Equivalent Finite Element And Damage Identification On Joint Weld With A Crack Of Grid Structure

Due to the rapid development of grid structure, welded hollow spherical joints are applied more and more widely. In the process of tube welding and during normal use, the weld cracking damage is easy to appear for welded hollow spherical joints. The injury occurred in welded hollow spherical joints reduces integral rigidity and stability of the structure, which can cause structural damage and sudden collapse, leading to enormous economic loss and heavy casualties. Therefore, the research on structural damage identification technology is very meaningful. The content of this paper is about the research on nodes damage identification using the fuzzy mode identification method, by establishing of the equivalent finite element model of grid structure containing damaged nodes.The main content and steps are as follows:1. Establish the mechanical model of welded hollow spherical joints with cracking damage by using finite element analysis software ANSYS, and by calculating get the axial stiffness coefficient and bending stiffness coefficient of damaged nodes when the ratio tube-ball diameter d/D and crack length is different. Based on curve fitting method, analyze the relationship between influencing factors and stiffness coefficient of damaged nodes by MATLAB software.2. Select the Matrix27 element of ANSYS software as the semi-rigid joint equivalent element, to establish the equivalent modal of grid structure with containing damaged nodes. With the different of weld damage degree, the variation of joints stiffness is by changing the corresponding real constant of the Matrix27 element.3. Based on the equivalent modal of grid structure, this paper uses the fuzzy mode method to identify nodes damage. First, divide the damage degree of joints into 23 kinds of damage model according to crack length. Then select the three key elements, and establish fuzzy mode library of nodes damage taking strain modal absolute difference as damage target. Lastly, the paper selects several damage conditions as numerical validation samples, and the result is very satisfactory verifying the feasibility of this method.This paper establishes the equivalent finite element model of grid structure with damaged nodes by analyzing mechanical model of damaged welded hollow spherical joints. The analysis shows that the fuzzy mode method can identify effectively location and degree of nodes damage taking strain modal absolute difference as identification target, which provides a kind of effective identification method for damage identification on grid structure with weld cracking damage.