Fretting Fatigue – An Integral Simulation Approach to Strengthening by Shot Peening

Fretting fatigue is a limiting factor in blade attachment design for turbomachinery. Shot peening is known to be a strength increasing measure against fatigue. It is applied not only to free surfaces of components under fatigue but also to contacting surfaces subject to fretting fatigue. The present work examines the effect of shot peening on fretting fatigue resistance in fixtures of rotor blades. The chosen integral approach allows the consideration of shot peening and subsequent fretting loading in one simulation. Thus, the residual stresses and material strengthening as well as the surface waviness due to the shot peening process are included in the fretting fatigue simulation. To achieve reasonable computation times a 2D model, calibrated to a 3D unit cell model, is employed. A comparative study on fatigue endurance limits is presented for the cases with and without shot peening. With view to the different failure mechanisms met in these two cases, an initiation evaluation is carried out with the Sines criterion for the un-peened condition; a fracture mechanics approach is shown to be necessary for the evaluation of the shot peened condition.