Abstract
Closure-free long cracks under the remote mode III loading grow in a more complicated way than those under the remote mode II. For bcc metals, a coplanar in-plane spreading of tongues driven by the local mode II loading components at crack-front asperities prevails while twisting of crack-front segments to mode I, often leading to factory-roof morphology, is typical for other materials. In bcc metals, therefore, the formulation of a quantitative relationship connecting effective thresholds in modes II and III demands to calculate the local mode II components of stress intensity factors at typical asperities of a crack front loaded in the remote mode III. Therefore, a numerical model of a serrated crack front was created and the results were compared with experimentally determined ratio of mode II and III effective thresholds for the ARMCO iron. Although the calculated crack-front roughness needs an experimental verification, the preliminary results indicate that the model can provide a quantitative explanation of the experimentally observed ratio of mode II and mode III effective thresholds in bcc metals.
Highlights
D espite the applied shear-mode II, III or II+III loading, the fronts of long cracks in metallic materials are, in the small-scale yielding case, always loaded in a local mixed mode I+II+III due to their 3D microscopic tortuosity and frictionally induced mode I (e.g. [1], [2])
The 2D modelling of the tortuous crack geometry is sufficiently relevant and, the finite element analysis of the local mode II component for a crack with serrated front loaded in the remote mode III was performed
Significance of this component was assessed by the ratio of the local mode II SIF k2 and the remote mode III SIF KIII determined for crack without ledges
Summary
D espite the applied (remote) shear-mode II, III or II+III loading, the fronts of long cracks in metallic materials are, in the small-scale yielding case, always loaded in a local mixed mode I+II+III due to their 3D microscopic tortuosity and frictionally induced mode I (e.g. [1], [2]). The formulation of a quantitative relationship connecting effective thresholds in modes II and III demands to calculate the local mode II components of stress intensity factors at typical asperities of a crack front loaded in the remote mode III.
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