Determination of Johnson-Cook damage model constants for commercial pure copper sheet
Abstract:
Nowadays, damage models are used to simulate and predict the failure occurrence regions in manufacturing processes. One of the most famous models that is widely used in finite element commercial codes is Johnson-Cook damage model. The aim of the present research is to determine the constants of Johnson-Cook damage model for pure commercial copper sheet. In this work, two methods of Bridgman analysis and the use of the response surface method are used for this. Three different tensile testing specimens (a smooth (standard) specimen and two notched specimen with different notch radii of 10 and 2 mm) were separated along with the rolling direction and the tensile tests were conducted on them. The stress triaxiality was determined for each of the specimens, by using the Bridgeman analysis. Then, according to the dependence of fracture strain to the stress triaxiality, the constants of Johnson-Cook damage model were determined. To assess the successfullity of the method of determination the Johnson-Cook damage model constants, finite element method simulation was used. For this, the error in displacement to fracture criterion was used and the value of it was determined for each of the specimens. The mean value of the error in displacement to fracture criterion of 9.7% was obtained three thensile testing. Also, response surface method was used to determine the parameters of the Johnson - Cook damage model, in a reversely method. The numerical simulation was performed for each one of experiments and the average error in fracture strain for the three test specimens was defined as the objective function. The response surface method was carried out in a multi level method and the error value for the first and second stages was 3.61 and 2.31 percent, respectively. The results show that the use of inverse response surface method provides better results than the Bridgman analysis method. The importance of using the damage model in the simulation of manufacturing processes and production was shown by simulating the blanking process in a separate part of the thesis.