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10 June 2020

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Stress Intensity Factor Solutions for Part-Elliptical Through Cracks

Engineering Fracture Mechanics 63: 209-226

Fawaz, S. A. (1999)

 

Abstract

The present analytical investigation is directed toward predicting the growth of large cracks in riveted lap-splice joints, similar to joints found in operational transport aircraft. The fatigue crack growth of large through cracks with oblique crack fronts can now be predicted using the results of this investigation. A characteristic of fatigue in riveted lap joints is crack growth under a complex stress system which, in its simplest form, consists of cyclic tension with superimposed cyclic bending due to the eccentricity in the lap joint. In reality, rivet squeezing causes hole expansion and built-in residual stresses. Rivet tilting in the rivet hole and contact problems are other complications. To predict the growth of part through cracks with a quarter elliptical shape in lap-splice joints, stress intensity solutions, such as the well-known Newman–Raju K-solutions are available. However, these cracks change into through cracks with oblique crack fronts and continue to grow due to the combined tension and bending. Since no K-solutions are available for through cracks with oblique fronts, the finite-element method and a three-dimensional virtual crack closure technique (3D VCCT) were adopted. The 3D VCCT is shown to be invariant to crack plane mesh orientation, permitting a minimal amount of pre-processing of the mesh to generate a new K solution. K-values are presented for a range of crack depth to crack length ratios (a/c1=0.2, 0.3, 0.4, 0.6, 1.0, 2.0), crack depth to sheet thickness ratios (a/t=1.05, 1.09, 1.13, 1.17, 1.21, 2.0, 5.0, 10.0) and hole radius to sheet thickness ratios (r/t=0.5, 1.0, 2.0).

 

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