Mechanics of Time-Dependent Materials最新文献

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.

This paper develops an analytical framework to investigate the thermo-viscoelastic stress distribution in adhesively bonded single stepped-lap (SSL) joints with functionally graded (FG) adherends subjected to tensile loading. The adhesive layer (AL) is modeled by the fractional Zener formulation within a four-parameter fractional thermo-viscoelastic framework, capturing its linear viscoelastic behavior. The FG adherends, consisting of nickel–aluminum oxide (Ni–Al₂O₃), are described using Timoshenko beam theory. Governing differential equations are derived from constitutive, equilibrium, and compatibility conditions at the reference temperature and subsequently extended to arbitrary temperatures through thermoelastic relations for the adherends and the time–temperature superposition principle for the adhesive. These equations are solved in the Laplace domain and inverted to the time domain using the Gaver–Stehfest algorithm. The proposed model provides a time- and temperature-dependent prediction of axial, shear, and peel stresses at any point within the adhesive layer or interfaces. Validation against finite element simulations in ANSYS Workbench demonstrates excellent agreement. Results reveal that temperature variations strongly influence the stress field, while elevated temperatures significantly accelerate the relaxation and stabilization of reduced stress components.

One important strategy for increasing the strength and load-bearing capability of damaged tunnel linings is to reinforce them with steel plates. An important factor in determining the long-term performance of the restored tunnel is the bond interface’s longevity. This study focuses on the bond interface creep behavior in steel plate-reinforced shield tunnels through experimental investigation. Accelerated testing was used to investigate the long-term creep response of the bond contact using the creep equivalence and Boltzmann superposition principles. The key takeaways are as follows: The progression of creep at the bond interface – from the moment of initial loading to when it reaches a stable state – can be broadly broken down into four phases: an instantaneous deformation phase, a stage of decay creep, a period of steady–stable creep, and accelerated creep phase. The bond contact of the shear specimen experiences accelerated creep after 186 hours when it is subjected to 90% of its maximum stress, while the bond interface of the tensile specimen reaches this stage in just 96 hours. As the stress level rises, so does the quantity of creep at the bond interface. As the distance from the loading end increases for the shear specimens, the amount of creep at the bond contact progressively diminishes. A notable 1000-fold increase in creep time is seen when Time-Stress Superposition Principle (TSSP) is used to speed up the characterization of experimental creep curves for the bond contact.

Creep stresses are evaluated in a hemispherical shell made of functionally graded transversely isotropic materials under uniform external pressure. The concept of transition theory is applied to evaluate the creep stresses in the shell under external pressure. The strength and compatibility of the hemispherical shell composed of magnesium, zinc, and beryl are compared based on creep stresses. This physical problem is regulated by a non-linear differential equation obtained by substituting the derived relations in the equilibrium equation. For estimating the creep stresses in the shell, the transition function (R) is considered as the difference of radial stress (T_{rr}) and circumferential stress (T_{theta theta } ). Analytical method is applied to solve the equations by taking the critical point (Prightarrow -1) of the governing differential equation into consideration. This study examines the hemispherical shell composed of Functionally graded transversely isotropic material, which is more robust and biocompatible than homogenous transversely isotropic material. Based on all the numerical calculations and graphs it is concluded that the circumferential and radial creep stresses are minimum for a hemispherical shell composed of functionally graded transversely isotropic material magnesium in comparison to zinc and beryl, it implies that the shell composed of (FGM) magnesium is experiencing the most stable or optimal state of deformation under the conditions of external pressure. Therefore, the hemispherical shell of functionally graded transversely isotropic material magnesium might be useful in practical applications like pressure vessels, tanks, or any spherical shell structures exposed to high pressure over long durations.

This study proposes a modified cumulative damage model for GAP-based composite solid propellants, considering thermal aging effects. Accelerated thermal aging experiments were conducted at 333.15 and 343.15 K to analyse the variations in mechanical properties, including elastic modulus and maximum elongation. The results revealed an approximately 15% increase in elastic modulus and an approximately 25% decrease in maximum elongation during 333.15 K thermal aging. Based on the Arrhenius equation, a predictive model for mechanical parameter degradation was established, and the evolution of cumulative damage parameters was simplified using three assumptions. The modified model, accounting for aging effects on parameter (beta ), demonstrated good agreement with direct computational results. Numerical simulations indicated that aging substantially amplifies cumulative damage in solid rocket motors under thermal cycling loads. This research provides a theoretical framework for assessing the structural integrity of solid rocket motor during long-term storage.

In response to the growing demand for sustainable construction practices, this study evaluates the potential use of calcined bentonite (CB) and recycled glass powder (GP) as supplementary cementitious materials in self-compacting mortar (SCM). The environmental objective is to reduce the reliance on Portland cement, which is a major contributor to CO₂ emissions, by incorporating industrial and post-consumer waste materials. In mixtures, CB was introduced at replacement levels of 5, 10, 15, and 20%, while GP was added at levels ranging from 5 to 25% by weight in binary and ternary binders. A comprehensive assessment of the fresh properties, including mini-slump flow, V-funnel flow time, yield stress, and plastic viscosity, was conducted, alongside mechanical and durability tests such as compressive strength, water absorption, acid resistance (5% HCl) and sulfate attack (5% K₂SO₄). Results indicate that, CB decreases the flowability of SCM mixtures, necessitating a higher dosage of superplasticiser. However, when combined with GP, the flowability improves significantly, reducing the demand for superplasticiser. Optimal mechanical performance was observed in mixtures containing 15% CB and 0% GP, as well as 10% CB with 5% GP, which achieved compressive strength improvements of 12% and 13%, respectively, after 90 days. Moreover, the incorporation of higher GP contents (15–25%) enhanced the mortar’s resistance to hydrochloric acid and potassium sulfate solution, highlighting its contribution to long-term durability. These findings support the valorization of calcined clays and glass waste as viable alternatives for developing sustainable and cost-effective SCM, while reducing environmental impact in the construction industry.

Rejuvenators used for hot mix recycling can be classified broadly into recycled rejuvenators (RR) and commercial rejuvenators (CR). A comparative evaluation between two RR and two CR is done in this study. A series of tests on rejuvenators (Brookfield viscometer, rolling thin film oven and Fourier Transformed Infrared Radiation tests), recycled binder blends (zero shear viscosity, frequency sweep, multiple stress creep recovery) and recycled mixes (uniaxial cyclic compression test and Indirect tensile asphalt cracking test) are performed. FTIR spectra revealed that all rejuvenators comprise aliphatic and aromatic hydrocarbons, which are similar to the maltenes portion of asphalt. Test results showed that RR are thermally stable than CR and recycled binder blends with RR are softer than CR. Hence, RR have higher cracking resistance and cross-over frequency, but lower Zero Shear Viscosity and rutting resistance. Also, recycled mixes with RR showed higher irrecoverable strains than mixes with CR. On top of performing well in rutting, recycled mixes with CR also showed better or comparable fatigue performance at 40% recycled content. From the ranking analysis, it is concluded that RR outperformed CR, and weight change after RTFO test has the best correlation with the global total rank value (GTRV).