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A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Computer Science and Symmetry/Asymmetry".

Deadline for manuscript submissions: closed (31 January 2021) | Viewed by 35245

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Prof. Dr. Marin Marin

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Department of Mathematics and Computer Science, Transilvania University of Brasov, 500093 Brasov, Romania
Interests: differential equations; partial differential equations; equations of evolution; integral equations; mixed initial-boundary value problems for PDE; termoelasticity; media with microstretch; environments goals; nonlinear problems
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Prof. Dr. Dumitru Baleanu

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Guest Editor

Cankaya Universitesi, Ankara, Turkey
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Prof. Dr. Sorin Vlase

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Guest Editor

Department of Mechanics, “Transilvania” University of Brasov, Brasov, Romania
Interests: mechanics; vibrations; elasticity; composite materials; analytical mechanics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In recent year, a use of composites materials in structural applications has been observed. The composites have revolutionized the field of materials and allow interesting and new developments in different engineering branches. At the same time, in all areas of engineering, there are some products or parts of products or components containing repetitive or identical elements. Here, different types of symmetry can occur. Such systems were studied by various researchers in the last few decades. In civil engineering, for example, most buildings, works of art, halls, etc. have, in their structure, identical parts and symmetries. This has happened since antiquity for different reasons: first, because of an easier, faster, and a cheaper design, and then, easy manufacturing and (less important for engineers but important to the beneficiaries) for aesthetic reasons.

The symmetry in the field of composite materials manifests itself in two different ways, at two levels: one due to the symmetries that appear in the composition of the composite materials and which determine the properties of the materials, and second in the structures manufactured with composites. The study of the obvious importance of the existence of symmetries in the design of composite materials or composite structures of a sandwich type, for example (but also other types), and of the existence of symmetries in structures constructed using also composite materials will be highlighted within this Special Issue. With this issue, we want to disseminate knowledge among researchers, designers, manufacturers, and users in this exciting field.

Prof. Dr. Marin Marin
Prof. Dr. Dumitru Baleanu
Prof. Dr. Sorin Vlase
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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Keywords

composites
symmetric structures
sandwich composite
design of composite
advanced materials

Published Papers (17 papers)

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Editorial

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Open AccessEditorial

Composite Structures with Symmetry

Marin Marin

Dumitru Băleanu

and

Sorin Vlase

Symmetry 2021, 13(5), 792; https://doi.org/10.3390/sym13050792 - 03 May 2021

Viewed by 985

Abstract

In recent years, the use of composite materials in structural applications has been observed. The composites have revolutionized the field of materials and allow for interesting and new developments in different engineering branches. At the same time, in all areas of engineering, there are some products or parts of products or components that contain repetitive or identical elements. Here, different types of symmetry can occur. Such systems have been studied by various researchers in the last few decades. In civil engineering, for example, most buildings, works of art, halls, etc. have, in their structure, identical parts and symmetries. This has happened since antiquity, for different reasons. First, because of their easier, faster, and cheaper design, and second, because of their easy manufacturing and (less important for engineers, but important to the beneficiaries) for aesthetic reasons. The symmetry in the field of composite materials manifests itself in two different ways, at two levels—one due to the symmetries that appear in the composition of the composite materials and that determine the properties of the materials, and second in the structures manufactured with composites. The study of the obvious importance of the existence of symmetries in the design of composite materials or composite structures of a sandwich type, for example (but also other types), and of the existence of symmetries in structures constructed also using composite materials will be highlighted within this Special Issue. With this Issue, we want to disseminate knowledge among researchers, designers, manufacturers, and users in this exciting field. Full article

(This article belongs to the Special Issue Composite Structures with Symmetry)

Research

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Open AccessArticle

New Design of Composite Structures Used in Automotive Engineering

Vasile Gheorghe

Maria Luminita Scutaru

Virgil Barbu Ungureanu

Eliza Chircan

and

Mihai Ulea

Symmetry 2021, 13(3), 383; https://doi.org/10.3390/sym13030383 - 27 Feb 2021

Cited by 9 | Viewed by 2269

Abstract

The paper proposes composite materials for the manufacturing of parts of the car body structure, namely a door. This work aims to analyze the possibility of replacing the metal door of a vehicle with a door made of composite materials. Specific issues related to this replacement are analyzed in the paper. Test specimens were made of composite materials of different sizes, using several types of constituents to determine which material might be most suitable to replace metal in the manufacturing of the door. The choice of materials for the car door was made starting from the characteristics of the analyzed composite materials, but also taking into account the manufacturing possibilities and other engineering limitations. The behavior of the automotive structure as analyzed, using the finite element method for determining the stresses in the structure. Experimental verifications were performed on an experimental stand which has been specially designed for this purpose, to validate the proposed model. Full article

(This article belongs to the Special Issue Composite Structures with Symmetry)

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Open AccessArticle

Application of Artificial Intelligence (AI) for Sustainable Highway and Road System

and

Symmetry 2021, 13(1), 60; https://doi.org/10.3390/sym13010060 - 31 Dec 2020

Cited by 8 | Viewed by 1843

Abstract

There are several environmental factors such as temperature differential, moisture, oxidation, etc. that affect the extended life of the modified asphalt influencing its desired adhesive properties. Knowledge of the properties of asphalt adhesives can help to provide a more resilient and durable asphalt surface. In this study, a hybrid of Bayesian optimization algorithm and support vector regression approach is recommended to predict the adhesion force of asphalt. The effects of three important variables viz., conditions (fresh, wet and aged), binder types (base, 4% SB, 5% SB, 4% SBS and 5% SBS), and Carbon Nano Tube doses (0.5%, 1.0% and 1.5%) on adhesive force are taken into consideration. Real-life experimental data (405 specimens) are considered for model development. Using atomic force microscopy, the adhesive strength of nanoscales of test specimens is determined according to functional groups on the asphalt. It is found that the model predictions overlap with the experimental data with a high R² of 90.5% and relative deviation are scattered around zero line. Besides, the mean, median and standard deviations of experimental and the predicted values are very close. In addition, the mean absolute Error, root mean square error and fractional bias values were found to be low, indicating the high performance of the developed model. Full article

(This article belongs to the Special Issue Composite Structures with Symmetry)

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Open AccessArticle

Experimental Study on Dynamic Properties of a Recycled Composite Sleeper and Its Theoretical Model

Zhenhang Zhao

Ying Gao

and

Chenghui Li

Symmetry 2021, 13(1), 17; https://doi.org/10.3390/sym13010017 - 24 Dec 2020

Cited by 2 | Viewed by 1211

Abstract

As a symmetrical structure in track system, the dynamic properties of recycled composite sleepers are important factors affecting the vibration characteristics of track structure. To study the viscoelastic dynamic properties of the composite sleeper, dynamic mechanical analysis (DMA) tests of a composite sleeper at −5 to 30 °C and 1–60 Hz were first carried out, and then the time-temperature superposition (TTS) and the Williams–Landel–Ferry (WLF) formula were used to predict the dynamic properties of a composite sleeper at a wider frequency range. Finally, the generalized Maxwell model was adopted to characterize the dynamic properties of the composite sleeper, which provides parameters and theoretical models for dynamic analysis. The research results show that the composite sleeper has obvious viscoelasticity. Its modulus is large at low temperature or high frequency. On the contrary, the modulus is small at high temperature or low frequency. Under the test conditions, its complex modulus ranges from 1500 to 2700 MPa. The loss factor is in the range of 0.08–0.13. Using the generalized Maxwell model (n = 4), which can better reflect the dynamic properties of the composite sleeper. Full article

(This article belongs to the Special Issue Composite Structures with Symmetry)

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Open AccessArticle

Creep Response of Neat and Carbon-Fiber-Reinforced PEEK and Epoxy Determined Using a Micromechanical Model

Mostafa Katouzian

and

Sorin Vlase

Symmetry 2020, 12(10), 1680; https://doi.org/10.3390/sym12101680 - 14 Oct 2020

Cited by 7 | Viewed by 1628

Abstract

A micromechanical model is developed to study the creep phenomena with neat and carbon-fiber-reinforced PEEK (Polyetheretherketon) and epoxy. The model considers that the continuous elastic circular fibers form a regular array inside the matrix material. In this study, the fibers are considered to be linear elastic and anisotropic, while the matrix has a nonlinear viscoelastic behavior. The approach describes the time-dependent response of unidirectional viscoelastic composites subjected to various types of loading conditions. A comparison between the finite element analysis and the proposed micromechanical model shows a good agreement. Experimental tests validate the results obtained using the proposed theoretical model. Full article

(This article belongs to the Special Issue Composite Structures with Symmetry)

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Open AccessArticle

Determination of Young’s Moduli of the Phases of Composite Materials Reinforced with Longitudinal Fibers, by Global Measurements

and

Symmetry 2020, 12(10), 1607; https://doi.org/10.3390/sym12101607 - 27 Sep 2020

Cited by 4 | Viewed by 1014

Abstract

The properties of a composite material are determined by the properties of the constitutive materials. In engineering practice, there are many situations in which we have composite material, but we do not have information about the properties of each phase component. The measurements we can make in such cases are on the existing material, thus being able to determine, experimentally, the global physical properties of the composite. The possibility of realizing an estimate of the mechanical properties of each component poses a problem if we start from these measurements. The paper proposes a method to achieve this, starting from the theoretical estimates established in the literature, then illustrated by an example to determine the properties of wood. Wood is a transverse isotropic material and therefore the constitutive law has symmetries that are manifested in the decrease of the number of parameters that define the stress-strain liason, defined only by five independent parameters. The proposed method can be extended to a diversity of models and materials used in the study of composite materials. Full article

(This article belongs to the Special Issue Composite Structures with Symmetry)

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Open AccessArticle

Preliminary Design and Cross-Sectional Form Study of Closed-Type Concrete-Filled Steel Tube Support for Traffic Tunnel

Lei Li

and

Ke Lei

Symmetry 2020, 12(8), 1368; https://doi.org/10.3390/sym12081368 - 17 Aug 2020

Cited by 2 | Viewed by 1797

Abstract

In view of the structural form and common construction methods of traffic tunnels, the bearing performance of the closed-type CFST support designed for traffic tunnels is studied. The closed-type CFST support, which consist of a CFST girder with external shotcrete, is improved from the CFST support used in mine roadways. The reasonable cross-sectional form of closed-type CFST support is analyzed by the FEM. The closed-type CFST support is mainly composed of CFST arches, a shotcrete layer, sleeves, and blind flanges. The post-buckling analysis of the closed-type CFST circular arch members using circular-shaped, rectangular-shaped, triangular-shaped, and trapezoidal-shaped steel tubes is implemented. The result shows that the closed-type CFST support has better performance than the traditional tunnel support. The study also found that for closed-type CFST support, the triangular-shaped steel tube section has the highest bearing capacity, stiffness, and steel utilization rate, which is the preferred cross-sectional form. The bearing capacity of the circular-shaped steel tube section is acceptable. Moreover, the circular-shaped steel tubes are more convenient to obtain and process, so it is also an optional cross-sectional form. The square-shaped and trapezoidal-shaped steel tube sections have neither performance advantages nor economic efficiency, so these two forms are not recommended. Full article

(This article belongs to the Special Issue Composite Structures with Symmetry)

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Open AccessArticle

The Response of Nanobeams with Temperature-Dependent Properties Using State-Space Method via Modified Couple Stress Theory

Ahmed E. Abouelregal

and

Marin Marin

Symmetry 2020, 12(8), 1276; https://doi.org/10.3390/sym12081276 - 02 Aug 2020

Cited by 66 | Viewed by 2060

Abstract

At present, with the development in nanotechnology, nanostructures with temperature-dependent properties have been used in nano-electromechanical systems (NEMS). Thus, introducing an accurate mathematical model of nanobeams with temperature-dependent properties is a major and important topic for the design of NEMS. This paper aims to discuss nonlocal nanobeams analysis depending on the theories of Euler–Bernoulli and modified couple-stress (MCS). It also is assumed that the thermal conductivity of the nanobeam is dependent on the temperature. Physical fields of the nanobeam are obtained utilizing Laplace transform and state-space techniques. The effects of the size and nonlocal parameters, variability of thermal conductivity and couple stress on various distributions are presented graphically and studied in detail. Numerical results are presented as application scales and the design of nanoparticles, nanoscale oscillators, atomic force microscopes, and nanogenerators, in which nanoparticles as nanobeams act as essential and basic elements. Full article

(This article belongs to the Special Issue Composite Structures with Symmetry)

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Open AccessArticle

Generalized Thermoelastic Functionally Graded on a Thin Slim Strip Non-Gaussian Laser Beam

Sayed M. Abo-Dahab

Ahmed E. Abouelregal

and

Marin Marin

Symmetry 2020, 12(7), 1094; https://doi.org/10.3390/sym12071094 - 02 Jul 2020

Cited by 24 | Viewed by 1560

Abstract

The present study utilizes the generalized thermoelasticity theory, with one thermal relaxation time (TR), to examine the thermoelastic problem of a functionally graded thin slim strip (TSS). The authors heated the plane surface bounding using a non-Gaussian laser beam with a pulse length [...] Read more.

2

ps. The material characteristics varied continually based on exponential functions. Moreover, the equations governing the generalized thermoelasticity for a functionally graded material (FGM) are recognized. The problem’s ideal solution was primarily obtained in the Laplace transform (LT) space. The LTs were converted numerically because of the considerable importance of the response in the transient state. For a hypothetical substance, the numerical procedures calculating the displacement, stress, temperature and strain were given. The analogous problem solution to an isotropic homogeneous material was provided by defining the parameter of non-homogeneity adequately. The obtained results were displayed using graphs to illustrate the extent to which non-homogeneity affected displacement, stress, temperature and strain. A comparison was been made between the present study and those previously obtained by others, when the new parameters vanish to show the impact of the non-homogeneity, TSS and laser parameters on the phenomenon. The results obtained indicate a significant strong impact of FGM, TSS and laser parameters. Full article

(This article belongs to the Special Issue Composite Structures with Symmetry)

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Open AccessFeature PaperArticle

An Improved Near-field Magnetic Probe Radiation Profile Boundaries Assessment for Optimal Radiated Susceptibility Pre-Mapping

Algimantas Valinevicius

Darius Andriukaitis

Mindaugas Zilys

and

Dangirutis Navikas

Symmetry 2020, 12(7), 1063; https://doi.org/10.3390/sym12071063 - 28 Jun 2020

Cited by 4 | Viewed by 2123

Abstract

In this paper, the near-field radiated susceptibility pre-mapping method is proposed using the improved near-field probe power radiation profile assessment. The modelling of the electromagnetic field strength in 80–3000 MHz range in the proximity of the near-field probe was performed. The −6 dB aperture boundaries of the near-field probe and their variation, due to the proximity of the radio frequency (RF) printed circuit board (PCB) components, were determined, while the aperture map distortion, arising from the proximity of the passive RF PCB components were evaluated. The scanning path requirements for the RF susceptibility mapping were determined. The simulation of improved near-field probe absolute magnetic field strength reference map in open-air conditions is carried out in this work. The comparative analysis using the absolute maximum difference metric of orthogonal absolute magnetic field map cross-sections between the reference map and magnetic field maps affected by the proximity of the components was carried out. The experimental study of the RF amplifier stage susceptibility map with susceptibility mapping measurement results are presented in this work. Full article

(This article belongs to the Special Issue Composite Structures with Symmetry)

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Open AccessArticle

A Bayesian Approach to Heavy-Tailed Finite Mixture Autoregressive Models

Mohammad Reza Mahmoudi

and

Symmetry 2020, 12(6), 929; https://doi.org/10.3390/sym12060929 - 02 Jun 2020

Cited by 3 | Viewed by 1675

Abstract

In this paper, a Bayesian analysis of finite mixture autoregressive (MAR) models based on the assumption of scale mixtures of skew-normal (SMSN) innovations (called SMSN–MAR) is considered. This model is not simultaneously sensitive to outliers, as the celebrated SMSN distributions, because the proposed MAR model covers the lightly/heavily-tailed symmetric and asymmetric innovations. This model allows us to have robust inferences on some non-linear time series with skewness and heavy tails. Classical inferences about the mixture models have some problematic issues that can be solved using Bayesian approaches. The stochastic representation of the SMSN family allows us to develop a Bayesian analysis considering the informative prior distributions in the proposed model. Some simulations and real data are also presented to illustrate the usefulness of the proposed models. Full article

(This article belongs to the Special Issue Composite Structures with Symmetry)

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Open AccessArticle

An Eigenvalues Approach for a Two-Dimensional Porous Medium Based Upon Weak, Normal and Strong Thermal Conductivities

and

Symmetry 2020, 12(5), 848; https://doi.org/10.3390/sym12050848 - 21 May 2020

Cited by 43 | Viewed by 1741

Abstract

This work is devoted to the investigation of a two-dimensional porous material under weak, strong and normal conductivity, using the eigenvalues method. By using Laplace–Fourier transformations with the eigenvalues technique, the variables are analytically obtained. The derived technique is assessed with numerical results that are obtained from the porous mediums using simplified symmetric geometry. The results, including the displacements, temperature, stresses and the change in the volume fraction field, are offered graphically. Comparisons are made among the outcomes obtained under weak, normal and strong conductivity. Full article

(This article belongs to the Special Issue Composite Structures with Symmetry)

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Open AccessArticle

New Weighted Opial-Type Inequalities on Time Scales for Convex Functions

Ahmed A. El-Deeb

and

Dumitru Baleanu

Symmetry 2020, 12(5), 842; https://doi.org/10.3390/sym12050842 - 21 May 2020

Cited by 8 | Viewed by 1676

Abstract

Our work is based on the multiple inequalities illustrated in 1967 by E. K. Godunova and V. I. Levin, in 1990 by Hwang and Yang and in 1993 by B. G. Pachpatte. With the help of the dynamic Jensen and Hölder inequality, we generalize a number of those inequalities to a general time scale. In addition to these generalizations, some integral and discrete inequalities will be obtained as special cases of our results. Full article

(This article belongs to the Special Issue Composite Structures with Symmetry)

Open AccessFeature PaperArticle

Determination of Forces and Moments Per Unit Length in Symmetric Exponential FG Plates with a Quasi-Triangular Hole

Mohammad Jafari

Mohammad Hossein Bayati Chaleshtari

Hamid Abdolalian

Eduard-Marius Craciun

and

Luciano Feo

Symmetry 2020, 12(5), 834; https://doi.org/10.3390/sym12050834 - 19 May 2020

Cited by 16 | Viewed by 1701

Abstract

In this study, the resultant forces and moments acting on infinite symmetric FGPs with a triangular hole subject to uniaxial tensile load were examined via an analytical method using the complex variable approach. The mechanical properties of graded plates are hypothesized to vary throughout the thickness exponentially. The impact of various factors, namely hole orientation, hole aspect ratio as well as the hole corner curve on stress distribution and moment resultants is considered. In order to approve the credibility of the analytical approach, its outcomes are compared to numerical results acquired from ABAQUS finite element modeling. This comparison showed a favorable agreement level among the acquired analytical and numerical outcomes. Based on these results, the mentioned factors entail a considerable effect on the distribution of resultant forces and moments at the proximity of the hole and the load bearing tolerance of functional grated plates with holes may be enhanced by suitable selection of the aforementioned parameters. Full article

(This article belongs to the Special Issue Composite Structures with Symmetry)

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Open AccessFeature PaperArticle

Frequency Response Evaluation of Guitar Bodies with Different Bracing Systems

Mircea Mihălcică

Mariana D. Stanciu

and

Sorin Vlase

Symmetry 2020, 12(5), 795; https://doi.org/10.3390/sym12050795 - 09 May 2020

Cited by 7 | Viewed by 5862

Abstract

Wood is a natural composite, having a porous structure, with a complex elastic symmetry specific to orthotropic solid, influenced by three mutually perpendicular planes of elastic symmetry. The classical guitar is obtained from different wooden species, each of them having their own elastic properties and, as a whole, forming a lignocellulosic composite structure. Generally, some constructive parts of the classical guitar body are based on symmetry, starting from the structural features of wooden plates, which are symmetrically cut, and some patterns of the stiffening bars. The other elements, such as the strings system, are not symmetric. This study aims to evaluate the frequency responses of the guitar body as a symmetrical mechanical system from constructive points of view. Because theoretical results (analytic and numeric) regarding the symmetrical systems cannot be applied to quasi-symmetric systems, the dynamic response was analyzed from experiments performed on four types of classical guitar body (without neck), different from each other by the pattern of stiffening bars placed inside of the top plate. The experiments were performed using a Brüel&Kjær mini-shaker to excite the structure, and the signal was captured with accelerometers. The symmetric behavior of coupled plates from the guitar body was noticed in the case of an applied dynamic force of 110 Hz and 440 Hz, but in the case of 146 Hz, 588 Hz, 720 Hz, quasi skew symmetrical modes were recorded. Full article

(This article belongs to the Special Issue Composite Structures with Symmetry)

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Open AccessFeature PaperArticle

A GL Model on Thermo-Elastic Interaction in a Poroelastic Material Using Finite Element Method

Tareq Saeed

Ibrahim Abbas

and

Marin Marin

Symmetry 2020, 12(3), 488; https://doi.org/10.3390/sym12030488 - 24 Mar 2020

Cited by 109 | Viewed by 3316

Abstract

The purpose of this study is to provide a method to investigate the effects of thermal relaxation times in a poroelastic material by using the finite element method. The formulations are applied under the Green and Lindsay model, with four thermal relaxation times. Due to the complex governing equation, the finite element method has been used to solve these problems. All physical quantities are presented as symmetric and asymmetric tensors. The effects of thermal relaxation times and porosity in a poro-thermoelastic medium are studied. Numerical computations for temperatures, displacements and stresses for the liquid and the solid are presented graphically. Full article

(This article belongs to the Special Issue Composite Structures with Symmetry)

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Open AccessArticle

A Study of Deformations in a Thermoelastic Dipolar Body with Voids

and

Symmetry 2020, 12(2), 267; https://doi.org/10.3390/sym12020267 - 09 Feb 2020

Cited by 4 | Viewed by 1397

Abstract

In this paper, we consider the mixed initial boundary value problem in the context of a thermoelastic porous body having a dipolar structure. We intend to analyze the rate of decay of solutions to this problem to ensure that in a finite time, they become null. In our main result, we find that the combined contribution of the dipolar constitution of the body together with voids dissipation and thermal behavior cannot cause vanishing of the deformations in a finite time. Full article

(This article belongs to the Special Issue Composite Structures with Symmetry)

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