Mechanics of Time-Dependent Materials最新文献

Accurate prediction of the lifetime of unidirectional fibre composites requires a model that captures matrix viscoplasticity across generic loading histories. We propose a compact, rate-dependent hardening law for highly crosslinked epoxies that unifies constant-strain-rate and creep behaviour. The yield stress depends exponentially on accumulated plastic strain and logarithmically on plastic strain rate, and the relationship is analytically invertible for direct use in a finite element code. Parameters are calibrated from compression tests at multiple strain rates and from hold-at-load creep tests; validation is performed on RTM-6 and new 736LT epoxy data. The model reproduces (i) the near-linear (sigma _{y})–(log dot{varepsilon }) trend from pre-yield through softening and hardening, (ii) the time-dependent transition from pre- to post-yield during creep, including the rate surge near softening, (iii) long-term (14.5 h) creep more faithfully than stress–time power laws, and (iv) trends in cyclic, variable-rate, and tensile tests. The resulting, easily calibrated formulation enables robust simulation of matrix viscoplasticity in composite-scale models, improving durability predictions for load-bearing structures such as pressure vessels and wind-turbine blades.

In order to investigate the long-term stability of subway shield tunnel surrounding rock crossing layered rock formations, this study first researched the numerical algorithms and solution procedures for the three-dimensional Nishihara creep model and the ubiquitous-joint model that characterizes the layered rocks. Additionally, a load damage variable was introduced, and the plastic model in the original Nishihara constitutive model was replaced with the ubiquitous-joint plastic model, thus establishing a three-dimensional nonlinear Nishihara-ubiquitous joint creep damage model. The study then focused on analyzing the long-term characteristics of the surrounding rock under different joint angles and creep times using the layered rock surrounding the shield tunnel in Nanchang as the research subject. The results indicated the following: 1) The secondary development model effectively represents the three-stage creep mechanical characteristics of layered rocks, and the simulation results confirm the rationality of the developed creep constitutive model. 2) With increasing creep time, the displacement of the shield tunnel surrounding rock gradually increases, and the plastic zone expands. 3) The displacement and plastic zone of the surrounding rock exhibit noticeable anisotropy among different joint angles. Therefore, the rationality and feasibility of the developed model were verified through practical engineering applications, providing valuable insights for the long-term stability analysis of tunnel surrounding rock structures in similar layered rock formations.

In the development of ultra-deep oil and gas resources, wellbore shrinkage and casing damage often occur, posing significant risks to safe drilling operations. Reported analyses on casing integrity have primarily focused on non-uniform external loads without considering geometric non-uniformity of the wellbore. In this work, a creep constitutive model and a casing collapse-strength model are established to model the shrinkage behavior of salt formations. A coupled formation–cement–casing mechanical model that accounts for wellbore non-uniformity is developed. Uniaxial tensile tests are performed to characterize the plastic deformation behavior of casing materials. The results indicate that, for a representative well in the Bozi block of the Tarim Basin, increasing drilling-fluid density gradually reduces both wellbore eccentricity and shrinkage. The optimal density range for safe operation is 2.30–2.35 g/cm³. Geometric irregularities in the wellbore amplify non-uniform external loads, leading to an 11.3% increase in casing stress compared to uniform conditions. When both geostress and geometric non-uniformities are considered, the safety factor against external compression decreases by 20.88%, and the residual collapse-strength coefficient decreases by 9%. Increasing casing wall thickness enhances the residual collapse-strength coefficient by 6.83% and the collapse-safety factor by 2.8%.

The increasing surplus of cotton fibers presents an opportunity for sustainable reuse in cementitious materials. This work investigates the effects of curing regime on the mechanical and physical properties of Controlled Low-Strength Material (CLSM) reinforced with various types of cotton fibers. CLSM mixtures with different water–cementitious (w/cm) ratios were prepared and subjected to distinct curing conditions to evaluate their effects on key performance parameters, including compressive strength, indirect tensile strength, and drying shrinkage. Results show that cotton filler enhances tensile performance and reduces shrinkage, while the curing regime plays a significant role in the rate and extent of strength development. Optimal performance was achieved under controlled moisture-curing conditions at moderate w/cm ratios, yielding improved mechanical stability and reduced cracking potential. The integration of cotton fibers also maintained acceptable flowability, making the modified CLSM suitable for backfill and structural support applications. Utilizing cotton waste in CLSM provides a sustainable and cost-effective approach to material improvement, aligning with circular economy principles. The combined effects of fiber reinforcement and optimized curing regimes demonstrate the potential of cotton-reinforced CLSM as an environmentally responsible material for construction and infrastructure applications.

Concrete in sewer environments frequently experiences microbial corrosion, making an understanding of time-dependent sulfate behavior essential for durability assessments. A major challenge lies in characterizing the evolution of surface sulfate concentration on sewage pipe walls, which directly affects the erosion rate of concrete. This paper proposes an approach for monitoring and modeling the erosion rate by dividing the sulfate evolution into two phases, accumulation and stabilization, based on the surface sulfate concentration on the sewage pipe surface (SCSPS). The accumulation phase is described using a mass-balance framework incorporating biological sulfate generation, accumulation, and diffusion, while the stabilization phase is obtained by fitting experimental SCSPS data to a hydrogen sulfide (H₂S) concentration model. The SCSPS model is calibrated using H₂S concentration and relative humidity, and an erosion rate model is developed by integrating key parameters including H₂S concentration, diffusion coefficient, and relative humidity. Model predictions effectively captured changes in sulfate concentration and erosion rate across different environmental and material conditions. Results indicate that higher H₂S concentrations accelerate sulfate accumulation and concrete degradation, except at very low concentrations where SCSPS remains nearly constant. The erosion rate increases with the diffusion coefficient, with model outputs suggesting that increasing the diffusion coefficient from (5times 10^{-12}text{ m}^{2}text{/s}) to (9times 10^{-12}text{ m}^{2}text{/s}) leads to approximately a 50% increase in erosion rate during the second year. Sensitivity analysis further shows that the diffusion coefficient is the major factor governing concrete erosion under the examined conditions.

The creep behavior of rock-like materials containing inclined soft interlayers was investigated in cyclic loading–unloading experiments. The stress–strain response, long-term strength, and deformation and failure characteristics were examined to characterize the time-dependent behavior of the specimens. The results show that higher seepage pressures promote more pronounced crack propagation and lead to a reduction in long-term strength. To capture the accelerated creep observed in the experiments, a nonlinear viscoplastic element was introduced to enhance the nonlinear Burgers model, resulting in a nonlinear seepage–creep constitutive formulation. Model parameters were determined by fitting the experimental data using the Levenberg–Marquardt least-squares algorithm. The proposed model accurately describes the instantaneous elastic response, primary creep, and steady-state creep, and effectively captures the accelerated creep stage. These findings provide valuable theoretical and practical insights into the coupled seepage–creep behavior of rock masses containing soft interlayers

Fractional calculus has proven to be highly effective in simulating the viscoelastic and memory-dependent behavior of materials. This paper presents a three-dimensional fractional derivative standard linear solid (FSLS) model and its numerical implementation. By introducing the Caputo fractional operator to define a new Koeller spring-pot element, a one-dimensional FSLS model is developed, which can degenerate into other fractional derivative models, including the fractional derivative Maxwell (FM) and fractional derivative Kelvin-Voigt (FKV) models. The three-dimensional constitutive relationships are derived using a tensor generation method, and high-precision difference equations are formulated using the (L_{1}) time-discretization scheme. The model is implemented in ABAQUS using the UMAT interface and validated through creep and relaxation tests. The results indicate that: (1) The FSLS model based on the Caputo fractional operator is better suited for finite element computations because it avoids singularity issues, preventing computational difficulties; (2) The (L_{1}) discretization formula, with improved accuracy of order 2-(alpha ), can be employed to develop three-dimensional fractional derivative models and facilitate their numerical implementation in engineering applications; (3) A comparison between model predictions with experimental data demonstrates that the proposed model effectively captures the time-dependent behavior of geotechnical materials. The proposed model and discretization method provide valuable support for understanding and simulating the time-dependent deformation of geomaterials.

Based on the test data of rock material under different confining pressure and freeze-thaw cycle, the statistical damage model parameters related to the confining pressure level are determined, and the microelement strength of rock can be directly measured by axial strain; Using the inflection points in the damage evolution process of freeze-thaw rocks, the strain hysteresis factor, which characterizes the peak strain and model parameters, was obtained, the variation characteristics of axial strain of rock material from peak strength to residual strength in the post-peak region are revealed, and the definition of rock brittleness and plasticity and their value ranges were achieved by the model parameters; The inflection point strain is defined as the axial strain when the peak stress drops to the residual strength, the damage value at the inflection point strain is defined as the ultimate damage, a ultimate damage model under the coupled action of freeze-thaw and stress is established. The research results indicate that axial strain is sensitive to the brittle characteristics and ultimate damage of rocks under low confining pressure, and the inhibitory effect of low confining pressure on the ultimate damage of rocks subjected to different numbers of freeze-thaw cycles is not obvious; Under the action of low freeze-thaw cycle, increasing confining pressure has a significant effect on inhibiting the development of rock damage or the expansion of pores and fractures; Under the influence of high confining pressure and numerous freeze-thaw cycles, rock materials gradually exhibit the accumulation of freeze-thaw damage, the weakening of confining pressure constraint and the damage threshold effects.

This analysis gives insight into unsteady radiative energy and Casson fluid flow across stretching and shrinking sheets with Biot boundary conditions, enhancing our comprehension of these intricate conditions. Examined the two mathematical representations with the help of a rigorous method. The initial model aligns with the approach usually used by researchers in this area, but its stationary solution stays trivial. The second method clearly illustrates the physically pertinent stationary solutions well examined in published works. In particular, unveiled the new similarity variables specifically for the energy equation solely within the initial model. Utilized the numerical method to solve the governing partial differential equations, while similarity variables can describe particular scenarios with uniform wall temperatures, more general cases may require non-similar analysis to fully capture heat transfer variations. Here, both analytical hypergeometric series and numerical methods were employed to study the impact of various physical impacts on boundary layer flows. The results of the current analysis reveal that enhance in thermal radiation and Biot number enhances the surface heat transfer by nearly 30%, while wall suction further improves it by about 22%. Similarly, a stretching boundary contributes an additional 18% rise compared to the shrinking case. Moreover, analyzing several non-Newtonian fluids provided insight into implications for related stagnation points and viscoelastic problems. A diversity of analytical approaches and computational techniques can thereby elucidate subtleties in transport for diverse geometries and material behaviours.

To investigate the mechanical behavior of deep anchored jointed rock masses (AJRMs) under long-term shear loading and impact disturbances with constant normal stiffness (CNS) boundary conditions, shear creep-impact tests were conducted. Specimens with three joint roughness coefficients (JRC) were tested under various shear creep stress levels and five levels of impact energy. The acoustic emission (AE) system and industrial CT were employed to reveal the internal structural damage degree and spatial evolution characteristics at the micro-scale. This study systematically analyzes the creep deformation behavior, creep rate characteristics, long-term strength, and parameter sensitivity. A dual-dimensional quantitative evaluation method based on a “mass-area” concept was established to quantitatively characterize the damage evolution of AJRMs, clarifying the cumulative damage mechanism during the shear creep-impact process. The results indicate that the shear strain evolution caused by two impacts exhibited opposite trends in specimens J₁ and J₃. Specimen J₂ displays a distinct critical damage state, with a “shear stress-impact energy” threshold at (tau = 60% tau _{max } ) and (Q = 7.84mathrm{J}). When (Q = 1.96mathrm{J}), both (R_{mathrm{a}}) and (R_{mathrm{m}}) decrease with increasing JRC. However, at (Q = 11.76mathrm{J}), the specimens with higher JRC present the greatest values of (R_{mathrm{a}}) and (R_{mathrm{m}}). CT scan results revealed that no large-scale disintegration occurred under impact disturbance; damage was primarily concentrated in the local area surrounding the anchor rod. In the final stage, AE signals exhibit a characteristic “AE critical quiet period,” which closely corresponds to the macroscopic accelerated failure process. This phenomenon can be considered a precursor to structural failure and has significant implications for early warning of instability in AJRMs.