Experimental determination and computational modelling of the damage developemtn during ductile fracture of a free-cutting steel

摘要

Ductile fracture of metallic materials is caused by micro0mechanical damage developing during plastic deformation and finally leading to the initiation and propagation of a crack. Usually the typical damage mechanism is micro-void growth. To characterise this process the micromechanisms of damage ahve to be taken into regard ("continuum damage mechanics", "local approach"). Local stress and strain properties are calculated by FEM-models to be used for the computational determination of the damage indicators. These damage properties should be able to charactrise fracture or crack initiation behaviour independent of stress state (stress triaxiality) or loading history (change of stress triaxiality). Experiments on differently notched tensile specimens have to be done to produce different stress traxialities. Specimens deformed to a strain lower than the initiation strain are micro-sectioned to measure the damage development in terms of void sizes or void shape parameters. On fracture surfaces of broken specimens the final void size can be measured by SEM observation.