Experimentally calibrated FE modelling of helical buckling of anisotropic slender shafts

Abstract

Helical buckling is very common in slender structures and it is characterized by the development of helical deformation patterns along their length. This phenomenon is particularly acute in very slender drill-strings as associated high stresses decrease drilling efficiency and shorten life expectancy of expensive drilling assemblies. Hence, understanding and predicting buckling behaviour is of paramount importance. In this paper, we investigated buckling phenomena of slender flexible shafts in forms of stranded wire ropes mimicking drill-strings, by experimental and numerical means. From experiments we obtained the loading curves for the flexible shafts and developed governing buckling equations using dimensional analysis. Based on these equations, we calculated the effective material properties of the stranded ropes and carried out FE modelling and analysis in Abaqus. Finally, we developed a robust method to predict the helical buckling behaviour, which matches well with experiment results.