A Review of the Nasa Textile Composites Research

During the past 15 years NASA has taken the lead role in exploiting the benefits of textile reinforced composite materials for application to aircraft structures. The NASA Advanced Composites Technology (ACT) program was started in 1989 to develop composite primary structures for commercial transport airplanes with costs that are competitive with metal structures. As part of this program, several contractors investigated the cost, weight, and performance attributes of textile reinforced composites. Textile composites made using resin transfer molding type processes were evaluated for numerous applications. Methods were also developed to predict resin infiltration and flow in textile preforms and to predict and measure mechanical properties of the textile composites. This paper describes the salient results of that program. Introduction The NASA Advanced Compopsites Technology program was started in 1989 to develop composite primary structures for commercial transport airplanes with costs that are competitive with those of current metallic airplanes. Textile composites were considered for many components to improve structural performance and to reduce costs. Boeing and Lockheed-Martin evaluated textile composites for fuselage frames, window belt reinforcements, and various keel components of the fuselage. Northrop-Grumman evaluated textile concepts for making stiffened skins using 3-D textile composites, and McDonnell Douglas evaluated knitted, braided, and stitched textile fabrics for a wing box. The NASA in-house program, in conjunction with university research grants focused on the development of analytical models to predict resin infiltration and flow in textile preforms, development of a ___________________ * Senior Research Engineer, Mechanics of Materials Branch. † Head, Mechanics of Materials Branch, Associate Fellow. Copyright  1997 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Title 17, U. S. Code. The U. S. Government has a royaltyfree license to exercise all rights under the copyright claimed herein for Governmental Purposes. All other rights are reserved by the copyright owner. database on damage tolerance and mechanical properties of new material forms, development of analytical models to predict elastic properties and strength of textile reinforced composite materials, and development of test methods for textile composites. This papers summarizes the results of the ACT textile composites program. Included are discussions on the application of textile composites to primary structural components, mechanics methodologies to predict textile material response, test methods to measure material properties, experimental methods to measure compaction and permeability behavior of textile preforms, and analytical methods to predict resin flow in textile preforms. Textile Composite Applications Textile material forms that have shown the highest potential for application to composite airframe structures are shown in Fig. 1. Fig. 2 indicates some of the advantages and limitations of each of the textile material forms of interest. Although each of these materials can meet a specific need, the material forms that created the most interest were triaxial braiding for complex structural shapes, multiaxial warp knitting for large area coverage, and stitching for improved damage tolerance. Fuselage Structures During Phases A and B of the NASA ACT program, trade studies were conducted to determine which structural elements could benefit the most from the use of textile composite materials. Fig. 3 shows typical fuselage structural elements that were selected to determine the applicability of textile material preforms and fabrication methods. The structural elements included stiffened side panels, circumferential frames, keel beam frames, and window belts. These structural elements are briefly discussed below. A fuselage side panel with stiffeners and frames is shown in Fig. 4. Using innovative 3-D weaving technology both the frames and the stiffeners are woven with continuous fibers in both directions. Since the weaving process selected can only weave in the 0° and 90° directions, additional ±45° material had to be stitched onto the base fabric to