Mechanics of Time-Dependent Materials最新文献

Polymer coatings with enhanced mechanical properties and deformation behavior, as well as energy dissipation capacity, have attracted increasing attention for broad functional applications. This work investigates the role of winding angles and diameter ratios on the tensile properties, damage behavior, and spatial Poisson’s ratio distribution of helical auxetic yarns (HAYs) and their polyurea-based composites. Optimal mechanical performance was observed for HAYs with a 5° winding angle and a 9:1 diameter ratio, resulting in a 1.6–2.4 fold increase in fracture energy and a maximum negative Poisson’s ratio of −11.18. When embedded in polyurea, HAYs increased the composite’s tensile strength by 1.50–2.46 times and energy dissipation by 2.65 times compared to pure polyurea. The composites also exhibited a significant negative Poisson’s ratio of −7.75. The deformation behavior was characterized by using digital speckle correlation method (DSCM) to determine strain and displacement fields in the elastic and plastic regimes. These findings establish a quantitative relationship between HAYs structural parameters and the mechanical response of such composite coatings.

Highly cross-linked epoxy resins are ubiquitous in high-performance structural applications, particularly when used as matrices for fibre-reinforced composites. The optimisation of composites requires a quantitative and predictive description of the mechanical behaviour of the matrix. To explore master trends in the mechanical response as well as to guide first-order modelling, the complete stress-strain response of six epoxies is characterised under uniaxial compression up to large strain and fracture. A number of characteristic properties are analysed and rationalised mainly through establishing partly physical and partly empirical relationships with the ratio (T / T_{g}) of test over glass transition temperature. Among others, an enhanced Eyring-type model is identified for the yield stress and found valid for a wide range of temperatures and strain rates below (T_{g}). The yield stress of all six epoxies is related to (T_{g}) within 10% error without any other adjustment of parameters. A similar relationship for the modulus with (T / T_{g}) also accounts for strain rate. Lastly, the failure stress and strain are found to also correlate to (T / T_{g}) in subgroups of resins with similar molecular structure, while the re-hardening modulus does not.

The present study aims to implement regression modeling using Response Surface Methodology (RSM) for analyzing the heat transfer and prediction of skin-friction coefficients of a magnetohydrodynamic (MHD) nanofluid flow across a vertical wedge along with its applications in data prediction and response optimization. The differential equations arising after the similarity transformations were solved using bvp4c in MATLAB. The importance of the present study lies in its application in forging of hot exhaust-valve heads, manufacture of water heaters, extrusion processes, cooling processes, turbine blades, and medical industries, etc. Some of the insightful results noted were increasing heat-transfer rates by (0.74%) for nonaggregation modeling and by (0.78%) for aggregated model with increase in the magnetic parameter from 0.2 to 0.8 followed by the increase in skin-friction coefficient for transition from nonaggregation to the aggregation model. Augmented velocity profiles by (2.08%) were observed for the nonaggregation as compared to the aggregation model. A face-centerd central composite design was implemented in RSM for determining the Analysis of Variance (ANOVA) for our results using a quadratic fitting model with (R_{1}^{2}=Adj R_{1}^{2}=100%) for both the aggregation and nonaggregation models. The velocity-ratio parameter showed negative sensitivity to the response parameter. (Pred R_{1}^{2}=99.99%) represented very high predictability rate for new observations. The predicted values recorded a maximum absolute error of the order (10^{-4}) when compared to the actual numerical data along with a desirability of (100%) to attain the extremum values for both models.

In deep underground engineering, the synergistic effects of dike interfaces and initial damage significantly influence the brittle-fracture characteristics and rockburst tendency of rock masses. To investigate this phenomenon, a multiscale experimental approach was adopted to characterize the mesostructural evolution of veined granite specimens with varying levels of damage, particularly focusing on the coupled mechanisms governing their brittle-failure behavior and susceptibility to rockbursts. The research results indicate that the presence of rock veins increases the complexity of the pore structure, causing more large pores. The orientations of weak planes differ across the rock-vein interface, mica flake structure, and quartz-particle cementation zone. Granite with rock-vein interface-like characteristics exhibits a staircase increase in the rate of AE energy before reaching its peak value, featuring progressive failure. Specimens with rock veins generate more AE events and show more pronounced characteristics of concentrated energy release. As the initial damage intensifies, the cumulative ring-down count (RDC) and the rate of release of AE energy show a more significant staircase growth, with the values reducing successively, suggesting that initial damage weakens the brittle-failure characteristics of the rock. When the initial damage value (D leq ) 0.33, the rock is at risk of rockbursts, but the intensity thereof is lower than that under undamaged conditions. When (D geq ) 0.41, the rock no longer meets the conditions for the occurrence of a rockburst.

To investigate the dynamic mechanical response characteristics of SiC ceramic/ultra-high molecular weight polyethylene (UHMWPE) composite ballistic plates under the high-speed impact of projectiles, this study established a mirrored 3D-DIC high-speed photography system and validated the accuracy of the system. The accuracy verification showed that the average maximum relative errors in the X, Y, and Z directions were only 0.688%. Additionally, ballistic tests were performed using Type 53 7.62 mm enhanced-charge armor-piercing incendiary (API) projectiles impact on the NIJ IV ballistic plates. The maximum bulge height of the ballistic plate obtained from mirrored DIC analysis was compared with side-view high-speed photography results, showing a maximum error of 1.71%. The results revealed that the ballistic plates bulge reached a maximum value of 36.20 mm at 1100 (mu )s. The ballistic plate was divided into four regions, and during impact, fibers were stretched along the orthogonal layup directions. The strain field exhibited an L-shaped distribution in each region, with a peak strain of 0.273 occurring at the corners. The mirrored 3D-DIC system of this study accurately measures the deformation of ballistic plates under high velocity impact of projectiles and provides a safer test method for measuring material strains under high speed impact conditions.

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.