Limit Strains for Thin-Walled Tubes With Initial Thickness Inhomogeneity

Limiting strains during tube bulging have been investigated for long tubes subjected to an internal pressure together with an external axial force. A strain instability criterion which takes into consideration the inevitable geometrical defects in the tube wall is developed. The results revealed that small eccentricities produce a substantial decrease in the amount of deformation sustained by the tube at instability conditions. Moreover, the sensitivity to such defects increases for tubes made of low strain-hardening materials. The developed strain instability criterion has been subjected to an experimental verification where commercially pure aluminium tubes have been bulged to fracture. Experimental results are found to be in good agreement with theory, thus justifying the validity of this instability criterion and the resulting limit strains.