• Restorative Dentistry and Endodontics
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• v.28 no.6
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• pp.457-466
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• 2003

The aim of study was to investigate the effect of flow, specimen geometry and adhesion on the measurement of linear polymerization shrinkage of light cured composite resins using linear shrinkage measuring device. Four commercially available composites - an anterior posterior hybrid composite Z100, a posterior packable composite P60 and two flowable composites, Filtek flow and Tetric flow-were studied. The linear polymerization shrinkage of composites was determined using 'bonded disc method' and 'non-bond-ed' free shrinkage method at varying C-factor in the range of 1∼8 by changing specimen geometry. These measured linear shrinkage values were compared with free volumetric shrinkage values. The viscosity and flow of composites were determined and compared by measuring the dropping speed of metal rod under constant load. In non-bonded method, the linear shrinkage approximated one third of true volumetric shrink-age by isotropic contraction. However, in bonded disc method, as the bonded surface increased the linear shrinkage increased up to volumetric shrinkage value by anisotropic contraction. The linear shrinkage value increased with increasing C-factor and approximated true volumetric shrinkage and reached plateau at about C-factor 5∼6. The more flow the composite was, reduced linear shrinkage was measured by compensation radial flow.

• Tunnel and Underground Space
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• v.14 no.5
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• pp.363-372
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• 2004

Double torsion (DT) tests were carried out to investigate the influence of the geometry of guide groove on stress corrosion index of Kumamoto andesite. The fracture toughness was measured in the constant displacement rate, which was set to 2.07 MN/m$^{3}$2/ in average regardless of crack velocity. Stress corrosion indices, n were evaluated using specimens with rectangular, circular and triangular grooves and were 37, 36 and 38 in average, respectively. The n values were constant regardless of the groove geometry, however the DT specimen with triangular groove geometry showed the largest standard deviation in the relationship between crack velocity and stress intensity factor. The DT test was found to be effective in using a rectangular-grooved specimen and the width of the groove must be greater than the average grain size of minerals.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.60-65
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• 2004

Kim et al. described and compared other methods of measuring stress triaxiality using the displacements near the side necking, proved the validities of these models and explored the effect of location where the displacements are measured using three-dimensional finite element analysis for a standard CT specimen with 20% side-grooves. In this paper, the applicability of these models to various specimen and materials are examined in detail. To consider the effects of side groove, thickness of specimen, crack length, specimen geometry and strain hardening exponents, three-dimensional finite element simulation has been performed for various specimen geometries. For a case without a side groove, in the whole the difference between the stress triaxilaity analytically evaluated and directly determined is similar. For a case with a 20% side groove the stress triaxiality is measured at the area where ${\theta}$ is smaller than $60^{\circ}$, which excludes a side grooved area.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.3
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• pp.454-464
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• 1987

The objective of this research is to analyze and evaluate the dynamic flow curve of metals under impact loading at both high strain rate (.epsilon.=1/h dh/dt > 10$\^$3/m/s/m) and large strain (.epsilon.=In h/h$\_$0/ > 1.0). A test method for dynamic compression of metal disc is described. The velocity of the striker face and the force on the anvil are measured during the impact period. From these primitive data the axial stress, strain, and strain rate of the disc are obtained. The Strain rate is determined by the striker velocity divided by the specimen height. This gives a slightly increasing strain rate over most of the deformation period. Strain rates of 100 to 10,000 per second are achieved. Attainable final strains are 150%. A discussion of several problem areas is presented. The friction on the specimen surfaces, the determination of the frictional coefficient, the influence of the specimen geometry (h$\_$0//d$\_$0/ ratio) on the friction effect, the lock-up condition for a given configuration, the friction correction factor, and the evaluation of several lubricants are given. The flow function(stress verus strain) is dependent on the material condition(e.g., prior cold work), specimen geometry, strain rate, and temperature.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.10a
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• pp.225-232
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• 2004

Recently, there has been a rapid development in computer technology, which has in turn led to develop the automated welding system using Artificial Intelligence (AI). However, the automated welding system has not been achieved duo to difficulties of the control and sensor technologies. In this paper, the classification of the optimized bead geometry such as bead width, height penetration and bead area in the Gas Metal Arc (GMA) welding with fuzzy logic is presented. The fuzzy C-Means algorithm (FCM), which is best known an unsupervised fuzzy clustering algorithm is employed here to analysis the specimen of the bead geometry. Then the quality of the GMA welding can be classified by this fuzzy clustering technique and the choice for obtaining the optimal bead geometry can also be determined.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.10a
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• pp.158-163
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• 1997

In this paper the tool geometry of the PSS test were optimized in order to assure the reliability of the test. Considering many factors for optimization of the tool geometry, computer-simulation technique using three-dimensional finite element method(FEM) was used. Three design variables -the punch length, punch crown and punch corner radius- are chosen to be optimized according to the Taguchi's experiment technique with the L9 orthogonal array. The optimum condition to ensure the plane strain mode over the overall area of the specimen was clarified. Moreover the simulation results are confirmed by experiment.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.11
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• pp.3415-3423
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• 1996

The compact tension specimen geometry has been widely used for measuring fatigue crack growth rates at elevated temperature when the fatigue load is under tension/tension condition. However, most of the elevated temperature components which have significant crack growth life experience fatigue load under tension/compression conditions. Thus test techniques are required since the compact tension specimen cannot be used for tension/compression loading. In this paper, a simplified test procedure for measureing fatigue crack growth rates is proposed, which employs a round bar specimen with a small surface crack. Fatigue crack growth rates under tension/ tension loading conditions at elevated temperature were measured according to the proposed procedure and compared with those previously measured by C/(T) specimens. Since both the measured crack growth rates were comparable, the fatigue crack growth rates under tension/ compression load can be reliably measured by the proposed procedure. For monitoring crack depth. DC electric potential method is employed and an optimal probe location and current input conditions were proposed.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2000.11a
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• pp.15-20
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• 2000

Filament winding process is a comparatively simple operation in which continuous reinforcements in the form of roving are wound over a rotating mandrel. And it is now well established as a versatile method for storage tanks and pipe for the chemical and other industries. In this study, tensile strength of a filament wound ring specimens were evaluated by split disk test fixture and dress disk test fixture. The results obtained from experiments were compared with the theoretical values obtained by the rule of mixtures in composites . And the purpose of this paper is the suggestion of an appropriate test method for the evaluation of tensile properties of filament wound structures. The tensile strength of a ring specimen tested by the dress disk test showed better agreement with the theoretical values than that of a ring specimen tested by the split disk test because the stress concentration in edges of a split disk test fixture is more severe than that of dress disk test fixture. The results showed that the tensile strength of a ring specimen was influenced by the geometry of test fixture, the continuity of fibers, fiber-tension, fiber-end and stress concentration in specimen.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.203-207
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• 2000

Filament Winding Process is a comparatively simple operation in which continuous reinforcements in the form of roving are wound over a rotating mandrel. And now well established as a versatile method for storage tanks and pipe for the chemical and other industries . In this study, tensile strength of a filament wound ring specimens were evaluated by split disk test fixture and dress disk test fixture , The results obtained from experiments were compared with the theoretical values obtained by the rule of mixtures. And the purpose of this paper is the suggestion of an appropriate test method for the evaluation of tensile properties of filament wound structures .The tensile strength of a ring specimen tested by the dress disk test showed better agreement with the theoretical values than of a ring specimen tested by the split disk test because the stress concentration in edges of a split disk test fixture is more severe than that of dress disk test fixture. The results showed that the tensile strength of a ring specimen was influenced by the geometry of test fixture, the continuity of fibers, fiber-tension, fiber-end and stress concentration in specimen.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.367-368
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• 2002

The design of capsule body for self-propelled endoscope is important from the frictional resistance point of view. The capsule should be able to overcome the frictional resistance in order to move along the intestine. The motivation of this work was to gain a better understanding of the capsule body design on the frictional resistance of the capsule inside an intestine. A special experimental set-up was built to measure the frictional resistance as the capsule was being pulled inside the pig intestine specimen. Tests were performed with open and closed intestine specimens. Experimental data showed that smooth cylindrical capsule geometry resulted in the least frictional resistance. The resistance inside the closed intestine specimen was about four times higher than that of the open specimen. It is expected that the results of this work will be used to design the optimum propulsion system for the microendoscope.