반복되는 열주기(Thermal Cycling)환경에 노출된 에폭시/탄소섬유 복합재료의 열산화 안정성 연구

이상호; 남재도; 정기모; 안규종; 김병선

Korean Journal of Rheology, Vol.10, No.2, 106-112, June, 1998

Export Citation

반복되는 열주기(Thermal Cycling)환경에 노출된 에폭시/탄소섬유 복합재료의 열산화 안정성 연구

Thermo-Oxidative Stability of Epoxy/Carbon Fiber Composites under Thermal Cycling Conditions

이상호, 남재도, 정기모, 안규종, 김병선

초록

항공기용 소재로 개발된 에폭시/탄소섬유 복합재료가 매트릭스의 유리전이온도에 육박하는 온도주기를 경험할 때 발생하는 복합재료의 구조 및 물성변화를 실험과 모델링을 통하여 연구하였다. 복합재료의 표준 경화 온도인 177℃에서 2시간 체류(aging)시킨 후 냉각시키는 반복 열주기 (thermal cycle)근 복합재료를 취약(brittle)하게 하여 결국 표면에서부터 미세크랙(microcrack)이 발생 한다는 것을 알 수 있었다. 이러한 열주기에 따른 미세크랙 현상은 매트릭스의 분해(degradation)반응이 발생할 수 있는 유효 표면적(effective surface area)을 증가시키고, 크랙을 통하여 산소의 투과를 용이하게 함으로서 산화반응을 가속화하여 복합재료시편의 무게 감소를 가속화시키는 것으로 판단된다. 특히 본 연구에서는 등온(isothermal)과 등속도 승온(dynamic heating) 조건을 주기적으로 반복하는 열주기 조건을 해석하기 위하여, 열주기 조건을 특정온도에서의 등온시간(isothermal holding time)으로 전환할 수 있는 equivalent cycle time(ECT)를 제안하였고, 이를 이용하여 열주기에 의한 복합재료 손상의 가속/감속 현상을 규명할 수 있었다.

Thermal cycling of carbon fiber/epoxy composite systems was investigated to understand the structure and property changes induced by the repeated heating/holding/cooling processes up to the glass temperature of the matrix. Collectively comparing two composite systems developed for structural applications and composite-tool applications, the toughened-epoxy composite system was more resistent to the cycle-induced surface cracking and weight loss. The microcracks propagating from the surface to the core accelerated the weight loss rate of composite laminates seemingly providing more oxidative surface area and enhancing oxygen transport. To compare the aging processes by thermal cycling and isothermal holding in the same axis, the equivalent cycle time (ECT) was developed by the kinetic theories and experimental results. Using the ECT, the cycling thermal history was converted to the equivalent time required for the equivalent property change at a specific temperature. According to the ECT analysis of the weight loss, the cycled specimens exhibited much lower weight loss than the isothermallv-aged specimens.

Keywords:epoxy;carbon fiber;composite;thermal stability;thermal cycling;environment equivalent time;degradation kinetics;weight loss

[References]

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[1] Morena JJ, Advanced Composite Mold Making, Society of Plastics Engineers, New York (1988)

[2] McLarty DL, 34th SAMPE Symp., 1294 (1989)

[3] Chau HN, 38th SAMPE Symp., 243 (1993)

[4] 정기모, 안규종, 남재도, 김준경, 송기국, 한국복합재료학회 추계 학술발표회 논문집, 83 (1994)

[5] Trayer AM, Chem. Eng. News, July, 37 (1990)

[6] 정기모, 안규종, 이상호, 서대원, 남재도, 한국복합재료학회 춘계 학술발표회 논문집, 61 (1995)

[7] 이상호, 서대원, 남재도, 정기모, 안규종, 한국화학공학회 추계 학술발표회 논문집, 83 (1995)

[8] 이상호, 서대원, 남재도, 정기모, 안규종, 한국고분자학회 추계 학술발표회 논문집, 133 (1996)

[9] Nam JD, Suh DW, Lee SH, Jung KM, Ahn KJ, 12th Annual Meeting in Polymer Processing Society, 533 (1996)

[10] 정정화, 최흥섭, 엄용성, 안규종, 남재도, 한국복합재료학회 추계 학술발표회 논문집, 95 (1994)

[11] Ahn KJ, Chung CM, Eom YS, Choi HS, Ha JM, Nam JD, 11th Annual Meeting in Polymer Processing Society, 277 (1995)

[12] Bowen G, "Composites Tooling II Proceedings," ed., by P.J. Hogg and D.H. Woolstencroff, Elsevier, Oxford, p. 11 (1992)

[13] Krevelen V, "Properties of Polymers," 3rd ed., Elsevier Amsterdam (1990)

[14] Flynn JH, Polym. Eng. Sci., 20(10), 675 (1980)

[15] Flynn JH, Thermochim. Acta, 134, 115 (1988)

[16] Bamford CH, Tiffer CFH, "Comprehensive Chemical Kinetics," 22, Elsevier, New York (1980)

[17] Garn PD, J. Thermal. Anal., 13, 581 (1987)

[18] MacCallum JR, Br. Polym. J., 11, 120 (1979)

[19] Cameron GG, Rudin A, J. Polym. Sci. B: Polym. Phys., 19, 1799 (1981)

[20] MacCallum JR, Tanner J, Eur. Polym. J., 6, 907 (1970)

[21] Cooney JD, Day M, Wiles DM, J. Appl. Polym. Sci., 28, 2887 (1983)

[22] Flynn JH, Thermochim. Acta, 37, 225 (1980)

[23] Flynn JH, Wall LA, J. Polym. Sci. C: Polym. Lett., 5, 192 (1967)

[24] Zsako J, J. Thermal. Anal., 5, 239 (1973)

[25] Nam JD, Seferis JC, J. Polym. Sci. B: Polym. Phys., 29, 601 (1991)

[26] Nam JD, Seferis JC, J. Polym. Sci. B: Polym. Phys., 30, 455 (1992)

[27] Rozycki C, Maciejewski M, Thermochim. Acta, 122, 339 (1987)

[28] Bagchi TP, Sen PK, Thermochim. Acta, 51, 175 (1981)

[29] Roman JS, Macdruga EL, Pargada L, Polym. Degrad. Stabil., 19, 161 (1987)

[30] Flynn JH, "Aspects of Degradation and Stabilization of Polymer," ed., by H.G. Jellinek, elsevier Scientific, New York, p. 573 (1978)

[31] Doyle CD, J. Appl. Polym. Sci., 5, 285 (1961)

[32] Seum GI, Yang RT, J. Thermal. Anal., 11, 455 (1977)

[33] Douglass Aircraft Company, Carbon Epoxy Prepreg-Impact Resistant, DMS 2224, DAC (1989)

[34] Nam JD, Seferis JC, SAMPE Quarterly, 24(1), 10 (1992)

[35] Bowles KJ, Jayne D, Leonhardt TA, Bors D, J. Adv. Mater., 26(1), 23 (1994)

[36] Bowles KJ, Nowak G, J. Compos. Mater., 22, 966 (1988)

[37] Potteer BD, Yuan FG, Pater RH, J. Adv. Mater., 25(1), 30 (1993)

[38] ASTM D2344-84 (1989)

[39] Ozawa T, J. Thermal. Anal., 2, 30 (1970)

[40] Bero CA, Plazek DJ, J. Polym. Phys., 29, 39 (1991)