Evolution of fracture mechanics parameters for cracks in residual stress fields

Abstract

The paper is devoted to determination of crack mouth opening displacements (CMOD), stress intensity factors (SIF) and T-stresses for cracks emanating from cold expanded holes and welds at different stages of cyclic loading. Rectangular plates made from aluminum alloys are the objects of present investigation. A sequence of narrow notches, which are performed under the constant external load, is used for crack modelling. The experimental approach employs optical interferometric measurements of local deformation response to small notch length increment. Initial experimental data represent in-plane displacement component values measured by electronic speckle-pattern interferometry in the vicinity of the crack tip. Thus, the CMOD values are derived directly. The transition from measured in-plane displacement components to required SIF and T-stress values follows from the relationships of modified version of the crack compliance method. Experimental results are obtained for uniaxial tension-compression loading of specimens with the force direction is perpendicular to the crack line. Experimental data provide constructing the dependencies of fracture mechanics parameters for cracks of fixed lengths from a loading cycle number, which are of great interest to estimate residual stress effect on fatigue crack growth.