PZT께 압전 세라믹스의 제조 및 기계적 특성에 관한 연구

崔永根,權鍾完 慶一大學校 1993 論文集 Vol.9 No.1

Densification behavior, microstructural evolution and mechanical properties of hot-pressed specimens using PZT ceramics with PbO additive were studied, and bulk density, microstructure, mechanical properties were investigated for sintering time. Fracture toughness of the spections containing 1mol% PbO was increased as the hot-pressing temperature up to 1080℃ and maximum value was 1.60MN/m??, while fracture toughness of the specimens containing 2mol% PbO was decreased. The enhanced fracture toughness by PbO is probably due to the crack deflection along the boundaries of the elongated grains. Vicker's hardness of the specimens was in the range of 270-320Kgf/mm² and was decreased due to the incrasing of pore according to PbO addition. As the sintering time becomes longer, fracture toughness was gradually decreased for the the increasing of grain size and vicker's hardness was shown the linear increasing lue to increase of density.

變分法에 衣한 體積一定下의 形狀決定에 對한 考察

權鍾完 慶北工業專門大學 1983 論文集 Vol.20 No.-

It is very important for structure analysis from the viewpoint of structurl design to know the appropriate shape of beam element. In this paper, The variational approach is formulated in two demensional isotropic plane stress problem and calculate the appropriate shape of element. An example problem, the calcuiation of thickness is showen for simple beam element under the concentrate load. In this study, following information is obtained. 1) An optimal shape condition is expressed by the term fo energy density quantity from principle of variation and example calculation coincides with the solution of uniform stress. 2) we presume the example calculation which is applied more compricate shape calculation problem.

2相 스테인리스鋼 熔接部의 後熱處理 溫度의 影響

陸鍾律,權鍾完 慶一大學校 1997 論文集 Vol.14 No.2

An experimental study was performed to investigate the metallurgical characteristics of weldment for duplex stainless steel. Considering that duplex stainless steel in a composite structure of α and γ phase, it can be found that mechanical variables of weldment structure are different from base metal by weld cycle, weld deformation and residual stress through weld input heat, it has some problems because it will be easily brittle through slow cooling by post weld heat treatment. It was observed the embrittlement phenomenon in high ferrite stainless steel and after impact test to identify the fracture characteristics of the weldment, the obserbed energy was lowest in about 1073K. Therefore, it should be avoided the post weld heat treatment about those temperature. The result could be anticipated that the range of γ-phase's precipitation of Widmanstatten, which occured in heat affected zone as changing microstructure by the variation of weld heat input.

二相 스테인리스鋼 熔接部의 疲勞龜裂傳播 特性과 微視的 機構

權鍾完 慶一大學校 1989 論文集 Vol.5 No.1

An experimental study was carried out to identify the fatigue crack propagation behavior of duplex stainless steel weldment. Experimental works were performed under stable crack propagation in room temperature and substitute ocean water was also studied. Experiments were studied to give insight of phenomennological understanding in terms of micro-structural changes. The crack propagation behavior was found to be dependent on phase ratio(α/γ). The crack propagation rate in welding zone first, in base-metal was second. The crack propagation rate in substitute ocean water was found to be faster than that obtained in air at room temperature. This may be caused by the corrosion of the fatigue fracture surface through chemical reaction. The crack propagation rate estimated by the measurement of striation spacing was higher than that obtained by crack length measurement in low △K region, however, both crack propagation rates were found to be identical.

鑄鐵 미끄럼摩擦의 摩耗에 對한 硏究

權鍾完 慶北工業專門大學 1979 論文集 Vol.16 No.-

Wear which occurs in the slidng of metal pair is very complicated. Because it is made up the various factors which are combined in a complicated way. In this paper, the relation between wear occurs in matal pair which had been proved depend mainly on the flow pressure of material and Holm's wear equation W=KPL/?? examined by wear test of cast iron. The wear test are carried out under the dry condition using upper and lower test pieces of cast iron the same quality. We proved that material hardness dominated surface temperature induced by frictional temperature. By expressing the hardness as a function of Olad and sliding speed. Results are summarized as follows. 1) ?? could be obtained theoretically from Holm's equation, W=KPL/?? where ?? is wear rate P the load V. the sliding speed. ?? : the hardness at room temperature. C constant depending on the properties of material ?? : flow pressure. 2) The equation did not hold at high load and speed, this cause is deduced that some factors other than the hardness act predominantly on the wear process.

2相 Stainless鋼의 異種熔接에 對한 靜的 强度特性

權鍾完 慶一大學校 1986 論文集 Vol.2 No.1

Recent trends in the fabrication of industrial plant have led to the increased use of welding for joining materials of different composition. In this study, is research of static strength for welding bond by dissimilar metals(25cr-5Ni stainless steel versus SM41 steel). Through investigation, we found phenomenon of maxium true strength and toughness decreasing near the bonded part of welding joint. It was caused by brittle layer formed in the deposite metal along the fusion line. We recognized accurate time for PWHT(post welding heat treatment 1hr or 2hr.) Brittle layer of welding bond is recovered by PWHT in this case.

三相스테인리스鋼의 溶體化處理溫度에 對한 靜的强度特性

權鍾完 慶一大學校 1988 論文集 Vol.4 No.1

Charactristics of static strength in duplex-stainless steel has been investigated withtemperature of solution heat treatment. In higher temperature, volume of ferrite phase and grain size increased in stainless-steel. At 1623 K, duplex-stainless steel is changed ferrite phase wholy. Static strength and hardness is proportion to volume of ferrite phase. At 1300K, static strength, ductilenss increased significantly. Increasing of cooling rate decreased static strength. The static strength revealed a very large influence of solution temperature at 773K.

炭素鋼의 疲勞限度의 豫測을 위한 評價因子

尹命辰,權鍾完 慶一大學校 1999 論文集 Vol.16 No.2

The fatigue strength of structural steels containing small defect or inclusion are so complicated that the prediction influence of the defect or inclusion is very difficult. This study simplifies these factors to evaluate the influence use projected area of the defect or inclusion in low and medium carbon steels. The investigation is carried out by a quantitative evaluation relationship between fatigue limit and √αγeα. We study this issue using SM15C and SM35C materials. (1) In the experiment, The critical crack length of _EFM is coincide to the intrinsic crack length of Haddad method. (2) Only defects and inclusion larger than a critical size have harmful effects on the fatigue strength of metals. The critical size is concerned with the length ιc of small non-propagating cracks which are observed at the fatigue limit of un-notched specimens. (3) The lower limit σwι of scatters of fatigue strength can be predicted by Murakami and colleagues method, in which the square root of the projected area (√αγeα) of inclusions are the crucial influential parameters. The value of σwι depends on the maximum inclusion(√αγeαmax) which is expected to be contained in specimens or machine components.

워엄 齒東의 齒面摩耗에 對한 考察

權鍾完 慶北工業專門大學 1980 論文集 Vol.17 No.-

A worm and worm gear are used to connect nonparallel, shafts and the gear reduction is generally quite large. But worm and worm gear have very large slip ratio on the tooth surface. It is one of important factor that they has different direction between component of contact line and normal velocity. In this paper, the author has considered a relation of contact angle (?) and wear value on the tooth surface. The expriment are carried out cylinder and circular plate in lubricant condition. Exprimental results are as follows; 1) The wear value of contact angle ?=-30˚is twice that of ?=90˚ 2) The wear value is highest at contact angle (?) about 6˚ any other point.

지연 담금질 열처리한 티타늄 합금의 균열 발생과 진전 특성에 관한 연구

權鍾完 慶一大學校 1996 論文集 Vol.13 No.2

This study was examined the microstructural parameters which influence the development and growth of short fatigue cracks in the Ti alloy with a view to improving the fatigue performance of the alloy by microstructural control and optimization. The short and long crack growth data has been generated for fully transformed beta and alpha plus transformed beta microstructures containing primary alpha phase volume fractions of 5, 15 and 2% and with prior beta phase grain sizes ranging from approximately 40㎛ up to 1.0㎜. The microstructural features associated with crack initiation and crack propagation have been identified and a simple empirical model has been developed allowing the prediction of fatigue crack growth rates at crack length both above and below the short to long crack transition. In the study have been extended in an attempt to as certain the effects of alpha phase morphology and distribution on the growth of both long and short fatigue cracks in dual phase microstructures. In addition, provisional in-situ SEM observations relating to crack path morphology and the development of crack closure in a 15% alpha microstructures are discussed and an attempt is made to develop a unified approach to fatigue life prediction.