SBIR-STTR Award

Advanced structural composites are being used extensively in modern military aircraft to improve performance, reduce life cycle cost and prolong structural life over metallic construction. Polymer composites used in airframe structural components are made from laminated layers (plies) of fiber reinforced polymer. The compressive strength and stiffness properties of a laminate are significantly reduced by the presence of random waviness and curvature in the reinforcement fiber. A new product called Graphlite Rods manufactured by Neptco Incorporated has recently been introduced to the composite industry. Graphite epoxy rods are fabricated using a proprietary process that maintains filament alignment to an angular deviation of less than .88 degrees. These rods offer superior compressive strength, and flexural stiffness relative to tape and fabric due to parallel carbon fiber alignment within the composite. To eliminate the 'knock down' in properties associated with fiber waviness, BRM in conjunction with its subcontractor Lockheed Fort Worth Company proposes to develop airframe structure containing 3-D composite elements with integrally woven structural rods. These rods will be integrally woven into structural elements that typically fail in compression.

Keywords:
STRUCTURAL RODS WOVEN PREFORMS LOW COST AIRCRAFT STRUCTURES

Specific mechanical properties of fiber-reinforced composites have made them an attractive material for application to many aircraft structures. Today, composite structure is typically made up of laminated layers (plies) of 2-D composite material with the fiber direction of each ply thoughtfully oriented to optimize structural efficiency. The goal of 'continued improvement' in structural efficiency and cost has inspired the development of a new and innovative structural concept. This concept is to automatically weave complete composite laminate preforms that are made up of optimally oriented discrete plies held together with an optimum density of Z-directional (thru-the-thickness) fibers. This concept, once developed will improve the interlaminar shear strength, damage tolerance, and fabrication cost of continuous fiber reinforced composite structure. Development of this concept will eliminate the manual cutting, placement, and debulk (typically ever four plies) of the thin (.005" to .014" thick) composite plies. Additionally, this concept will increase the interlaminar shear and damage tolerance of the structure with minimal impact to in-plane properties by introducing an optimum density of Z-directional fiber. Bally Ribbon Mills in conjunction with Lockheed Fort Worth Company as subcontractor will evaluate the feasibility of this technology and its application to fighter aircraft mid-fuselage structure.