Dispersion of waves in FG porous nanoscale plates based on NSGT in thermal environment

Ebrahimi, Farzad,Seyfi, Ali,Dabbagh, Ali Techno-Press 2019 Advances in nano research Vol.7 No.5

In the present study, nonlocal strain gradient theory (NSGT) is developed for wave propagation of functionally graded (FG) nanoscale plate in the thermal environment by considering the porosity effect. $Si_3N_4$ as ceramic phase and SUS304 as metal phase are regarded to be constitutive material of FG nanoplate. The porosity effect is taken into account on the basis of the newly extended method which considers coupling influence between Young's modulus and mass density. The motion relation is derived by applying Hamilton's principle. NSGT is implemented in order to account for small size effect. Wave frequency and phase velocity are obtained by solving the problem via an analytical method. The effects of different parameters such as porosity coefficient, gradient index, wave number, scale factor and temperature change on phase velocity and wave frequency of FG porous nanoplate have been examined and been presented in a group of illustrations.

Evaluation of additional elements in MCrAlY coating deposited by low pressure plasma spray to study phase constituent

Ali Ebrahimi,Mahdi Bozorg Nezhad Nobijari,Ali Bakhshi 한국표면공학회 2013 한국표면공학회 학술발표회 초록집 Vol.2013 No.11

On bending characteristics of smart magneto-electro-piezoelectric nanobeams system

Shariati, Ali,Ebrahimi, Farzad,Karimiasl, Mahsa,Selvamani, Rajendran,Toghroli, Ali Techno-Press 2020 Advances in nano research Vol.9 No.3

The content of this study focuses on bending of flexoelectric Magneto-Electro-Elastic (MEE) nanobeams inserted within the foundation of Winkler-Pasternak according to nonlocal elasticity theory. Applying Hamilton's principle, the nonlocal nanobeams' governing equations in the framework higher order refined beam theory are attained and resolved through adapting an analytical solution. A parametric research is demonstrated for studying the effects that magneto-electro-mechanical loadings, the nonlocal parameter, flexoelectric, as well as the aspect ratio all have on the deflection properties of nanobeams. A discovery lead to beam geometrical parameters, the boundary conditions, flexoelectricity and nonlocal parameter partake substantial effects on nanoscale beams' dimensionless deflection.

Investigation of microstructure and surface effects on vibrational characteristics of nanobeams based on nonlocal couple stress theory

Shariati, Ali,Barati, Mohammad Reza,Ebrahimi, Farzad,Toghroli, Ali Techno-Press 2020 Advances in nano research Vol.8 No.3

The article brings the study of nonlocal, surface and the couple stress together to apparent the frequency retaliation of FG nanobeams (Functionally graded). For the examination of frequency retaliation, the article considers the accurate spot of neutral axis. This article aims to enhance the coherence of proposed model to accurately encapsulate the significant effects of the nonlocal stress field, size effects together with material length scale parameters. These considered parameters are assimilated through what are referred to as modified couple stress as well as nonlocal elasticity theories, which encompasses the stiffness-hardening and softening influence on the nanobeams frequency characteristics. Power-law distribution is followed by the functional gradation of the material across the beam width in the considered structure of the article. Following the well-known Hamilton's principle, fundamental basic equations alongside their correlated boundary conditions are solved analytically. Validation of the study is also done with published result. Distinct parameters (such as surface energy, slenderness ratio, as nonlocal material length scale and power-law exponent) influence is depicted graphically following the boundary conditions on non-dimensional FG nanobeams frequency.

Wave dispersion characteristics of porous graphene platelet-reinforced composite shells

Farzad Ebrahimi,Ali Seyfi,Ali Dabbagh,Francesco Tornabene 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.71 No.1

Wave propagation analysis of a porous graphene platelet reinforced (GPLR) nanocomposite shell is investigated for the first time. The homogenization of the utilized material is procured by extending the Halpin-Tsai relations for the porous nanocomposite. Both symmetric and asymmetric porosity distributions are regarded in this analysis. The equations of the shell’s motion are derived according to Hamilton’s principle coupled with the kinematic relations of the first-order shear deformation theory of the shells. The obtained governing equations are considered to be solved via an analytical solution which includes two longitudinal and circumferential wave numbers. The accuracy of the presented formulations is examined by comparing the results of this method with those reported by former authors. The simulations reveal a stiffness decrease in the cases which porosity influences are regarded. Also, one must pay attention to the effects of longitudinal wave number on the wave dispersion curves of the nanocomposite structure.

Investigating vibrational behavior of graphene sheets under linearly varying in-plane bending load based on the nonlocal strain gradient theory

Shariati, Ali,Barati, Mohammad Reza,Ebrahimi, Farzad,Singhal, Abhinav,Toghroli, Ali Techno-Press 2020 Advances in nano research Vol.8 No.4

A study that primarily focuses on nonlocal strain gradient plate model for the sole purpose of vibration examination, for graphene sheets under linearly variable in-plane mechanical loads. To study a better or more precise examination on graphene sheets, a new advance model was conducted which carries two scale parameters that happen to be related to the nonlocal as well as the strain gradient influences. Through the usage of two-variable shear deformation plate approach, that does not require the inclusion of shear correction factors, the graphene sheet is designed. Based on Hamilton's principle, fundamental expressions in regard to a nonlocal strain gradient graphene sheet on elastic half-space is originated. A Galerkin's technique is applied to resolve the fundamental expressions for distinct boundary conditions. Influence of distinct factors which can be in-plane loading, length scale parameter, load factor, elastic foundation, boundary conditions, and nonlocal parameter on vibration properties of the graphene sheets then undergo investigation.

On transient hygrothermal vibration of embedded viscoelastic flexoelectric/piezoelectric nanobeams under magnetic loading

Shariati, Ali,Ebrahimi, Farzad,Karimiasl, Mahsa,Vinyas, M.,Toghroli, Ali Techno-Press 2020 Advances in nano research Vol.8 No.1

This paper investigates the vibration characteristics of flexoelectric nanobeams resting on viscoelastic foundation and subjected to magneto-electro-viscoelastic-hygro-thermal (MEVHT) loading. In this regard, the Nonlocal strain gradient elasticity theory (NSGET) is employed. The proposed formulation accommodates the nonlocal stress and strain gradient parameter along with the flexoelectric coefficient to accurately predict the frequencies. Further, with the aid of Hamilton's principle the governing differential equations are derived which are then solved through Galerkin-based approach. The variation of the natural frequency of MEVHT nanobeams under the influence of various parameters such as the nonlocal strain gradient parameter, different field loads, power-law exponent and slenderness ratio are also investigated.

Analysis of propagation characteristics of elastic waves in heterogeneous nanobeams employing a new two-step porosity-dependent homogenization scheme

Ebrahimi, Farzad,Dabbagh, Ali,Rabczuk, Timon,Tornabene, Francesco Techno-Press 2019 Advances in nano research Vol.7 No.2

The important effect of porosity on the mechanical behaviors of a continua makes it necessary to account for such an effect while analyzing a structure. motivated by this fact, a new two-step porosity dependent homogenization scheme is presented in this article to investigate the wave propagation responses of functionally graded (FG) porous nanobeams. In the introduced homogenization method, which is a modified form of the power-law model, the effects of porosity distributions are considered. Based on Hamilton's principle, the Navier equations are developed using the Euler-Bernoulli beam model. Thereafter, the constitutive equations are obtained employing the nonlocal elasticity theory of Eringen. Next, the governing equations are solved in order to reach the wave frequency. Once the validity of presented methodology is proved, a set of parametric studies are adapted to put emphasis on the role of each variant on the wave dispersion behaviors of porous FG nanobeams.

Investigating vibration behavior of smart imperfect functionally graded beam subjected to magnetic-electric fields based on refined shear deformation theory

Ebrahimi, Farzad,Jafari, Ali Techno-Press 2017 Advances in nano research Vol.5 No.4

In this disquisition, an exact solution method is developed for analyzing the vibration characteristics of magneto-electro-elastic functionally graded (MEE-FG) beams by considering porosity distribution and various boundary conditions via a four-variable shear deformation refined beam theory for the first time. Magneto-electroelastic properties of porous FG beam are supposed to vary through the thickness direction and are modeled via modified power-law rule which is formulated using the concept of even and uneven porosity distributions. Porosities possibly occurring inside functionally graded materials (FGMs) during fabrication because of technical problem that lead to creation micro-voids in FG materials. So, it is necessary to consider the effect of porosities on the vibration behavior of MEE-FG beam in the present study. The governing differential equations and related boundary conditions of porous MEE-FG beam subjected to physical field are derived by Hamilton's principle based on a four-variable tangential-exponential refined theory which avoids the use of shear correction factor. An analytical solution procedure is used to achieve the natural frequencies of porous-FG beam supposed to magneto-electrical field which satisfies various boundary conditions. A parametric study is led to carry out the effects of material graduation exponent, porosity parameter, external magnetic potential, external electric voltage, slenderness ratio and various boundary conditions on dimensionless frequencies of porous MEE-FG beam. It is concluded that these parameters play noticeable roles on the vibration behavior of MEE-FG beam with porosities. Presented numerical results can be applied as benchmarks for future design of MEE-FG structures with porosity phases.

The experimental and numerical study of the effects of welding angle on forming multilayered sheets in U-bending operations

Ali Adelkhani,Hadi Ebrahimi,Mohammad Mahdi Attar 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.1

Performed was a set of experimental tests to scrutinize the effect of the welding angle and material properties on the spring-back and the displacement as well as the amount of required load in the standard bending test according to ASTM B820-18 with some numerical simulation conducting to compare those results and calculate stress through the bending process. The applied sheets were made of Copper, Aluminum and St12, DIN1623 with a thickness of 1 mm. In this study, prepared is a welding line at three angles, 30 0 , 45 0 and 90 0 whilst two punch’s radiuses have been considered. Additionally, three orientations 0 0 , 45 0 and 90 0 have been considered to check the homogeneity of the plate. Added to this, a numerical analysis utilizing finite element methods was conducted to validate the results obtained from the experimental tests. based on results, there wasn’t seen any considerable difference (less than 10 %) in terms of un-homogeneity in results while the minimum springback pressure for the St12-Cu sheet was equal to 3.6, and measured 3.70 for St12-Al. In the numerical solution, the maximum stress for the welding angle, 30, in St12-Al sheet was 305 MPa with the springback decreasing from 0.1 to 0.5 whenever the pitch radius changing from 5 to 10 mm.