14th International Conference on Shot Peening

Changes in Residual Stresses induced by High Frequency Mechanical Impact Treatment (HFMI) under cyclic loading and their Influence on Fatigue

Jan Schubnella, Majid Farajiana , Eva Carla , Robert Wimpory

Fraunhofer Institute for Mechanics of Materials, Component Safety and Leightweight Construction , Woehlerstr.11, Freiburg, Germany – jan.schubnell@iwm.fraunhofer.de / majid.farajian@iwm.fraunhofer.de / eva.carl@iwm.fraunhofer.de

Helmholtz Zentrum, Department Microstructure and Residual Stress Analysis, Hahn-Meitner-Platz 1, Berlin, Germany – robert.wimpory@helmholtz-berlin.de

Introduction

The post-weld mechanical surface treatment method High Frequency Mechanical Impact (HFMI) process is a statistically proved method to increase the comparably low fatigue strength of welded joints [1]. Furthermore, a high portion of this fatigue life increase is attributed to the HFMI-induced compressive residual stresses [1, 2]. Previous studies on welded specimens [2, 3] revealed that significant changes of the residual stress state during loading occur, especially in the case of high stress peaks.

Objectives

Herein, the change of the near-surface residual stress states after HFMI-treatment was investigated in comparably simple notched specimens and on welded joints made of two different steel grades. Furthermore, the changes of the residual stress state was incorporated in the fatigue life assessment (crack initiation phase) by means of damage mechanic approaches. The performed fatigue tests showed a good agreement to the fatigue life calculations.