Effect of Constitutive Equations on Dynamic Bend Buckling Analysis of Thin Steel Sheet Hollow Columns
Nobusato KOJIMA, Koji MIMURA, Tsutomu UMEDA and Yoshiaki NAKAZAWA
Abstract:Selecting a suitable constitutive equation which takes account of the precise strain rate sensitivity of the material is, in general, very important for dynamic-crash analyses. Tanimura-Mimura (T-M) model is one of a few constitutive equations which are able to describe the specific characteristics of many ferritic steels that the strain rate sensitivity in flow stress decreases with increasing plastic strain, however, it has not been examined well how the crash analyses are improved when this model is employed. In this paper, both experimental and numerical analyses of dynamic three-points bend test of thin steel sheet hollow column were conducted at the impact velocity of 4m/s in order to evaluate the effectiveness of T-M model. In the numerical analyses, Cowper-Symonds (C-S) model and strain rate insensitive (I-S) model as well as T-M model were employed, and their calculated results were compared with the experimental result. The calculated load-stroke relations by T-M model showed good agreement with the experimental ones over the whole stroke, on the contrary C-S model was in agreement only in the small stroke region. Shape profiles of the buckling portions of columns in the experiment were compared with the simulated results based on each model. The width of the buckling zone was getting smaller in the order of T-M model, I-S model and C-S model, and T-M model was found to give the best agreement with the experiment since its low strain hardening profiles in stress-strain relations at high strain rates promote the localization in the buckling zone. From these results, T-M model can be considered to improve accuracy of numerical simulation, especially in the case that significant strain localization such as buckling occurs. Key Words:Constitutive equation, Tanimura-Mimura model, Numerical simulation, Three-points bend test, Dynamic buckling