The relationship between fatigue crack behaviour and microstructure in 7178 aluminium alloy

Abstract Relationships between fatigue crack growth rates and crack path have been studied in under aged, peak aged and over aged 7178 aluminium alloy microstructures. The superior resistance to crack growth of over aged material is derived from the greater crack tip irregularity that the microstructure imposes. Conversely, the poor crack growth resistance of material aged to peak hardness is associated with relatively flat fracture surfaces. Changes in crack tip regularity while the crack is extending control the slope of the crack growth rate curve.