Simulation of Material and Structural Instability Phenomena During the Flaring Process of Cylindrical Shells

Abstract

Pushing a conical die into a pipe, a forming process also known as ‘flaring’, is a way of changing the shape of a thin cylindrical tube into that of a conical shell. Interest in predicting the forming limits for this specific process motivated the present study, in which experiments and Finite Element simulations were employed for the identification of two limiting mechanisms: (a) diffuse necking caused by local loss of material stability at the free, expanding end of the pipe, and (b) loss of global stability due to elasto‐plastic ‘Concertina’ buckling of the straight pipe part. The former mechanism leads to the formation of periodic necks and subsequent failure by strain localization and rupture, while the latter mechanism is characterized by a periodic buckling pattern that is similar to the one observed in typical crash elements.Whether collapse or rupture is the limiting factor depends on geometrical parameters and material parameters, such as, for example, the hardening exponent in the Ludwik law. T...