Fatigue crack growth rates for very short cracks developing at fastener holes in 7075 and 7010 aluminium alloys

Fatigue crack growth rates have been determined for very short corner and bore cracks developing from fastener holes. This was made possible by the use of a simple load programme which provided a contrasting fracture feature or marker. The programme consisted of a high-low-high switch of load ratio (R) usually in blocks of 100 loads. A constant Δσ was maintained within each block. The crack growth rate data for short cracks was in reasonable agreement with the published long crack data for 7075 and 7010 alloy. Strong retardation effects were in evidence and certain features of the fractures shed new light on the retardation models, and also on those of fatigue fracture itself.