P.O. Judt et alii, Frattura ed Integrità Strutturale, 34 (2015) 208-215; DOI: 10.3221/IGF-ESIS.34.22 208 Focussed on Crack Paths Crack path predictions and experiments in plane structures considering anisotropic properties and material interfaces P.O. Judt, A. Ricoeur University of Kassel, Institute of Mechanics, 34125 Kassel, Germany judt@uni-kassel.de , ricoeur@uni-kassel.de A BSTRACT . In many engineering applications special requirements are directed to a material's fracture behavior and the prediction of crack paths. Especially if the material exhibits anisotropic elastic properties or fracture toughnesses, e.g. in textured or composite materials, the simulation of crack paths is challenging. Here, the application of path independent interaction integrals ( I -integrals), J -, L - and M -integrals is beneficial for an accurate crack tip loading analysis. Numerical tools for the calculation of loading quantities using these path-invariant integrals are implemented into the commercial finite element (FE)-code ABAQUS. Global approaches of the integrals are convenient considering crack tips approaching other crack faces, internal boundaries or material interfaces. Curved crack faces require special treatment with respect to integration contours. Numerical crack paths are predicted based on FE calculations of the boundary value problem in connection with an intelligent adaptive re-meshing algorithm. Considering fracture toughness anisotropy and accounting for inelastic effects due to small plastic zones in the crack tip region, the numerically predicted crack paths of different types of specimens with material interfaces and internal boundaries are compared to subcritically grown paths obtained from experiments. K EYWORDS . J -, M -, L -integral; Interaction integral; Fracture toughness anisotropy; Material interfaces; Crack paths; Fracture process zone. I NTRODUCTION or the sake of an accurate prediction of crack paths, the loading analysis at cracks is one crucial part of the model. Here, the application of path-independent integrals with remote integration contours is beneficial compared to local approaches, as no special requirements regarding the crack tip meshing have to be considered. Integrating along large contours far from the crack tip essentially exploits numerically reliable data. The theory of forces at defects and singularities was established by Eshelby [1] and applied to cracks and notches by Cherepanov [2] and Rice [3], introducing the path-independent J -integral. Investigations by Günther [4] and Knowles and Sternberg [5] provided balance equations including the J -, M - and L -integrals, which were generalized to linear elastic fracture mechanics (LEFM) by Budiansky and Rice [6]. Later these balance laws founded the theory of the material or configurational forces [7]. In LEFM, the J k -integral vector, representing the crack driving force, is related to the stress intensity factors (SIF) [8] and the energy release rate (ERR). Large integration contours at curved cracks require the integration along crack faces, F

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