Fatigue Testing and Life Prediction for Notched Specimens of 2024 and 7010 Alloys Subjected to Aeronautical Spectra

Abstract

Tension compression fatigue tests were carried out on notched specimens made of aluminum Alloys 2024 and 7010. For Alloy 2024, the specimens were submitted to an aeronautical spectrum developed from a transport aircraft spectrum using different percentages of low-level cycle omission (omission of cycles as a function of the mean stress). For Alloy 7010, a landing gear load spectrum was used. Other tests were carried out with simplified loading sequences in order to study the influence of under- or over-stressing on the fatigue damage. The experimental fatigue life up to crack initiation was measured using the electrical potential drop method (crack initiation on the order of 0.1 to 0.4 mm). Tests were also carried out in order to determine the fatigue properties of the materials tested. Three methods of fatigue life prediction were tested. In the first method, developed by Office National d'Etudes et de Recherches Açrospataics (ONERA), the notch effect was taken into account using the Neuber calculation and the fatigue damage was calculated using a nonlinear damage accumulation law (Lemaitre-Chaboche). The two other methods consist of using the local strain life approach with Fatimas software or Glinka's method that takes the notch aspect into account using the Neuber calculation and the fatigue damage calculation using Miner's law. A comparison of the results obtained using these three methods of fatigue life prediction shows that a better prediction is obtained when a nonlinear damage accumulation law is used. Nevertheless, it can be noted that the three different methods used in the study often give a nonconservative prediction of the fatigue life.