The Configuration Force Between Crack And Inclusion & The Shielding Effects Of Plastic Zone At Mode Ⅱ Crack-tip

The stress intensity factor (SIF) at the crack-tip is strongly affected by the plastic zone and the inclusion near the crack-tip. Thus, it is very important to analyze the interaction between them for understanding the behavior of crack growth and the damage mechanisms of the materials.In this thesis, based on the transformation toughening theory and Eshelby equivalent inclusion theory, we firstly present a general approximate solution for predicting the configuration force between mode I, II mixed crack and an inclusion of arbitrary shape. Explicit formulas for two special inclusion shapes are proposed, from which some basic characters of the configuration force are identified. Secondly, according to the similarities between transformation toughening and plastic zone toughening, a plastically deformed zone around a crack tip is mechanically equivalent to a transformation inclusion with a transformation strain. An analytical solution for prediction of the stress intensity factor induced by plastically deformed zone at mode-II crack tip is then presented under small scale yielding conditions.It is indicated that the plastic zone at mode II crack-tip has a significant shielding effect on the SIF, which is strongly affected by the strain-hardening behavior of the material, by the applied stress and the T -stress, and that the configuration force provides a novel approach to interpret the important phenomenology of the crack deflection and interfacial debonding observed in composite materials.