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Fracture Mechanical Studies on Polyethylene Erectro-Fusion Joint Containing Three-Dimensional Circumferential Crack

含三维周向裂纹的聚乙烯电熔接头断裂力学研究

基本信息

批准号：
09650102
负责人：
SAITO Kenji
金额：
$ 2.11万
依托单位：
Kyoto Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09650102/
关键词：
Fracture Mechanics Fracture Toughness Polyethylene Electro-Fusion Joint Circumferential Crack Stress Intensity Factor Finite Element Analysis Creep 円筒き裂

项目摘要

The electro-fusion joint is widely used to connect Polyethylene pipes each other. The non-fused region which is produced between the joint and the outer circumferential edge of the pipe is served as a three-dimensional circumferential crack. The fracture of the joint is observed experimentally to start from the tip of the crack. Therefore, the joint should be designed first of all based on the fracture mechanics. In this study, the stress intensity factors at the tip of the circumferential crack were calculated by FEM analysis using a three-dimensional isoparametric singular element. The dependence of the sizes of the joint, such as the length of fused region, the thickness of the joint, the crack length, etc., on stress intensity factor K_I, and K_<II> at the tip of the crack can be obtained. The fracture toughness of a Polyethylene was evaluated experlimentally over the temperature range from -196ﾟC to -120ﾟC.The value of the plane strain fracture toughness of Polyethylene decreases … More with increasing temperature within the range from -196ﾟC to -120ﾟC.The minimum value of K_<IC> is 3.47MPam^<1/2> at - 120ﾟC.From the analytical results, the value of the combined stress intensity factor K = (K_I^2 +K_<II>^2 )^<1/2> is about O.45MPa^<1/2> under the maximum internal pressure which may be applied to the joint and pipes. The value of the safety factor of the joint can be concluded to be about 7 from these results, In addition to these studies, the one-dimensional creep constitutive equation was evaluated as a form obeying the Bailey-Norton's law by performing the creep tests. The constitutive equation obtained was extended to the three-dimensional form by adopting the Mieses theory. The creep strain at the tip of sharp notch was analyzed by the updated lagrangian FEM analysis using the extended constitutive equation. As a result, the creep strain at the tip of notch increases with increasing the elapsed time. As the tip of the notch becomes more sharp, the value of the creep strain increases irrespective of the elapsed time. Less

电熔接头广泛用于聚乙烯管道的连接。在接头与管道外圆周边缘之间产生的非熔合区作为三维环向裂纹。实验观察到接头的断裂是从裂纹尖端开始的。因此，接头设计首先应基于断裂力学。在这项研究中，在圆周裂纹尖端的应力强度因子的有限元分析，使用三维等参奇异元计算。研究了接头尺寸，如熔合区长度、接头厚度、裂纹长度等对接头性能的影响，对裂纹尖端应力强度因子K_I和K_I<II>的影响。在-196 ° C ~-120 ° C温度范围内，聚乙烯的平面应变断裂韧性随温度的升高而降低 ...更多信息在-120 ℃时，K_（1/2）最小，<IC>为3.47MPam^<1/2>。分析结果表明，在<II>接头和管道可能承受的最大内压下，复合应力强度因子K =（K_I^2 + K_^2）^<1/2>约为0.45MPa ^<1/2>。从这些结果可以得出的值的安全系数的节点是约7，除了这些研究，一维蠕变本构方程进行评估，作为一种形式服从贝利-诺顿的法律进行蠕变试验。采用米塞斯理论将得到的本构方程推广到三维形式。采用扩展的本构方程，采用更新拉格朗日有限元法分析了尖缺口尖端的蠕变应变。结果表明，缺口尖端的蠕变应变随时间的增加而增加。随着切口尖端变得更尖锐，蠕变应变的值增加，而与经过的时间无关。少