Surface Semi-elliptical Crack In Finite Element Analysis And Research. Thick-walled Elbow

Thick-walled curved pipe is vital component of the industrial pressure pipe. For a long time, there are many flaws in the curved pipe processing, which has not been perfectly fixed. Compared with undefected curved pipe, adverse working condition gives the defected curved pipe much greater chance of fatigue cracking. Considering the importance of the curved pipe and the actual needs of fracture safety assessment, this article gives a detailed and in-depth finite element analysis to the thick-walled curved pipe with semi-elliptical crack in its surface and obtains some useful research results:1. After trying kinds of three-dimensional crack modeling method, this article develops a more convenient one. At the same time, the corresponding command stream files are built up. Using these files, you can get access to your desired results easily.2. Under two loads of internal pressure and moments, this article studies the equivalent stress distribution and finds that there are many difference between smooth bend and defective bend. At the same time, the linear elastic stress intensity factor KI is calculated. And then, this paper studies the variation law of KI with various parameters, including c/a,c/t,Ro/Ri,K,P,M.3. Under just one loads of internal pressure, this article studies the expanding law of plastic zones and the final failure mode. After initial loading, the vicinity of the crack free surface yields firstly but does not form plastic hinges. With further increase of internal pressure, redistribution of stress and strain occurred. And the axial expansion of plastic zones is much faster than the expansion along thickness direction. When the internal pressure reaches the limit state, the inner surface of curved pipe are completely yielding and the plastic zones are fully penetrating pipe wall, which leads to pipe failure. So the failure mode is overall failure.4. Under just one loads of internal pressure, this article calculates plastic limit load and studies the law of changes with influential factors. And then it comes to the conclusion that we can get much greater PL values with greater K,greater Ro/Ri,lower c/t,greater c/a. At the same time, this paper analyzes the influence of dimensionless parameters L/D over limit load of curved pipe and finds the influence is small.