Continuum Mechanics and Thermodynamics最新文献

In the present work a formulation of evolutive laws and complementarity conditions in non-smooth elastoplasticity is discussed. The treatment addresses the problem of non-smooth elastoplasticity which is represented by functions characterized by singularities and defined by non-smooth yielding limit conditions and non-differentiable functions. The mathematical theory of subdifferential calculus is properly advocated to provide the suitable mathematical framework in order to treat non-differentiable functions and non-smooth problems. Extended expressions of evolutive laws and complementarity conditions in non-smooth elastoplasticity are illustrated within the adopted generalized mathematical treatment. Relations between the presented mathematical formulations and the expressions in classical elastoplasticity are pointed out and discussed. The proposed treatment has significant advantages since it provides a geometrical framework to the maximum dissipation principle for non-smooth problems in elastoplasticity. Furtherly, the proposed treatment gives insights in the interpretation of the adopted geometrical framework for different types of evolutive laws for new materials and solids such as for instance in some types of new metamaterials with non-smooth constitutive behavior. In addition, the present formulation is also useful in the design of metamaterials, such as pantographic ones, where the plasticity of the pivots is relevant.

Our study falls within the linear theory of thermoelasticity of Cosserat media. Unlike other works that fall into similar contexts and that use the entropy balance low, our approach is based on an entropy production inequality. The entropy flux tensor is introduced and thermoelastic media are considered for which the stress tensors are dependent on the temperature gradients. In this way, a fourth-order differential equation satisfied by temperature is obtained. In this context the mixed initial-boundary value problem is formulated for which an uniqueness result regarding the solution of this problem is proven. Also, a continuous dependence result is deduced for the solution of the mixed formulated problem with regard to the charges and the initial values.

Underground tunnels serve as vital infrastructure for road and rail transportation, oil and gas pipelines, power grids, and military applications; they are inherently subject to harsh environments characterized by extreme temperatures, chemical erosion, and sudden impacts. To address these challenges, the sophisticated coupled thermoelastic diffusion dynamic model has been developed based on Biot’s wave equation, Fick’s law, viscoelastic theory, and Ezzat’s fractional-order thermoelastic theory. The research presented here delves into the intricate thermoviscoelastic diffusion dynamic response of the system, exploring how it reacts when simultaneously confronted with a thermal source, normal load, and chemical shock directly applied to the surface of the cylindrical tunnel cavity. The Laplace transform and the Crump numerical inversion method have been used to obtain the non-dimensional displacement, temperature, chemical potential, concentration, radial stress, hoop stress, and axial stress. A meticulous analysis reveals the intricate interplay between the fractional coefficient, temporal evolution, and diverse shock load types on these variables. The fractional-order coefficients have a certain effect on the analysis of all physical variables except the non-dimensional chemical potential. The action time has a significant effect on all non-dimensional physical variables. The two different viscoelastic relaxation time factors have no significant effect on non-dimensional temperature and chemical potential, however, have obvious effects on non-dimensional concentration, radial stress, hoop stress, and axial stress.

This paper proposes a method for determining the mechanical properties of thin films of highly elastic materials. The method is based on an experiment of indenting a circular specimen with a hole in the center by a ball indenter. The value of the maximum indenting force is used as experimental data. This method determines the neo-Hookean model parameter for incompressible materials, factoring in indenter-specimen friction across various hole and indenter sizes.

We consider a transversely isotropic piezoelectric spheroidal inhomogeneity embedded in an infinite transversely isotropic piezoelectric matrix subjected to a uniform remote axisymmetric electromechanical loading. The inhomogeneity-matrix interface is spring-type in elasticity and weakly conducting in dielectricity. The same degree of interface imperfection in elasticity is realized in both the normal and tangential directions and the interface is characterized by two imperfect interface functions. We identify the two interface functions leading to a uniform interior electroelastic field within the spheroidal inhomogeneity. Explicit expressions for the internal uniform stresses and electric displacement within the inhomogeneity are presented and illustrated. The uniformity property within an imperfectly bonded spheroidal piezoelectric inhomogeneity under a uniform remote antisymmetric electromechanical loading is also proved and illustrated.

At the microscale and nanoscale, materials exhibit size-dependent behaviors that classical models cannot capture. This analysis introduces a size-dependent higher-order thermoelastic heat conduction model, incorporating spatial and temporal nonlocal effects in a micropolar visco-thermoelastic medium subjected to laser pulse heat flux. The two-phase delay model, featuring higher-order temporal derivatives, captures the complex interactions among mechanical, thermal, and viscous properties in materials where size effects are significant. By including phase lag, the model effectively addresses non-Fourier heat conduction in short-duration laser pulse scenarios. It accurately predicts temperature distribution, stress response, and microrotation effects in microscale and nanoscale materials. The study visually represents how factors such as micropolarity, higher-order effects, phase delay, nonlocal index, and viscosity influence the size-dependent mechanical behavior of the half-space structure. The numerical results highlight the importance of size-dependent phenomena in nanostructures, revealing deviations from classical predictions due to nonlocal interactions. Overall, the proposed spatiotemporal nonlocal homogenization model serves as a valuable tool for analyzing the complex mechanical and thermal characteristics of nanomaterials.

Aluminum alloys are light and corrosion-resistant materials, which is why they are widely used in structures in many industrial fields (construction, automotive, electric cables). The article deals with the aluminum busduct structure. Therefore, the mechanical and especially electrical properties of busduct welds are the basic criteria for assessing the quality of welds. The aim of the work was to present the advantages of a process combining metal inert gas welding with immediate microjet cooling (MJC). The parameters of aluminum welding using the micro-jet method were estimated in order to obtain products with the desired strength, mechanical and electrical parameters. Information regarding the influence of various microjet parameters on the metallographic structure was also recorded. Then, the metallographic properties and some physical properties of the welding structures (mechanical resistance, electrical conductivity) were examined. In addition, computer simulations of the welding process with micro-jet cooling were performed. The heat affected zone in the welded material was determined. The proposed numerical method will allow the assessment of the parameters of the welding process with micro-jet cooling depending on the parameters of the materials undergoing the welding process. The numerical approach will significantly reduce costly and time-consuming in situ work. Planning the welding of large structures (such as busducts) will be more economical using the results of computer simulations.

The use of thermal conduction models, particularly the double-phase lag thermal wave model, is vital for improving thermal therapies in biological tissues. However, existing models have limitations that hinder their practical application. This paper introduces a modified Pennes fractional thermal equation for biological heat transfer that integrates the double-phase lag concept and the fractional Atangana-Baleanu operator with a non-singular kernel. The model’s predictions were validated against measured temperature responses of laser-irradiated skin tissue and compared to established models. A one-dimensional layer of human skin tissue was analyzed using the Laplace transform method, with graphical results for each scenario. The comparative analysis showed that the AB fractional model outperforms other fractional models in capturing memory effects related to temperature variations and accurately models thermal interactions in living tissues while considering time delays. These findings highlight the model’s potential to improve the design and optimization of thermal therapies in clinical practice.

This study presents a comprehensive analysis of corneal biomechanics using shear wave elastography, leveraging finite element modeling to investigate the mechanical properties of corneal tissue. A 3D axis-symmetric corneal model was developed and subjected to various simulated conditions, including changes in intraocular pressure (IOP), boundary conditions, excitation pressure, and corneal curvature. The model incorporates hyper-viscoelastic material properties, allowing for an accurate representation of the cornea nonlinear behavior within physiological pressure ranges. Parametric studies were conducted to assess the sensitivity of shear wave velocity to variations in corneal biomechanical parameters. The results revealed that intrinsic material properties, particularly viscoelastic constants, significantly influence shear wave propagation, while external factors such as IOP and boundary conditions have minimal impact. The study also employed the Taguchi method for parametric optimization, identifying the first relaxation time as a critical factor affecting shear wave velocity. This work offers valuable insights into corneal biomechanics, with implications for improving diagnostic techniques and enhancing our understanding of corneal behavior under different physiological conditions. The findings support the potential application of shear wave elastography as a non-invasive tool for assessing corneal stiffness and advancing clinical practice in ophthalmology.

In this study, a coupled transient thermomechanical finite element model is developed to examine the laser powder bed fusion (L-PBF) process of the Inconel 718 (IN718) and Oxide Dispersion Strengthened (ODS) superalloys (ODS-IN718). The linear isotropic elastic perfectly plastic constitutive model is implemented for the mechanical part whereas all the thermophysical properties are defined as fully temperature dependent. This new model enables three states of the metal including powder, liquid, and solid phases in the continuum-based finite element simulations. Besides, it can meticulously simulate multi-layered samples to assess thermomechanical performance and residual stress between layers. First, benchmark problems are revisited to verify the high accuracy of the present model for predicting transient temperature profile and residual stress accumulation. Then, thermomechanical analysis of a single-track three-layer test case is performed to investigate the L-PBF process of IN718 and ODS-IN718 samples for various laser powers and scan speeds. Also, the thermal characterization of ODS-IN718 samples is experimentally conducted. It is demonstrated that the numerical melt pool dimensions provide good agreement with experiments with an average error of 17% for melt pool dimensions. Moreover, mechanical results reveal that high tensile residual stresses accumulate in the middle part of the track. The manufacturing quality of the IN718 and ODS-IN718 samples are comprehensively compared based on the variations of stress distribution at different layers for different laser scan speeds. Also, the optimal laser scan speed is achieved to minimize the residual stresses for the ODS-IN718 alloy. Overall, ODS-IN718 has a lower residual stress than IN718 especially at lower laser scan speeds due to the enhanced thermomechanical behavior attributed to the change in material properties due to the presence of dispersed particles.