Mechanics of Time-Dependent Materials最新文献

Polymer microfibers are ubiquitous in modern industry, with applications ranging from textiles and filtration to environmental protection and healthcare. However, their widespread use also contributes significantly to microplastic pollution. Cigarette filters, composed of cellulose acetate microfibers (CA-μFs), are a particularly concerning source, with an estimated 4 trillion or more smoked cigarettes littered annually, presenting an opportune material testbed for mechanical characterization. This study investigates the time-dependent mechanical behavior of CA-μFs extracted from pristine and smoked cigarette filters, characterizing their creep and recovery responses under constant stress and temperature conditions. Specifically, dynamic mechanical analysis (DMA) was employed to measure the viscoelastic response at 2 MPa (within the elastic regime) and 4 MPa (after the elastic–plastic transition), as well as at 30 °C, 40 °C, and 50 °C (representing a range of environmentally relevant temperatures). A six-parameter generalized viscoelastic model was fitted to the creep-strain data, while a Prony series representation was used to capture the shear creep modulus. Scanning electron microscopy (SEM) was used to characterize the morphology of the CA-μFs before processing, after processing, and posttesting, allowing for observation of individual microfiber responses under different loading conditions. The resolved deformed geometries of CA-μFs obtained from finite-element analysis (FEA) coincided with the physically observed deformation characteristics, further elucidating the mechanical response. This research establishes a fundamental understanding of CA-μF behavior, isolating the effects of temperature, stress, and smoking on the creep and recovery properties. This work lays the groundwork for future studies to leverage the mechanical response of CA-μFs for upcycling.

Upon contact with seawater, concrete undergoes degradation caused by the diffusion of aggressive ions into its porous network and their reaction with cement hydration products. In addition, time-dependent deformations occur resulting from long-term operational use and mechanical loading. The analysis of these coupled chemomechanical phenomena is complex and requires the development of innovative approaches. A micromechanical model has been developed to analyze these phenomena at the microscopic scale. A multiscale approach has been performed for the evaluation of their effects in mortars. Creep loading has opposite effects compared to chemical degradation due to seawater ingress and the evolution of cement hydration at early ages. After 3 days of loading, the model can reproduce the experimental measurements as the chemical reactions occur slowly, but differences are larger during the first 3 days. The contradictory effects of the formed phases balance each other out, resulting in similar creep behavior in tap water and seawater. This indicates that to limit the failure risk of offshore concrete structures it is necessary to reduce the loading at the early stages during the first days of seawater attack.

Civil construction underutilizes non-pozzolanic industrial fine powder waste such as stone dust powder (SDP), marble powder (MP), and granite powder (GP) in concrete manufacturing. These materials, which are often disposed of in landfills, represent substantial environmental dangers. Despite their abundance, their use in concrete remains restricted. A major factor for this underutilization is a lack of understanding of their potential advantages and effective application strategies. This study looks at the usage of these fine powders as a fourth component in concrete using two approaches: cumulative replacement of both fine and coarse aggregates and sand replacement. With 400 kg/m³ of cement, 0.37 w/c ratio, and up to 300 kg/m³ of fine powder, a total of 38 sets of mix designs were prepared. The mechanical, durability, and fresh properties of concrete made with these waste materials were assessed. Concrete incorporating fine powders retained compressive strength while significantly improving durability. Water penetration depth decreased by 13.4–22% at 100 kg/m³ and 54.5–63.1% at 300 kg/m³ for mixes with M-sand, and by 12.1–24.4% and 52.3–60.2% respectively for river sand mixes, using SDP, MP, and GP powders in both CR and SR types indicating enhanced resistance to water permeability. Despite a slight increase in admixture demand, it remained marginal compared to the control. Cost analysis showed up to a 2.5% reduction in concrete cost alongside conservation of natural resources. The use of fine powders thus offers a sustainable approach, enhancing performance while promoting eco-friendly construction through the utilization of non-pozzolanic industrial waste.

To enhance the long-term strength assessments of water-bearing rocks under stress relaxation conditions by stress relaxation tests at different water content, pore-water pressure, and confining pressure, we delve deeply into the stress relaxation characteristics of sandstone, thereby improving the method for determining long-term strength. The results indicate that: The rock’s modulus of elasticity decreases while the Poisson’s ratio increases as water content and pore-water pressure increase. The characteristics of rock stress relaxation become pronounced during the phase of crack extension. Furthermore, an increase in confining pressure, pore-water pressure, and water content serves to intensify the degree of stress relaxation. In investigating the laws governing radial deformation during rock stress relaxation, it is more precise and scientific to employ the traits of radial strain variations as criteria for demarcating stress relaxation phases. The radial deformation can also be used to distinguish rock’s pre-peak or post-peak states. An improved method for determining the long-term strength of rocks by investigating the deformation inter-conversion characteristics at different stages of rock stress relaxation, achieving an accuracy of 10 percent. Understanding stress relaxation characteristics and the laws governing long-term strength under diverse water content conditions offers different insights to ensure the long-term safety and stability of engineering projects.

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.