CLASSIFICATION OF CRACK-TIP ISOCHROMATICS IN ORTHOTROPIC COMPOSITES

Classification of crack-tip isochromatics in unidirectional orthotropi c composites, when the crack is parallel to the fibre and perpendicula r to the fibre direction, is considered for mode I, mode II and mixed- mode type of loadings. The knowledge of the mode of fracture helps in identifying the appropriate governing equation to evaluate the Stress Intensity Factor (SIF) from the experimental fringe patterns. The effe ct of material orthotropy, change of material and a/w ratio in influen cing the geometry of the fringe loops is studied in detail for mode I type of loading. Typical experimental fringe patterns are obtained by photo-orthotropic elasticity for mode I, mode II and mixed-mode loadin gs. The inclusion of the term sigma(ox) to the sigma(x) stress term in troduced by Mojtahed and Zachary is validated. The necessity for devel oping a higher order theory in evaluating the SIF from experimental fr inge loops when the crack tip is closer to a free boundary is emphasis ed.