Continuum Mechanics and Thermodynamics最新文献

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.

We propose a continuum viscoplasticity model for metals where the kinematic aspects and those pertaining to microstructural reorganizations are intrinsically described through Riemannian geometry. Towards this, in addition to a Euclidean deformed manifold, we introduce a time-parametrized Riemannian material manifold where a metric tensor characterizes the irreversible configurational changes due to moving defects, e.g. dislocations or grain boundaries causing plastic deformation. Moreover, we also make use of a time-parametrized Euclidean reference manifold which shares the same macroscopic shape/size as the material manifold. The setup dispenses with the need for a multiplicative decomposition of the deformation gradient. Constitutive closure of the unknown fields, appearing in the metric tensor, is organised through two-temperature non-equilibrium thermodynamics. The approach naturally leads to terms containing higher order gradients of variables describing plastic deformation. Use of the virtual power principle yields a macroscopic force balance for mechanical deformation and a microscopic force balance giving the nonlocal flow rule. Evolution equations for the two temperatures are also coupled with plastic deformation. Numerical simulations on homogeneous and inhomogeneous deformation in oxygen-free high conductivity copper are carried out to validate the model. Simulations of an inhomogeneous deformation scenario, the Taylor impact test to wit, are then performed. To further explore the model, we simulate shear band propagation in a doubly notched plate under impact. The study offers interesting insights into the role of Riemann curvature in band formation.

Harmonic boundary excitation of localized oscillatory waves in a mass-in-mass metamaterial is studied. It is shown that switch-on/off of the boundary excitation gives rise to a formation of a sequence of such waves, which propagate keeping its form and velocity. The wave formation is achieved only outside the band gap interval of the excitation frequencies. The boundary reflection of the localized oscillatory waves is observed and analysed.

In this study, the effect of varying weight percentages of carbon fiber powder (CFP) (10 wt.%, 20 wt.% and 30 wt.%) on the mechanical properties of polycarbonate (PC) components produced by plastic injection molding was investigated using analytical, numerical and experimental methods. This research is a novel study in terms of comparing experimental data with microscopic features and full-scale analysis. The micro-scale study was carried out using the Halpin-Tsai (HT) and Generalized Modified Halpin Tsai (G-HT) models as well as the representative volume element (RVE). Findings from RVE were then transferred to the finite element analysis (FEA) module for full-scale comprehensive analysis. A comparison of the experimental tensile test results demonstrated an increase of 56.90% and 191.47% in the tensile strength and Young’s modulus of the composite containing 30 wt. % CFP compared to pure PC, respectively. The minimum and maximum differences between Young’s modulus and the experimental Young’s modulus were determined to be 0.39% and 7.92% using RVE and G-HT, respectively. The maximum and minimum value of the difference between experimental and FEA strengths were determined as 3.44% and 1.91%, respectively. Young’s modulus of the composite with increasing fiber weight ratio was successfully predicted by RVE, G-HT and FEA.

We propose a three-dimensional macroscopic continuum model designed to predict the remodeling phenomenon of bone tissue. In the proposed model, we focus on the evolution of two crucial stiffness parameters: the bulk and shear moduli. These parameters independently adapt to the mechanical demands to which bone tissue is subjected, mainly to withstand hydrostatic and deviatoric deformations. These mechanical stimulations influence the activity of bone cells, leading to changes in bone structure and strength and, in turn, the above-mentioned moduli. The formulation is simplified, serving as an initial step towards a more comprehensive modeling approach. The evolution of these stiffness parameters is proposed based on an energetic argument to describe the functional adaptation process. Numerical experiments, conducted on a cylindrical specimen resembling a femur, demonstrate the feasibility of modeling the bone remodeling process with distinct evolutions for multiple material parameters, in contrast to the conventional approach that permits only one-parameter evolution.

In this article, the nonlinear coupled two-dimensional space-time fractional order reaction-advection–diffusion equations (2D-STFRADEs) with initial and boundary conditions is solved by using Shifted Legendre-Gauss-Lobatto Collocation method (SLGLCM) with fractional derivative defined in Caputo sense. The SLGLC scheme is used to discretize the coupled nonlinear 2D-STFRADEs into the shifted Legendre polynomial roots to convert it to a system of algebraic equations. The efficiency and efficacy of the scheme are confirmed through error analysis while applying the scheme on two existing problems having exact solutions. The impact of advection and reaction terms on the solution profiles for various space and time fractional order derivatives are shown graphically for different particular cases. A drive has been made to study the convergence of the proposed scheme, which has been applied on the proposed mathematical model.

The connection of two orthogonal families of parallel equispaced duoskelion beams results in a 2D microstructure characterizing so-called tetraskelion metamaterials. In this paper, based on the homogenization results already obtained for duoskelion beams, we retrieve the internally-constrained two-dimensional nonlinear Cosserat continuum describing the in-plane mechanical behaviour of tetraskelion metamaterials when rigid connection is considered among the two families of duoskelion beams. Contrarily to duoskelion beams, due to the dependence of the deformation energy upon partial derivatives of kinematic quantities along both space directions, the limit model of tetraskelion metamaterials cannot be reduced to an initial value problem describing the motion of an unconstrained particle subjected to a potential. This calls for the development of a finite element formulation taking into account the internal constraint. In this contribution, after introducing the continuum describing tetraskelion metamaterials in terms of its deformation energy, we exploit the Virtual Work Principle to get governing equations in weak form. These equations are then localised to get the equilibrium equations and the associated natural boundary conditions. The feasibility of a Galerkin approach to the approximation of tretraskelion metamaterials is tested on duoskelion beams by defining two different equivalent weak formulations that are discretised and then solved by a Newton–Rhapson scheme for clamped-clamped pulling/pushing tests. It is concluded that, given the high nonlinearity of the problem, the choice of the initial guess is crucial to get a solution and, particularly, a desired one among the several bifurcated ones.