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일방향 혼합방사형 탄소섬유/폴리아미드 6 복합재료판의 제작조건과 굽힘파괴거동
최낙삼,Choi, Nak-Sam 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.2
Unidirectional commingled-yarn-based carbon fiber(CF)/polyamide(PA) 6 composite was fabricated under molding pressures of 0.4, 0.6 and 1.0 MPa to study its flexural deformation and fracture behavior. Fiber/matrix interfacial bonding area became larger with an increase of molding pressure from 0.4 to 0.6 MPa. For molding pressures .geq. 0.6 MPa, good flexural performance of similar magnitudes was attained. For the fracture test, four kinds of notch direction were adopted : edgewise notches parallel (L) and transverse (T) to the major direction of fiber bundles, and flatwise notches parallel(ZL) and perpendicular(ZT) to this direction. Nominal bend strength for L and ZL specimens exhibited high sensitivity to notching. ZL specimens revealed the lowest values of the critical stress intensity factor $K_c$ which was slightly superior to those of unfilled PA6 matrix. Enlargement of the compression area for T specimens was analyzed by means of the rigidity reduction resulting from the fracture occurrence.
모드 I 하중조건하에 있는 다방향 적층 복합재료의 층간파괴거동
최낙삼,Choi, Nak-Sam,Kinloch, A.J. 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.3
The delamination fracture of multidirectional carbon-fiber/epoxy laminates under the Mode I condition has been studied using the modified beam analysis for a fracture mechanics approach. It was found that the variation of fracture energy $G_IC$ with increasing length of the propagating crack exhibited a minimum for the pure interlaminar fracture and a maximum for the intraply fracture,i.e. a rising "R-curve", which was strongly affected by the degree of fiber bridging and crack-tip splitting arising in the global delamination. The maximum $G_IC$ value was significantly dependent on such types of delamination as no crack jumping, crack jumping into the adjacent ply and edge-delamination. It was shown also that the value of "effective flexural modulus" estimated from the modified beam analysis increased much with the development of fiber bridging behind the crack tip.ehind the crack tip.
최낙삼(NakSam Choi),곽승범(SeungBum Kwak),신세문(SeiMoon Shin),강봉성(BongSung Kang),신외기(WaeGi Shin) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Coolant rubber hoses for automobile radiators co be degraded and thus failed due to the influence of contacting stresses of air and coolant liquid under the thermal and mechanical loadings. In this study, test analysis was carried out for evaluating the degradation and failure mechanisms of coolant hose materials. An increase of surface hardness and a large reduction of failure strain were shown due to the formation of oxidation layer for the specimens which had been kept in a high temperature air chamber. Coolant ageing effects hardly took place, which corresponded to only the pure thermal degradation. The degraded specimens by electro-chemical degradation (ECD) test showed a swelling behavior and a considerable increase in weight oil account of the penetration of coolant liquid into the skin and interior of rubber. The ECD induced material softening and fatal decreases in strength and failure strain. A procedure fur reliability analysis and evaluation of the degradation and failure mechanisms of FPDM rubbers used in coolant hoses for automobile radiators was proposed.
최낙삼(Nak-Sam Choi),이성혁(Sung-Hyuk Lee) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
Local buckling behaviors of aluminum square tube beams reinforced by aluminum plates under three point bending loads have been analyzed using experimental tests combined with theoretical and finite element analyses. For this analysis true stresses were determined from applied loads and cross-sectional area records of a tensile specimen with a rectangular cross-section by real-time photographing. True strains were also obtained from in-situ local elongation measurements of the specimen gage portion by the multi-point scanning laser extensometer. Six kinds of aluminum tube beam specimens reinforced by aluminum plates were employed for the bending test. The bending deformation behaviors up to the maximum load analyzed by the numerical simulation agreed well with experimental ones. After passing the maximum load, reinforcing plate hindering the local buckling of the tube beam was debonded from the aluminum tube beam. An aluminum tube beam strengthened by aluminum plate on the upper web showed the most excellent bending capacity, which could be explained on the basis of the neutral axis shift and the local buckling deformation range.