INFLUENCE OF WORK HARDENING TYPE ON THE HYSTERESIS SEEN ON A CYCLIC INDENTATION CURVE
Résumé
Springback is a phenomenon found particularly during the metal sheet forming. This phenomenon is precisely calculated for conventional materials used in the automotive industry. The new requirements of the reduction of the total mass of cars lead to the study of new materials whose springback phenomenon is not precisely predicted. This lead us to study previously neglected factors influencing springback. Among these factors, the kinematic hardening is usually overlooked when it can influence the springback. The aim of this work is to try to evaluate the influence of each type of work hardening (kinematic and isotropic) of materials by using the indentation test. The indentation test is a non-destructive test enabling the characterization of local mechanical properties. This test allows studying the variation of the applied load, F, by the indenter on the tested material as a function of the indentation depth, h. The use of several indentation cycles leads to the formation of hysteresis which are directly influenced by the rate of kinematic hardening of the tested material. In order to evaluate the effect of kinematic hardening on hysteresis observed on a cyclic indentation F-h curve, a comparison is done between numerical and experimental F-h curves. Experimental F-h curves are obtained by indenting at several cycles a reference material (C100G steel) and two aluminum alloys (AG3 and Au4G). For numerical F-h curves, we proceed as follows: a tensile test is performed to derive the experimental stress-strain curve of each material. This curve is modeled by a Chaboche law considering the work hardening first as pure isotropic and then as pure kinematic. In each case, we perform a numerical indentation test which allows to deduce two F-h indentation curves, the first considering the hardening of the material as pure isotropic and the second as pure kinematic. The comparison between these two numerically obtained curves and the experimental curve allows knowing which one of the two types of work hardening is predominant. Finally, we discuss about the determination of the mixed hardening parameters of the Chaboche law obtained from the inverse analysis method and the indentation test.