Polymer(Korea), Vol.21, No.1, 83-92, January, 1997
플라스틱 파이프의 잔류응력에 관한 연구; Ⅲ. 정적균열성장 거동에 미치는 영향
Residual Stresses in Plastic Pipes and Fittings Ⅲ.Effect on Stable Crack Growth Behavior
초록
플라스틱 파이프 구조물에 존재하는 잔류응력과 분포가 파이프의 성능과 밀접한 관계를 이루는 정적균열성장 거동에 미치는 영향에 대해 살펴보았다. 본 연구에서 개발된 시험방법은 파이프 내의 잔류응력을 원상태 그대로 균열성장에 적용하는 방법으로서, 폴리에틸렌 파이프로부터 얻어진 링모양의 시편에 plane-strain상태의 균열이 개시될 수 있는 최소 길이의 크랙 (0.5 mm)을 시편내의 압축 또는 인장 잔류응력에 노출시켜 균열 성장속도를 측정하였다. 인장 잔류응력 상태로부터의 성장속도는 압축 잔류응력에서 보다 약 3배 빠른 속도로 진행되는 것이 관찰되었고, 이에 대한 물리적 증거는 파괴 표면에서 크랙 전면모양으로부터 얻을 수 있었다. 처음 균열 길이에서의 응력확대인자는 압축잔류응력에 노출되었을 경우 300 KPam0.5 이었으며, 아닐링에 의한 무잔류응력상태에서는 550 KPam0.5로 측정되었다. 이로서 잔류응력은 정적균열성장의 추진력인 응력확대 인자에 큰 영향을 주는 것을 알 수 있었다.
The effect of residual stresses on stable crack growth (SCG) behavior in polyethylene pipes was investigated. For the investigation, a new SCG specimen and test method were developed which offered a promise for characterizing the slow crack growth behavior in pipe sections without disturbing the existing residual stress state. The specimen was in the form of diametrically loaded rung, obtained from a pipe, having a notch either at outer surface or at inner surface, corresponding to a state of compressive and tensile residual stresses, respectively. It was demonstrated that crack growth from the compressive stress region was delayed due to circumferential compressive residual stress while accelerated under the tensile residual stress. In the absence of residual stress the slow crack growth was independent of whether the crack was initiated at inner or outer surfaces. The estimated stress intensity factors for the outer notched samples were 300 KPam0.5 and 550 KPam0.5 for as received and annealed pipes, respectively, clearly demonstrating the value of SCG specimen with regard to residual stress effect on the crack driving force. The physical evidence for the residual stress effect is presented from the respective crack front shapes.
- Bhatnager A, Choi S, Broutman LJ, Proc. of 10th Plastic Fuel Gas Pipe Symp., AGA, 324 (1987)
- Bhatnager A, Choi S, Broutman LJ, GRI Report No. 86/0068 (1986)
- Bell B, Choi S, Broutman LJ, Proc. 8th Plastic Fuel Gas Pipe Symp., AGA, 57 (1983)
- Sciammarella CA, Yang Y, Choi S, Broutman LJ, Illinois State OSWR Report No. 012009 (1995)
- Broutman LJ, Duvall DE, So PK, Proc. 48th SPE-ANTEC, 1495 (1990)
- Uralil FS, Hulbert LE, GRI Report No. 85/0045, GRI (1985)
- Chan MKV, Williams JG, Polymer, 24, 234 (1983)
- Brown N, Proc. 9th Plastic Fuel Gas Pipe Symp., AGA, 283 (1985)
- Huang Y, Brown N, J. Polym. Sci., 28, 2007 (1990)
- Lu XC, Zhou ZQ, Brown N, Polym. Eng. Sci., 34(2), 109 (1994)
- Strebel JJ, Moet A, J. Mater. Sci., 26, 5671 (1991)
- Frassine R, Rink M, Pavan A, Proc. 9th Plastics Pipes, 257 (1995)
- Choi SW, Broutman LJ, Polym.(Korea), 21(1), 71 (1997)
- Choi S, Broutman LJ, Proc. 9th Defor. Yield Frac. Symp., 48/1 (1994)
- Choi SW, Broutman LJ, Polym.(Korea), 21(1), 93 (1997)
- Leech JR, Proc. 9th Plastic Fuel Gas Pipe Symp., 3 (1985)
- Timoshenko SP, "Theory of Elasticity," 3rd Ed., p. 136, McGraw-Hill, New York (1970)
- Frocht MM, "Photoelasticity," Vol. II, p. 193, John-Wiley & Sons, New York (1948)