Dynamic impact analysis of the grid structure using multi-point constraint (MPC) equation under the lateral impact load

摘要

The objective of this research is to propose the methodology that could predict the dynamic failure behaviour of the grid structure for the pressurized water reactor (PWR) fuel assembly. To perform this objective, two kinds of approaches are taken in this work: First, in order to obtain the test data on the dynamic failure behaviour of the spacer grid, an impact test is performed with a 5x5 cell size partial grid specimen, which is made of Zircaloy-4 thin plate. Second, a finite element method for predicting the buckling behaviour on the spacer grid structure is established by a commercial finite element (FE) code ABAQUS/explicit. In this FE analysis method, appropriate boundary conditions and impact loading conditions are applied to simulate the actual test conditions. The dynamic impact analysis is performed to predict the buckling behaviour of a grid structure under the lateral impact load by a finite element method. The grid structure which are compose of inserted thin plates laser welded at the cross-points and the connection points of the inner/outer plates. The finite element model is produced using pre-processor I-DEAS, and solved using non-linear commercial solver ABAQUS/explicit. In this work, two models are proposed for FE analysis: One is the simplified model and the other is the multi-point constraint (MPC) model. Applied boundary conditions for dynamic impact analysis were almost the same as the actual boundary conditions for the impact test. The dynamic impact parameters of a grid structure such as critical impact acceleration, impact force and buckling mode and so on, were over-estimates compared with the test results. Based on these results, it was necessary to modify the stiffness of a grid cell structure in the FE analysis model of the grid structure. According to these results, the FE model is modified to estimate the buckling behaviour of the grid structure. This modified FE model will be compared with test and analysis results using the simplified model. In addition, this analysis model is in good agreement with the impact test results, therefore this FE model and the analysis procedure will be used as good tools for predicting the dynamic buckling behaviour of the grid structure.