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

During cold forming processes materials are subjected to non-monotonic complex multiaxial loadings. To obtain complex shapes at low temperature requires the use of particularly ductile materials. The damage behaviour of two ductile steels is studied here at different scales. At the macro-scale, tensile tests are performed in different directions with respect to the grain flow orientation in order to highlight the anisotropy of the behaviour. Tensile tests after pre-compression stages are performed to study the influence of pre-compression on damage evolution. For these two steel grades it is observed that pre-compression tends to increase ductility. At the micro-scale, in situ tensile tests are performed in a scanning electron microscope (SEM) as well as in an X-ray tomography device (synchrotron-ESRF). These techniques are particularly well suited to observe and understand the stages of nucleation, growth and coalescence of voids in the vicinity of inclusions. The influence of inclusion. shape and orientation on damage anisotropy and pre-compression behaviour is discussed. (C) 2008 Elsevier B.V. All rights reserved.