Critical Damage and Ductile Fracture: Quantitative Experimental Determination

Summary Original metallographic observations are used to determine quantitatively the porosity and porosity gradients near fracture surfaces. The techniques combining Ion Beam Polishing, Scanning Electron Microscopy, manual drawings on tracing-paper and quantitative metallography lead to valid porosity measurements. The main results are: porosity at fracture is not a material constant, it decreases sharply with stress triaxiality; porosity at fracture is low: 0.5 – 10%; the areas concerned by these porosities are very small, 70-1000 μm 2 . To predict fracture, models have to be able to describe slightly porous materials at very fine scale. At this scale, the critical damage value leading to fracture cannot be determined by classical mechanical testing or physical investigations.