Optimizing high cycle fatigue predictions in notched Al 7075-T6: An analytical approach to rotating bending behavior

Abstract

Fatigue strength is affected by discontinuities in specimens, such as notches, holes and cracks. In this study, cylindrical specimens of Al-70-75-T6 were used, both without notches and with notches at a depth of 0.2 mm and 1 mm at angles of 30°, 45° and 60°. High fatigue rotational bending tests were performed at a stress ratio of -1 and a machine frequency of 60 Hz, with bending stress amplitudes of 180 MPa, 220 MPa, 260 MPa and 340 MPa. To predict fatigue properties, such as fatigue stress concentration factors and fatigue life, an analytical model supported by cohesive stress measurements obtained with an advanced finite element model for ductile damage was used. The effective fatigue concentration factors (Kf) and notch sensitivity of the material were determined using the Peterson formula. SEM analysis was performed to obtain a comprehensive understanding of the fracture mechanism.The fatigue limit was determined to be 180 MPa over 5 million complete cycles and a strong correlation was found between notch angle and fatigue life, providing valuable data for the development of rational design tables. The elastic stress concentration factor was scarcely affected by variations in the angle of entry and showed almost identical values at all angles tested. The analytical model showed good agreement with the experimental results, with a deviation of about 4.25 %. All failure modes exhibited ductile properties, with microcracking throughout the inner surface significantly influencing the failure mechanisms. Failure modes were analyzed to better understand the failure mechanisms of aluminum alloy under cyclic loading.

Keywords

• Fatigue
• Rotating bending
• Notch
• Fracture
• Peterson stress concentration