Influence of Piezo Peening on the Fatigue Strength of quenched and tempered AISI 4140

Author:  F. Lienert, J. Hoffmeister, A. Erz, V. Schulze
Source:  Conf Proc 2014: ICSP-12 Goslar, Germany (pgs.517-522)
Doc ID:  2014130
Year of Publication:  2014
Abstract:  
Piezo Peening is a new alternative mechanical surface treatment process and can be assigned to machine hammer peening processes. Similar to ultrasonic impact treatment (U IT) processes a piezo actuator with an indenter is causing mechanical deformation of the surface area by multiple impacts in a previously defined pattern. However, in contrast to UIT, there is no horn or sonotrode to increase the amplitude. Only the piezo actuator induces the oscillation of the indenter. By different combinations of process parameters like frequency, amplitude, indenter hardness and diameter etc. a wide range of specific surface layer states with varying residual stress depth distributions and surface roughnesses can be created. By this process the whole range of surface layer characteristics from shot peening to deep rolling can be adjusted. An optimal surface layer state concerning axial cyclic loading of the utilized sample geometry with a measuring diameter of 7 mm was chosen and characterized concerning residual stresses, work hardening and surface roughness. An S-N curve for this parameter combination was determined and compared to the initial state. To show the benefit of this new process this is compared to shot peening and deep rolling as well. For this purpose a variation of Almen intensity and deep rolling pressure was performed in order to identify the best parameters for axial cyclic loading at 650 MPa. The S-N curve was determined afterwards for the sample with the highest number of cycles to failure, respectively. Furthermore the location of crack initiation was analyzed to show that a transition from crack initiation at the surface to crack initiation below the surface is possible.