ELECTRIC-FIELD INDUCED CRACK CLOSURE IN LINEAR PIEZOELECTRIC MEDIA

摘要

Electric-field induced crack closure is studied along with its significant effect on the near tip elec- troelastic field in linear piezoelectric materials. 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 cracks. It is found that, in a poled ferroelectric, crack closure occurs for a conducting crack parallel to the poling axis under an electric field applied in the poling direction, and for an insulting crack perpendicular to the poling axis under an electric field applied opposite to the poling direction. 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 solutions are obtained for both closed insulating and conducting cracks. One desirable 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 for 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 conventional traction-free crack model which pre- dicts that an electric field cannot produce any stress intensity factor at cracks in linear piezoelectric materials.