Small Crack under Cyclic and Static Loading

The experimental data on small crack growth (from several shares of millimeter up to several millimeters) in aircraft Al-alloys are presented. The method is proposed to define residual strength for elements with small cracks based on replacement of a real crack by the equivalent through-thickness-crack equal to the real one in the area and it is also based on modifying fracture toughness function limit Ic = Kc1c). The calculated and experimental residual strength curves have been compared for small cracks at various notches. The features of initial fatigue crack sites at various types of cyclic loading as well as the feature of small crack growth have been considered. The experimental data of crack growth rate and their scatter are presented for small crack range. The model of submicrocracks growth prediction is suggested. It is based on crack-closure model and change of stress intensity factor threshold (Kth) in small crack range. The complete fatigue life for “strip with a hole ” specimens has been calculated under various load using the suggested model