Measurement and modelling of residual stress effects on cracks

Defects that form by mechanisms such as fatigue and stress corrosion cracking are influenced both by external loads on engineering structures and internal, residual stresses that are generated during the manufacture and operation. This paper describes a programme of experimental and analytical work on a high-strength, low-toughness aluminium alloy (AL2024-T351) to assess the influence of residual stress on crack opening displacement (COD) and crack-driving force (CDF) for a range of fatigue crack lengths in compact tension (CT) specimens containing a mechanically induced residual stress field. Comparison of experimentally measured and numerically predicted CODs, at the mid-plane and surface of CT specimens, show generally good agreement for cracks introduced into the finite-element model in a progressive, element-by-element manner. Cracks introduced in a simultaneous manner give larger than observed CODs. The CDFs for the progressively introduced crack are always smaller than for simultaneously introduced. These results have implications for the assessment of initiation for slowly growing cracks. © 2006 Blackwell Publishing Ltd.