Mechanics of Time-Dependent Materials最新文献

This study investigates the characterization and mechanical performance of Stone Mastic Asphalt (SMA) mixtures modified with two types of polymers: styrene–butadiene–styrene (SBS) and high-molecular-weight polyethylene (PE). Neat asphalt cement PG 64-16 was modified using a higher content of SBS and PE at concentrations of 6%, 7%, and 8% by weight of asphalt through the dry blending method to produce Highly Modified Asphalts (HiMA). The physical and rheological properties of the modified binders were evaluated using penetration, softening point, rotational viscosity, and dynamic shear rheometer (DSR) tests. Also, their phase compatibility and morphological changes were evaluated using the storage stability testing and scanning electron microscopy (SEM) analysis. The mechanical performance of the corresponding SMA mixtures was assessed through Marshall stability and flow, moisture susceptibility, crack tolerance index (CT-index), resilient modulus, and rutting resistance tests. Also, a mechanistic durability analysis was conducted using the KENLAYER software. Results indicated that both polymers enhanced the binder’s stiffness and high-temperature performance, with SBS exhibiting greater overall improvements. SBS-modified binders displayed a relatively low softening point difference ((Delta )T) of 5.1 °C to 5.8 °C, indicating good thermal stability and uniform polymer dispersion. In contrast, PE-modified binders exhibited significantly higher (Delta )T values, reaching 13.5 °C with 8% PE content, indicating a greater tendency toward phase separation. Moreover, Marshall stability improved substantially, increasing by 43% for 8% SBS-modified mixes and 28% for 8% PE-modified mixes compared to the neat SMA mix. Flow number (FN) results indicated enhanced rutting resistance, with FN values increasing by 2.45 times for SBS mixes and 2.1 times for PE mixes at 8% polymer content. Additionally, moisture susceptibility was significantly improved, as evidenced by the tensile strength ratio (TSR) values of 97% with 8% SBS and 92% with 8% PE, compared to 81% for the neat mix. Resilient modules increased notably, with a 38% rise for 8% SBS mixes and a 24% rise for 8% PE mixes, reflecting enhanced stiffness and load-bearing capacity. Also, the CT-index significantly improved, reaching values of 154 for the 8% SBS mix and 127 for the 8% PE-modified mix, compared to 86 for the neat mix, indicating enhanced resistance to cracking. Finally, both polymer-modified mixes demonstrated improved durability, where the 8% SBS mix exhibited the longest design life (21.66 years) and the highest number of allowable load repetitions (5.42 × 10⁶), followed by 8% PE (13.98 years and 3.50 × 10⁶ repetitions).

The Performance Grading (PG) criterion plays a pivotal role in grading bitumen for various applications, such as trading, road construction, and research and development works. The definition of high PG temperature hinges on the point where the Superpave rutting parameter, G*/sin(delta ), attains a value of 1 kPa. In this study, we present a novel mathematical model developed to accurately predict the high PG temperature of bitumen. To ascertain the PG temperature of the bitumen, we conducted the Original Binder Grading (OBG) test using a rheometer. Leveraging the data obtained from this test, our developed model forecasts the true high PG temperature based on the average value of G*/sin(delta ) measured at 64 °C. Notably, the model yields rapid results within approximately 15 minutes after initiating the OBG test, which effectively reduces test duration and empowers users to manage their work more efficiently. We anticipate that this model will be readily embraced by rheometer manufacturing industries, as it provides a direct and reliable means of determining the bitumen’s high PG temperature. This technological advancement promises to enhance testing procedures, streamline research, and support better decision-making processes across the bitumen industry. However, the model is not validated for polymer-modified binders and should be applied to unmodified binders only.

Rock is a fundamental material in mining engineering, and its creep behavior plays a critical role in determining the long-term stability of roadways. Consequently, investigating the creep constitutive models of rocks with varying brittleness holds significant practical importance. To investigate the evolution law of energy in uniaxial creep of rocks and establish a constitutive model, this study systematically examined the evolution of creep energy and energy distribution in four kinds of rocks—coal, mudstone, white sandstone, and red sandstone—through uniaxial creep-unloading tests. We constructed the fractional derivative damage constitutive models by introducing fractional derivative elements based on energy dissipation damage variables. The findings reveal the following: (1) The elastic strain energy density ((u^{mathrm{e}})) of rocks exhibits a linear decreasing trend with prolonged creep time, indicating a linear attenuation characteristic. (2) A method for calculating rock creep energy was proposed, leveraging the linear attenuation characteristics of (u^{mathrm{e}}). (3) The dissipated strain energy density ((u^{mathrm{d}})) and input strain energy density ((u)) of the four rocks with varying brittleness levels increase over time, and this growth can be partitioned into three stages: decay growth, steady growth, and accelerated growth. (4) As creep time increases, the proportion of (u^{mathrm{d}})/(u) gradually rises, reaching its maximum at the end of accelerated creep. Rocks with higher brittleness exhibit a greater proportion of (u^{mathrm{d}}) at these critical points. (5) A fractional derivative damage constitutive model was successfully developed, with the parameter (alpha ) of the fractional derivative element reflecting the degree of rock brittleness.

As a weak link in engineering structures, the shear mechanical properties of rock joints are crucial for evaluating the stability of rock masses. To investigate the mechanism of shear stress oscillation in regular toothed joints and its relationship with specimen size and material parameters, this study conducted direct shear tests on five wave angles and six dimensions using RDS-200 under different normal stresses. The results show that (1) The peak shear strength of regular tooth-shaped rock-like joints shows a positive linear relationship with normal stress and undulating angle. For fixed-size specimens, increasing the undulating angle enhances both peak strength and pre-peak stiffness. When the sample size increases, the peak strength of the joints with the same undulating angle initially increases and then decreases, while the pre-peak stiffness generally decreases. (2) Shear stress oscillations predominantly occur under low normal stress or small undulating angles. Larger undulating angles reduce the oscillation climbing ratio, interval length, and frequency. (3) Increasing specimen size amplifies the oscillation climbing ratio, interval length, and average amplitude but lowers frequency, while higher normal stresses decrease both the oscillation climbing ratio and the number of oscillations but increase amplitude. The results provide a reference for optimizing the design and stability of rock structure.

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.