Mechanics of Time-Dependent Materials最新文献

Basic creep plays an important role in assessing the risk of early-age cracking in massive structures. In recent decades, several models have been developed to characterize how the hydration process impacts the development of basic creep. This study investigates the basic creep of various concrete mixes across different ages at loading. The analysis focuses on the very early stages (less than 24 hours) and early stages (less than 28 days) of concrete development. It is shown that a logarithmic expression that contains two parameters describing the material can accurately model basic creep from a very early age. One parameter relates to the creep amplitude and depends solely on the composition of the concrete. The other relates to the kinetics of creep and depends on the age of the material at loading and the nature of the concrete mixture. The logarithmic expression corresponds to a rheological model consisting of a single dashpot wherein viscosity exhibits a linear evolution over time. The model offers the advantage of eliminating the need to store the entire stress history for computing the stress resulting from the restriction of the free deformation. This approach significantly reduces computation time. A power-law correlation is also observed between the material aging parameter and the degree of hydration. This relationship depends on the composition. At least two compressive creep tests performed at two different degrees of hydration are needed to calibrate the material parameters and consider the effect of aging on basic creep compliance.

Three-dimensional concrete printing is a transformative technology ushering in revolutionary architectural design and construction automation changes. With recent advancements of this technology, a notable absence of theoretical models predicting structural buildability is required. This investigation aims to bridge this knowledge gap by introducing an innovative theoretical model for estimating the total number of layers printed by a concrete 3D printer. This proposed model considers material behavior, building rate, and failure criteria. The material properties are depicted by modeling structural buildability in two cases, (i) bilinear and (ii) exponential. The buildability is characterized by three subcases, namely (i) constant, (ii) increasing, and (iii) decreasing building rates. These subcases hinge on printing velocity, treated as a function of time. Furthermore, the failure modes of 3D printable concrete structures are delineated based on (i) the Mohr–Coulomb theory and (ii) elastic and plastic failure criteria. Additionally, a strength-correction factor is employed to consider the confinement effect of the printed layer. The ultimate expression of the proposed model embodies an exponential approach to gauging the structural buildability of the printed structures. The study encompasses model validation and extensive parametric analysis to scrutinize the impact of printing velocity, structuration rate, printing path, density, and yield stress.

Stormwater management is still a major concern confronting many countries all over the world. The need to collect the runoff water is highly prioritised to save natural resources and restore groundwater supplies. Pervious concrete is a special type of concrete that possesses the unique characteristic of allowing water to pass through it. Hence, the study of the hydraulic characteristics of pervious concrete is highly required to understand the material’s ability and utilise it to the maximum. The main motive of this experimental investigation is to study the hydraulic conductivity of pervious concrete slabs using two different methods, namely the constant and falling head permeability tests. Seven different pervious concrete mix proportions were examined in this work. A total of 21 pervious concrete slabs of size 1000 mm × 1000 mm × 200 mm were cast with different degrees of compaction and tested for hydraulic conductivity. From each slab, three concrete cores of size 100 mm diameter × 200 mm height were drilled and extracted to test the hydraulic conductivity and to compare with the test results of the pervious concrete slabs. The test results revealed that compaction is the predominant factor that affects the hydraulic conductivity of the pervious concrete slabs. It has also been observed that all the pervious concrete slabs exhibited non-Darcian behaviour irrespective of the degree of compaction. From the results, it is clear that the hydraulic conductivity of the pervious concrete varies according to the test methods and hydraulic gradients. The results from the extracted cores exhibited similar trend behaviour of the concrete slabs, confirming the non-Darcian flow in pervious concrete. The results also showed that the estimated hydraulic conductivity by the constant head method was higher due to the lower hydraulic gradients considered during the experiment. The outcomes of the test results will be helpful in the rational design of pavements using pervious concrete.

A split Hopkinson pressure bar (SHPB) was used to characterize the high-strain rate behavior of saturated and frozen granite specimens. The effects of low temperatures and strain rates on dynamic mechanical response and failure behavior were investigated. The damage constitutive model of granite was established, considering both strain rate effect and low-temperature effect. The damage constitutive relationship took into account the statistical damage model based on Weibull distribution and nonlinear viscoelastic behavior. Results show that the dynamic compressive strength of the saturated and frozen granite at low temperatures (−20 °C to 15 °C) generally increases first and then decreases with the decrease of temperature. The peak strain decreases with the decrease of temperature and the peak strain at low temperatures (0 °C to −20 °C) decreases more than that at 15 °C. The dynamic Young’s modulus of the samples shows an increasing trend from 0 °C to −20 °C, and the range of variation decreases with the decrease of temperature. At low temperature, the brittle characteristics of saturated granite are more pronounced due to water-ice phase change and cold shrinkage of the rock matrix, while the ductility is gradually reduced. The modeling results on the stress-strain relationships are consistent with experimental data. It is verified that the constitutive relationship can describe the high strain rate characteristics of saturated frozen granite.

Modeling stress distributions in multi-layer soft viscoelastic materials has great importance for evolving robotics and mechanism of machines, where soft viscoelastic materials are increasingly replacing traditional rigid materials. Nevertheless, tackling this problem remains a challenge, particularly when considering the viscoelastic properties of soft materials. This research presents a theoretical model for stress distribution in a two-dimensional sliding contact between a spherical rigid indenter tip and a plane composed of multi-layer soft viscoelastic material. The material is characterized using the viscoelastic Kelvin–Voigt model, where the viscosity coefficient defines the viscoelastic behavior. Explicit mathematical formulas for stress and strain determination in the multiple soft layers are derived using mathematical transformations based on the Fourier transformation. The system of third-order nonlinear differential equations of the contact model is tackled using the finite difference method, within the given boundary conditions. Then, a numerical algorithm is proposed to effectively solve the finite difference equations, considering various parameters of soft viscoelastic material’s properties and sliding velocity. The effectiveness of our proposed model is validated by numerical simulations and the machine learning method. The developed contact model is expected to be a platform for modeling and analyzing the sliding-spherical contact in novel mechanism designs, such as soft robotics, soft tactile sensors, and intelligent integration in soft bodies.

Our present work aims to deal with a conceptual structure to investigate the generalized magneto-thermodiffusion relations in an isotropic medium in the context of four-phase lag thermoelastic model using a memory-dependent derivative (MDD). In this new model, the traditional Fourier’s heat conduction law and Fick’s mass diffusion law have been modified by introducing an improvised Taylor’s series expansion, which assimilates the MDD and incorporates four phase lags (FPL) generalized thermoelastic model. Utilizing the Laplace transformation technique as a mechanism, the control equations are presented in the Laplace domain, where they are decoded by incorporating a finite element (Galerkin) approach. The impact of the FPL parameters in several studied fields like stresses, temperature, and chemical potential has been demonstrated in the presence of MDD and magnetic field. A comparison of the results for different models like classical thermo-elasticity model, Lord-Shulman model, and FPL model is presented.

This paper reports the behavior of plane wave propagation through the interface of an elastic half-space (ES) and a transversely isotropic piezoviscothermoelastic half-space composed of dual phase lag and hyperbolic two-temperature (PTHD). Two waves are reflected when P waves move longitudinally, or SV waves move transversally to reach the ES medium, and the four waves are transmitted through the PTHD medium. The amplitude ratios for reflected and transmitted waves are determined by satisfying the boundary conditions. These ratios are subsequently utilized to calculate energy ratios for those waves. The effects of viscosity, hyperbolic two-temperature (HTT), classical two-temperature (CTT), and one-temperature (OTT) on the energy ratios are analyzed. The balance of energy conservation is analyzed for some cases.

The paper investigates the short- and long-term compressive stress relaxation behavior of isotropic and anisotropic magneto-sensitive elastomers (MSEs) prepared by incorporating carbonyl iron microparticles into a silicone rubber. The effects of applied compressive strain, magnetic field, and temperature on the short-term stress relaxation behavior of the isotropic and anisotropic MSEs were determined up to 1200 s. The stress relaxation behavior of the MSEs considerably depended on the applied compressive strain, magnetic field, and temperature. The stress of the MSEs increased with increasing compressive strain and magnetic-field intensity, but decreased with increasing temperature. The isotropic MSE exhibited approximately linear elastic behavior, while the anisotropic MSE revealed nonlinear elastic characteristics. The compressive stress and the relaxation modulus of the anisotropic MSE are considerably higher than those of the isotropic MSE. The compressive stress relaxation behavior of the isotropic and anisotropic MSEs was simulated using a fractional derivative viscoelastic Kelvin–Voigt model. The model parameters were identified by fitting the relaxation modulus to the short-term measured data of the MSEs. The compressive stress estimated from the studied model with fitted parameters was in excellent agreement with the measured data of the MSEs at different compressive strains, magnetic fields, and temperatures. The model was then used to estimate the long-term stress relaxation of the MSEs. An excellent agreement between long-term predicted results and experimental data of the MSEs has been reached when fitting the model to the medium-term experimental data.

To address control of the coal wall rib spalling in a work face with large mining height, an investigation was conducted on the Caojiatan mine 122107 work face as a case study. Using a combination of theoretical analysis, orthogonal experiments, and numerical simulations, we determined the influence of hydraulic support parameters on coal wall rib spalling. Our results show that reducing the end-face distance and the resultant force application point and increasing the vertical force and the horizontal force of a hydraulic support provide increased stability of the coal wall. Extensive verification was made through simulations. The work presented herein suggested a structural zoning of the coal wall rib spalling, it also established the coal wall stability coefficient, and determined the lower limit of the coal wall’s nonstructural area stability coefficient. Additionally, this study provided methods for the prevention and control of coal wall rib spalling in a large mining height work face, via improving the nonstructural area mechanical parameters, and optimization of the hydraulic support.

High-density polyethylene (HDPE) pipelines are widely used for the transportation of natural gas. The butt-fusion welded joints melt and cool during the welding process, resulting in changes in mechanical properties, molecular chain spatial position microstructure, and functional groups. Herein, we investigate the aging behavior of an HDPE butt-fusion welded joint in accelerated thermal-oxidative aging tests under various temperature gradients. The Vicat softening temperature, oxidation induction time, and infrared spectrum were measured, and the microstructures were observed. The results indicated that the mechanical and chemical properties of the butt-fusion welded joint degraded with incresing aging temperature. Analysis was conducted to identify the molecular chain intersection mechanism in the heat-affected zone and the weld joining mechanism. The findings help understand the aging behavior of HDPE and provide guidelines to reduce the risk caused by butt-fusion welded joint degradation.