Development of the peening processes micropeening and ultrasonic wet peening to work hardening

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The processes micro-peening and ultrasonic wet peening offer the possibility of mechanical surface treatment to significantly increase fatigue strength of steels, with several advantages over established methods such as shot peening. This includes not only a high surface quality with little effect of blasting media impacts on the roughness but also a very low peening intensity, which allows for the processing of thin-walled components. Another notable effect is the occurrence of nanocrystalline regions on the surface, which affect the mechanical properties of the boundary layer. In the first phase of the grant Armco iron was used as the model material to separate the factors influencing the fatigue strength and are based on developed and validated a material model of grain refinement and consolidation of a modified concept of local endurance. In the second phase of the project this understanding of the mechanisms will now be transferred to the quenched and tempered steel 42CrMo4 V450. This bears the difficulty that a parameter separation by heat treatment as in the Armco iron, is not possible. Furthermore, the individual states of the boundary layer cannot be clearly separated in this heat treatment condition. In addition, the heavily modified deformation behavior, which also affects the surface layer state, must be considered in the modelling approach. The concept to be developed on the basis of previous FEM simulations will also be validated with an experimental characterization of the microstructure and the fatigue behavior. This is to be finally applied to a sequential mechanical surface treatment of conventional shot peening followed by micro-peening or ultrasonic wet peening. This should achieve an optimized combination of high penetration with optimized near-surface properties so that a significant increase in lifetime results for thick-walled components.