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조경목,이후철,현태욱 대한금속재료학회(대한금속학회) 1985 대한금속·재료학회지 Vol.23 No.1
A study on the fracture toughness of WC-Co using alloys is made single-edge notched beam specimens pre-cracked by electron-discharge machining. The microstructural parameters are determined on the electron micrographs by linear analysis. The relations between K_(IC) and the microstructural parameters show that K_(IC) tends to increase with increased binder volume fraction and cobalt mean free path and tends to decrease with increases in WC contiguity, but cannot be related only to one microstructural parameter. A structure model is sugested to estimate the fracture path in WC-Co alloys and the critical strain energy release rate is evaluated from this fracture model.
자동차 차체용 고강도 IF 강에서 미세조직과 기계적 성질에 미치는 Mn 의 영향
조경목,정우창 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.6
The purpose of this study was to develope IF(interstitial free) steels for the application to automotive body panels. IF steels containing less than 20 wt ppm of C and N, and 1.2 to 2.8 wt% of Mn were prepared to investigate the effect of Mn on the microstructure and mechanical properties. Microstructure observation of IF steels annealed at austenitic region revealed network type polygonal ferrite due to Mn gradient for the steels containing 1.23% Mn(A) and 1.94% Mn(B), and granular bainitic ferrite with high dislocation density for the steel containing 2.76%Mn(C). Tensile strength of A. B and C after annealing (800-920℃) was measured as about 400, 450 and 500 ㎫, respectively Tensile strength decreased slightly for A and B, butincreased for C with increasing annealing temperature. Granular bainitic ferrite of C might induce the strengthening effect at a high annealing temperature. (Fe. Ti) P precipitates formed when IF steels were annealed at ferritic region, which lead to the shortage of effective Ti content to remove solute carbon. The major texture of IF steels was found to be (554)[225 ̄] that is favorable to improve the formability. However, intensity of (554)[225 ̄] was decreased with increasing Mn content.
$Al_2O_3$와 $Al_2O_3$ -$SiC_w$ 복합재료의 동적 및 정적 파괴인성에 관한 연구
조경목,이성학,표성규,장영원 한국세라믹학회 1990 한국세라믹학회지 Vol.27 No.4
This paper presents the influence of the loading rate on the room temperature fracture toughness of a brittle Al2O3 and a SiC whisker reinforced Al2O3 composite. Dynamic fracture toughness tests were conduced using compressive fatigue pre-cracked notched round bars loaded in tension to produce a stress intensity rate K1=106 MPa√m/sec. The experimental results show that for each loading rate the fracture toughness values obtained for the ceramic matrix composite are higher than the corresponding values for the single phase alumina. In addition, both the reinforced and unreinforced ceramic are singnificantly tougher under dynamic loading than static loading. This dynamic and quasi-static fracture initiation behaviro can be interpreted by identifying quantitatively the mode of fractuer initiation as a function of loading rate.
조경목,이희태,김수영,조영기 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.4
In the present study, wear properties, of cast Al-SiC_p composites were characterized. Wear tests were performed as a function of teat conditions including applied load, sliding speed and sliding distance under dry wear condition employing a block-on-roller type wear test machine. Wear mechanism of Al-SiC_p composites was also investigated by the analysis of worn surfaces and wear debris. Results show that wear resistance of Al alloy is improved with reinforcement of SiC_p especially with severer wear conditions such as high applied load and long sliding distance. Weight loss of Al-SiC_p composites almost linearly increases with applied load and sliding distance. There exists a transition point of wear behavior at which a minimum wear rate encountered in terms of the sliding speed. Wear mechanism is abrasive at the low speed and at .the transition speed, and adhesive/abrasive wear at the high speed range. It was found that uniform distribution of SiC_p reinforcement is desirable to improve the wear resistance of Al-SiC_p composites.