Non-planar mixed-mode growth of initially straight-fronted surface cracks, in cylindrical bars under tension, torsion and bending, using the symmetric Galerkin boundary element method-finite element method alternating method

In this paper, the stress intensity factor (SIF) variations along an arbitrarily developing crack front, the non-planar fatigue-crack growth patterns, and the fatigue life of a round bar with an initially straight-fronted surface crack, are studied by employing the 3D symmetric Galerkin boundary element method-finite element method (SGBEM-FEM) alternating method. Different loading cases, involving tension, bending and torsion of the bar, with different initial crack depths and different stress ratios in fatigue, are considered. By using the SGBEM-FEM alternating method, the SIF variations along the evolving crack front are computed; the fatigue growth rates and directions of the non-planar growths of the crack surface are predicted; the evolving fatigue-crack growth patterns are simulated, and thus, the fatigue life estimations of the cracked round bar are made. The accuracy and reliability of the SGBEM-FEM alternating method are verified by comparing the presently computed results to the empirical solutions of SIFs, as well as experimental data of fatigue crack growth, available in the open literature. It is shown that the current approach gives very accurate solutions of SIFs and simulations of fatigue crack growth during the entire crack propagation, with very little computational burden and human–labour cost. The characteristics of fatigue growth patterns of initially simple-shaped cracks in the cylindrical bar under different Modes I, III and mixed-mode types of loads are also discussed in detail.