On the birefringent-coating method of stress analysis for fiber-reinforced laminated composites

A general relation based upon laminated-plate theory is developed which relates the state of stress throughout the thickness of the fiber-reinforced composite laminate to experimentally determined surface strains. The usefulness of the developed relation is discussed through an example given for a typical graphite-epoxy structural laminate. Birefringent coatings employed as a method to determine laminate surface strains are investigated. Isochromatic disturbances in the vicinity of a laminate free-edge, due to a Poisson's ratio mismatch between coating and laminate and interlaminar stress transfer between discrete lamina of the laminate, are investigated through exact elasticity solutions.