Notch sensitivity of composites

Fiber reinforced composite materials have excellent specific strength and stiffness, but have a linear-elastic response and tend to fail suddenly since mechanisms such as plasticity that create ductility in metals are not available. Composites are therefore notch sensitive, with stress concentrations causing a significant reduction in static strength. This is in contrast to the behavior of metals where load redistribution due to plastic deformation means notches have a less significant effect. Composite structures are often bolted, and the resulting stress concentrations are important. Open hole tensile and compressive strength are two critical parameters which can control design, and as a result the full potential and high strains the materials are capable of reaching cannot be fully exploited. Other types of notches arise because of component geometry or damage due to events such as engine disk bursts or foreign object damage. A lot of research has been conducted on notched composites, and the early work was reviewed by Awerbuch and Madhukar.¹ Failure mechanisms are very complex because of the interaction between matrix cracking, delamination, and fiber failure, which are each dependent on different material properties, the laminate stacking sequence and geometry. Much progress has been made in understanding these mechanisms, particularly in recent years with more detailed information on the damage states from high resolution computer tomography (CT) scans. Advances in modeling have also led to better understanding of how the different mechanisms affect the overall response and have improved our ability to predict behavior. In this chapter the basic failure....