Mechanics of Time-Dependent Materials最新文献

The extensive use of materials in the construction industry imposes risks of depleting natural aggregates and increased carbon emissions, thereby motivating the search for sustainable alternatives. This work investigates the influence of supplementary cementitious materials (SCMs), including fly ash (FA), silica fume (SF), and ground-granulated blast-furnace slag (GBFS) on the durability and mechanical behavior of recycled heterogeneous aggregate concrete (RAC) subjected to sulfate erosion and dry–wet cycles (SEDWCs). Durability performance was evaluated through observation of surface appearance and mass variation, and digital image correlation (DIC) was used to monitor crack evolution and failure modes under uniaxial compression. Microscale mechanisms were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP). Incorporating SCMs mitigated surface deterioration, stabilized mass change, and enhanced compressive strength. DIC observations revealed delayed crack initiation and less severe damage in SCM-modified RAC, with failure modes shifting from predominant shear to combined shear–cohesion failure. Microstructural analyses confirmed that SCMs densified the cement matrix and refined the interfacial transition zone (ITZ). Among the SCMs, silica fume exhibited the strongest resistance to SEDWCs, while fly ash and GBFS also improved durability compared with RAC without SCMs. These results demonstrate that the combined use of recycled aggregates and supplementary cementitious materials can significantly enhance the long-term performance of concrete in sulfate-rich cyclic environments, advancing the development of sustainable construction materials.

Enhancing the melting rate of Phase Change Materials (PCMs) is critical for improving the efficiency of Thermal Energy Storage (TES) systems. Although optimized fin geometries have been widely studied, the combined role of nanoparticle-enhanced molten-salt PCMs with fins has received limited attention. A numerical investigation is conducted on the melting behavior of molten salt PCMs incorporated with Cu and TiO₂ nanoparticles in a cylindrical TES unit featuring three fin geometries: longitudinal, Y-shaped, and tuning fork-shaped. Simulations are performed using ANSYS Fluent software and validated against published experimental data. The primary performance indicators, including the temperature distribution, velocity fields and liquid fraction, are analyzed. At a comparable melt fraction (∼97%), the addition of nanoparticles significantly reduced the melting time across all fin configurations, from 345 s to 192 s for longitudinal fins, from 244 s to 137 s for Y-shaped fins and from 202 s to 114 s for fork-shaped fins. These results demonstrate that nanoparticle integration accelerates the melting process by approximately 44-50%, with performance strongly dependent on the fin design. These findings indicate the synergistic benefits of fin geometry and nanoparticle additives, which provide practical guidelines for the design of high-efficiency TES devices.

Effective heat transfer is crucial for engineering applications such as heat exchangers, electronics cooling, and HVAC systems. Moreover, this paper provides an extensive examination of the physical properties of viscoelastic liquids that are emerging in relation to important profiles, considering the copper oxide (left ( CuO right )), silver (left ( AgO right )), and zirconium dioxide (left ( Zr O_{2} right )), immersed in the base fluid ethylene glycol (EG). Viscous dissipation, porosity, and joule heating effects are introduced in the formulation of the problem. The differential equations are dimensionless after the mathematical formulations via a non-similarity conversion. The local non-similarity method transforms non-similar PDEs into ODEs, which are then solved numerically using MATLAB’s bvp4c. Important physical parameters are given in tabular form, such as skin friction and Nusselt values. The temperature distribution has been seen to increase when the viscoelastic parameter (second-grade fluid) increases. It is discovered that the findings converge more quickly and are validated for limited circumstances. Here are some key applications of the present work: industrial cooling systems, polymer processing, chemical engineering, biomedical engineering, heat exchangers, energy systems, cooling of microelectronic devices.

Negative stiffness honeycombs are energy absorbers that absorb energy by transitioning from one buckling mode to another, and their snap-through behaviour in cells. They have a fundamental property as an energy absorber; in this type of absorber, negative stiffness causes reversibility after impact. In this study, the effect of negative stiffness honeycomb material in increasing energy absorption is investigated experimentally and numerically. Quasi-static tests are performed on negative stiffness honeycombs made of polyamide 11 (PA11) and polyamide 12 (PA12). Then, the finite element (FE) model of the structure is simulated under quasi-static compression. The FE model requires the nonlinear elastic and viscoelastic properties of the materials used to make the honeycombs. For this purpose, tensile and stress relaxation tests are performed. The Prony series coefficients for polyamide materials 11 and 12 are extracted and used in the FE model. Next, the energy absorption performance of negative stiffness honeycombs of PA11 and PA12 is compared experimentally and numerically. The comparison shows that the energy absorption per unit mass (SEA) for a negative stiffness honeycomb made of PA11 is 1.7 times higher in the experimental data and 1.62 times higher in the FE result than negative stiffness honeycomb made of PA12. Other fundamental parameters of energy absorption also confirm the higher efficiency of negative stiffness honeycombs made of PA11. This study provides a unique contribution by integrating experimentally determined nonlinear viscoelastic properties into the FE model and offering a comparison of energy absorption performance between PA11 and PA12 in negative stiffness honeycombs.

Fine recycled concrete aggregate (RCA) exhibits inferior bonding properties with cement due to its high water absorption and porosity. Incorporating fine RCAs in cementitious materials leads to the significant reduction in dynamic mechanical performance. To address this issue, a compound inspired by tea stains, tannic acid (TA), is used to treat the fine RCAs. The results suggest that the width of the interface transition zone (ITZ) between fine RCA and the new matrix is significantly reduced after this treatment, indicating the improvement in bonding properties. Dynamic compression tests are conducted to examine the impact resistance performance of cement mortar containing fine RCAs through employing the Split Hopkinson Pressure Bar (SHPB) apparatus. When subjected to impact loads, mortars with treated fine RCAs indicate higher dynamic compressive strength and enhanced completeness. The dynamic compressive strength and total energy absorption exhibit the exponential positive correlation with the strain rate. The strain rate effect is more pronounced when the strain rate is below 100 s⁻¹. Importantly, mortars with treated fine RCAs manifest superior total energy absorption, enabling them to absorb and dissipate more impact energy. The mortar containing fine RCAs treated with 0.5%TA reveals excellent impact resistance performance, surpassing even that of the cement mortar with natural fine aggregates. Moreover, 0.5%TA group shows better economic benefits than the plain mortar, indicating that the TA treatment method has good application prospects.

The Small Amplitude Oscillatory Strain (SAOS) testing is commonly used to measure linear viscoelastic functions such as elastic moduli, which are denoted respectively (G^{*}(iomega )) and (E^{*}(iomega )) in simple shear and tension-compression. Beyond the linear regime, Large Amplitude Oscillatory Strain (LAOS) is a widely used experimental technique to investigate nonlinear phenomena. From mathematical standpoint, Fourier transform and Fourier series are used to handle SAOS and LAOS data. In general, SAOS-tests do not account a strain jump discontinuity to make easy measurement data processing. Thereby, we focus on the influence of a strain jump discontinuity (or not) on the response of the Cauchy stress. First, we investigate the problem of strain discontinuity (or not) within framework of one-dimensional isotropic linear viscoelasticity by considering both the integral approach and the fractional Maxwell constitutive model. Second, we assume that, the Large Amplitude Oscillations Strain (LAOS) is equivalent to small oscillations around a static pre-deformation. It means that, the jump at the origin is shifted to minus infinity in the time scale. Therefore, we investigate the first and third harmonics within framework of the nonlinear Kelvin-Voigt model. We conclude with some future perspectives for the present work.

For crystalline polymers used as a matrix polymer at fiber-reinforced thermo-plastics, effects of crystallinity of polypropylene on creep characteristics were investigated. Measurements taken using DSC, DMA, SAXS, and WAXS elucidated crystallization behavior and crystallinity along with changes in the annealing temperature and annealing time. Although crystallinity increases with the annealing temperature and annealing time, a relation was found between the annealing temperature and time: crystallinity can be shifted by a shift factor. The time–temperature crystallinity superposition holds for crystalline polymers. Using this relation, creep time change caused by aging can be predicted. The relation between crystallinity and storage modulus (E') was described using a Takayanagi type two-phase model. We proposed a mechanical model that extends the Takayanagi type two-phase model to express the phenomenon by which the creep time increases because of increased crystallinity together with a viscous element of a model implementing the Guth–Gold model. This model can express behaviors of increasing creep time caused by increased crystallinity.

This study aimed to predict the yield stress and plastic viscosity of Superabsorbent Polymer (SAP)-modified cement pastes using the Yield stress mODEL (YODEL) and the Krieger-Dougherty (K-D) equation. Predictions were made for cement pastes with SAP dosages of 0.2–0.5% (by weight of cement) and water-to-cement (w/c) ratios of 0.4–0.6, over 5–35 minutes, and were compared with experimental data. In the YODEL model, the percolation threshold ((phi _{0})) and surface-to-surface separation distance (H) were fitted. The (phi _{0}) values (0.20–0.27) decreased over time, indicating paste stiffening and reduced percolation. The values of H (1.5–3 nm) declined with higher SAP dosages and over time due to water absorption and hydration, leading to increased flocculation and stiffening. In the K-D model, intrinsic viscosity [(eta )] was adjusted; [(eta )] increased with higher SAP dosages, greater w/c ratios, and time, consistent with thickening caused by SAP water uptake and hydration. For w/c = 0.4, predictions agreed with experiments from 5–15 min, with larger deviations occurring later. For w/c = 0.5 and 0.6, predictions aligned from 5–20 min, with slight overestimations and underestimations afterward. The K-D equation generally provided close agreement with experimental viscosities, showing only minor deviations. Overall, YODEL effectively captured early-age yield stress behavior, while the K-D equation successfully predicted viscosity trends, demonstrating the combined potential of these models for describing the rheology of SAP-modified cement paste.

This study aimed to evaluate the geomechanical changes in carbonates after matrix acidizing via acetic acid at different contact times (36/72/108 h). Synthetic carbonate rocks without fractures and with fractures were produced and subjected to matrix acidizing tests. X-ray microcomputed tomography, porosity and permeability tests were performed to identify the dissolution processes. Unconfined compressive strength tests (UCS) were performed on acidified and nonacidified samples to compare their stress–strain behavior, Young’s modulus and Poisson’s ratio before and after acidification. Petrophysical changes, such as increased porosity and permeability caused by the dissolution of the rock matrix with increasing injected acid, promote the formation of wormholes, affecting their structure. The samples exhibited a gradual decrease in mechanical strength with increasing contact time with acid; they were classified as moderately hard to hard (41.32 MPa to 50.80 MPa for nonacidified rocks) to soft (12.45 MPa to 24.18 MPa) after 36 h of testing; they also progressed from soft to very soft (4.61 MPa to 11.20 MPa and 4.12 MPa to 6.69 MPa) after 72 h and 108 h of acidification, respectively; and they exhibited a change in elastic behavior (brittle) to plastic (ductile) and a reduction in stiffness, as evidenced by a decrease in Young’s modulus, in addition to a reduction in Poisson’s ratio. Evaluating the impact of acid treatment on rock mechanics is essential for determining mechanical degradation after acid treatment to ensure that the stimulation technique does not compromise the integrity of the reservoir to the point at which its collapse.

This study presents a meshfree computational framework for analyzing the vibration behavior of functionally graded graphene origami-enabled auxetic metamaterial (FG-GOEAM) plates resting on a Pasternak foundation and subjected to blast loading in a thermal environment. The work is motivated by the demand for efficient tools to model advanced functionally graded metamaterials, which exhibit complex mechanical responses due to multiphysics coupling and auxetic characteristics. The governing equations of motion are derived using the refined first-order shear deformation theory (r-FSDT) combined with Hamilton’s principle. To solve these equations, a meshfree computational framework based on moving Kriging (MK) interpolation is developed. The proposed framework benefits from the Kronecker delta property, which enables the direct and efficient enforcement of boundary conditions, and further enhances accuracy by eliminating the need for pre-defined correlation parameters. The method is validated against benchmark results from the literature, confirming its accuracy and reliability. A series of simulations is then carried out to systematically explore the influence of the number of layers, temperature, foundation stiffness, boundary conditions, graphene origami (Gori) weight fraction, and Gori distribution patterns on the vibration behavior of FG-GOEAM plates. The findings demonstrate that the proposed method not only improves accuracy compared with conventional finite element method (FEM) and other mesh-based approaches but also provides new insights into the complex interplay among input parameters. These results highlight the feasibility of the proposed framework for optimizing the design and guiding the practical application of FG-GOEAM plates in engineering structures.