NASA Research in Composite Structure Damage Tolerance and Composite Applications In the Oil Industry

Abstract

Many factors influence the successful introduction of composite materials into structural applications including a recognized need for improvement over existing technology, material property advantages, innovative structural concepts, advanced design capability, and cost. Motivation to use composite structures in the aerospace industry is dri ven primarily by weight saving which provide enhanced performance benefits. Weight saving is also an important factor for special applications proposed for the oil industry, especially deepwater developments. Other assets of composites are also important including fatigue and corrosion resistance. Consideration of reliability and safety is especially important in both industries. Composites exhibit unique failure modes compared to metals and it is important to understanding the reductions in strength caused by damage. Early pioneering work at NASA on composites established that compression; and especially the reduction in compression strength following damage, placed severe limits on the design allowables for highly loaded components such as aircraft wi ng and fuselage structure. Research by NASA established important design constraints for composite structures which were subsequently integrated into guidelines for the design of composites for commercial aircraft. Early research concentrated on establis hing the limitations imposed by the effect of damage on compression strength and to develop innovative ways to improve performance. Approaches studied included: damage tolerant resins and innovative design concepts such as soft -skin stiffened panels, hybrid composites, bonded and bolted stiffeners, and laminate stitching. In addition, test methods were developed to access improvement advancements including: open hole compression, open hole tension, and compression after impact. Optimization design methods were exercised to develop minimum-weight composite comparisons with aluminum designs including consideration of the limitations imposed by damage. Many of the foundation principles in composites developed at NASA have been applied to applications in the oil industry. The paper discusses the pioneering work in damage tolerance conducted at NASA and describes how the technology developed has been applied in the development of composites technology for applications in the oil industry such as spoolable high pressure composite pipe, composite risers, carbon fiber tendons and synthetic fiber mooring ropes. The paper is intended as a memorial to Dr. James H. Starnes, Jr. with whom the author worked closely at NASA in the area of composites mechanics and design for 15 years.