Crack Propagation of 7050 Aluminum alloy Under Constant Amplitude Loading and Peak Overloads

Aluminium alloys of the 7000 series are largely used in aeronautical structural applications. In this work a fatigue crack propagation study was done in 7050 aluminium alloy under constant load amplitudes as well as under peak overloads. The tests were carried out using MT specimens in a servohydraulic machine at a frequency of 25 Hz. For the constant amplitude tests three different stress ratios were analysed: R=0.05, 0.3 and 0.5. Crack closure was monitored in all tests by the compliance technique using a pin microgauge. The crack opening loads were derived from the load-crack opening displacement records after mathematics derivation and used to calculate □Keff values from which the da/dN-□□Keff curve is obtained. The crack closure parameter U was obtained and related with □K and the stress ratio. Under peak overloads the crack closure data show basically the same trend as the corresponding experimentally observed crack growth rate transient response.