Classification of crack-tip isochromatics in orthotropic composites

Abstract

Classification of crack-tip isochromatics in unidirectional orthotropic composites, when the crack is parallel to the fibre and perpendicular 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 effect of material orthotropy, change of material and a/ w ratio in influencing 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 loadings. The inclusion of the term σ ox to the σ x stress term introduced by Mojtahed and Zachary is validated. The necessity for developing a higher order theory in evaluating the SIF from experimental fringe loops when the crack tip is closer to a free boundary is emphasised.