Correlating Fatigue Life with Elastic and Plastic Strain Data

It is widely accepted that residual compressive stresses in aerospace materials enhance fatigue performance. Conventional shot peening and the cold expansion of holes are two techniques for imparting beneficial compressive stresses. Stresses can be directly measured with x-ray diffraction (XRD), while the corresponding elastic and plastic strains are characterized with XRD peak shifts and widths. This paper presents elastic and plastic strain data, residual compressive stress state, and the resulting fatigue performance of aerospace materials shot peened over a range of common peening intensities. With few exceptions, the data correlated well in that higher intensities provided greater residual compressive stresses and strains. However, the greatest fatigue performance was observed on the lower end of the peening intensity range.