Chapter 4 - Failure criteria

Abstract

After having analyzed the stresses and strains in composite materials, we will now present the main failure criteria for these materials. The degradation of the composites is characterized by one of the following local modes: - damage dominated by fiber degradation (rupture, micro buckling, etc.), - damage dominated by matrix degradation (crazing, etc.), - damage dominated by singularities at the fiber–matrix interface (crack propagation, delamination, etc.). Composite failure is a gradual process, as the damage in a layer results in a redistribution of stresses in the laminate. How failure occurs in the foll: maximum stress theory, maximum strain theory, polynomial failure criteria, Tsai-Hill criterion, Tsai–Wu criterion, and Hoffman criterion are seen. 4.5. Tensile and shear strength of a unidirectional layer and Determination of failure stresses from three tension tests. Failure of the composite occurs as soon as the stress field no longer satisfies any of the given relationships. From these expressions, the failure stresses in tension and shear are positive, those in compression are negative.