Even if metal thin film is the same material, it does not know that different mechanical characteristics form a bulk material are shown, and general fatigue behavior showing a bulk material does not necessarily appear. The present condition is that research of the fatigue behavior in the repetition shear load of a metal thin film is not made compared with the thing of load direction axis and bending. From studies of thin films in the cyclic loading to date, a crack with a locally slip in S10C occurs. The cause such crack occurs, the strain in the ferrite by applying the cyclic shear loading occurs, pearlite is considered to crack been concentrated deformed part that is sandwiched between the pearlite harder than ferrite because no deformation occurs. In addition, with respect to micro fatigue crack propagation in the repeated shear load of the bulk material, it was confirmed that the stiff cracks were inhibited by hard pearlite crystal grains, but the propagating cracks also progressed into the pearlite grains. Therefore, in this study, fatigue cracks are generated and developed by applying a repeated shearing load to the thin film material of S10C, and the influence of the observation / microstructure of its progress process was examined. As a result, it was confirmed that the pearlite crystal grains of the thin film material prevented the crack growth as well as the bulk material, and the propagating cracks also progressed into the pearlite crystal grains.
