Issue34

A. Campagnolo et alii, Frattura ed Integrità Strutturale, 34 (2015) 190-199; DOI: 10.3221/IGF-ESIS.34.20 190 Focussed on Crack Paths Three-dimensional effects on cracked discs and plates under nominal Mode III loading A. Campagnolo, F. Berto University of Padova, Department of Management and Engineering, Stradella S. Nicola 3, 36100, Vicenza (Italy) campagnolo@gest.unipd.it, berto@gest.unipd.it L. P. Pook 21 Woodside Road, Sevenoaks TN13 3HF (United Kingdom) les.pook@tesco.net A BSTRACT . The existence of three-dimensional effects at cracks has been known for many years, but understanding has been limited, and for some situations still is. Understanding improved when the existence of corner point singularities and their implications became known. Increasingly powerful computers made it possible to investigate three-dimensional effects numerically in detail. Despite increased understanding, three- dimensional effects are sometimes ignored in situations where they may be important. The purpose of the present contribution is to review the study carried out by the same authors in some recent investigations, in which a coupled fracture mode generated by anti-plane loading of a straight through-the-thickness crack in linear elastic discs and plates has been analysed by means of accurate 3D finite element (FE) models. The results obtained from the highly accurate finite element analyses have improved understanding of the behaviour of through cracked components under anti-plane loading. The influence of plate bending is increasingly important as the thickness decreases. It appears that a new field parameter, probably a singularity, is needed to describe the stresses at the free surfaces. Discussion on whether K III tends to zero or infinity as a corner point is approached is futile because K III is meaningless at a corner point. The intensity of the local stress and strain state through the thickness of the cracked components has been evaluated by using the strain energy density (SED) averaged over a control volume embracing the crack tip. The SED has been considered as a parameter able to control fracture in some previous contributions and can easily take into account also coupled three-dimensional effects. Calculation of the SED shows that the position of the maximum SED in the discs case is a function of the thickness. In the plates case instead the position of the maximum SED is independent of plate thickness, contrary to disc results. K EYWORDS . Fracture mechanics; Finite element analysis; Anti-plane loading; Stress intensity factor; Corner point effects. I NTRODUCTION rack tip surface displacements in the vicinity of a corner point in which a crack front intersects a surface are often of practical interest. Assuming that Poisson’s ratio, v > 0, then kinematics considerations for an antisymmetric loading [1] show that modes II and III crack tip surface displacements cannot exist in isolation. Mode II induces C