Towards the prediction of multiple necking during dynamic extension of round bar : linear stability approach versus finite element calculations

18th APS-SCCM; 24th AIRAPT

Maï, S El^1 ; Mercier, S.^2 ; Petit, J.^1 ; Molinari, A.^2

Commissariat À l'Energie Atomique, Centre de Gramat, Gramat

46500, France^1

Laboratoire de Physique et Mécanique des Matériaux, CNRS, Université Paul Verlaine, Ile du Saulcy, Metz Cedex

57045, France^2

关键词: Dynamic condition;    Dynamic expansion;    Dynamic extension;    Fragment distributions;    Good correlations;    Numerical results;    Perturbation growth rate;    Stability and bifurcation analysis;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/500/15/152005/pdf
DOI  :  10.1088/1742-6596/500/15/152005

来源: IOP

【 摘 要 】

The fragmentation of structures subject to dynamic conditions is a matter of interest for civil industries as well as for Defence institutions. Dynamic expansions of structures, such as cylinders or rings, have been performed to obtain crucial information on fragment distributions. Many authors have proposed to capture by FEA the experimental distribution of fragment size by introducing in the FE model a perturbation. Stability and bifurcation analyses have also been proposed to describe the evolution of the perturbation growth rate. In the proposed contribution, the multiple necking of a round bar in dynamic tensile loading is analysed by the FE method. A perturbation on the initial flow stress is introduced in the numerical model to trigger instabilities. The onset time and the dominant mode of necking have been characterized precisely and showed power law evolutions, with the loading velocities and moderately with the amplitudes and the cell sizes of the perturbations. In the second part of the paper, the development of linear stability analysis and the use of salient criteria in terms of the growth rate of perturbations enabled comparisons with the numerical results. A good correlation in terms of onset time of instabilities and of number of necks is shown.