Ductile damage assessment using continuum damage mechanics and methodology for high strain-rate damage analysis

The interest of this research is to assess the experimental techniques used for ductile damage measurement both in quasistatic and high strain-rate conditions. The results can later be used for the calibration of Continuum Damage Mechanics (CDM) models.

A procedure for the evaluation of damage accumulation in quasi-static conditions is presented. The technique used to measure damage is based on the elastic modulus calculation from unloading and reloading cycles performed at different stages of plastic deformation. Tests have been performed in a continuous manner and the strain variations have been recorded using a small gauge extensometer. This methodology includes a second experiment in which the geometry of the specimen is monitored, allowing to extract the true stress-strain behaviour of the material even after necking phenomenon starts. The proposed methodology has been applied to stainless steel 304L.

Regarding the high strain-rate conditions, a continuous test cannot be performed due to physical as well as practical difficulties. Therefore, an interrupted methodology has been devised in which the plastic deformation is applied at high strain-rate and the damage measurement is performed separately in quasi-static conditions. An experimental rig has been developed to interrupt high-speed tensile tests at strain-rates up to 10^3s−1. Its design and preliminary calibration are analysed and its future use for damage assessment discussed.