Study On Utilization Of Advanced Composites In Fuselage Structures Of Large Transports

Author : Paul A. Lagace
Publisher :
ISBN 13 :
Total Pages : 29 pages
Book Rating : 4.:/5 (96 download)

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Download or read book Composite Fuselage Technology written by Paul A. Lagace and published by . This book was released on 1999 with total page 29 pages. Available in PDF, EPUB and Kindle. Book excerpt: Introduction: The aircraft industry continues to pursue the use of advanced composite materials in aircraft structures in order to save weight and produce more efficient, and potentially cost-effective, aircraft. As of the beginning of this work in 1989, advanced composite materials had been applied for over two decades in a number of aerospace structures. Although the list of applications at that time (including aircraft such as the Boeing 757 and 767, the Beech Starship, The Osprey V-22, the F-18, and the AV-8B) represented important engineering achievements, the National Research Council Committee on the Status and Viability of Composite Materials for Aircraft Structures noted in its 1987 report that: "Despite these and other examples, filamentary composites still have significant unfulfilled potential for increasing aircraft productivity [1]." An area identified for application of composite materials, at the time of this work, was primary load-bearing structure in large commercial transports. Although smaller aircraft, such as the Beech Starship, have had primary loadbearing structure, such as wings and fuselages, constructed from composite materials, it is not practical to geometrically scale up a general aviation aircraft into a large transport due to differences such as in the loading indices. There was thus an identified need to pursue further research into the behavior of composite materials and their structures so that increased benefits, such as further reduction in the structural load fraction, can be achieved. Two critical technology areas as related to aircraft are the technologies associated with wings and with fuselages. In considering such applications, an overriding concern is safety. In and of itself, safety is a very wide ranging issues. But, with regard to structure, safety generally deals with the ability of the structure to maintain its integrity while subjected to the loads and environment experienced in operation. A central issue in the case of a primary load-bearing structure is damage. There are three facets to the central issue of damage: damage resistance, which involves the ability of a structure to undergo events without (minimal) damage occurring and which thus addresses the question "how does damage get there"; damage tolerance, which involves the ability of a structure to undergo loading with damage present without failing and which thus addresses the question of "when does damage propagate/cause failure?"; and damage arrest, which involves the ability of a structural configuration to stop propagating damage before such damage causes catastrophic failure and which thus addresses the question "how can the propagating damage be stopped?". Answers to these three questions must be provided in order for a safe structure to be designed. In addressing these issues as they pertain to fuselage configurations made from advanced composite materials, a number of other important technical issues arise. A key issue is that of orthotropy. Due to their inherent orthotropy, composite materials provide the designer the ability to vary the properties of the structure with the structural needs in the various directions of the structure. This "structural tailoring" will affect the damage issues previously enumerated and the designer needs to know how to best tailor the specific fuselage structure to meet the structural needs and to meet the demands placed by the damage issues of resistance, tolerance, and arrest. A further issue deals with the effects of size. Aircraft fuselages are constructed of various dimensions and test articles are often of much smaller size. In order to apply the technology across the entire spectrum of possible sizes, it is necessary to understand the role of scale in the three damage issues. If scaling "laws" or working principles can be established, then the data and lessons learned on one fuselage can be more readily transferred to that of a different geometry and size. A final issue that could be immediately identified was that of configuration and its effects on the three facets of damage. A common structural configuration for aircraft fuselages is that of skin and frame where the underlying frame carries the longitudinal and bending loads while the skin provides the pressure surface and shear capability. In contrast to this typical approach used in metallic airframes, the Beech Starship fuselage has a more monocoque configuration utilizing a sandwich structure with inner and outer graphite/epoxy skins surrounding a Nomex honeycomb core. In this configuration, the sandwich skins provide the bending, longitudinal, pressure, and shear capabilities of the fuselage. In the skin/frame configuration, issues such as the interaction between the skin and the frame and how the skin is attached to the frame must be treated. In the sandwich configuration, issues concerning sandwich construction including debonding of the skins from the honeycomb must be addressed. Again, these need to be addressed in the context of the three facets of damage as to how they affect damage resistance, damage tolerance, and damage arrest. The underlying need is to provide the structural designer with the capability to choose the structural configuration that will most efficiently carry out its mission.