• Explosives and Blasting
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• v.26 no.1
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• pp.57-66
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• 2008

It has been proven that the pre-cracking notches in a blasting hole are applicable to control crack growth along specific direction. This study compared the roughnesses of the fracture plane resulting from test blasts using a regular charge hole and notched charge hole to investigate the effect of the notches of charge hole on the formation of fracture plane. A notch bit system was used to drill the notched hole in the rock specimens. The surfaces of the fracture planes were reconstructed as Digital Elevation Model (DEM) using digital photogrammetric method and the roughnesses of the surfaces were estimated with Surface Roughness Profile Index (SRp).

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.10a
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• pp.703-704
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• 2012

• Explosives and Blasting
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• v.37 no.3
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• pp.25-33
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• 2019

Controlling the blast-induced damage zone(BDZ) in mining excavation is a significant issue for the safety of employees and the maintenance of facilities. Numerous studies have been conducted to accurately predict the BDZ in underground mining. This study employed the dynamic fracture process analysis (DFPA) to estimate the BDZ from a single hole blasting. The estimated BDZ were compared with the results obtained by Swedish empirical equation. The DFPA was also used to investigate the control mechanism of BDZ and fracture plane formation around perimeter holes for underground mining blasting.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.193-203
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• 2022

In this study, in order to compare the seismic performance of steel structure beam-column connection details and non-scallop connection details mainly used in Korea, a full-scale static cyclic loading test and FEM analysis were conducted through the same modeling as the experiment. For quantitative numerical comparison, the strain concentration ratio and moment transfer efficiency used in previous studies were cited. As the welding area of the beam web decreased, the deformation rate of the beam flange increased, and the plastic deformation capacity according to the rotation angle decreased or brittle fracture occurred. Comparing the analysis results with the experimental results, the possibility of brittle fracture tended to increase when the web welding ratio for the total cross-sectional area of H-shaped fell below 60%.

• Journal of the Korean Society of Mechanical Technology
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• v.13 no.4
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• pp.125-130
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• 2011

Technological mode progress demands the use of materials at high temperature and pressure. Constant load creep tests have been carried out over the range of stresses at high temperatures. One of the most critical factors in considering such applications as the most critical one is the creep behavior. In order to investigate the creep behavior in this study, the stress exponents during creep were determined over the temperature range of $275^{\circ}C$ to $325^{\circ}C$ and the stress range of 36MPa to 72MPa. The applicability of modified Monkman-Grant relationship was also discussed.

• Composites Research
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• v.12 no.2
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• pp.53-61
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• 1999

A failure criterion must be considered in each failure mode and loading condition to provide easy determining strength parameters, flexibility and rational simplicity. In this study, new failure criterion was developed by introducing equivalent strength under biaxial loading of tension and torsion. The experimental results showed that the equivalent biaxial strength has a power law relation with respect to a parameter, cos($tan^{-1}R_b$). Failure strength under biaxial loadings could be predicted as a function of tensile strength, torsional strength and biaxial ratio. The scattering of experimental data could be predicted using a Weibull distribution function and the concept of equivalent biaxial strength. Also, in this study, a fatigue theory was developed based on a plane stress model which enabled the S-N curve for combined stress states to be predicted from the S-N data for uniaxial loading. The prediction models can be predicted a biaxial strength and fatigue life of general laminated composite naterials under multi-axial loadings.

• Journal of Korean Ophthalmic Optics Society
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• v.13 no.4
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• pp.89-94
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• 2008

Purpose: To observe the high temperature creep test and the fracture surface of the samples of 9% Ni alloy steel generally used for all kinds of mahine parts and predict the durability of that by determining a constant of C with a Larson-Miller variable. Methods: The equipment of this test was made into lever-beam style designed by Andrade and F. Garofalo et al.. The condition of creep test was set under 16 kinds of conditions after fixing 4 kinds of temperature condition and 4 kinds of stress condition to check how it effects the samples. Results: The temperature of creep test was increased, the stress index (n) of creep deformation was gradually decreased from 3.97 to 3.55. The activation energy of creep deformation was decreased from 90.39 to 83.64 kcal/mol when the stress was increased. A constant of C value by calculation of larson-Miller variable was about 22 and if temperature for use is suggested, the durability could be calculated. Conclusions: By analyzing the fracture phenomenon and suggesting the observation result of the fracture surface of the samples and creep test of 9% Ni alloy steel, the basic design data for the practical use of accessories in the field of equipment could be constructed and used to predict the durability of the equipment.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.3
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• pp.775-787
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• 1996

An optimization procedure is proposed for the design of cylindrically laminated composite shell having midplane symmetry and subjected to axial force, torsion and internal pressure. Tsai-Wu and Tsai-Hill failure criteria are taken as objective functions. The stacking sequence represents the design variable. The optimal design formulation based on state space method is adopted and solution proccedure is described with the emphasis on the method of calculations of the design sensitivities. A gradient projection algorithm is employed for the optimization process. Numerical results are presented for the several test problems.

• Journal of Power System Engineering
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• v.10 no.3
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• pp.45-50
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• 2006

In this paper, creep tests of Mg-Zn-Mn and Mg-Zn-Mn-Ca alloy casted by mold under the temperature range of 473.00-573.00K, and the stress range of 23.42-87.00Mpa were done with the equipment of automatic controlled temperature and computer for data acquisition. The activation energies were obtained by relationship between creep rate and temperature, and the stress exponents were obtained by relationship between creep rate and stress. From the experiment results, the activation energies of Mg-Zn-Mn and Mg-Zn-Mn-Ca alloy were 149.87kJ/mol, 147.97kJ/mol, respectively, and the stress exponents of those alloy were 5.13, 5.59, respectively, under the temperature of 473.00-493.00K and the stress range of 62.43-78.00Mpa. And the activation energies of those alloy were 134.41kJ/mol, 129.22kJ/mol, respectively, and the stress exponent of those alloy were 3.48, 3.77, respectively, under the temperature of 553-573Mpa and the stress range of 23.42-39.00Mpa. Also the lifes of Mg-Zn-Mn-Ca alloy were higher than those of Mg-Zn-Mn alloy, and the results of SEM showed fracture surfaces under low temperature had smaller dimples than those under high temperature.

• Journal of Ocean Engineering and Technology
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• v.22 no.6
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• pp.58-63
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• 2008

The short-term high temperature creep rupture behavior of Ni-based Alloy718 steels jointed by friction welding wasinvestigated at the elevated temperatures of 550 to $700^{\circ}C$ under constant stress conditions. The creep rupture characteristics such as creep stress, rupture time, steady state creep rate, and initial strain were evaluated. Creep stress has a quantitative correlation between creep rupture time and steady state creep rate. The stress exponents (n, m) of the experimental data at 550, 600, 650 and $700^{\circ}C$ were derived as 26.1, -22.4, 22.5, -18.5, 17.4, -14.3 and 6.9, -8.1, respectively. The stress exponents decreased with increasing creep temperature. The creep life prediction was derived by the Larson-Miller parameter (LMP) method and the result equation obtained is as follows: T(logtr+20)=-0.00148${\sigma}^2$-3.089${\sigma}$+23232. Finally, the results were compared with those of the base metal for Alloy718.