Damage mechanical investigations at ductile fracture of free-cutting steels by means of microscopy - void growth and fracture surface topography

At ductile fracture of metallic materials the growth of micro-voids generat ed by particles in the metallic matrix as for example manganese sulfides ca n be observed as the dominating damage mechanism. In order to measure and m odel this damage usually damage parameters such as for example the void rad ius are used. The final size of grown voids at crack initiation can be esti mated by measuring the dimple sizes on the fracture surfaces, Beside these values topometric parameters were applied to characterise the fracture beha viour of the material by its fracture surface. The final void sizes at crac k initiation measured on the fracture surfaces partly show a decreasing ten dency with higher stress triaxiality, that means a competition between stre ss state and void growth can be observed. The measured void sizes are gener ally comparable to values from model calculations. Using the fractal dimens ion it is possible to distinguish fracture surface topographies resulting i n materials showing different fracture toughness values.