Crack propagation of 7050 aluminum alloy under constant amplitude loading and peak overloads

摘要

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 25Hz. 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 DKeff values from which the da/dNODKeff curve is obtained. The crack closure parameter U was obtained and related with DK 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.