• Smart Structures and Systems
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• v.22 no.1
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• pp.27-40
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• 2018

The governing equations of motion are derived for analysis of a sandwich microbeam in this paper. The sandwich microbeam is including an elastic micro-core and two piezoelectric micro-face-sheets. The microbeam is subjected to transverse loads and two-dimensional electric potential. Higher-order sinusoidal shear deformation beam theory is used for description of displacement field. To account size dependency in governing equations of motion, strain gradient theory is used to mention higher-order stress and strains. An analytical approach for simply-supported sandwich microbeam with short-circuited electric potential is proposed. The numerical results indicate that various types of parameters such as foundation and material length scales have significant effects on the free vibration responses and dynamic results. Investigation on the influence of material length scales indicates that increase of both dimensionless material length scale parameters leads to significant changes of vibration and dynamic responses of microbeam.

• Computers and Concrete
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• v.26 no.5
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• pp.439-450
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• 2020

In this research, bending and buckling analyses of porous functionally graded (FG) plate under mechanical load are presented. The properties of the FG plate vary gradually across the thickness according to power-law and exponential functions. The material imperfection is considered to vary depending to a logarithmic function. The plate is modeled by a refined trigonometric shear deformation theory where the use of the shear correction factor is unnecessary. The governing equations of the FG plate are derived via virtual work principle and resolved via Navier solutions. The accuracy of the present model is checked by comparing the obtained results with those found in the literature. The various effects influencing the stresses, displacements and critical buckling loads of the plate are also examined and discussed in detail.

• Structural Engineering and Mechanics
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• v.24 no.5
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• pp.621-639
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• 2006

Stability of a cylindrical shell subject to a uniform axial compression, which is a power function of time, is examined within the framework of small strain elasto-plasticity. The material of the shell is incompressible and the effect of the elastic unloading is considered. Initially, employing the infinitesimal elastic-plastic deformation theory, the fundamental relations and Donnell type stability equations for a cylindrical shell have been obtained. Then, employing Galerkin's method, those equations have been reduced to a time dependent differential equation with variable coefficient. Finally, for two initial conditions applying a Ritz type variational method, the critical static and dynamic axial loads, the corresponding wave numbers and dynamic factor have been found. Using those results, the effects of the variations of loading parameters and the variations of power of time in the axial load expression as well as the variations of the radius to thickness ratio on the critical parameters of the shells for two initial conditions are also elucidated. Comparing results with those in the literature validates the present analysis.

• Advances in nano research
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• v.6 no.2
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• pp.93-112
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• 2018

An analytical solution of the buckling governing equations of functionally graded piezoelectric (FGP) nanobeams obtained by using a developed third-order shear deformation theory is presented. Electro-mechanical properties of FGP nanobeam are supposed to change continuously in the thickness direction based on power-law model. To capture the small size effects, Eringen's nonlocal elasticity theory is adopted. Employing Hamilton's principle, the nonlocal governing equations of a FG nanobeams made of piezoelectric materials are obtained and they are solved using Navier-type analytical solution. Results are provided to show the effect of different external electric voltage, power-law index, nonlocal parameter and slenderness ratio on the buckling loads of the size-dependent FGP nanobeams. The accuracy of the present model is verified by comparing it with nonlocal Timoshenko FG beams. So, this study makes the first attempt for analyzing buckling behavior of higher order shear deformable FGP nanobeams.

• Journal of KSNVE
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• v.8 no.2
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• pp.336-345
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• 1998

The dynamic instability of cylindrical shell with clamped-free boundary condition subjected to constant follower force or $P_0 + P_1cos {\Omega}_t$ type pulsating follower force is analyzed. The motion of shell is modeled using the shell theory considering rotary inertia and shear deformation, and analyzed with finite element method. In case of constant follower force, the changes of eigenvalues dependent on the magnitude of applied load are investigated and the critical loads are obtained. In case pulsating follower force, instability regions of exicitation frequency are obtained by modal transform with right and left modal matrix and by multiple scales method. The effects of thickness ratio and aspect ratio on the instability of shell are studied.

• Advances in aircraft and spacecraft science
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• v.6 no.4
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• pp.297-314
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• 2019

Dynamic stability of a porous metal foam nano-dimension plate on elastic substrate exposed to bi-axial time-dependent forces has been studied via a novel 3-variable plate theory. Various pore contents based on uniform and non-uniform models have been introduced. The presented plate model contains smaller number of field variables with shear deformation verification. Hamilton's principle will be utilized to deduce the governing equations. Next, the equations have been defined in the context of Mathieu-Hill equation. Correctness of presented methodology has been verified by comparison of derived results with previous data. Impacts of static and dynamical force coefficients, non-local coefficient, foundation coefficients, pore distributions and boundary edges on stability regions of metal foam nanoscale plates will be studied.

• Advances in nano research
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• v.13 no.2
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• pp.113-120
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• 2022

In this paper, a finite element (FE) simulation has been developed in order to examine the nonlinear stability of reinforced sandwich beams with graphene oxide powders (GOPs). In this regard, the nonlinear stability curves have been obtained asuming that the beam is under compressive loads leading to its buckling. The beam is considered to be a three-layered sandwich beam with metal core and GOP reinforced face sheets and it is rested on elastic substrate. Moreover, a higher-order refined beam theory has been considered to formulate the sandwich beam by employing the geometrically perfect and imperfect beam configurations. In the solving procedure, the utalized finite element simulation contains a novel beam element in which shear deformation has been included. The calculated stability curves of GOP-reinforced sandwich beams are shown to be dependent on different parameters such as GOP amount, face sheet thickness, geometrical imperfection and also center deflection.

• Coupled systems mechanics
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• v.13 no.2
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• pp.115-132
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• 2024

This paper introduces an improved shear deformation theory for analyzing the buckling behavior of functionally graded plates subjected to varying temperatures. The transverse shear strain functions employed satisfy the stress-free condition on the plate surfaces without requiring shear correction factors. The material properties and thermal expansion coefficient of the porous functionally graded plate are assumed temperature-dependent and exhibit continuous variation throughout the thickness, following a modified power-law distribution based on the volume fractions of the constituents. Moreover, the study considers the influence of porosity distribution on the buckling of the functionally graded plates. Thermal loads are assumed to have uniform, linear, and nonlinear distributions through the thickness. The obtained results, considering the effect of porosity distribution, are compared with alternative solutions available in the existing literature. Additionally, this study provides comprehensive discussions on the influence of various parameters, emphasizing the importance of accounting for the porosity distribution in the buckling analysis of functionally graded plates.

• Journal of the Korean Geotechnical Society
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• v.33 no.1
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• pp.79-91
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• 2017

An experimental study has been conducted by using the Cyclic Direct Simple Shear apparatus to evaluate the influence of average and cyclic shear stresses on the undrained shear failure behavior of marine silty sand considering various relative densities. The obtained results show that despite using different relative densities, similar trends were gained in the cyclic shear deformation. Moreover, the cyclic shear deformation is affected mainly by the average and cyclic shear stresses. The number of cyclic loads for failure is significantly affected by the cyclic shear stress ratio and relative density, and is less affected by the average shear stress ratio. The proposed three-dimensional stress-dependent failure contour can be used effectively to assess the soil shear strength considering various relative densities in the design of foundation used for offshore structures.

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.6
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• pp.717-726
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• 2005

Statement of problem. One of the common problems of provisional crown and fixed partial denture materials is that when they are subjected to constant loads for a long period of time, they exhibit a dimensional change (creep). Purpose. The aim of this study was to investigate the viscoelastic behaviour of polymer-based provisional crown and fixed partial denture materials with time at constant compressive load. Material and methods. Three dimethacrylate-based materials (Protemp 3 Garant, Temphase, Luxatemp) and one monomethacrylate-based material (Trim) were selected. Dimensional changes of the specimens were recorded by a LVDT to evaluate their viscoelastic behavior and creep strain. For all specimens, two loading procedures were used. At first, static compressive stress of 4 MPa was applied for 30 minutes and followed by 1 hour of strain recovery. Then, after 24 hours of water storage, the specimens were loaded again. The creep values between materials were statistically analyzed using one-way ANOVA and multiple comparison $Scheff\acute{e}$ test. Independent samples t-test was also used to identify the difference of creep strain between first and secondary loading conditions at the significance level of 0.05. Results. Following application of the first loading, Trim showed the highest maximum creep strain (32.7%) followed by Luxatemp, Protemp 3 Garant and Temphase, with values of 3.78%, 2.86% and 1.77%, respectively. Trim was significantly different from other materials (P<0.05), while there were no significant differences among Luxatemp, Protemp 3 Garant and Temphase (P>0.05). The highest recovery and permanent set of Trim, were significantly different from those of others (P<0.05). At the secondary loading of the dimethacrylate-based materials, creep deformation, recovery and permanent set decreased and the percentage of recovery increased, while in Trim, all values of the measurements increased. This result showed that the secondary loading at 24 hours produced a significant creep magnitude. Conclusion. The dimethacrylate-based provisional crown and fixed partial denture materials showed significantly higher creep resistance and lower deformation than the monomethacrylate-based material. Thus, monomethacrylate-based materials should not be used in long-term stress-bearing situations.