Electric-field induced crack closure in linear piezoelectric media

Electric-field induced crack closure is studied along with its significant effect on the near tip electroelastic field in linear piezoelectric materia ls. First, the general conditions for crack closure are given explicitly in terms of the remote loading parameters, which delimit the applicability of the conventional traction-free model for both insulating and conducting cr acks. It is found that, in a poled ferroelectric, crack closure occurs for a conducting crack parallel to the poling axis under an electric field appl ied in the poling direction, and for an insulting crack perpendicular to th e poling axis under an electric field applied opposite to the poling direct ion. Further, based on the assumption that the normal traction and displace ment are continuous while the tangential traction vanishes along the closed crack, the mixed boundary value problems are solved and the exact solution s are obtained for both closed insulating and conducting cracks. One desira ble feature of the solution is that the condition for non-positivity of the normal traction on the closed crack faces is identical to the condition fo r crack closure. Additionally, the present solutions predict that electric- field loading causes a non-zero mode-I stress intensity factor at a closed insulating or conducting crack. This result is in sharp contrast to the con ventional traction-free crack model which predicts that an electric field c annot produce any stress intensity factor at cracks in linear piezoelectric materials. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science L td. AN rights reserved.