Enhancement of Accuracy in Hot Compression Results with the Consideration of Testing Machine Characteristics

The prediction accuracy of metal forming process models depends on the validity of the material model as well as the accuracy of input data like flow stress of the work material, frictional and thermal characteristics at the tool-material interfaces. In a compression test, the linear variable differential transformer (LVDT) on testing machine records the response of the specimen during testing, which also includes the deflection and compliance of several machine and tool components that are bounded by it. A series of tests conducted for characterizing the test system have shown that the tool deformation is significant especially at low ramp-rates of load and temperatures above 800 degrees C, which is analogous to the creep behaviour of metals. In consideration of this behaviour, an empirical model is developed based on the experimental results and is presented in the form of decision tables. The model is capable of providing necessary correction to the test data obtained with such testing machines.