ELASTOPLASTIC DYNAMIC INSTABILITY OF LONG CIRCULAR CYLINDRICAL-SHELLSUNDER PURE BENDING

This paper presents a numerical study which is concerned with the pred iction of the response and instabilities in long circular cylindrical shells under dynamic pure bending. Of particular interest is the respo nse of such shells, bent into the plastic range of the material, and t he various instability characteristics of the shells under dynamic ben ding (sudden step load). It was found that the major deformation chara cteristic of the shells is essentially similar to that observed in the static bending when the applied moment is much smaller than the criti cal dynamic moment. However, when the applied moment is close to the c ritical dynamic moment, the ovalization of the shell cross-section was found to be localized over a length of several shell diameters in the central region, even though the response of the shell curvature was s hown to be still stable in this case. When the applied moment reaches the critical dynamic moment, the response of the shell curvature was s hown significantly increasing with time and the shell buckled catastro phically. For thicker shells, it was found that the development of loc alized ovalization of the shell cross-section is the major factor that causes shell dynamic instability. For thinner shells, however, beside s the localized ovalization, the bifurcation induced by short waveleng th ripples on the compressed side of the shell was also observed in th e initial buckling patterns. After the bifurcation, the initial buckli ng pattern was replaced by the final postbuckling mode characterized b y a localized sharp cupping in the centre of the shell.