Mini-punch experimental device development and analysis for ductile damage identification of naval structures

Metallic naval structures can undergo progressive damage from external incidents, affecting their ability to withstand subsequent impacts. Ductile damage is known to be sensitive to the stress state according to two scalars, the stress triaxiality ratio n and the Lode parameter L, that determine respectively the loading type applied and the position of the medium principal stress according to maximum and minimum ones. Ductile damage is studied experimentally with specific geometries targeting specific (n; L) values. Bulge Explosion Tests (BETs) are used for naval structures qualification to impact. Thick plates undergo various loading conditions, including an equi-biaxial tensile loading condition (0.66; 1). One way of obtaining this stress state is by using a punch test, where a fixed disk is punched up to fracture. Due to friction, the loading condition is not guaranteed in the rupture area. It is important to include such stress state for damage models calibration, which should be able to predict the ductile failure initiation under such conditions. This work focuses on both development and methodology used for a mini-punch system dedicated to damage parameters calibration, using DIC (Digital Image Correlation) and numerical simulations with various (n; L) conditions.