ORAL/POSTER REFERENCE: 100340R Effect of Electric Field Reversal on Crack Growth Behavior of Poled Piezoelectric Ceramic G.C. Sih Department of Mechanical Engineering and Mechanics, Lehigh University, Bethelehem, PA 18015, USA and Institute of Engineering Mechanics, Hebei University of Technology, Tianjin 300130, China ABSTRACT A long standing unexplained crack growth behavior of poled PZT ceramics is that crack tends to grow longer under a positively applied electric field and shorter under a negatively applied field as compared to the situation when no electric field is applied. While this behavior was observed experimentally, the prevailing mathematical models have not been able to quantify the results. The attempted explanation speaks of separating the electrical and mechanical parts while realizing that the electromechanical energy field is coupled. The energy in a unit volume of material, once stored, could not distinguish the portion from the electric to the mechanical. Based on the energy density criterion, an analytical approach is developed to show qualitatively the behavior of crack growth enhancement and retardation when the electric field is reversed. Crack growth segments are computed for the PZT-4 ceramic material to show that indeed a crack tends to grow longer and shorter depending on whether the applied electric is positive or negative. This confirms the experimental observation. KEYWORDS: Piezoelectric, Crack Growth, Electromechanical 1. INTRODUCTION Piezoelectric ceramics are prone to cracking because they are inherently brittle, an undesirable character that has limited the use of this class of materials. Much research has been done to understand how electrical and mechanical disturbances could lead to unexpected fracture. Indenters [1,2] have been dropped onto PZT (lead-zirconate-titanate) ceramic specimens to produce longer cracks when the poled direction coincides with that of the electric field. The opposite holds for electric field that is applied against the poled direction. The same phenomenon was observed in PZT-4 for a compact tension specimen with an edge crack [3]. Mathematical models have since been developed to quantify these observations without success. Controversies continue to prevail despite numerous unsuccessful attempts [4-6] of using the energy release rate or path independent integral as the fracture criterion. Only in recent times that the energy density criterion [7,8] was applied and resolved the long standing inconsistencies mentioned earlier [3,6]. In what follows, the energy density criterion shall be used to determine how crack growth would be
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