• Smart Structures and Systems
• /
• 제18권5호
• /
• pp.1029-1062
• /
• 2016

In this research, the nonlinear free vibration analysis of boron-nitride micro ribbon (BNMR) on the Pasternak elastic foundation under electrical, mechanical and thermal loadings using modified strain gradient theory (MSGT) is studied. Employing the von $K{\acute{a}}rm{\acute{a}}n$ nonlinear geometry theory, the nonlinear equations of motion for the graphene micro ribbon (GMR) using Euler-Bernoulli beam model with considering attached mass and size effects based on Hamilton's principle is obtained. These equations are converted into the nonlinear ordinary differential equations by elimination of the time variable using Kantorovich time-averaging method. To determine nonlinear frequency of GMR under various boundary conditions, and considering mass effect, differential quadrature element method (DQEM) is used. Based on modified strain MSGT, the results of the current model are compared with the obtained results by classical and modified couple stress theories (CT and MCST). Furthermore, the effect of various parameters such as material length scale parameter, attached mass, temperature change, piezoelectric coefficient, two parameters of elastic foundations on the natural frequencies of BNMR is investigated. The results show that for all boundary conditions, by increasing the mass intensity in a fixed position, the linear and nonlinear natural frequency of the GMR reduces. In addition, with increasing of material length scale parameter, the frequency ratio decreases. This results can be used to design and control nano/micro devices and nano electronics to avoid resonance phenomenon.

• Steel and Composite Structures
• /
• 제26권3호
• /
• pp.273-287
• /
• 2018

Buckling and free vibration analysis of sandwich micro plate (SMP) integrated with piezoelectric layers embedded in orthotropic Pasternak are investigated in this paper. The refined Zigzag theory (RZT) is taken into consideration to model the SMP. Four different types of functionally graded (FG) distribution through the thickness of the SMP core layer which is reinforced with single-wall carbon nanotubes (SWCNTs) are considered. The modified couple stress theory (MCST) is employed to capture the effects of small scale effects. The sandwich structure is exposed to a two dimensional magnetic field and also, piezoelectric layers are subjected to external applied voltages. In order to obtain governing equation, energy method as well as Hamilton's principle is applied. Based on an analytical solution the critical buckling loads and natural frequency are obtained. The effects of volume fraction of carbon nanotubes (CNTs), different distributions of CNTs, foundation stiffness parameters, magnetic and electric fields, small scale parameter and the thickness of piezoelectric layers on the both critical buckling loads and natural frequency of the SMP are examined. The obtained results demonstrate that the effects of volume fraction of CNTs play an important role in analyzing buckling and free vibration behavior of the SMP. Furthermore, the effects of magnetic and electric fields are remarkable on the mechanical responses of the system and cannot be neglected.

• Structural Engineering and Mechanics
• /
• 제64권5호
• /
• pp.527-541
• /
• 2017

In this work, a new hyperbolic shear deformation beam theory is proposed based on a modified couple stress theory (MCST) to investigate the bending and free vibration responses of functionally graded (FG) micro beam made of porous material. This non-classical micro-beam model introduces the material length scale coefficient which can capture the size influence. The non-classical beam model reduces to the classical beam model when the material length scale coefficient is set to zero. The mechanical material properties of the FG micro-beam are assumed to vary in the thickness direction and are estimated through the classical rule of mixture which is modified to approximate the porous material properties with even and uneven distributions of porosities phases. Effects of several important parameters such as power-law exponents, porosity distributions, porosity volume fractions, the material length scale parameter and slenderness ratios on bending and dynamic responses of FG micro-beams are investigated and discussed in detail. It is concluded that these effects play significant role in the mechanical behavior of porous FG micro-beams.

• Advances in nano research
• /
• 제8권2호
• /
• pp.115-134
• /
• 2020

In this paper, the free vibrations analysis of the nanoplates made of three-directional functionally graded material (TDFGM) with small scale effects is presented. To study the small-scale effects on natural frequency, modified strain gradient theory (MSGT) has been used. Material properties of the nanoplate follow an arbitrary function that changes in three directions along the length, width and thickness of the plate. The equilibrium equations and boundary conditions of nanoplate are obtained using the Hamilton's principle. The generalized differential quadrature method (GDQM) is used to solve the governing equations and different boundary conditions for obtaining the natural frequency of nanoplate made of three-directional functionally graded material. The present model can be transformed into a couple stress plate model or a classic plate model if two or all parameters of the length scales set to zero. Finally, numerical results are presented to study the small-scale effect and heterogeneity constants and the aspect ratio with different boundary conditions on the free vibrations of nanoplates. To the best of the researchers' knowledge, in the literature, there is no study carried out into MSGT for free vibration analysis of FGM nanoplate with arbitrary functions.

• 한국안전학회지
• /
• 제16권2호
• /
• pp.80-84
• /
• 2001

Work stress and health are very important factors related to workers' condition and work safety, Author has conducted a couple of tests to check up three people's pulses before they work during their work for three types of safety guard in construction site. Work type, age, weight, sex experience year, ambient temperature n recorded as variables in this study. These are checked and asked by the author directly, before their pulse check Also, workers' Pulses were measured at height H-0 and H-9.0m to understand psychological the degree of psychological nervousness degree. POLAR protrainer NVTM HRM system(wrist recorder and sensor) was used for the site test. There are three(3) different types of construction safety guard which have been used for, this study. They are usually or frequently used and found in the site. Four different ranges of age groups(20's, 30's 40's, 50's) carpenters are assisted to the test sites with wearing pulse recorder and sensor respectively. All three types of safety guards have the same height 90㎝ even though they are different types. On top of five(5) stories tublar framed scaffolding is fabricated, similar to the one in site, where those safety guards are installed. The older(=more experienced) the workers are the more stable they are. it is shown. Also, It is verified the visually uncomfortable rail type can cause workers to psychologically be unstable.

• Advances in nano research
• /
• 제8권1호
• /
• pp.69-82
• /
• 2020

In this study, the free and forced vibration analysis of micro sandwich plate with porous core layer and magneto-electric face sheets based on modified couple stress theory and first order shear deformation theory under simply supported boundary conditions is illustrated. It is noted that the core layer is composed from balsa wood and also piezo magneto-electric facesheets are made of BiTiO₃-CoFe₂O₄. Using Hamilton's principle, the equations of motion for micro sandwich plate are obtained. Also, the Navier's method for simply support boundary condition is used to solve these equations. The effects of applied voltage, magnetic field, length to width ratio, thickness of porous to micro plate thickness ratio, type of porous, coefficient of porous on the frequency ratio are investigated. The numerical results indicate that with increasing of the porous coefficient, the non-dimensional frequency increases. Also, with an increase in the electric potential, the non-dimensional frequency decreases, while and with increasing of the magnetic potential is vice versa.

• Steel and Composite Structures
• /
• 제33권1호
• /
• pp.93-109
• /
• 2019

In the present study, vibration analysis of double bonded micro sandwich cylindrical shells with saturated porous core and carbon/boron nitride nanotubes (CNT/BNNT) reinforced composite face sheets under multi-physical loadings based on Cooper-Naghdi theory is investigated. The material properties of the micro structure are assumed to be temperature dependent, and each of the micro-tubes is placed on the Pasternak elastic foundations, and mechanical, moisture, thermal, electrical, and magnetic forces are effective on the structural behavior. The distributions of porous materials in three distributions such as non-linear non-symmetric, nonlinear-symmetric, and uniform are considered. The relationship including electro-magneto-hydro-thermo-mechanical loadings based on modified couple stress theory is obtained and moreover the governing equations of motion using the energy method and the Hamilton's principle are derived. Also, Navier's type solution is also used to solve the governing equations of motion. The effects of various parameters such as material length scale parameter, temperature change, various distributions of nanotube, volume fraction of nanotubes, porosity and Skempton coefficients, and geometric parameters on the natural frequency of double bonded micro sandwich cylindrical shells are investigated. Increasing the porosity and the Skempton coefficients of the core in micro sandwich cylindrical shell lead to increase the natural frequency of the structure. Cylindrical shells and porous materials in the industry of filters and separators, heat exchangers and coolers are widely used and are generally accepted today.

• 한국추진공학회지
• /
• 제11권3호
• /
• pp.7-12
• /
• 2007

마찰용접은 소재를 서로 마찰시켜 마찰열에 의해 용접하는 방법이다. 본 연구는 내부에 유동부를 갖는 부분을 마찰용접을 이용하여 용접했을 때 유체의 유동에 영향이 없는 유동부를 설계하는데 목적을 두고 있다. 용접부의 설계 변수를 결정하고 이에 대하여 마찰용접 해석을 DEFORM-2D를 이용하여 해석을 수행하였다. 마찰용접 해석을 수행하기 위해 온도변화에 따른 마찰계수와 업셋 압력, 소재의 분당회전수, 그리고 유동응력을 입력해 주었다. 해석결과에 따라서 유동에 영향이 없는 용접부의 최적형상을 결정하였다.

• Structural Engineering and Mechanics
• /
• 제69권4호
• /
• pp.467-477
• /
• 2019

Digital image correlation (DIC) is now a popular and extensively used full-field metrology technique. In general, DIC is performed by using a turnkey solution offered by various manufacturers of DIC. In this paper, a simple and economical set-up for DIC is proposed which uses easily accessible digital single-lens reflex (DSLR) camera rather than industrial couple-charged device (CCD) cameras. The paper gives a description of aspects of carrying a DIC experiment which includes experimental set-up, specimen preparation, image acquisition and analysis. The details provided here will be helpful to carry DIC experiments without specialized DIC testing rig. To validate the responses obtained from proposed DIC set-up, tension and fatigue tests on specimens made of IS 2062 Gr. E300 steel are determined. Tensile parameters for a flat specimen and stress intensity factor for an eccentrically-loaded single edge notch tension specimen are evaluated from results of DIC experiment. Results obtained from proposed DIC experiments are compared with those obtained from conventional methods and are found to be in close agreement. It is also noted that the high resolution of DSLR allows the use of proposed approach for fracture characterization which could not be carried out with a typical turnkey DIC solution employing a camera of 2MP resolution.

• Computers and Concrete
• /
• 제24권3호
• /
• pp.185-192
• /
• 2019

In this paper, the buckling of micro sandwich hollow circular plate is investigated with the consideration of the porous core and piezoelectric layer reinforced by functionally graded (FG)carbon nano-tube. For modeling the displacement field of sandwich hollow circular plate, the high-order shear deformation theory (HSDT) of plate and modified couple stress theory (MCST) are used. The governing differential equations of the system can be derived using the principle of minimum potential energy and Maxwell's equation that for solving these equations, the Ritz method is employed. The results of this research indicate the influence of various parameters such as porous coefficients, small length scale parameter, distribution of carbon nano-tube in piezoelectric layers and temperature on critical buckling load. The purpose of this research is to show the effect of physical parameters on the critical buckling load of micro sandwich plate and then optimize these parameters to design structures with the best efficiency. The results of this research can be used for optimization of micro-structures and manufacturing different structure in aircraft and aerospace.