The durability of fiber composites: The case for mechanism-based models

Abstract

Long-duration durability (particularly fatigue) testing of composites is time consuming and expensive. There is, therefore, a stronger incentive to reduce reliance on such testing than in other areas of design. Mechanism-based models offer the potential to reduce the reliance on test programs. Such models have been derived for several fatigue damage mechanisms, notably: delamination, fiber-bridged cracking, and off-axis ply cracking. There has been less success at modeling fatigue processes at higher levels, such as at notches. Examples of existing models are presented from the literature, and their capabilities and deficiencies are discussed in the context of improving the processes of materials selection and design for durability. Key principles are advocated, including modeling damage propagation utilizing Paris-type expressions, the importance of length scales in modeling fatigue processes, and the need to improve the capability to model multiple, interacting, damage processes.