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Nonlocal strain gradient-based nonlinear in-plane thermomechanical stability of FG multilayer micro/nano-arches

Yang Zhicheng, Hurdoganoglu Dogus, Sahmani Saeid, Nuhu Abubakar Abdussalam, Safaei Babak

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 2

art. no. e90, 2023

EN

In various microelectromechanical systems, arch-type micro- or nanostructures are extensively used because of their specific geometry. In this regard, the present research exploration deals with the size-dependent nonlinear in-plane stability characteristics of functionally graded (FG) multilayer composite micro/nano-arches subjected to uniform radial pressure together with temperature changes. To this intension, the nonlocal strain gradient (NSG) continuum elasticity is implemented in a higher-order shear flexible arch model to capture nonlocal stress tensor as well as strain gradient size dependencies. With the aid of the Halpin-Tsai homogenization scheme, the material the effective Young’s modulus is extracted layer to layer corresponding to different FG multilayer pattern of composite micro/nano-arches. The NSG-based radial load-defection and radial load-axial load nonlinear equilibrium paths are traced corresponding to several parametrical case studies. It is revealed that the both effects of the nonlocal stress tensor and strain gradient size dependency on the value of lower and upper limit radial pressures are more signifcant than those on the lower and upper limit resultant axial forces. Furthermore, it is observed that by increasing the value of temperature change, the effects of nonlocality and strain gradient size dependency on the NSG-based lower limit radial pressure enhance, while these efects on the NSG-based lower limit resultant axial force decrease.

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Nonlinear buckling mode transition analysis of axial-thermal-electrical‑loaded FG piezoelectric nanopanels incorporating nonlocal and couple stress tensors

Rao Rui, Ye Zijie, Yang Zhicheng, Sahmani Saeid, Safaei Babak

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 3

art. no. e125

EN

Piezoelectric nanostructures are one of the essential components in the design of electromechanical systems and devices at nanoscale. In the present exploration, a size-dependent panel model accommodating the both softening and stiffening features is introduced for nonlinear stability characteristics of functionally graded (FG) piezoelectric cylindrical nanopanels under combinations of axial mechanical load with external electric actuation and temperature change. In accordance with this objective, an efficient numerical strategy based upon the moving Kriging meshfree (MKM) technique is employed within the framework of the nonlocal couple stress (NCS) continuum elasticity. The established NCS-based numerical model has the capability to incorporate the buckling mode transition phenomenon as well as satisfying the function property of Kronecker delta via imposing essential boundary conditions with no use of predefined mesh and directly at the associated nodes. The NCS-based nonlinear equilibrium curves are traced including the modal transition corresponding to various parameter investigations of FG piezoelectric nanopanels. It is deduced that the nonlocal stress tensor leads to increase the difference between the minimum postbuckling loads associated with the first and second buckling modes, while the couple stress tensor causes to reduce it. It is also demonstrated that by changing the sign of electric actuation from negative to positive, the softening character of nonlocality as well as the strengthening character associated with the couple stress size dependency become a bit more significant. Furthermore, the roles of both unconventional stress tensors are more prominent in the value of the second bifurcation point in comparison with the first one.

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Isogeometric couple stress continuum-based linear and nonlinear flexural responses of functionally graded composite microplates with variable thickness

Yang Zhicheng, Lu Hanwen, Sahmani Saeid, Safaei Babak

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 3

497--515

EN

The proposed study scrutinizes the small scale-dependent geometrical nonlinear flexural response of arbitrary-shaped microplates having variable thickness made of functional graded (FG) composites. Accordingly, the modified couple stress continuum elasticity incorporating the von Karman large deflection supposition is established within a quasi-three dimensional (quasi-3D) plate framework in which the transverse shear deformation and normal deflection are assumed to be distributed in and trigonometric schemes. The thickness variation of microplates are assumed in linear, convex and concave patterns. Next, to resolve the couple stress-based nonlinear bending problem, the isogeometric technique incorporating non-uniform B-spline functions is taken into consideration to implement the both discretized-based estimation and accurate geometric description. The gradient of rotation associated with the couple stress type of size dependency causes a stiffening phenomenon in the both linear and nonlinear flexural responses. Also, through considering a change in the thickness variation pattern firstly from the convex kind to the linear one, thereafter from the linear kind to concave one, the role of couple stress size dependency becomes a bit more pronounced. In addition, it is deduced that the gap between nonlinear flexural curves associated with the convex, linear and concave patterns of thickness variation gets larger by changing the boundary conditions of the FG composite arbitrary-shaped microplates from clamped ones to simply supported ones.