Fatigue Behavior of VARTM Manufactured Biaxial Braided Composites

Abstract

Braided composites have good properties in mutually orthogonal directions, more balanced properties than traditional tape laminates, and have potentially better fatigue and impact resistance due to the interlacing. Another benefit is reduced manufacturing cost by reducing part count. Because of these potential benefits braided composites are being considered for various applications ranging from primary/secondary structures for aerospace structures [1]. These material systems are gaining popularity, in particular for the small business jets, where FAA requires taken off weights of 12,500 lb. or less. The new process, Vacuum Assisted Resin Transfer Molding (VARTM), is low cost, affordable and suitable for high volume manufacturing environment. Recently the aircraft industry has been successful in maufacturing wing flaps, using carbon fiber braids and epoxy resin and the VARTM process. To utilize these VARTM manufactured braided materials to the fullest advantage (and hence to avoid underutilization), it is necessary to understand their behavior under different loading and environmental conditions. This will reduce uncertainty and hence reduce the factor of safety in the design. Any typical structural member made of composite material is subjected to different types of loading such as static, impact, cyclic causing fatigue, and environmental effects such as change in temperature and exposure to moisture and other corrosives. It is well known that cyclic loading reduces the strength of a material and its useful life or, the fatigue strength of a material is lower than its static strength. This is true of all materials—metals, plastics, composite materials, etc. In structural applications, fatigue loading is unavoidable especially in aerospace and ground transportation applications. This research addresses the tensiontension fatigue behavior of biaxial braided composites.