In this article, thermal buckling and resonance frequency of a composite cylindrical nanoshell reinforced with graphene nanoplatelets (GNP) under bi-directional thermal loading are presented. The ...temperature-dependent material properties of piece-wise GNP-reinforced composites (GNPRC) are assumed to be graded in the thickness direction of a cylindrical nanoshell. Also, Halphin-Tsai nanomechanical model is used to surmise the effective material properties of each layer. The size-dependent GNPRC nanoshell is analyzed using modified couple stress parameter (FMCS). For the first time, in the presented study show that bi-directional thermal buckling occurs if the percent of relative frequency change tends to 30%. The novelty of the current study is in considering the effects of bi-directional thermal loading in addition of FMCS on relative frequency, resonance frequencies, thermal buckling, and dynamic deflection of the GNPRC nanoshell. The governing equations and boundary conditions are developed using Hamilton’s principle and solved with the aid of analytical method. The results show that, various bi-directionasl thermal loading and other geometrical and mechanical properties have important role on resonance frequency, relative frequency change, thermal buckling, and dynamic deflection of the GNPRC cylindrical nanoshell. The results of the current study are useful suggestions for design of materials science, micro-mechanical and nano-mechanical systems such as microactuators and microsensors.
This is the first research on the nonlinear frequency analysis of a multi-scale hybrid nanocomposite (MHC) disk (MHCD) resting on an elastic foundation subjected to nonlinear temperature gradient and ...mechanical loading is investigated. The matrix material is reinforced with carbon nanotubes (CNTs) or carbon fibers (CF) at the nano- or macroscale, respectively. We present a modified Halpin–Tsai model to predict the effective properties of the MHCD. The displacement–strain of nonlinear vibration of multi-scale laminated disk via third-order shear deformation theory (TSDT) and using Von Karman nonlinear shell theory is obtained. Hamilton’s principle is employed to establish the governing equations of motion, which is finally solved by generalized differential quadrature method (GDQM) and perturbation method (PM). Finally, the results show that FG patterns, different orientation angle of the fiber, the
V
F
and
W
CNT
parameters, axial load, nonlinear temperature gradient, and applied temperature of the top surface play an essential impact on the linear and nonlinear dynamic responses of the MHCD. The more significant outcome of this research is that the effects of the
V
F
,
W
CNT
,
θ
, and
β
parameters on the nonlinear frequency of the MHCD can be considered at the higher value of the large deflection parameter and the effect of negative axial load on the dynamic responses of the structure is more intensive. As an applicable result show that the best functionally graded (FG) pattern for serving the highest nonlinear dynamic response of an MHC reinforced annular plate is FG-A.
In this study, buckling and vibrational characteristics of a nanoshell reinforced with graphene nanoplatelets under uniform axial load are investigated. The material properties of the piece-wise ...graphene-reinforced composites (GPLRCs) are assumed to be graded in the thickness direction of a nanoshell and are estimated using a nanomechanical model. The effects of the small scale are analyzed based on nonlocal stress–strain gradient theory (NSGT). The governing equations and boundary conditions (BCs) are developed using Hamilton’s principle and are solved with assistance of the generalized differential quadrature method. The novelty of the current study is the consideration of GPLRC and size effect as well as satisfying various boundary conditions implemented on the proposed model using NSGT. The results show that, nonlocal parameter, graphene platelet (GPL) distribution pattern, length scale parameter, number of layers, and GPL weight function have significant influence on the buckling and natural frequency of the GPLRC nanoshell. Another significant result is that nonlocal parameter does not have any effect on the buckling load for each BC. The results of the current study are useful for design of the nanoactuators and nanosensors.
In this article, vibrational behavior and critical voltage of a spinning cylindrical thick shell covered with piezoelectric actuator (PIAC) carrying spring-mass systems are investigated. It should be ...noted that, the installed sensors on the proposed systems are considered as a tip mass. This structure rotates about axial direction and the formulations include the Coriolis and centrifugal effects. In addition, various cases of thermal (uniform, linear, and nonlinear) distributions are studied. The modeled cylindrical thick shell covered with PIAC, its equations of motion, and boundary conditions are derived by the principle of minimum total potential energy and based on a new three-dimensional refined higher-order theory (RHOST). For the first time in the present study, attached spring-mass systems have been considered in the rotating cylindrical thick shells covered with PIAC. The accuracy of the presented model is verified compared with previous studies. The novelty of the current study is consideration of the applied voltage, rotation, various temperature distributions and spring-mass systems implemented on the proposed model using the RHOST. The generalized differential quadrature method is presented to discretize the model and to approximate the governing equations. In this study the simply supported conditions have been applied to edges
θ
=
π
/
2
,
3
π
/
2
and cantilever (clamped-free) boundary conditions have been studied in x = 0, L, respectively. The results show that, applied voltage, angular velocity, temperature changes and spring-mass systems play an important role on the critical voltage, critical angular speed, critical temperature, and natural frequency of the structure. Another significant result is that, by increasing the lumped mass and coefficient of the spring in the first frequency of the cantilever cylindrical shell, increase or decrease of the natural frequency depends on the nonlinear temperature change parameter. The results of the current study are useful suggestions for designing electromechanical systems such as hydraulic pipes with the installation of the sensors to them.
In this article, thermal buckling and frequency analysis of a size-dependent laminated composite cylindrical nanoshell in thermal environment using nonlocal strain–stress gradient theory are ...presented. The thermodynamic equations of the laminated cylindrical nanoshell are based on first-order shear deformation theory, and generalized differential quadrature element method is implemented to solve these equations and obtain natural frequency and critical temperature of the presented model. The results show that by considering C–F boundary conditions and every even layers’ number, in lower value of length scale parameter, by increasing the length scale parameter, the frequency of the structure decreases but in higher value of length scale parameter this matter is inverse. Finally, influences of temperature difference, ply angle, length scale and nonlocal parameters on the critical temperature and frequency of the laminated composite nanostructure are investigated.
The stability analysis of cantilevered curved microtubules in axons regarding various size elements and using the generalized differential quadrature method for solving equations is reported. The ...impacts of covering MAP Tau proteins along with cytoplasm are taken into account as the elastic medium. Curved cylindrical nanoshell considering thick wall is used to model the microtubules. The factor of length scale (
l/R
= 0.2) used in modified couple stress theory would result in more accuracy when it comes to comparison with experiments, while alternative theories presented in this paper provide less precise outcomes. Due to the reported precise results, at the lower value of the time-dependent viscoelastic factor (
τ
s
)
by rising the size-dependent factor, the frequency response of the cantilever microtubule increases and this relation between the size-dependent parameter and the structure’s natural frequency is changed from direct to indirect for the higher amount of the time-based viscoelastic factor that scientists should attend to this matter when it comes to the microtubule. Furthermore, physical neighboring situations in a cell will be prominent in microtubules’ dynamic stability responses, such as membrane and cell-matrix. Since microtubules are likely to be applied as biosensors, this feature could be employed to disclose virulent tumors.
This research presents bending responses of FG-GPLRC plates based upon higher order shear deformation theory (HSDT) for various sets of boundary conditions. The rule of the mixture and modified ...Halpin–Tsai model are engaged to provide the effective material constant of the composite layers. By employing Hamilton’s principle, the governing equations of the structure are derived and solved with the aid of the differential quadrature method (DQM). Afterward, a parametric study is done to present the effects of three kinds of FG patterns, weight fraction of the GPLs, radius ratio, and thickness to inner radius ratio on the bending characteristics of the FG-GPLRC disk. Numerical results reveal that in the initial value of the
Z
t
/
h
, using more GPLs for reinforcing the structure provides an increase in the normal stresses but this matter is inverse for the higher value of the
Z
t
/
h
. The results show that considering the smaller radius ratio is a reason for boosting the shear stresses of the structure for each
Z
t
/
h
. Another consequence is that for the negative value of
Z
t
/
h
, it is true that by increasing
h
/
R
i
, the normal stresses increases but if there is positive value for
Z
t
/
h
, the radial and circumferential stresses fall down by having an increase in the
h
/
R
i
.
In the present study, we aimed to quantify the effects of COVID-19 restrictions and speech treatment approaches during lockdowns on autistic children using CBCL and neuro-fuzzy artificial ...intelligence method. In this regard, a survey including CBCL questionnaire is prepared using online forms. In total, 87 children with diagnosed Autism spectrum disorders (ASD) participated in the survey. The influences of three treatment approaches of in-person, telehealth and public services along with no-treatment condition during lockdown were the main factors of the investigation. The main output factors were internalized and externalized problems in general and their eight subcategory syndromes. We examined the reports by parents/caregivers to find correlation between treatments and CBCL listed problems. Moreover, comparison of the eight syndromes rating scores from pre-lockdown to post-lockdown periods were performed. In addition, artificial intelligence method were engaged to find the influence of speech treatment during restrictions on the level of internalizing and externalizing problems. In this regard, a fully connected adaptive neuro fuzzy inference system is employed with type and duration of treatments as input and T-scores of the syndromes are the output of the network. The results indicate that restrictions alleviate externalizing problems while intensifying internalizing problems. In addition, it is concluded that in-person speech therapy is the most effective and satisfactory approach to deal with ASD children during stay-at-home periods.
This is the first research on the frequency analysis of a graphene nanoplatelet composite circular microplate in the framework of a numerical-based generalized differential quadrature method. ...Stresses and strains are obtained using the higher order shear deformation theory. The microstructure is surrounded by a viscoelastic foundation. Rule of the mixture is used to obtain varying mass density and Poisson’s ratio, whereas the module of elasticity is computed by a modified Halpin–Tsai model. Governing equations and boundary conditions of the graphene nanoplatelet composite circular microplate are obtained by implementing Hamilton’s principle. The results show that outer to inner radius ratio
(
R
o
/
R
i
)
, ratios of length scale and nonlocal to thickness (l/h and
μ
/
h
), and graphene nanoplatelet weight fraction
(
g
GPL
)
have significant influence on the frequency characteristics of the graphene nanoplatelet composite circular microplate. Another necessary consequence is that by increasing the value of
R
o
/
R
i
, the distribution of the displacement field extends from radial to tangent direction, especially in the lower mode numbers; this phenomenon appears much more remarkable. A useful suggestion of this research is that for designing the graphene nanoplatelet composite circular microplate at a low value of
R
o
/
R
i
,
g
GPL
and
R
o
/
R
i
should be given more attention, simultaneously. An interesting result which has come down from the article is that the effect of
R
o
/
R
i
on the dimensionless frequency of the structure is really dependent on the value of C
d
.
This study presents the frequency analysis of a size-dependent laminated polymer composite microtube using a nonlocal strain-stress gradient (NSG) model. By applying energy methods (known as ...Hamilton's principle), the motion equations of the laminated micro tube composites are developed. The thermodynamic equations of the laminated microtube are based on first-order shear deformation theory (FSDT), and a generalized differential quadrature method (GDQM) is employed to find the model for the natural frequencies. The results show that by considering C-F boundary conditions (BCs) and every even layers' number in lower value of length scale parameter, the frequency of the structure drops by soaring this parameter. However, this matter is inverse in its higher value. Eventually, the ply angle's influences, nonlocality as well as length scale element on the vibration of the laminated composite microstructure are investigated.
PDF