Effects of Surface Treatments on the Fatigue Response of High Strength Fasteners

The aim of the present work was the assessment of the impact of deep-rolling and shotpeening performed in the underhead and in the unthreaded shank of two high strength screws (36 NiCrMo and 42 CrMoV) for fatigue life enhancement. The experimental tests consisted of six combinations, including the non-treated state. The aforementioned treatments were evaluated alone or with shot-peening performed after deep-rolling in the underhead fillet of the screws. Deep rolling was carried out at the optimal rolling force, whereas two shot diameters were considered for shotpeening (Z100 and UFS70). The results showed a beneficial impact of deep rolling on fatigue, especially for the 42 CrMoV steel. Instead, shot-peening generally leads to a worsening of the fatigue limit in relation to the induced superficial roughness.