Fatigue Crack Growth Predictions of Surface Cracks under Constant-Amplitude andVariable-Amplitude Loading

摘要

Failures of thick components in aircraft structures are very often caused byfatigue crack growth of part-through cracks (surface or corner cracks). The focus of the present study is on fatigue crack growth of semi-elliptic surface cracks, both under constant-amplitude and variable-amplitude loading. The study includes several test series and an analysis of the results by predictions with models based on crack closure. The tests were carried out on plate specimens (thickness 9.6 mm) of 2024-T3 and 7075-T6, provided with a small semi-elliptical starter notch. The crack opening stress in constant-amplitude tests was measured along the crack front with a fractographic technique. Fractography was also adopted to study crack shape developments, for which marker loads were applied. The analytical part of the study concentrated on predictions of crack shape developments, fatigue crack growth and crack growth lives until breakthrough. The numerical prediction technique includes crack increment predictions at several points of the curved crack front. The CORPUS model and the modified CORPUS model were used for the predictions of the variable-amplitude test results.