• Proceedings of the Korean Society of Precision Engineering Conference
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• 1994.10a
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• pp.61-66
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• 1994

Tool condition monitoring is one of the most important aspects to improve productivity and quality and to achieve intelligent machining system. The tool state is classified into three groups as chipping, wear and fracture. In this study, wear of a ceramic cutting tool for hardened die material (SKD11) was investigated. Flank wear was occured more dominant than crarer wear. Therefore, to predict flank wear, the modeling of cutting force has been performed. The modeling of cutting force by an assumption that act the stress distribution on the tool face obtained through a numerical analysis. The relationships between the cutting force and the tool wear can be constructed by machining paraneters with cutting conditions. Experiments were performed under the various cutting conditions to ensure the validity of force models. The theoretical predictions of the flank wear is approximately in good agreement with experimental result.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.6
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• pp.1290-1295
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• 1988

Theoretical considerations in the development of new cutting tool materials for high speed machining is presented. The progressive wear of cutting tools is assumed to consist of the abrasive and solution components as major modes. Theoretical calculations of relative wear rates between various tool materials based on the two modes are possible using their hardness and solubility data. Assuming cementite as the major hard particles in machining steels, relative wear rates of possible tool materials were calculated. The results indicate that $Al_{2}$O$_{3}$ in oxides, HfN in nitrides and HfC in carbides are the optimal tool materials from the view point of mechanical and thermochemical wear resistance. And several methods for improving the fracture toughness of the above tool materials are suggested.

• Journal of Trauma and Injury
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• v.32 no.1
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• pp.40-46
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• 2019

Purpose: We perform an analysis of infection risk factors for fracture patients and confirm that the risk factors reported in previous studies increase the risk of actual infection among fractured patients. In addition, injury severity score (ISS) which is used as an evaluation tool for morbidity of trauma patients, confirms whether there is a relationship with infection after orthopedic fracture surgery. Methods: We retrospectively reviewed 1,818 patients who underwent fixation surgery at orthopedic trauma team, focused trauma center from January 1, 2015 to December 31, 2017. Thirty-five patients were infected after fracture surgery. We analyzed age, sex, open fracture criteria based on Gustilo-Aderson classification 3b, anatomical location (upper extremity or lower extremity) of fracture, diabetes, smoking, ISS. Results: Of 1,818 patients, 35 (1.9%) were diagnosed with postoperative infection. Of the 35 infected patients, nine (25.7%) were female and five (14.0%) were upper extremity fractures. Three (8.6%) were diagnosed with diabetes and eight (22.8%) were smokers. Thirteen (37.1%) had ISS less than nine points and six (17.1%) had ISS 15 points or more. Of 1,818 patients, 80 had open fractures. Surgical site infection were diagnosed in 12 (15.0%) of 80. And nine of 12 were checked with Gustilo-Aderson classification 3b or more. Linear logistic regression analysis was performed using statistical analysis program Stata 15 (Stata Corporation, College Station, TX, USA). In addition, independent variables were logistic regression analyzed individually after Propensity scores matching. In all statistical analyzes, only open fracture was identified as a risk factor. Conclusions: The risk factors for infection in fracture patients were found to be significantly influenced by open fracture rather than the underlying disease or anatomical feature of the patient. In the case of ISS, it is considered that there is a limitation. It is necessary to develop a new scoring system that can appropriately approach the morbidity of fracture trauma patients.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.2
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• pp.14-22
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• 2007

In this paper, the acoustic emission(AE) behaviors were investigated with single-and 2-spot resistance spot welded SPCC specimens. Test specimens were welded horizontally and/or vertically according to the rolling direction of base netal in 2-spot welding. In the case of 2-spot welding, when tensile-shear test has below amplitudes: crack initiation $50{\sim}60dB;$ tear fracture $40{\sim}50dB$. And when cross tensile test has below amplitudes: early stage $75{\sim}85dB;$ yielding point $65{\sim}75dB;$ post yielding $40{\sim}60dB;$ plug fracture $70{\sim}80dB\;or\;90{\sim}100dB$. Also, from the b-value that is slope of AE amplitude, we knew that there are lots of low amplitudes if b-value is big(i.e., tensile-shear $specimen{\rightarrow}tear$ fracture or shear fracture), and there are lots of high amplitudes if b-value is small(i.e.. cross tensile $specimen{\rightarrow}plug$ fracture). As the results of fiacture mechanism analyses through AE amplitude distributions, change of the b-value represented fracture patterns of materials. Correspondingly, low amplitude signals appeared in crack initiation, and high amplitude signals appeared in base metal fracture. We confirmed that these amplitude distributions represented the change or degradation of materials.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.9 no.2
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• pp.87-95
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• 2000

By using AIP(Arc Ion Plating) of a physical vapor deposition for the first time in Korea a ceramic tool whose surface is coated single layeredly with TiN is developed. In addition cutting resistance appearing in the process of finishing cut of hardened carbon tool steel STC3 is studied. The principal and radial components of cutting resistance in those cutting conditions appear to be the same or similar and the feed component is relatively small. The feed component is found to be in proportion to cutting width and the radial component in proportion to cutting thickness. Owing to coating the cutting resistance of a TiN coated ceramic tool increas-es compared with that of a general ceramic tool.

• Structural Engineering and Mechanics
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• v.16 no.1
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• pp.47-62
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• 2003

The nonlinear dependence aspect of various conical tool indentation parameters leading to an optimum tool semi angle value for easiest perforation is plotted and discussed explicitly in this work with the conclusion that tool angle has an optimum response towards most of the indentation parameters. Around this optimum angle, the aluminium sheets showed minimum fracture toughness as well as minimum work input to overcome the offered resistance. At the end, the mechanism leading to this phenomenon is presented with the conclusion that plastic flow dominates as the dimple semi cone angle reaches 35 and both pre and post plastic flow perforations lead the tool semi cone angle value towards this dimple cone semi angle of plastic flow initiation for its optimum performance. It is also concluded that specimen material failure is solely under tensile hoop stress and hence results into radial cracks initiation and propagation.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.5 no.3
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• pp.15-21
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• 1996

This study is focused on the prediction of appropriate tool life by clarifying the correlation between progressive tool wear and AE(Acoustic Emission) signals, while cutting stainless steel by end mill on the machining center. The results of this study were that RMSAE tends to increase linearly along with the increase of the cutting speed, and it was more sensitive to depth of cut than to the variation of feed rate at the same cutting conditions, and RMSAE increases around 0.21mm flank wear hereby AE-HIT also increases. AE signals depend upon tool wear and fracture from the above results. Therefore, the AE signals can be utilized in order to monitor the tool condition.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.6
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• pp.38-43
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• 2006

A slot cut in end milling processes is one of the laborious works because the cutting force is likely to deflect the tools excessively, then to make large errors or to fracture the tool. This difficulty is owing to the poor stiffness of slender shaped end mills. Though, in most cases, additional finish cuts are followed after rough cuts, the accuracy of rough cuts is still important because it affects the final accuracy after finish cuts and productivity. The accuracy in slot cuts depends on the tool stiffness and the cutting conditions including depth of cut and feed. In order to meet the desired accuracy, diameter of end mill and cutting allowance have to be selected carefully. This study suggests several guidances for selecting the end mill diameter and the slot cut allowance to improve machining accuracy and productivity in slot end millings. Some experiments were done with the various cutting parameters of tool diameter, depth of cut and feed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.6
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• pp.693-700
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• 2004

The probabilistic fracture mechanics(PFM) is a useful analytical tool to assess the integrity of reactor pressure vessel(RPV) at the event of pressurized thermal shock(PTS). In PFM, the probabilities of flaw initiation and propagation are estimated by comparing the applied stress intensity factor with the fracture toughness calculated by the simulation of various stochastic variables. It is known that the results of PFM analyses are dependent on the choice of the stochastic parameters and assumptions. Of the various variables and assumptions, we investigated the effects of the RT$_{NDT}$ shift equations, fracture toughness curves, and flaw distributions on the PFM results for the three PTS transients. The results showed that the combined effects of the RT$_{NDT}$ shift equations and fracture toughness curves are complicated and dependent on the characteristics of the transients, the chemistry of the materials, the fast neutron fluence, and so on.

• Journal of the Korean Society of Safety
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• v.27 no.6
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• pp.93-98
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• 2012

In order to capture the fast crack propagation in an unmanipulated concrete fracture test, we employed mechanoluminascent(ML) material, which emits visible light when stressed, as a crack visualization tool. Three-point bending fracture test setup, a paint type ML material and a high speed camera were used to capture the images of fast moving cracks. The maximum size of coarse aggregates of concrete was used as an experimental parameter. The crack images, loading, and crack mouth opening displacement were successfully recorded as a function of time elapsed. From the test results, several interesting cracking behavior in the unmanipulated fracture test was observed in such that (1) the crack moves fast while the load is slowly decreased after the maximum loading, and (2) the crack in concrete with larger coarse aggregates moves faster than the others.