Identification of orthotropic damages within a thin uniform plate

The line crack-like damage generated within a small material volume may change the material behavior of the material volume from initially isotropic to effectively orthotropic, depending on damage orientation. Thus, the change in material behavior can be used to identify the orientation of line crack-like damage with respect to the reference coordinates. Motivated from this observation, first the equation of motion is derived for the thin uniform plate with line crack-like local damages. The locations and severities of damages are characterized by using a damage distribution function, and a damaged small material volume is represented by the effective orthotropic elastic stiffnesses, which are derived in terms of damage orientation and size. Next, a new damage identification theory is developed to identify the orientations of local damages, in addition to their locations and severities, by using the frequency response functions measured from the damaged plate. Finally, the effects of damage orientation on the vibration responses of a plate are numerically investigated, and the numerically simulated damage identification tests are conducted to verify the present damage identification theory.