On the influence of particle distribution and reverse loading on damage mechanisms of ductile steels

An enhanced Lemaitre model formulation for materials processing damage computation

“…These elongated inclusions come from the rolling process used to produce these cylindrical bars. It has been shown in [29] that such materials can exhibit a strong anisotropy depending on the direction of inclusions. It is also interesting to point out the fact that on the collar, maximal principal stresses are oriented towards the circumferential direction.…”

“…However, for cold forming processes, the initial steel billet usually comes from previous extrusion or rolling processes. These processes clearly give a preferential orientation to the material's microstructure: grains and inclusions are oriented in the rolling or extrusion direction [29]. If no thermal treatment is performed, important anisotropic behaviour can be observed at the forging step.…”

“…Fig. 2a shows that ductility is much more important in the longitudinal direction than in the radial direction [29]. This kind of anisotropic ductility often comes from the rolling process used to obtain cylindrical steel billets.…”

“…Indeed this anisotropic ductility may come from the highly oriented microstructure with grain flow orientation in the direction of the rolling process. In [29], the authors have shown the important role of particles orientation on damage mechanisms. However, the phenomenological approach presented here aims at improving damage prediction in a simple manner with a scalar damage approach.…”

“…If dX n is the kneading direction at increment n, then at increment n+1, the grain flow orientation is simply obtained by: (29) Fig. 3 shows the numerical and experimental grain flow orientation obtained after the compression of a cylindrical billet with an initial vertical grain flow orientation.…”