APPLICATION OF A MICROMECHANICAL DAMAGE MODEL TO THE ANALYSIS OF DUCTILE FRACTURE OF A THERMOMECHANICALLY TREATED STEEL WITH DIFFERENT MICROSTRUCTURES

A possibility to characterize the different stages of the process of d uctile fracture from a more microscopic point of view are micromechani cal damage models, On a steel 27MnSiVS6 microalloyed additionally with titanium, which belongs to the group of the microalloyed precipitatio n hardening ferritic-pearlitic steels, different states of microstruct ure (ferrite-pearlite, tempered martensite, bainite) were produced usi ng thermomechanical treatment. On such specimens fracture mechanics te sts were done with side-grooved 1/2 CT-specimens and the results were compared with those obtained by a numerical simulation based on the mo dified Gurson model. A good agreement between calculated and measured J(R)-curves also for a thermomechanical treated steel with separations was found. The critical distance l(c) has a great influence on the re sults of this numerical model. A qualitative relation between this par ameter and the average inclusion spacing, which depends on the microst ructure, was found.