Enabling Criteria for Flaw Tolerant Composite Design

The implementation of composites in the aerospace industry has been limited because of the inherent unpredictability of composite structure failures. Typically, very conservative designs are saddled with requirements for fail safe fasteners resulting in heavy and expensive structures. Many recent designs such as F-22 began with large percentages of composite structures, but eventually became primarily metallic designs because of these considerations. To fully realize the benefits of composites on high performance aircraft, more flaw tolerant joints must be implemented. Z-Fiber and 3D weaving technologies represent a fundamentally new way to produce large, unitized composite structures. Using Z-Fiber, co-cured joints can be manufactured which are inherently flaw tolerant and do not require additional fail-safe measures to be taken. However, to date, the implementation of Z-Fiber technology has been hobbled by the current industry design criteria that were developed for 2D composites. With the advent of the new Joint Service Structures Specification, a clear set of enabling criteria have been developed which delineate the requirements for co-cured and co-bonded structures on military aircraft. These criteria now provide a clear path to developing the data necessary to implement Z-Fiber and other 3D technologies. The purpose of this program is to begin the process of gathering data to demonstrate that Z-Fiber reinforcement provides a flaw and damage tolerant joint that meets the requirements of the Joint Service Structures Specification.