Finite Element Method Based Boundary Loads Computatation For Structure Fracture Analyssis

Various defects always exist in welding structures which are prone to crack initiation and propagation in worse working conditions,resulting in structure failure such as rake dozer.The commonly method used to avoid mass calculations produced by the structures fracture analysis is to analyze the local welding parts with defects separated from the whole one.So,in this paper the Finite Element Method based Loads Inverse Computation is introduced to determine boundary loads of the local parts,meanwhile the Least Squares Method and the Regularization Method are used to solve the stabilization of ill-posed equations relating the measured strains and the equivalent boundary loads.The idea of Finite Element Method based loads inverse computation is to reconstruct the full-field of displacement,stress,strain and boundary conditions through local strain of separate structure.The technology of Finite Element Method for Loads Inverse Computation mainly includes the Finite Element Theory and the Inverse Problem Theory:The Finite Element Theory is used to establish the mathematical model between local strain and full-field data;The Inverse Problem Theory ensures the existence,uniqueness and stability of the solution.In this paper,the linear relationship of the matrix is analyzed to determine the existence and uniqueness of solution.The Least Square Method and the Regularization Method are adopted to ensure the stability of the ill-posed problem.The Least Square Method can cause the solution of equations gradually converge to the true values when the number of measured strains belonging to an appropriate interval increases.The solutions from the Least Square Method and the Regularization Method are compared by simulation.In the end of this paper,J-integral is calculated by XFEM model to analyze the structure fracture of elastic-plastic model containing internal welding defects.The data of strain come from the measurement of H-shaped beam in rake dozer under working process.The results of analysis can provide important reference for structural design and manufacture.