Mechanics of Time-Dependent Materials最新文献

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.

A novel comparative examination is conducted on homogeneous flexible microbeams to explore the impact of various electrical voltage sources on their thermomechanical properties. A mathematical model based on the modified couple stress theory has been established, allowing the prediction of size-dependent phenomena observed in microbeam resonators. In addition, the heat transfer inside the microbeam is characterized by the use of a non-Fourier law that involves thermal relaxation, implying an infinite speed of heat propagation. The developed theoretical framework is applied to investigate the thermoelastic response of an Euler–Bernoulli microbeam simply supported at both ends and subjected to a sinusoidal heat pulse. Moreover, a graphene strip, connected to an electrical voltage supply, acts as a heat source at a specific end of the microbeam. The Laplace transform method is used to solve the coupled heat transfer and motion equations. This gives closed formulas that describe the physical fields of thermoelastic microbeams. Numerical case studies are performed in a comparative analysis between the results obtained and those derived from conventional models using graphical representations. Additionally, an investigation is conducted to explore the influence of various factors, such as coupling stress, voltage, electrical resistance, and heat pulses, on the dynamic behavior of all the investigated fields.

Two epoxy resins (flexible and rigid) with new formulations that are more respectful of the environment are used to make five blends of epoxy resins in different proportions reinforced by 30% date palm fibers (DPF). The purpose is to determine how the blend’s composition and the addition of DPF affect the material’s thermal, water absorption, and viscoelastic properties. It was found that water absorption increases with the increase of flexible epoxy content. The incorporation of DPF multiplies the water absorption by about 6. Thermogravimetric analysis (TGA) revealed that the maximum degradation temperature (T_max) increases with increasing flexible epoxy content. The incorporation of DPF causes a slight decrease in T_max. Dynamic mechanical analysis (DMA) showed that raising the amount of flexible epoxy reduces the storage modulus (E’) while expanding the size of the transition zone. Conversely, the incorporation of DPF increases E’ over the studied temperature range. Similarly, increasing the percentage of flexible resin decreases the glass transition temperature (Tg) from 65.15 °C (100% rigid) to 29.75 °C (100% flexible). On the other hand, the incorporation of DPF improves the Tg. Isochronous stress-strain curves revealed that, at room temperature, the R50S50 epoxy (50% flexible + 50% rigid) and the R50S50R composite (R50S50 + 30% DPF) have linear viscoelastic behavior for tensile stress of 0.5 MPa and nonlinear one for higher stresses. The Schapery model was successfully used to model the nonlinear viscoelastic behavior of R50S50 epoxy and R50S50R composite.

Abstract

The aim of this work is to study the behaviour of a structural adhesive in an aggressive setting such as the marine environment. For this purpose, an ageing procedure is carried out under marine environmental conditions and a comparison of the properties before and after the process is performed. This is especially important as the characteristics of an adhesive can be heavily affected by factors such as temperature and humidity. For the assessment of the mechanical properties of the material bulk tensile tests are conducted, digital image correlation (DIC) is also employed to obtain parameters such as Poisson’s ratio or Young’s modulus. A dynamic mechanical analysis (DMA) is also carried out, on which the time-temperature superposition principle (TTS) is applied to make a long-term prediction of the behaviour of the adhesive, constructing the master curves for dynamic loads by means of a frequency test and for sustained loads through a creep test. This ageing procedure has led to a reduction in the strength of the material, but has also made it more ductile and flexible, while the master curve obtained from the frequency sweeps shows a smaller dependence of frequency in the aged material and the master curve obtained from the creep tests shows a similar behaviour for both the aged and unaged material.

Medical scientists frequently employ the Pennes bioheat equation as a computational tool to comprehend the intricate dynamics of thermal energy dispersion within living tissues. This equation, endowed with pronounced utility, finds paramount significance in the realm of therapeutic interventions, notably hyperthermia, wherein regulated elevation of tissue temperatures is administered for multifarious medical objectives. The utilization of this technology significantly enhances the optimization of treatment protocols and the preservation of temperature levels within crucial anatomical regions of the human body. To ensure the effectiveness of therapies and to uphold the utmost welfare of patients, meticulous monitoring of the thermal response of tissues subjected to thermal stimuli becomes imperative. This study introduces a mathematical formulation of the Pennes equation, specifically tailored for capturing the biothermal conduction phenomena transpiring in the intricate structure of skin tissue by employing the Moore–Gibson–Thompson (MGT) equation. This model enables accurate predictions of the thermal response of human skin to temperature variations. The key differentiating factor of this model is the incorporation of the concept of time delay. This inclusion serves the purpose of minimizing the rapid propagation of thermal energy within biological tissues, ultimately restricting its diffusion at limited rates. The proposed model is employed to characterize the intricacies of heat transfer in a slender, constrained stratum of skin tissue that is subject to a harmonic thermal stimulus. The computational outcomes are presented with the aid of illustrative figures, effectively highlighting the impact of model parameters on the temperature and deformation distributions within the material.

Deep underground civil works such as surrounding rocks of oil, gas pipelines and geothermal wellbore that pass through groundwater are often affected by the combined influences of thermal, hydraulic, and mechanical factors. In order to investigate the long-term stability of rock masses of this environment, creep experimental of quartz sandstone under the coupling effect of thermo-hydro-mechanical conditions. The study involved analyzing the long-term creep deformation, isochronous stress-strain curves, and long-term strength variations. Additionally, a fractional-order viscoelastic-plastic creep damage model was developed by integrating statistical damage analysis, Biot’s coefficient, and fractional-order integration theory. This model aimed to characterize the three-stage creep properties of different temperatures and water pressures. The experimental results indicate that the creep strain of quartz sandstone gradually increases with temperature and pore water pressure, while the long-term strength decreases. The axial creep strains of quartz sandstone are 0.330% at 20 °C, 0.381% at 50 °C, 0.448% at 70 °C, and 0.473% at 90 °C, respectively. This observation suggests that the coupled effect of temperature and pore water pressure has caused a certain level of damage to the rock. Furthermore, the proposed creep model effectively captured characteristics subjected to coupling effects of thermo-hydro-mechanical factors. The results provide a relevant reference value for the theoretical study of the creep mechanical behavior of rocks in multi-field environments.

Rolling resistance dictates a large part of the energy consumption of trucks. Therefore, it is necessary to have a sound understanding of the parameters affecting rolling resistance. This article proposes a semi-physical thermodynamic tyre rolling resistance model, which captures the essential properties of rolling resistance, such as transient changes due to temperature effects and the strain-amplitude dependency of the viscous properties. In addition, the model includes cooling effects from the surroundings. Both tyre temperature and rolling resistance are obtained simultaneously in the simulation model for each time step. The nonlinear viscoelasticity in rubber is modelled using the Bergström–Boyce model, where the viscous creep function is scaled with temperature changes. The cooling of the tyre is considered with both convective and radiative cooling. Moreover, the article explains different material parameters and their physical meaning. Additionally, examples of how the model could be used in parameter studies are presented.

Fiber-reinforced concrete (FRC) has become popular due to its ability to enhance mechanical properties. However, FRC has limitations regarding aging, durability, and corrosion. A superelastic shape memory alloy (SMA) is an alternate reinforcement material that can enhance a structure’s lifespan. This study evaluates the mechanical, durability, and corrosion resistance characteristics of hybrid combinations of nickel–titanium (Ni–Ti) SMA fibers and steel fibers in mortar. Three hybrid fiber combinations (GH1-75% steel fiber+ 25% SMA fiber, GH2-50% steel fiber+50% SMA fiber, and GH3-25% steel fiber+75% SMA fiber) were investigated in this study, with a total of 0.50% fiber volume ratio. To enhance the durability properties of the mortar, ground granulated blast furnace slag (GGBS) was used as a partial replacement for cement. The engineering properties of these hybrid fiber combinations in GGBS mortar were evaluated through compressive strength, flexural strength, and split tensile strength. Durability features were assessed based on acid, sulfate, chloride, and marine water resistance. The results showed that the hybrid mix with a greater quantity of steel fiber (GH1) had superior mechanical properties due to the steel fiber’s greater modulus of elasticity. However, when exposed to an aggressive environment, the hybrid combination with a greater quantity of Ni–Ti SMA fibers (GH3) in mortar showed higher durability and corrosion resistance. The samples from durability studies were further tested for Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-Ray Diffraction Analysis, and Fourier Transform Infrared Spectroscopy. The microstructural studies revealed the factors contributing to the enhanced durability and corrosion resistance of Ni–Ti SMA fibers in the composite.

The main aim of this study is to further extend isogeometric analysis (IGA) based on higher-order shear deformation theory (HSDT) with Soldatos’s continuous function (f(z)) for examining the free vibration characteristics of bio-inspired helicoid laminated composite (BiHLC) plates resting on elastic foundation (EF). The foundation follows Pasternak’s model with springer stiffness ((k_{1})) and shear stiffness ((k_{2})). The governing equation is derived by using Hamilton’s principle. The performance of the proposed formula is confirmed by comparing the obtained results with those of previous publications. In addition, an artificial neural network (ANN) model is set up by using Matlab software to accurately predict the natural frequencies of BiHLC plates without running code. Finally, some examples are conducted to provide novel results in the free vibration of BiHLC plates with different values of geometrical dimensions, material properties, boundary conditions (BCs), and foundation stiffness.