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Publications (10 of 31) Show all publications
Salvati, E. (2018). Nanoscale Structural Damage due to Focused Ion Beam Milling of Silicon with Ga ions. Materials letters (General ed.), 13, 346-349
Open this publication in new window or tab >>Nanoscale Structural Damage due to Focused Ion Beam Milling of Silicon with Ga ions
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2018 (English)In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 13, p. 346-349Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-65234 (URN)10.1016/j.matlet.2017.11.043 (DOI)
Available from: 2017-11-17 Created: 2017-11-17 Last updated: 2018-06-25Bibliographically approved
Salvati, E., Brandt, L. R., Papadaki, C., Zhang, H., Mousavi, M., Wermeille, D. & Korsunsky, A. M. (2018). Nanoscale structural damage due to focused ion beam milling of silicon with Ga-ions. Materials letters (General ed.), 213, 346-349
Open this publication in new window or tab >>Nanoscale structural damage due to focused ion beam milling of silicon with Ga-ions
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2018 (English)In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 213, p. 346-349Article in journal (Refereed) Published
Abstract [en]

The exposure of sample to Focused Ion Beam leads to Ga-ion implantation, damage, material amorphisation, and the introduction of sources of residual stress; namely eigenstrain. In this study we employ synchrotron X-ray Reflectivity technique to characterise the amorphous layer generated in a single crystal Silicon sample by exposure to Ga-ion beam. The thickness, density and interface roughness of the amorphous layer were extracted from the analysis of the reflectivity curve. The outcome is compared with the eigenstrain profile evaluated from residual stress analysis by Molecular Dynamics and TEM imaging reported in the literature. (c) 2017 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:kau:diva-65964 (URN)10.1016/j.matlet.2017.11.043 (DOI)000419049300087 ()
Available from: 2018-01-25 Created: 2018-01-25 Last updated: 2018-07-04Bibliographically approved
Ouakad, H. M., El-Borgi, S., Mousavi, M. & Friswell, M. I. (2018). Static and dynamic response of CNT nanobeam using nonlocal strain and velocity gradient theory. Applied Mathematical Modelling, 62, 207-222
Open this publication in new window or tab >>Static and dynamic response of CNT nanobeam using nonlocal strain and velocity gradient theory
2018 (English)In: Applied Mathematical Modelling, ISSN 0307-904X, E-ISSN 1872-8480, Vol. 62, p. 207-222Article in journal (Refereed) Published
Abstract [en]

This paper examines the length-scale effect on the nonlinear response of an electrically actuated Carbon Nanotube (CNT) based nano-actuator using a nonlocal strain and velocity gradient (NSVG) theory. The nano-actuator is modeled within the framework of a doubly-clamped Euler–Bernoulli beam which accounts for the nonlinear von-Karman strain and the electric actuating forcing. The NSVG theory includes three length-scale parameters which describe two completely different size-dependent phenomena, namely, the inter-atomic long-range force and the nano-structure deformation mechanisms. Hamilton's principle is employed to obtain the equation of motion of the nonlinear nanobeam in addition to its respective classical and non-classical boundary conditions. The differential quadrature method (DQM) is used to discretize the governing equations. The key aim of this research is to numerically investigate the influence of the nonlocal parameter and the strain and velocity gradient parameters on the nonlinear structural behavior of the carbon nanotube based nanobeam. It is found that these three length-scale parameters can largely impact the performance of the CNT based nano-actuator and qualitatively alter its resultant response. The main goal of this investigation is to understand the highly nonlinear response of these miniature structures to improve their overall performance.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Carbon nanotube (CNT) Euler–Bernoulli nanobeam, Differential quadrature method (DQM), Material length scales, Nonlocal strain and velocity gradient theory, Static and eigenvalue problem, Actuators, Differentiation (calculus), Eigenvalues and eigenfunctions, Equations of motion, Nanowires, Nonlinear equations, Velocity, Yarn, Bernoulli, Differential quadrature methods, Eigenvalue problem, Material length scale, Velocity gradients, Carbon nanotubes
National Category
Mechanical Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:kau:diva-68387 (URN)10.1016/j.apm.2018.05.034 (DOI)000442067500014 ()2-s2.0-85048573359 (Scopus ID)
Available from: 2018-07-04 Created: 2018-07-04 Last updated: 2018-09-07Bibliographically approved
Tahaei Yaghoubi, S., Balobanov, V., Mousavi, M. & Niiranen, J. (2018). Variational formulations and isogeometric analysis for the dynamics ofanisotropic gradient-elastic Euler-Bernoulli and shear-deformable beams. European journal of mechanics. A, Solids, 69, 113-123
Open this publication in new window or tab >>Variational formulations and isogeometric analysis for the dynamics ofanisotropic gradient-elastic Euler-Bernoulli and shear-deformable beams
2018 (English)In: European journal of mechanics. A, Solids, ISSN 0997-7538, E-ISSN 1873-7285, Vol. 69, p. 113-123Article in journal (Refereed) Published
Abstract [en]

A strain and velocity gradient framework is formulated for centrosymmetric anisotropic Euler-Bernoulli and third-order shear-deformable (TSD) beam models, reducible to Timoshenko beams. The governing equations and boundary conditions are obtained by using variational approach. The strain energy is generalized to include strain gradients and the tensor of anisotropic static length scale parameters. The kinetic energy includes velocity gradients and a tensor of anisotropic length scale parameters and hence the static and kinetic quantities of centrosymmetric anisotropic materials are distinguished in micro- and macroscales. Furthermore, the external work is written in the corresponding general form. Free vibration of simply supported centrosymmetric anisotropic TSD beams is studied by using analytical solution as well as an isogeometric numerical method verified with respect to convergence.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Anisotropic strain and velocity gradient, Shear-deformable beam, Centrosymmetric, Isogeometric analysis
National Category
Applied Mechanics
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:kau:diva-67108 (URN)10.1016/j.euromechsol.2017.11.012 (DOI)000430767100010 ()
Available from: 2018-04-20 Created: 2018-04-20 Last updated: 2019-11-11Bibliographically approved
Yaghoubi, S., Mousavi, M. & Paavola, J. (2017). Buckling of centrosymmetric anisotropic beam structures within strain gradient elasticity. International Journal of Solids and Structures, 109, 84-92
Open this publication in new window or tab >>Buckling of centrosymmetric anisotropic beam structures within strain gradient elasticity
2017 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 109, p. 84-92Article in journal (Refereed) Published
Abstract [en]

Buckling of centrosymmetric anisotropic beams is studied within strain gradient theory. First, the three dimensional anisotropic gradient elasticity theory is outlined. Then the dimension of the three dimensional theory is reduced, resulting in Timoshenko beam as well as Euler–Bernoulli beam theories. The governing differential equations together with the consistent (classical and non-classical) boundary conditions are derived for centrosymmetric anisotropic beams through a variational approach. By considering von Kármán nonlinear strains, the geometric nonlinearity is taken into account. The obtained nonlinear formulation can be used to study the postbuckling configuration. The analysis of size effect on anisotropic beam structures is missing in the literature so far, while the present model allows one to characterize the size effect on the buckling of the centrosymmetric anisotropic micro- and nano-scale beam structures such as micropillars. As a specific case, the governing buckling equation is obtained for the more practical case of orthotropic beams. Finally, the buckling loads for orthotropic simply supported Timoshenko and Euler–Bernoulli beams as well as a clamped Euler–Bernoulli beam are obtained analytically and the effect of the internal length scale parameters on the buckling load is depicted.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Buckling; Anisotropic beam; Strain gradient; Orthotropy; Timoshenko beam; Euler–Bernoulli beam
National Category
Mechanical Engineering
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:kau:diva-62796 (URN)10.1016/j.ijsolstr.2017.01.009 (DOI)000394071700008 ()
Available from: 2017-08-24 Created: 2017-08-24 Last updated: 2019-12-02Bibliographically approved
Li, K., Mousavi, M. & Hostikka, S. (2017). Char cracking of medium density fibreboard due to thermal shock effect induced pyrolysis shrinkage. Fire safety journal, 91, 165-173, Article ID SI.
Open this publication in new window or tab >>Char cracking of medium density fibreboard due to thermal shock effect induced pyrolysis shrinkage
2017 (English)In: Fire safety journal, ISSN 0379-7112, E-ISSN 1873-7226, Vol. 91, p. 165-173, article id SIArticle in journal (Refereed) Published
Abstract [en]

Pyrolysis experiments were conducted on medium density fibreboard (MDF) in inert atmosphere and different ambient pressures, to investigate the char shrinkage and cracking. It is found that the char cracking under uniform heat flux is a typical thermal shock process induced by unbalance shrinkage along the sample thickness during pyrolysis. To predict the number of char fissures, the critical stress criterion and energy conservation theory are used to develop mathematical models under plane constitutive stress state, which reveal that under the same surface degradation the number of char fissures (blisters) strongly relates to the pyrolysis depth at cracking time. Increasing external heat flux decreases the pyrolysis depth and increases the number of char fissures. Both experiments and numerical modelling are used to validate the models. The experimental results show that the horizontal shrinkage is 11% of original length and the micro-structure of char fissures of MDF is less uniform compared to the one of natural wood with a cellular pattern. The surface stresses after cracking are found similarly close to the tensile strength under different heat fluxes, while the surface stresses are very different assuming no crack, which indicates the cracking process reduces the surface stress to lower than the tensile strength. The modelled cracking times are different from the observed cracking time as the fissures are hard to identify at its initial stage and only when they have expanded to certain size the fissures are visually observed. Using the modelled cracking time, the number of char blisters can be well correlated with the pyrolysis depth.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Pyrolysis; Char; Wood; Thermal shock; Shrinkage; Cracking
National Category
Mechanical Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-62797 (URN)10.1016/j.firesaf.2017.04.027 (DOI)000407982400018 ()
Available from: 2017-08-24 Created: 2017-08-24 Last updated: 2019-08-02Bibliographically approved
Fernandes, R., El-Borgi, ., Mousavi, M., Reddy, J. & Mechmoum, . (2017). Nonlinear size-dependent longitudinal vibration of carbon nanotubesembedded in an elastic medium. Physica E: Low-dimensional Systems and Nanostructures, 88, 18-25
Open this publication in new window or tab >>Nonlinear size-dependent longitudinal vibration of carbon nanotubesembedded in an elastic medium
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2017 (English)In: Physica E: Low-dimensional Systems and Nanostructures, ISSN 1386-9477, Vol. 88, p. 18-25Article in journal (Refereed) Published
Abstract [en]

In this paper, we study the longitudinal linear and nonlinear free vibration response of a single walled carbonnanotube (CNT) embedded in an elastic medium subjected to different boundary conditions. This formulation isbased on a large deformation analysis in which the linear and nonlinear von Kármán strains and their gradientare included in the expression of the strain energy and the velocity and its gradient are taken into account in theexpression of the kinetic energy. Therefore, static and kinetic length scales associated with both energies areintroduced to model size effects. The governing motion equation along with the boundary conditions are derivedusing Hamilton's principle. Closed-form solutions for the linear free vibration problem of the embedded CNTrod are first obtained. Then, the nonlinear free vibration response is investigated for various values of lengthscales using the method of multiple scales.

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kau:diva-62798 (URN)10.1016/j.physe.2016.11.007 (DOI)000395615200004 ()
Available from: 2017-08-24 Created: 2017-08-24 Last updated: 2019-09-20Bibliographically approved
Yaghoubi, S. T., Mousavi, M. & Paavola, J. (2017). Size effects on centrosymmetric anisotropic shear deformable beam structures. Zeitschrift für angewandte Mathematik und Mechanik, 97(5), 586-601
Open this publication in new window or tab >>Size effects on centrosymmetric anisotropic shear deformable beam structures
2017 (English)In: Zeitschrift für angewandte Mathematik und Mechanik, ISSN 0044-2267, E-ISSN 1521-4001, Vol. 97, no 5, p. 586-601Article in journal (Refereed) Published
Abstract [en]

In this paper, the size effect on beam structures with centrosymmetric anisotropy is studied within strain gradient elasticity theory. Applying dimension reduction to the three dimensional anisotropic gradient elasticity, the third-order shear deformable (TSD) beam is analysed. A variational approach is used to determine the equilibrium equations of TSD beam together with consistent (classical and non-classical) boundary conditions. The TSD beam theory which is suitable for deep beam structures can be replaced by (less complicated) Euler-Bernoulli beam model for thin beam structures. The anisotropic Euler-Bernoulli beam model is also formulated within the framework of strain gradient theory. This anisotropic beam theory can be used to study size effects for any types of centrosymmetric anisotropy. To address the more practical cases of composite structures, the formulation is simplified for orthotropic and transversely isotropic materials. Finally, the analytical solutions are provided for bending of simply supported (TSD and Euler-Bernoulli) beams as well as clamped Euler-Bernoulli beams. The effect of the crystal orientation with respect to the beam geometry is investigated in these examples.

Place, publisher, year, edition, pages
John Wiley & Sons, 2017
Keywords
Anisotropy, strain gradient, shear deformable beam, orthotropy, centrosymmetric
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kau:diva-65049 (URN)10.1002/zamm.201600153 (DOI)000403057800006 ()
Available from: 2017-11-01 Created: 2017-11-01 Last updated: 2019-09-20Bibliographically approved
Mousavi, M., Reddy, J. N. & Romanoff, J. (2016). Analysis of anisotropic gradient elastic shear deformable plates. Acta Mechanica, 227(12), 3639-3656
Open this publication in new window or tab >>Analysis of anisotropic gradient elastic shear deformable plates
2016 (English)In: Acta Mechanica, ISSN 0001-5970, E-ISSN 1619-6937, Vol. 227, no 12, p. 3639-3656Article in journal (Refereed) Published
Abstract [en]

In this paper, Reddy’s third-order shear deformable plate theory is employed for the analysis of centrosymmetric anisotropic plate structures within strain gradient elasticity. The general three-dimensional anisotropic gradient theory is reduced to a two-dimensional formulation for the analysis of thick plate structures. The third-order shear deformation theory (TSDT) takes into account quadratic variation of the transverse shear strains of the plate and does not require shear correction factors. In order to investigate the case of small strains but moderate rotations, the von Kármán strains are considered. The TSDT is also simplified to anisotropic Kirchhoff plate theory within gradient elasticity. To study specific material properties in more detail, the (Kirchhoff and TSDT) gradient plate theory of general anisotropy is simplified to the more practical case of orthotropic plates. It is observed that the gradient theory provides the capability to capture the size effects in anisotropic plate structures. As case studies, the bending and buckling behaviors of the simply supported orthotropic (Kirchhoff and TSDT) plates are studied. Variationally consistent boundary conditions are also discussed. Finally, analytical solutions are presented for the bending and buckling of simply supported orthotropic Kirchhoff plates. The effects of internal length scales on deflections and buckling loads are presented.

Place, publisher, year, edition, pages
Springer, 2016
National Category
Applied Mechanics
Research subject
Mechanical Engineering
Identifiers
urn:nbn:se:kau:diva-65042 (URN)10.1007/s00707-016-1689-z (DOI)000390025500019 ()
Available from: 2017-11-01 Created: 2017-11-01 Last updated: 2019-09-20Bibliographically approved
Mousavi, M. (2016). Dislocation-based fracture mechanics within nonlocal and gradient elasticity of bi-Helmholtz type - Part II: Inplane analysis. International Journal of Solids and Structures, 105-120
Open this publication in new window or tab >>Dislocation-based fracture mechanics within nonlocal and gradient elasticity of bi-Helmholtz type - Part II: Inplane analysis
2016 (English)In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, p. 105-120Article in journal (Refereed) Published
Abstract [en]

Abstract This paper is the sequel of a companion Part I paper devoted to dislocation-based antiplane fracture mechanics within nonlocal and gradient elasticity of bi-Helmholtz type. In the present paper, the inplane analysis is carried out to study cracks of Modes I and II. Generalized continua including nonlocal elasticity of bi-Helmholtz type and gradient elasticity of bi-Helmholtz type (second strain gradient elasticity) offer nonsingular frameworks for the discrete dislocations. Consequently, the dislocation-based fracture mechanics within these frameworks is expected to result in a regularized fracture theory. By distributing the (climb and glide) edge dislocations, (Modes I and II) cracks are modeled. Distinctive features are captured for crack solutions within second-grade theories (nonlocal and gradient elasticity of bi-Helmholtz type) comparing with solutions within first-grade theories (nonlocal and gradient elasticity of Helmholtz type) as well as classical elasticity. Other than the total stress tensor, all of the field quantities are regularized within second-grade theories, while first-grade theories give singular double stress and dislocation density and classical elasticity leads to singularity in the stress field and dislocation density. Similar to gradient elasticity of Helmholtz type (first strain gradient elasticity), crack tip plasticity is captured in gradient elasticity of bi-Helmholtz type without any assumption of the cohesive zone. ", keywords = Crack; Inplane; Dislocation; Nonlocal elasticity of bi-Helmholtz type; Gradient elasticity of bi-Helmholtz type; Nonsingular, isbn = 0020-7683, doi=https://doi.org/10.1016/j.ijsolstr.2016.03.025

Place, publisher, year, edition, pages
Elsevier, 2016
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kau:diva-65030 (URN)10.1016/j.ijsolstr.2016.03.025 (DOI)000378468600010 ()
Available from: 2017-11-01 Created: 2017-11-01 Last updated: 2019-12-02Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-8515-9907

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