13th International Conference on Fracture June 16–21, 2013, Beijing, China Integrated Damage Mechanics Approach to Brittle and Ductile Crack Propagation Geralf Hütter1,*, Thomas Linse2, Uwe Mühlich1, Meinhard Kuna1 1 Institute of Mechanics and Fluid Dynamics, TU Bergakademie Freiberg, 09596 Freiberg, Germany 2 Institute of Solid Mechanics, TU Dresden, 01062 Dresden, Germany * Corresponding author: Geralf.Huetter@imfd.tu-freiberg.de Abstract With decreasing temperature the failure of typical engineering metals changes from ductile fracture to cleavage. A possible cleavage initiation in the brittle-ductile transition region is typically evaluated by stress-based criteria like those after Ritchie-Knott-Rice or of Weibull-type. Such models describe the experimental results adequately in the lower brittle-ductile transition region but problems arise in the upper part of the transition region. In the present study cleavage is modeled by a cohesive zone and ductile damage is described by a non-local Gurson-model. With this modeling of both failure mechanisms the fracture initiation and propagation can be simulated in the whole brittle transition region. The results show that the crack tip constraint has a considerable influence on the stability of the crack propagation. Keywords fracture mechanics, brittle-ductile transition, non-local Gurson model, FEM simulation 1. Introduction In the range of room temperature typical engineering metals fail by a ductile mechanism. Thereby, the voids nucleated at non-metallic inclusions grow and coalesce finally to a macroscopic crack. Due to the plastic deformations much energy is dissipated with this mechanism leading to a high macroscopic fracture toughness. In contrast, at low temperatures fracture by cleavage occurs at favorably oriented crystallographic planes in the particular grains. With this mechanism considerably less energy is dissipated compared to the ductile mechanism which is why the macroscopic material behavior is termed as brittle. In the ductile-brittle transition region both mechanisms are observed, see Fig. 1. In this regime a large scatter of the fracture toughness values is observed for specimens of nominally identical material. This behavior is caused by the strong sensitivity to local material imperfections. Due to the relevance in engineering applications numerous approaches were developed to describe the behavior in the ductile-brittle transition region. Mostly, the ductile mechanism is incorporated Fig. 1: Ductile-brittle fracture surface [1] Fig. 2: Models for brittle-ductile transition -1-
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