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Simulation of Short Crack Propagation ‐ Transition from Stage I to Stage II
Author(s) -
K?nkler B.,
Fritzen C.P.,
D?ber O.,
Krupp U.,
Christ H.J.
Publication year - 2005
Publication title -
pamm
Language(s) - English
Resource type - Journals
ISSN - 1617-7061
DOI - 10.1002/pamm.200510147
Subject(s) - crack closure , crack tip opening displacement , crack growth resistance curve , materials science , fracture mechanics , slip (aerodynamics) , perpendicular , lüders band , grain boundary , mechanics , stress intensity factor , boundary element method , dislocation , composite material , structural engineering , geometry , finite element method , microstructure , physics , mathematics , engineering , thermodynamics
The life‐time of cyclically loaded components with smooth surfaces is mainly determined by the initiation and propagation of microstructurally short fatigue cracks. The phase of short crack propagation can be subdivided into crack growth along single slip bands (stage I, in the direction of maximum shear stress in front of the crack tip) and the growth along alternating slip bands (stage II, perpendicular to the direction of maximum normal stress). Hence, the propagation starts in a single grain and continues through several grains in stage I. Then, additional slip bands are activated and the crack grows on alternating glide planes perpendicular to the direction of maximum normal stress. During the whole propagation process of the still relatively short crack, the plastic deformation on slip bands is blocked by grain boundaries. Due to the strong interaction with the microstructure, a description of the short crack propagation based on linear elastic fracture mechanics is not possible. Thus, an extended two‐dimensional yield‐strip model [1] based on the ideas of Navarro and de los Rios [2] has been developed. The boundary‐element method is used to calculate the displacements along the crack, treating the plastic zones in front of the crack tip as yield strips. Each boundary element consists of a mathematical dislocation at its beginning and its end, describing a constant normal and tangential displacement in the element. Geometrical crack closure can be considered by constraints allowing only positive normal displacements within the crack elements. The model is extended to the transition of stage I crack growth on single slip systems to crack propagation on multiple slip systems, which is presented here. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)