Mechanics of Time-Dependent Materials最新文献

The use of rejuvenators is essential for restoring the properties of aged asphalt binders in reclaimed asphalt pavement (RAP) mixtures. This study examined the effects of three commercially available rejuvenators (A, B, and C) on the physical, rheological, and performance characteristics of RAP binders and mixtures. The optimum rejuvenator dosage was determined using the high-temperature performance grade (PG) criterion. Further, to compare the effect of rejuvenator type, an average dosage of 10% by weight of RAP binder was considered as a reference for all the rejuvenators. Binder-level tests, including softening point, ductility, PG grading, MSCR, and LAS were complemented with stage extraction tests to evaluate rejuvenator diffusivity. Mixture performance was assessed using wheel tracking and IDEAL-CT tests. Results showed that rejuvenation effectively restored RAP binder properties to levels comparable with the target VG40 binder. Rejuvenator A, with lower viscosity and better diffusion efficiency, enhanced fatigue resistance and cracking tolerance, whereas rejuvenators B and C, with higher aging indices and limited diffusivity, improved rutting resistance. Mixture-level testing confirmed these trends, with recycled mixtures outperforming the control in rutting and cracking resistance. Overall, the study highlights that rejuvenator properties, particularly viscosity, aging index, and diffusivity, govern their effectiveness in restoring binder rheology and ensuring balanced mixture performance. The stage extraction test proved useful for distinguishing rejuvenators based on diffusion efficiency, offering a more realistic assessment than conventional binder tests.

The creep behavior of red-stratum mudstone plays a critical role in the long-term stability and safety of major engineering projects, making a systematic investigation of its consolidation creep characteristics of significant engineering relevance. In this paper, one-dimensional consolidation creep experiments were conducted on red-stratum mudstone using an incremental loading method to determine the effects of initial dry mass density, moisture content, and normal stress on its consolidation creep behavior. Based on the observed characteristics of the consolidation creep curves, a hyperbolic empirical consolidation creep constitutive model incorporating the effects of initial dry density, moisture content, and normal stress was developed. The experimental results indicate that the consolidation creep behavior of red-stratum mudstone can be divided into three stages: instantaneous creep, decelerated creep, and stable creep. Higher moisture content, lower initial dry density, and greater normal stress result in increased total deformation, larger secondary consolidation coefficients, and longer durations to reach creep stability. The proposed constitutive model accurately captures the consolidation creep characteristics of red-stratum mudstone, providing a theoretical basis for assessing and improving geological safety in red-mudstone engineering regions.

To investigate dynamic fatigue behavior of foam in military protective applications, such as helmets, additively manufactured (AM) foams were compressively strained into the plateau region using a reduced design of experiments. A simple power law was found to govern the decline in dynamic stiffness (complex modulus) as the foams underwent the purchase order requirement of 10,000 cycles of small deformation in the plateau region. This rate of decline was newly found to correlate with the degree of nonlinearity in the material’s deformation, quantified using total harmonic distortion. Materials with low nonlinearity exhibited relatively stable stiffness across cycles, while those with high nonlinearity experienced greater losses. The observed nonlinearity depended on both applied stress and strain rate. A strong linear correlation ((mathrm{R}^{2} = 0.78)) was identified between second-order nonlinearity and the time-dependent stiffness response. Two lattice structures were examined: face-centered tetragonal (FCT) and simple cubic (SC). The SC material exhibited higher total harmonic distortion (5%) and lower stiffness retention than the FCT (2%). These results suggest that for cyclic compression applications in a wide variety of industries such as packaging, personal protective equipment, or aerospace, selecting materials with lower stress and greater structural uniformity can enhance the stability of dynamic performance.

Based on the characteristics of microplastic strain and strain hardening during single loading process of rock materials, high-cycle and low-cycle fatigue damage models describing the characteristics of micro-plastic strain and strain hardening of rocks under freeze-thaw cycles were obtained; a fatigue life equation linking microplastic strain and strain hardening is established. According to the high cycle and low cycle fatigue damage models and freeze-thaw cycle experimental data, the fatigue life and other model parameters in the high cycle and low cycle fatigue damage models are determined under double logarithmic coordinate system. In view of the micro pore expansion and the stress increase caused in rocks due to freeze-thaw cycles, the coupled damage variables and its damage range under the combined action of freeze-thaw and stress were derived. The research results indicate that with the increase of freeze-thaw cycles, the coupled damage shows a high cycle fatigue damage followed by low cycle fatigue damage; when determining the damage value of freeze-thaw rock, low cycle fatigue damage can be equivalent to the increase of high cycle fatigue cycle number; the equivalent damage model based on the Lemaitre strain equivalence hypothesis and high-cycle fatigue damage model only describe the damage evolution within the microplastic strain range; whereas the low-cycle fatigue damage model can reveal the damage evolution from microplastic strain to strain hardening range; in the process of microplastic strain to strain hardening development, the damage evolution rate of freeze-thaw rock gradually decreases, showing brittle reduction and plastic increase.

Under prolonged wet–dry cycling, the structural integrity of reef limestone in island and reef coastal zones deteriorates, resulting in significant reductions in rock strength and engineering stability. This study investigates the degradation behavior and mechanisms of reef limestone subjected to repeated wet–dry cycles. Uniaxial compression, splitting tensile, and Split Hopkinson Pressure Bar (SHPB), combined with X-ray Fluorescence Spectrometer (XRF) and Scanning Electron Microscope (SEM) analyses, were conducted to evaluate strength degradation, damage evolution, and microstructural changes under varying cycle numbers ((N)). Fractal analysis of fracture debris established a linear relationship between (N) and the fractal dimension, quantitatively linking macroscopic mechanical degradation with microstructural evolution. Results show that as (N) increases, compressive and tensile strengths decline from 7.45 MPa to 3.13 MPa and 4.20 MPa to 2.08 MPa, respectively, with failure modes shifting from brittle to shear failure. Dynamic compressive strengths decreased to 20.43 MPa, 23.49 MPa, and 25.50 MPa. Increasing fractal dimensions indicate progressive fragmentation, while SEM and XRF reveal mineral dissolution, pore expansion, and microcrack connectivity as key degradation mechanisms. Overall, reef limestone exhibits significant mechanical and structural weakening under wet–dry cycling, highlighting the strong coupling between microstructural evolution and macroscopic damage—of critical importance to island and reef engineering.

Primary stope frequently experience partial backfill collapses during subsequent stoping and backfilling operations due to insufficient strength of the primary stope. To enhance the stability and mechanical performance of the primary stope, an enhancement layer was introduced into the middle layer of the backfill. In this paper, the mechanical properties, energy evolution, and damage progression of cemented tailings backfill (CTB) and stratified cemented tailings backfill (SCTB) were systematically investigated through triaxial compression tests on specimens cured for 3, 7, and 28 days. The results indicate that the stress-strain response of SCTB exhibit four distinct stages, interlayer voids and pore closure, rapid increase of stress, slow increase of stress, and stress decline, with elastoplastic deformation becoming more pronounced under higher confining pressures. The SCTB specimens cured for 3 days exhibit inferior mechanical properties compared with CTB specimens of the same age; however, when the curing age extended to 7 and 28 days, SCTB demonstrates superior strength and deformation characteristics. The failure modes of SCTB transitions from conjugate shear and tensile failure to a bulging and shear hybrid failure, whereas CTB primarily undergoes uniform shear failure, indicating that the enhancement layer effectively suppresses crack propagation. The energy storage limit of SCTB cured for 7 days is 13.5% higher than that of CTB, increasing to 61.1% at 28 days. The SCTB exhibit a delayed onset of accelerated damage compared with CTB. These findings provide valuable guidance for designing cost-effective, high-performance backfill systems in mining engineering while balancing structural strength and sustainability.

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.