Multi-layered small-scale structures have engrossed a great deal of attention in the past few years.
Nano/micro-structures are found as multi-layered in nature which shows the importance of studying them
considering the layer interactions. To this end, in this paper, a brief review on the highlighted previous
investigations on modelling small-scale structures considering layer interactions is presented in the
framework of dynamic analysis. The importance of correctly modelling the size-dependence mechanical
formulation and layer interaction is discussed in detail for both nano and micro scale structures.
A well-known class of small-scale are multi-layered size-dependent structures which
may be fabricated using different fabrication processes such as roll-to-roll process, nanotransfer
printing, etc. [1,2]. Due to the very small geometric size of such structures, molecular
interactions and van der Waals forces become considerable and therefore the continuum
classical models are incapable of modelling such structures; hence, it is important to use an
appropriate accurate model to study such structures. Since experimentally studying such
structures require high-tech laboratories and investigating considerable budget, it is more
logical and convenient to find an accurate way of modelling the mechanical behavior using
theoretical formulations. To this end, this review paper presents the previous investigations
on multi-layered small-scale structures to show the importance of considering the layer
interactions and size- dependency effects; however, the previous studies on single-layered
small-scale structures could be found in [3-13] for micro structures and [14-22] for nanostructures
which is out of the scope of this review. Accordingly, as shown in (Figure 1), this
review paper is divided into four main sections; in the first section, an introduction is given on
layered small-scale structures emphasizing on the importance of modelling these structures.
In Section 2, highlighted research studies on dynamics of micro-scale layered structures
are presented which is divided into two subsections discussing nano-beam structures and nano-plate structures. Similarly, Section 3 presents the highlighted
literature on the dynamics of nanoscale layered structures which is
also divided into nano-beams and nano-plates as subsections.
Figure 1: Flowchart of the structure of this mini review paper.
As mentioned previously, in small-scale structures, the classical
continuum theories are invalid, and a proper type of modelling
needs to be used. Modified couple stress theory (MCST) [23-28]
and its derivation strain gradient theory (SGT) [29-31] have been
used by researchers over past few years to model and analyze
micro-scale structures. Accordingly, in this section, the dynamics of
multi-layered micro-scale structures are investigated which have
great potential applications in MEMS.
Multi-layered micro-beams
For the case of dynamic analysis of multi-layered micro-scale
structures, Ghayesh et al. [32] investigated the nonlinear dynamic
response of three-layered micro-beams via the MCST; higher-order
shear deformable beam theory was used to model the micro-beams
considering imperfection in the structures. Frequency-responses of
the layered micro-beams was presented and both hardening and
softening behavior were observed. Newton-Raphson method was
used by Farokhi et al. [33] to comprehend the mechanical response
of clamped layered micro-beams. Farokhi et al. [34] examined
the nonlinear vibration behavior of extensible micro-beams
using Timoshenko beam theory and MCST; it was shown that the
longitudinal, transverse, and rotational motions show hardening
effect in the nonlinear frequency-response. Nonlinear resonance
[35-38] of layered micro-beams with cantilevered boundary
condition has also been studied by Ghayesh et al. [39] using
Bernoulli-Euler beam theory. The effects of the excitation amplitude
and the MCST small-scale parameter were discussed in detail.
Khaniki [40] investigated the forced dynamic response of multilayered
micro-beams under the action of moving nanoparticle.
Euler-Bernoulli beam theory in conjunction with MCST was used to
model the micro-beam system resting on a Winkler elastic medium;
it was shown that increasing the MCST parameter leads to lower
dynamic deformations. Curved micro-structures have also been
examined by researchers in the past few years. Ghayesh et al. [41]
studied the complex motion of small-size arches. Timoshenko beam
theory together with von-Karman nonlinearity and MCST was used
to model the structure and solved using a well-optimized numerical
technique.
Multi-layered micro-plates
For the case of plate analysis, Ghayesh [42] investigated the
nonlinear oscillation behavior of three-layered microplates; the
MCST in conjunction with von-Karman nonlinearity, Kirchhoff plate
theory and Hamilton’s principle [43-52] were used to model the
microstructure accurately it was shown that the general behavior
of such micro structures is hardening type. Moreover, Yang [53]
examined the linear vibration response of multi-layered microplates
using a revised MCST; it was shown that the size-dependent
term has a considerable effect in varying the natural frequency
parameters.
For nano-scale structures, as for micro-scale structures, the
classical continuum theories are invalid, and a proper type of
modelling needs to be used. Nonlocal continuum theory is used
by researchers to study the nano-scale structures which have
been presented in differential [54,55], integral [56] and two-phase
[57,58] forms. Accordingly, in this section, multi-layered nano-scale
structures are discussed which have broad applications in NEMS.
Multi-layered nano-beams
Layered nano-beams have received a great deal of attention in
the past years. For the sake of free vibration analysis, Karličić et al.
[59] examined the free vibration response of multi-layered nanobeams.
The Euler-Bernoulli beam theory, Winkler elastic model
and differential form of the nonlocal theory were used to model the
nano-system; it was shown that increasing the number of layers
have a considerable effect in changing the natural frequency term
of each layer. Khaniki [60,61] presented the dynamic response of
double- layered isotropic and functionally graded nano-beams using
the two-phase local/nonlocal model. Natural frequencies were
observed for different boundary conditions and the ill-posed issue
overcame. Dynamic response of multi-layered nano-beams acting
upon a moving mass or force was studied lately by researchers.
Hashemi [62,63] examined the forced deformation of layered nanobeams
with elastic and viscoelastic [64-66] interactions. Nonlocal
elastic theory, the Euler-Bernoulli beam theory and the Kelvin-
Voigt viscoelastic models were used; it was shown that the sizeeffect
has a considerable effect on the enhancement of the forced
deformations.
Multi-layered nano-plates
Similarly, layered nano-plates have been investigated by
researchers in the past years. Karličić et al. [67,68] investigated
the free vibration response of multi-layered nano-plate systems.
Kelvin-Voigt viscoelastic model [69] was used to model the
layer interactions and Kirchhoff-Love plate theory was used in
conjunction with nonlocal theory to model the nano- plates; the
influence of different parameters on the vibration response was
discussed, showing the importance of considering size-effects.
Mahmoudpour [70] studied the nonlinear vibration of multilayered
nano-plates with simply supported boundary conditions.
Mindlin plate theory and von-Karman large deformation model
were used to model the plates with van der Waals interactions
between layers. Scale effect was modeled using a combination of
nonlocal theory with SGT; it was shown that the amplitude of the
response decreases by increasing the number of layers. Khaniki [71]
examined the dynamic deformation of double-layered orthotropic
nano-plates acted upon moving nanoparticle. Plates were assumed
to be bi- axially loaded and the nanoparticle was modelled with
linear and circular motions; it was shown that increasing the
nonlocal parameter increases the deformation in both layers of
the system. By using the Reissner-Mindlin plate theory, Ansari [72]
investigated the vibration behavior of layered nano-plates with van
der Waals interlayer forces. It was shown that the presence of the elastic foundation has a significant effect on increasing the natural
frequencies.
Over the past few decades, the importance of having an accurate
model for analyzing the multi-layered small-scale structures has
been a challenging task regarding the size-dependence effect
and the layer interactions. In this review paper, efforts made by
researchers in the past few years in modelling and analyzing
multi-layered small-scale structures are discussed by presenting
highlighted works in this field. The size-dependency terms in
modelling micro-scale structures (using MCST and STG) and nanoscale
structures (using nonlocal theory) play a dominant role in
modifying the classical continuum models for macro-structures. In
summary, by analyzing previous literature on the dynamic behavior
of layered small- scale structures, it can be seen that although there
have been several studies on both nano and micro-structures, the
topic is still novel and requires more investigations to accurately
model the dynamics, especially for large deformations and forced
vibrations.
Farokhi H, Ghayesh MH (2016) Size-dependent behavior of electrically actuated microcantilever-based MEMS. International Journal of Mechanics and Materials in Design 12(3): 301-315.
Hashemi SH, Khaniki HB (2017) Dynamic behavior of multi-layered viscoelastic nanobeam system embedded in a viscoelastic medium with a moving nanoparticle. Journal of Mechanics 33(5): 559-575.
Professor, Chief Doctor, Director of Department of Pediatric Surgery, Associate Director of Department of Surgery, Doctoral Supervisor Tongji hospital, Tongji medical college, Huazhong University of Science and Technology
Senior Research Engineer and Professor, Center for Refining and Petrochemicals, Research Institute, King Fahd University of Petroleum and Minerals (KFUPM), Dhahran, Saudi Arabia
Interim Dean, College of Education and Health Sciences, Director of Biomechanics Laboratory, Sport Science Innovation Program, Bridgewater State University