the healing of bituminous mixes, in addition to their established benefits in lowering temperatures.