Numerical Simulation of Failure Prediction for Ceramics Tools: Comparison with Forging Test Results

Abstract : A fracture prediction criterion for brittle materials has been introduced in the POLLUX finite element code, in order to predict the risk-of-rupture of ceramic tools during a forging operation. POLLUX is a software dedicated to the simulation of forging operations, initially developed by INSA (Lyon). The chosen probabilistic fracture model is based on the weakest link theory and on the statistical theory of Weibull. A surface approach or a volume approach can be retained, from the type of critical flaws in the ceramic. Two different criteria are available in order to characterise the stress state considering the tension normal stresses and neglecting the compression stresses. An identification procedure of critical flaw type is presented for a particular ceramic material. Statistical parameters of ceramic fracture have been experimentally determined using bending tests performed in environmental conditions close to the forging ones. A constitutive equation of the workpiece material has been proposed, issued from torsion tests. In order to validate the model in the case of ceramic tools subjected to multiaxial stress states, a particular configuration has been defined to compare the simulation predictions with the experimental results. A forging test has been then developed, in which a billet of superalloy is formed in a ceramic tool up to its fracture at the temperature of 1423K. The experimental distribution of tool fracture, according to the strain of the billet, are in good agreement with fracture predictions computed by the simulation.