Indentation Fatigue Behavior Of Polycrystalline Copper

Indentation experiments have been widely used to extract the mechanical properties of materials for its fast, simple, precise and non-destructive merits. However, most of them are focused on static loading conditions. In the present study, the detailed indentation fatigue behavior of polycrystalline copper under fatigue loading has been studied experimentally using the flat cylindrical indenter. The paper aims at building the relationship between the indentation fatigue testing and conventional tension -compression fatigue testing. The main conclusion can be drawn as follows:The equations on the indentation load-indentation depth have been deduced for the elastic and visco-elastic infinite body under a fatigue loading, respectively. Those equations indicate that the indentation depth varies linearly with the fatigue loading time for the flat cylindrical indenter, while it is non-linear for other indenter geometrical shapes such as spherical indenter, sharp indenter and etc. The comparison of the indentation load - indentation depth for different indenter geometrical shapes, it can be concluded that the flat cylindrical indenter has more advantages than other indenter geometrical shapes for the indentation fatigue. In addition, those equations indicate a new method to determine the elastic modulus.The indentation fatigue behavior of polycrystalline copper under the fatigue amplitude with the flat cylindrical indenter has been carried out. The experimental results show that the indentation depth - cycle curves are analogous to the conventional strain - cycle curve of uniaxial fatigue test, which has a primary stage of decaying indentation depth per cycle followed by a secondary stage of nearly constant rate of indentation depth per cycle.It is found that the steady state indentation depth per cycle is an approximate linear function of maximum indentation load (P_max) and indentation load vary (ΔP= P_max - P_min) in the log-log grid. This relationship can be given with power-law expression as an analogy equation of steady state ratcheting rate. A comparison is made between the conventional uniaxial fatigue test and indentation fatigue test for the steady state stage. It is shown that the conventional uniaxial fatigue parameters can be obtained by the indentation fatigue method.The indentation fatigue behavior of polycrystalline copper under varied fatigue...