IS IT POSSIBLE TO IDENTIFY JOHNSON-COOK LAW PARAMETERS FROM MACHINING SIMULATIONS?

Material laws are central to any machining simulation. Johnson-Cook material law, owing to its simplicity, has often been used for machining simulations. However, at high strain rates (similar to 10(6) s(-1)) which are normally encountered during high speed machining, the same Johnson-Cook parameters are used for simulation which are usually measured at much lower strain rates. A possible solution to this problem is to conduct inverse simulation experiments to deduce the Johnson-Cook parameters. At high cutting speeds the chip formation takes place very rapidly and is essentially adiabatic. Thus through the study of the adiabatic stress-strain curves one can deduce information about the chip formation process [1]. In this numerical study, different sets of Johnson-Cook parameters that give rise to almost identical adiabatic stress-strain curves are identified by using the Levenberg-Marquardt optimization algorithm. High-speed machining simulations performed with these parameters show almost indistinguishable results, indicating that uniquely identifying material parameters from inverse analysis may be difficult.