Analysis of damage in metal forming

Investigation of central burst formation in direct extrusion is presented with experimental and numerical studies. On the experimental side, selecting certain unfavorable die angles and reduction ratios from the Chrysler processing standard for chevron-free extrusions curve [1], a set of extrusion tests are performed. Accordingly, chevrons are produced in the first and second pass for 100Cr6 and Cf53, respectively. On the numerical side, a multiplicative finite plasticity framework is coupled with a Lemaitre variant Continuum Damage Mechanics (CDM) model giving account for the crack closure effect and implemented as ABAQUS/VUMAT subroutine. Materializing an explicit finite element scheme, the effects of main process parameters, such as friction, semi-cone angle and reduction ratio on damage accumulation zones and intensities are studied. It is shown that, for the identical geometries, with an appropriately selected crack closure parameter and an element deletion procedure, the discrete periodic cracks can be captured, which are in correlation with the conducted experimental outputs.