Rotary compression as a new calibration test for prediction of a critical damage value

The article presents the problem of ductile fracture of metals and metal alloys formed in hot working conditions. The basic damage criteria used in modelling fracture as well as calibrating tests used to determine the critical damage values were discussed. A concept of a new calibrating test based on rotary compression of a disc or a cylinder was presented. Using the proposed calibrating test along with nine damage criteria the critical damage values for 50HS (1.5026) grade steel, formed in the temperature range 950 °C to 1150 °C were determined. A significant dependency of the critical damage value on temperature was observed. The stress states occurring in rotary compression and the cross-wedge rolling, skew rolling in a two-roll rolling mill and helical-wedge rolling processes were compared. On the basis of the results obtained it was advised to apply rotary compression of a cylinder samples to determine the critical damage values used in the analyses of cross- and skew rolling.