Abstract
The stress fields at initiation of a kinked (daughter) crack starting from a (mother) crack subjected to mode-II loading conditions and the influence of these stress fields on the instability condition are investigated. Often the stress distribution along the prospective propagation direction of the daughter crack (before it is actually formed), is considered to be the actual driving force for the crack formation. Emphasis is given in this paper to the changes the stress fields experience in the transition phase from before to after the kinked crack is initiated; in addition, the situation is studied for growing lengths of the daughter crack. It is found that the stress distribution along the prospective path of the daughter crack represents a pseudo-mode-I stress distribution. Numerical calculations using the BEM are performed, proving that a singular stress field according to the regular mode-I loading condition results, showing both radial and circumferential stress singularities, as soon as the daughter crack is formed. The validity of the numerical data is confirmed by experimental results using experimental techniques. These different stress characteristics and their consequences are discussed with the aim of finding an appropriate model for describing realistically the instability process of mode-II loaded cracks.
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