“…By contrast, at σa = 36.9 MPa, a high tensile stress greater than the axial stress remained near the center of the direction of thickness even at the time of the return to a straight position. This result was obtained because a compressive stress was generated in the vicinity of the upper surface during the return due to the yield of the upper area during bending, and a tensile stress greater than the axial stress was generated as a reaction force around the center of the direction of thickness, which acted as a residual stress [32,33]. When the stress amplitude increased further, at σa = 82.9 MPa, the upper half area of the test specimen and the area near the lower surface yielded greatly to the tensile and compression sides, respectively, during bending.…”