Dong-Chul Shin

Influence of the Electromechanical Contribution on the Fracture Behavior of Piezoelectric Ceramic

Within the framework of the theory of linear piezoelectricity, a study on linear contributions of the total energy release rate in fracture of the piezoelectric material with a Griffith crack perpendicular to the poling axis was carried out by using the double-torsion technique. The three linear contributions of the total energy release rate due to linear processes are related to the pure mechanical and the electromechanical (or piezoelectric) compliance, and the pure electrical capacitance of the piezoelectric specimen, respectively. For determination of the contributions, the mechanical and the electromechanical (or piezoelectric) compliances were calculated from the measured load-displacement curves at each electric field, and the electric capacitance was obtained from the property and geometric dimension of the sample. In this work, we defined that the pure mechanical compliance and the pure electrical capacitance are the constant values according to the geometrical size as the intrinsic values without considering the electric effects and the mechanical effects, respectively, but the piezoelectric compliance is a dependent variable owing to the electromechanical coupling effects. As the results based on these definition, it was found that the piezoelectric behaviors related to the piezoelectric compliance aid the fracture of C-82 piezoelectric ceramic irrespective to the direction of electric fields and have more influence on the positive electric fields, and the total energy release rate, Gtot (=Gm + Gp) in permeable crack model is more effective than the mechanical one, GM in this research.

Three-dimensional stress analysis of O-ring under uniform squeeze and internal pressure by photoelastic experimental hybrid method

Until now, it is known that stresses on the plane (y-z plane) perpendicular to the circumferential direction (x axis) of Oring exist and stresses on the plane (x-y plane and x-z plane) parallel to the circumferential direction of O-ring does not exist when O-ring is under uniform squeeze rate and internal pressure. But it was known that stresses of x-y plane and xz plane of O-ring under uniform squeeze and internal pressure were existed by this research. To analyze 3 dimensional stress distributions of O-ring under those loadings, stress distributions of every plane should be analyzed. Therefore, photoelastic experimental hybrid method for 3 dimensional stress distributions of O-ring under uniform squeeze and internal pressure were developed in this research. Photoelastic experimental procedures for 3 dimensional stress distributions of O-ring under those loadings were introduced. Stress distributions of O-ring under those loadings were analyzed by photoelastic experimental hybrid method developed in this research. Von Mises equivalent stresses at arbitrary point of O-ring under those loadings were analyzed.