크리프와 반복 피로하중에 의한 폴리에틸렌의 실시간 구조 변화

전혜진; 유석근; 표수호; 최선웅; 송현훈; Hye-Jin Jeon; Seokgn Ryu; Sooho Pyo; Sunwoong Choi; Hyun Hoon Song

Polymer(Korea), Vol.36, No.1, 88-92, January, 2012

Export Citation

크리프와 반복 피로하중에 의한 폴리에틸렌의 실시간 구조 변화

In-situ Determination of Structural Changes in Polyethylene upon Creep and Cyclic Fatigue Loading

전혜진, 유석근, 표수호, 최선웅, 송현훈^†

한남대학교 신소재공학과

Hye-Jin Jeon, Seokgn Ryu, Sooho Pyo, Sunwoong Choi, and Hyun Hoon Song^†

Department of Advanced Materials, Hannam University, 461-6 Jeonmin-dong, Yuseong-gu, Daejeon 305-811, Korea

E-mail:

초록

일정 하중에 지속적으로 노출되는 고분자의 장기간 사용을 위해서는 재료의 수명을 평가할 수 있는 가속화된 시험 방법이 필요하다. 반복 피로하중 시험법은 이러한 방법들 중 하나로 많은 관심을 받고 있다. 본 연구에서는 X-선 회절법을 이용하여 고밀도 폴리에틸렌의 반복 피로하중에 의한 구조적 변화와 크리프 변형을 비교하고자 하였다. 이를 위하여 별도의 인장시험기를 제조, X-선 회절기에 부착하여 장시간 변형 과정을 성공적으로 관찰하였다. 그 결과 크리프와 반복 피로하중 사이의 거시적이고 뚜렷한 차이에도 불구하고 결정화도, 결정크기 및 면간거리와 같은 결정의 미세구조는 두 방법에서 거의 동일하게 관찰되었다. 그러나 항복점 전(BYP), 항복점(YP) 그리고 항복점 후(AYP)로 각각 변형시킨 후 시험한 시료의 경우 AYP와 다른 두 시료간 뚜렷한 구조적 차이를 확인할 수 있었다.

Long-term performance of polymer under constant sustained load has been the main research focus, which created a need for the accelerated test method providing proper lifetime assessment. Cycling fatigue loading is one of the accelerated test method and has been of great interest. Microstructure change of high density polyethylene under cyclic fatigue loading and creep was examined utilizing a tensile device specially designed for creep and fatigue test and also can be attachable to the X-ray diffractometer. In this way, the crystal morphology change of polyethylene under creep and cyclic fatigue load was successfully monitored and compared. Despite the marked differences in macroscopic deformation between the creep and cyclic fatigue tests, crystal morphology such as crystallinity, crystal size, and d-spacing was as nearly identical between the two test cases. Specimens pre-deformed to different strains, i.e., before yield point (BYP), at yield point (YP) and after yield point (AYP), however, showed markedly different changes in crystal morphology, especially between AYP and the other two specimens.

Keywords:crystal morphology;cyclic fatigue test;creep test;X-ray diffraction.

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[2] Choi S, Pyo S, Suh YS, Seo Y, Plast. Rubber Compos., 36, 219 (2007)

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[15] Reneker DH, Geol PH, J. Appl. Phys., 31, 1916 (1960)

[16] Keller A, O’Connor A, Discuss. Faraday Soc., 25, 114 (1958)