EXPERIMENTAL AND THEORETICAL INVESTIGATION OF THE EFFECT OF KINEMATICHARDENING ON SPHERICAL INDENTATION

When investigating material properties, the indentation test is often used in spite of the fact that very complicated nonhomogeneous process es are involved. In order to understand this test in more detail, an a nalysis was given by Huber and Tsakmakis using Finite Element calculat ions. It was shown that then exists an analogy between uniaxial homoge neous tensile experiments and spherical indentation for cyclic loading conditions. In fact, in both cases, existence, e.g., of kinematic har dening can be identified by the existence of hysteresis loops in the s train-stress diagram and the depth-load plot, respectively. The presen t paper deals with an experimental verification of the existence of su ch hysteresis loops for the case of depth-sensing indentation tests. F urther, two measures are considered in order to quantify the size of h ysteresis loops. The first one is the area enclosed by the hysteresis loop while the second one is a suitable defined middle opening of the hysteresis loop. Using various Finite Element calculations, it is show n that both measures can be regarded to be correlated. These theoretic al relationships an proved to be in agreement with experimental result s as well. Finally, the effect of kinematic hardening on the hysteresi s loops is discussed experimentally by studying the opening of the hys teresis loop as a function of the depth. (C) 1998 Elsevier Science Ltd .