Prevention of Internal Cracks in Forward Extrusion by Means of Counter Pressure: A Numerical Treatise


Soyarslan C., TEKKAYA A. E.

STEEL RESEARCH INTERNATIONAL, vol.80, no.9, pp.671-679, 2009 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 80 Issue: 9
  • Publication Date: 2009
  • Doi Number: 10.2374/sri08sp170
  • Title of Journal : STEEL RESEARCH INTERNATIONAL
  • Page Numbers: pp.671-679
  • Keywords: forward extrusion, counter pressure, chevron cracks, ductile damage, finite elements, CONTINUUM DAMAGE MECHANICS, COLD-EXTRUSION, PREDICTION, WORKABILITY, FRACTURE, MATRIX, ALLOY

Abstract

In the context of forward bulk extrusion, where product defects are frequently observed, the effect of counter pressure on damage accumulation materializing a Continuum Damage Mechanics (CDM) approach is presented. A Lemaitre variant damage model accounting for unilateral damage evolution coupled with a multiplicative finite plasticity is utilized for this purpose. After a presentation of the crack governing mechanism, it is demonstrated that application of counter pressure introduces a marked decrease in the central damage accumulation, which in turn increases the formability of the material through keeping the tensile triaxiality in tolerable limits. It is also shown that, for a crack involving process, through systematic increase of the counter pressure, the crack sizes diminish; and at a certain level of counter pressure chevron cracks can be completely avoided.