• Steel and Composite Structures
• /
• v.25 no.2
• /
• pp.141-155
• /
• 2017

This paper presents an investigation into the magneto-thermo-mechanical vibration and damping of a viscoelastic functionally graded-carbon nanotubes (FG-CNTs)-reinforced curved microbeam based on Timoshenko beam and strain gradient theories. The structure is surrounded by a viscoelastic medium which is simulated with spring, damper and shear elements. The effective temperature-dependent material properties of the CNTs-reinforced composite beam are obtained using the extended rule of mixture. The structure is assumed to be subjected to a longitudinal magnetic field. The governing equations of motion are derived using Hamilton's principle and solved by employing differential quadrature method (DQM). The effect of various parameter like volume percent and distribution type of CNTs, temperature change, magnetic field, boundary conditions, material length scale parameter, central angle, viscoelastic medium and structural damping on the vibration and damping behaviors of the nanocomposite curved microbeam is examined. The results show that with increasing volume percent of CNTs and considering magnetic field, material length scale parameter and viscoelastic medium, the frequency of the system increases and critically damped situation occurs at higher values of damper constant. In addition, the structure with FGX distribution type of CNTs has the highest stiffness. It is also observed that increasing temperature, structural damping and central angle of curved microbeam decreases the frequency of the system.

• Journal of Welding and Joining
• /
• v.18 no.1
• /
• pp.46-51
• /
• 2000

Ultrasonic nondestructive evaluation (UNDE) technique is commonly used for detecting inner defects in the materials. Recently, new methods are trying to apply for detecting surface and subsurface flaws using Rayleigh wave or creeping wave. These techniques, however, have following problems. Echo amplitude is remarkably affected by the surface conditions and discrimination of echo pattern is usually difficult because shear wave propagate in the material at the same time. We can apply surface SH-wave(which is horizontally polarized shear wave traveling along near surface layer) technique to detect surface flaws. In this paper, directivity, distance amplitude characteristics and detectability of surface flaws at fillet weld hills of the 5 MHz and 2 MHz surface flaws at fillet weld hills of the 5 MHz and 2 MHz surface Sh-wave are experimentally investigated. As a result of the study, it was found out that these techniques are valuable for the detection of fatigue cracks at fillet weld heels which can not be detected by other ultrasonic techniques such as angle beam technique and which are inaccessible for non-destructive testings e.g. MT(magnetic particle testing) or PT(liquid penetrant testing).

• Transactions of Materials Processing
• /
• v.29 no.1
• /
• pp.27-36
• /
• 2020

The Goss texture component of {110}<001> is well known as one of the best texture components to improve the magnetic properties of electrical steel sheets. The small amount of the Goss texture component is obtained at the surface of the steel sheet by shear deformation due to friction between the steel sheet and the roll during conventional symmetric rolling. This study aims to identify a method to obtain high intensity of the Goss texture component not only at the surface but in the whole layer of the steel sheet by shear deformation of asymmetric rolling. Low carbon steel sheets, which have different initial texture, were asymmetrically rolled by about 50%, 70%, and 80%. The pole figures of the top, center, and bottom layers of the initial and asymmetrically rolled low carbon steel sheets were measured by an X-ray diffractometer. Based on the measured pole figures of these samples, the intensities of the main texture components were analyzed for the initial and asymmetrically rolled low carbon steel sheets. As a result, the initial low carbon steel sheet with the γ-fiber component showed a higher intensity of the Goss texture component in the whole layer than the steel sheet with other texture components after asymmetric rolling.

• Advances in nano research
• /
• v.9 no.4
• /
• pp.221-235
• /
• 2020

The following composition establishes a nonlocal strain gradient plate model that is essentially related to mass sensors laying on Winkler-Pasternak medium for the vibrational analysis from graphene sheets. To achieve a seemingly accurate study of graphene sheets, the posited theorem actually accommodates two parameters of scale in relation to the gradient of the strain as well as non-local results. Model graphene sheets are known to have double variant shear deformation plate theory without factors from shear correction. By using the principle of Hamilton, to acquire the governing equations of a non-local strain gradient graphene layer on an elastic substrate, Galerkin's method is therefore used to explicate the equations that govern various partition conditions. The influence of diverse factors like the magnetic field as well as the elastic foundation on graphene sheet's vibration characteristics, the number of nanoparticles, nonlocal parameter, nanoparticle mass as well as the length scale parameter had been evaluated.

• Journal of Magnetics
• /
• v.22 no.2
• /
• pp.281-285
• /
• 2017

To suppress the wall slip effect and improve the yield stress measurement precision of magnetorheological fluid, measurement disks with different grooves are first manufactured. Then, the influence of groove characteristics on the yield stress of magnetorheological fluid is investigated by the method of experiments. Finally, the optimization wall grooves of measurement disks are obtained, and the yield stress of a self-prepared magnetorheological fluid is measured. Results indicate that the groove type and groove width have a slight influence on the shear yield stress, whereas the measured yield stress increases with enhanced groove density, and the optimized groove depth is 0.3 mm. The measured shear yield stress of self-prepared MR fluid can be improved by 18 % according to the optimized grooved disks, and the maximum yield stress can reach up to 65 kPa as the magnetic flux density is 0.5 T.

• Structural Engineering and Mechanics
• /
• v.70 no.6
• /
• pp.683-702
• /
• 2019

The present study aims to analyze the magneto-electro-elastic (MEE) vibration of a functionally graded carbon nanotubes reinforced composites (FG-CNTRC) cylindrical shell. Electro-magnetic loads are applied to the structure and it is located on an elastic foundation which is simulated by visco-Pasternak type. The properties of the nano-composite shell are assumed to be varied by temperature changes. The third-order shear deformation shells theory is used to describe the displacement components and Hamilton's principle is employed to derive the motion differential equations. To obtain the results, Navier's method is used as an analytical solution for simply supported boundary condition and the effect of different parameters such as temperature variations, orientation angle, volume fraction of CNTs, different types of elastic foundation and other prominent parameters on the natural frequencies of the structure are considered and discussed in details. Design more functional structures subjected to multi-physical fields is of applications of this study results.

• Pediatric Gastroenterology, Hepatology & Nutrition
• /
• v.22 no.3
• /
• pp.282-290
• /
• 2019

Characterizing inflammation and fibrosis in Crohn's disease (CD) is necessary to guide clinical management, but distinguishing the two remains challenging. Novel ultrasound (US) techniques: contrast-enhanced US (CEUS) and shear wave elastography (SWE) offer great potential in evaluating disease activity in pediatric patients. Three patients ages 16 to 20 with known CD underwent CEUS and SWE to characterize bowel wall inflammation and fibrosis. Magnetic resonance enterography, endoscopy, or surgical pathology findings are also described when available. The patients' disease activity included acute inflammation, chronic inflammation with stricture formation, and a fibrotic surgical anastomosis without inflammation. CEUS was useful in determining the degree of inflammation, and SWE identified bowel wall fibrosis. Used together these techniques allow for better characterization of the degree of fibrosis and inflammation in bowel strictures. With further validation CEUS and SWE may allow for improved characterization of bowel strictures and disease flares in pediatric patients suffering from CD.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.23 no.9
• /
• pp.797-805
• /
• 2013

In this paper vibration and stability analysis of laminated composite shells based on the first order shear deformation theory(FSDT) for two different boundary conditions(clamped-clamped, simply supported) are performed. Structural model of cross-ply symmetric laminated composite cylindrical shells subjected to a combination of magnetic and thermal fields is developed via Hamilton's variational principle. These coupled equations of motion are based on the electromagnetic equations(Faraday, Ampere, Ohm, and Lorenz equations)and thermal equations which are involved in constitutive equations. Extended Galerkin method is adopted to obtain the discretized equations of motion. Variations of dynamic characteristics of composite shells with applied magnetic field, temperature gradient, laminate thickness-ratio and radius ratio for two boundary conditions are investigated and pertinent conclusions are derived.

• Structural Engineering and Mechanics
• /
• v.74 no.6
• /
• pp.809-819
• /
• 2020

For the first time, the influence of in-plane magnetic field on wave propagation of Graphene Nano-Platelets (GNPs) polymer composite nanoplates is investigated here. The impact of three- parameter Kerr foundation is also considered. There are two different reinforcement distribution patterns (i.e. uniformly and non-uniformly) while the material properties of the nanoplate are estimated through the Halpin-Tsai model and a rule of mixture. To consider the size-dependent behavior of the structure, Eringen Nonlocal Differential Model (ENDM) is utilized. The equations of wave motion derived based on a higher-order shear deformation refined theory through Hamilton's principle and an analytical technique depending on Taylor series utilized to find the wave frequency as well as phase velocity of the GNPs reinforced nanoplates. A parametric investigation is performed to determine the influence of essential phenomena, such as the nonlocality, GNPs conditions, Kerr foundation parameters, and wave number on the both longitudinal and flexural wave characteristics of GNPs reinforced nanoplates.

• Economic and Environmental Geology
• /
• v.29 no.3
• /
• pp.357-367
• /
• 1996

A total of 113 samples (basalts, tuffs, and siltstones from coal-bearing sediments) was collected from 14 sites of the Tertiary Changgi basin in southeastern Korea, and studied palaeomagnetically. Site-mean declination of the ChRM from 5 sites was found to be deflected clockwise about $30^{\circ}$. Other 5 sites showed no vertical-axis deflection of ChRM direction. In consideration of previous palaeomagnetic data from other Tertiary basins in the vicinity, it is interpreted that the deflection of ChRM directions has been caused by NNW-SSE simple shear associated with the opening of the East Sea, and the time of rotation should be about 16 Ma. Other 2 sites showed counterclockwise deflection of site-mean ChRM. These sites might be located among lager tectonic blocks which were rotating clockwise. AMS (anisotropy of magnetic susceptibility) study revealed $NE{\rightarrow}SW$ directed magnetic lineation at two tuffaceous sites. This might indicate flow direction of tuffs during the time of deposition. Most of the other sites showed load-foliation lying subparallel to the bedding plane. This must have been caused by gravitational loading acted vertically to the strata.