MIXED-MODE STRESS INTENSITY FACTORS IN FINITE, EDGE-CRACKED ORTHOTROPIC PLATES

A generalized experimental method for measuring mixed-mode stress intensity factors is described for use in orthotropic materials. Moire interferometry has been used to record the whole field surface displacements of double-edge cracked specimens made from unidirectional laminated composites. The moire patterns were subsequently used to determine mode I and mode II stress intensity factors (K(I) and K(II)) by utilizing the displacement fields around the crack tip. The equations expressing K(I) and K(II) as functions of the displacement fields were reformulated to encompass the orthotropic material constants. A method for deriving these has been described. The accuracy of the results was found to depend on the precision in determining the location of the crack tip, as well as the measurement of the fringe spacing.