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This work is devoted to the application of the micromechanical Gurson-Tvergaard-Needleman (GTN) model to study the ductile tearing of 12NiCr6 steel. GTN model is widely used to describe the three stages of ductile tearing: nucleation, growth and the coalescence of micro-voids. A new approach based on the identification of the GTN damage model coupled or not with hardening laws using inverse analysis. After identification, the obtained results show a good agreement between the experimental curve tensile test of an axisymetric notched bar (AN2) and those numerically obtained for GTN model coupled with the hardening laws. In order to validate the identified GTN parameters, a simulation of tear test is conducted on 12 NiCr6 steel CT specimen. The numerical results are compared with experimental results found in the literature and a good agreement is obtained. This identification procedure is more accurate than when the damage parameters are identified independently of the hardening laws.

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This study compares micro-abrasive wear in two kinds of grey cast iron. Classical lamellar cast iron with fully pearlitic matrix (FGL1) and lamellar micro-alloyed cast iron with phosphorus and boron (FGL2) are used. FGL2 has a fully pearlitic matrix reinforced by the hard phosphorus eutectic phase. The microstructures of these two types of iron are mechanically characterized using nanoindentation tests. Vickers microindentation and microscratch tests are also performed on these iron samples. The indent and scratch images obtained via scanning electron microscopy were used to compare the scratch damage to the two kinds of iron. The friction coefficient is discussed in terms of applied load, indenter attack angle, and scratch damage. Nanoindentation tests show an improvement in graphite's mechanical properties and an increase in the matrix hardness of the FGL2, relatively to FGL1. The same damage forms for both microindentation and microscratch testing were observed for the two iron samples. However, cracking of the hard phase is observed in FGL2. The results show that the scratching of the micro-alloyed iron (FGL2) leads to less matrix damage and to an extended microploughing wear mechanism. However, at low normal load, the reinforcement of the matrix can increase the friction coefficient.