• Journal of the Korean Ceramic Society
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• v.31 no.2
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• pp.161-170
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• 1994

For the preparation of short ceramic fibers of which average length might be in accordance with the opening size of sieve, e.g., 150${\mu}{\textrm}{m}$ or 300${\mu}{\textrm}{m}$, bulk fibers were grounded on sieve screen by applying both compressing and shearing force, and passed through the sieve screen. The grounded fibers were subjected to gravitational settling processes. The classified fibers were observed by scanning electron microscopy and the length of each fiber was measured to correlate the average length with the opening size of the sieve used for grinding bulk fibers. Theoretical analysis show that a free settling technique is ineffective for the classification of fibers by length compared with that of particles. The average lengths of classified fibers estimated by scanning electron microscopy were in good agreement with those obtained by relative packing volume of the fibers. Accordingly, it is confirmed that average fiber lengths can be determined from bulk volume data without photographing, counting and averaging results for hundreds of fibers.

• Steel and Composite Structures
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• v.48 no.3
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• pp.263-273
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• 2023

This paper investigates dynamic characteristics of a graphene nanoplatelets reinforced composite (GNPRC) sandwich doubly curved shell based on the first-order shear deformation theory (FSDT) and Hamilton's principle. The sandwich doubly curved shell is fabricated from a core made of honeycomb materials sandwiched by composite GNPs reinforced face-sheets. Effective materials properties of composite face-sheets are assumed to vary based on Halpin-Tsai micromechanical models and rule of mixture. Furthermore, the material properties of honeycomb core are estimated using Gibson's formula. The fundamental frequencies of the shell are computed with changes of main geometrical and material properties such as amount and distribution type of graphene nanoplatelets, side length ratio, thickness to length ratio of and side length ratio of honeycomb. The Navier's technique is presented to obtain responses. Accuracy and trueness of the present model and analytical solution is confirmed through comparison of the results with available results in literature. It is concluded that an increase in thickness to length ratio yields a softer core with lower natural frequencies. Furthermore, increase in height to length ratio leads to significant decrease in natural frequencies.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2008.04a
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• pp.614-617
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• 2008

This paper presents the numerical investigation of the characteristics of biaxial flexure specimens for the Biaxial Flexure Test(BFT) which was recently developed to measure the biaxial tensile strength of concrete. Using FEM, the effect of size and eccentricity on the specimens was evaluated. The parameters such as radious of the support and the loadings, thickness and free length were studied. The results of the FE analysis were entirely consistent with the predictive solution, when b/agt;0.4, h/alt;0.6 and the thickness of the specimens were increased. On the other hands, when b/agt;0.4, those with lesser free length showed good results. To limit the difference between the stresses at the end points of 2b as the specimen was sustained and the stress at the center point of the specimen are not over 10%, lateral eccentricity was analyzed to be in the limits of 3%.

• Journal of Welding and Joining
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• v.18 no.1
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• pp.104-109
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• 2000

Based on the principle of complementary energy, an analytical method is developed which focused on the end effects for determining thermal stress distributions in the clad beam. This method gives the stress distributions which completely satisfy the stress-free boundary condition at the edge. Numerical results shows that shear and peeling stress at the interface between the substrate and clad are significant near the edge and become negligible in the interior region. Even thought the relative location where the maximum or minimum stresses take place moves to interior as the length of the beam becomes smaller, the absolute location from the free end and the value of these stresses are the same in spite of the variation of the length of beam.

• Proceedings of the KWS Conference
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• 1999.10a
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• pp.306-309
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• 1999

Based on the principle of complementary energy, an analytical method is developed which focused on the end effects for determining thermal stress distributions in the claded beam. This method gives the stress distributions which completely satisfy the stress-free boundary condition at the edge. Numerical result shows that shear stress and peeling stress at the interface between the substrate and clad are significant near the edge and become negligible in the interior region. Even though the relative location where the maximum or minimum stresses take place moves to interior as the length of the beam become smaller, the absolute location from the free end and the value of these stresses are the same in spite of the variation of the length of beam.

• Progress in Superconductivity and Cryogenics
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• v.3 no.2
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• pp.55-61
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• 2001

A free piston and free displacer (FPFD) Stirling cryocooler for cooling infrared and cryo-sensor is currently under development at korea Institute of Machinery & Materials. The FPFD Stirling cryocooler consists of two compressor pistons driven by linear motors which make pressure waves and a pneumatically driven displacer piston with regenerator. It is the most suitable design for a mechanical cryocooler utilized in night vision environment In this study, performance test of the Stirling cryocooler with different length of the split tube and operating frequency were performed to get characteristics of the cryocooler.

• Communications for Statistical Applications and Methods
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• v.23 no.2
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• pp.119-129
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• 2016

A new sampling method is introduced based on the idea of a ranked set sampling scheme in which taken samples in each set are dependent on previous ones. Some theoretical results are presented and distribution-free confidence intervals are derived for the quantiles of any continuous population. It is shown numerically that the proposed sampling scheme may lead to 95% confidence intervals (especially for extreme quantiles) that cannot be found based on the ordinary ranked set sampling scheme presented by Chen (2000) and Balakrishnan and Li (2006). Optimality aspects of this scheme are investigated for both coverage probability and minimum expected length criteria. A real data set is also used to illustrate the proposed procedure. Conclusions are eventually stated.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1991.04a
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• pp.22-31
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• 1991

Machining with boring bars frequently induce chatter vibration because of the low stiffness and damping of cantilever shape of boring bars. To increase stiffness and damping, a carbon fiber epoxy composite boring bar was designed, manufactured and tested. The natural frequency of the carbon fiber epoxy composite boring bar in the free-free end condition was incerased more than 50% over that of the steel boring bar, and the damping of the carbon fiber epoxy composite boring bar was also increased 450%. The fundamental natural frequency of the carbon fiber epoxycomposite boring bar in the cantilever beam condition was found to be increased 20-30% over that of the steel boring bar in overhang length range 140-200mm. In machining S45C tapered workpieces, the limit of the overhang length of the steel boring bar was about 170mm in cutting speed 140m/min.

• Advances in aircraft and spacecraft science
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• v.7 no.6
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• pp.517-536
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• 2020

The present study investigates axial vibration of a FG nanobeam using nonlocal elasticity theory under clamped-clamped and clamped-free boundary conditions. Power law, exponential law and sigmoid law are applied as grading laws to examine the effect of the material distribution on axial vibration of the FG nanobeam. A parametric study was done to examine the effect of length scale on the dynamic behavior of the structure and the results are presented. It was observed that consideration of the nonlocal length scale is essential when analyzing the free vibration of a FG nanobeam. The results of the present study can be used as benchmarks in future studies of FG nanostructures.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2003.10a
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• pp.259-266
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• 2003

This paper introduces a relation to determine the span ratio between exterior and interior spans, which is strongly required in the preliminary design stage of bridges constructed by Free Cantilever Method (FCM). A relation for the initial tendon force is derived on the basis of an assumption that no vertical deflection occurs at the far end of a cantilever beam due to the balanced condition between the self-weight and the cantilever tendons. In advance, the span ratio can be determined by using an assumption that the negative maximum moment must be the same with the positive maximum moment along the entire spans to be a rational bridge design. Finally, many rigorous lime-dependent analyses are conducted to establish the validity of the introduced relations. The obtained numerical results show that the rational design of FCM bridges may be achieved when the span length ratio of the exterior span to the interior span ranges about 0.75 to 0.8.