Study On The High-temperature Creep Behavior And The Estimation Of Creep Crack Parameter C～* Of Cracks In Bi-material CT Specimen

The technological equipments in the fields of petroleum industry,chemical industry,electric power industry and so on have been improving to higher temperature,higher pressure and more macro-scale in order to increase the efficiency of equipments,at the same time,the safety and reliability of the equipments should be put into a more important place.There are plenty of high-temperature and high-pressure equipments in these fields,and they are commonly manufactured with certain welded structure which take creep crack lapse as the main lapse form.This is the main factor endangering the long and safe operation of the equipments.Therefore,study on the creep law of welded structure is the basis of limit design and lifetime prediction of high-temperature structures,and it not only has the value of theoretical research but also has the value of technical application.The estimation of creep crack parameter C^* of mismatched welded joint in high-temperature structures has been mainly discussed in this article.Firstly, according to the theoretical research,it has been concluded that C^* of bi-material CT specimen could be calculated by the weighted average for C^* of homogeneous base-metal and weld-metal respectively,then the concept of weighted average C^* has been put forward,at last,large numbers of analysis calculations have been carried out on the creep crack behavior of three-material CT specimen using the finite element analysis software ABAQUS6.6 with finite element method as follows:(1)CT specimen with cracks in the welded joint interface:four models with different geometrical structure have been established,through numbers of calculation with finite element method,the relationship between mismatched factor M andα,creep exponent n andα,geometrical parameter a/W andαhave been obtained.Then,the function for C^* estimation of CT specimen with given geometrical structure have been advanced according to non-linear regression.At last, this method for C^* predication has been validated through technical example.(2)CT specimen with cracks in the center of welded joint:five models with different geometrical structure have been established,through numbers of calculation with finite element method,the relationship between mismatched factor M andα,creep exponent n andα,geometrical parameter(?)andαhave been obtained.Then,the function for C* estimation of CT specimen with given geometrical structure have been advanced according to non-linear regression.At last, this method for C^* predication has been validated through technical example.(3)CT specimen with cracks in the eccentric position of welded joint:five models with different geometrical structure have been established,through numbers of calculation with finite element method,the relationship between mismatched factor M andα,creep exponent n andα,geometrical parameter h₁h andαhave been obtained.Then,the function for C^* estimation of CT specimen with given geometrical structure have been advanced according to non-linear regression. At last,this method for C^* predication has been validated through technical example.