CompositesWorld

AUG 2016

CompositesWorld

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AUGUST 2016 12 CompositesWorld DESIGN & TESTING ยป e Greek philosopher Heraclitus of Ephesus once said, "Change is the only constant." We can see the inherent truth behind this statement when we look at the evolution of materials in aerospace. e Wright Flyer was the first successful heavier- than-air powered aircraft. Built in 1903, the Flyer had a wooden frame. e straight parts were spruce and the curved parts were ash. e frame was covered with a finely woven cotton cloth and was sealed with canvas paint similar to what mariners of the time used on their sails 1-3 . In the next era of aircraft construction, builders used metallic alloys, which were much stronger than wood, allowing for improved performance. Today, most aircraft are constructed from a combination of metallic and composite materials as performance continues to improve. e Boeing Co. (Chicago, IL, US) first used fiberglass in its 707 passenger jet in the 1950s, and it comprised roughly 2% of the structure. Since that time, each generation of Boeing aircraft has had an increased percentage of composite materials. Boeing's 787 Dreamliner is approximately 50% (by weight) composites 4 . Airbus, Boeing's main competition in the large transport aircraft category, has countered with the A350, which makes extensive use of composites, as well, also roughly 50% by weight. However, because safety is the number one priority of the aerospace industry, mate- rials have evolved gradually over time. In the late 1970s and early 1980s, NASA, through its Aircraft Energy Efficiency (ACEE) Advanced Composites Structures Program, challenged large-transport manufacturers to use graphite material to redesign existing aircraft components. e program's goal was to develop the neces- sary data and technology to achieve produc- tion commitments to advanced composites. e graphite/epoxy horizontal stabilizers that were developed by Boeing for its 737 as part of this effort were put into commercial service in 1984. ey have performed outstandingly, with no service incidents reported 5 . is led to increased confidence in, and acceptance of, composites for primary aircraft structure. e mission of the FAA is to provide the safest, most efficient aerospace system in the world. e FAA develops aviation regula- tions that set the minimum acceptable levels of safety in aviation. As materials and structures continue to evolve, the FAA constantly must evaluate the adequacy of its regulations, policy and guidance materials. Title 14 of the Code of Federal Regulations (CFR) contains all of the regulations for aeronautics and space 6 . ese regulations are generally performance-based rather than prescrip- tive, which means both composite and metallic structures have to perform to the same standard of safety. In addition to certifying the aircraft flying in the United States National Aerospace System (NAS), the FAA is proactively working to ensure the safe transition to composites. e William J. Hughes The FAA: Keeping up with aerocomposites evolution Technical Center (Atlantic City, NJ, US) is the FAA facility in which engineers research a wide variety of materials, including compos- ites. In 2003, the FAA created the Joint Advanced Materials and Structures (JAMS) Center of Excellence 7 , a consortium of universi- ties that conducts research for the FAA in the areas of testing and analysis, bonding and repair, damage tolerance, environmental factors and crashworthiness. e FAA, the aerospace industry and academia work side by side continually to raise the bar for safety. e FAA also takes a proactive approach towards composites through the Composite Materials Handbook-17 (CMH-17), which provides information and guidance necessary to design and fabri- cate end items from composite materials. Its primary purpose is the standardization of engineering data development methodologies related to testing, data reduction and reporting of property data for current and emerging composite materials 8 . Experts from all over the world meet each year to develop content for the Handbook, which is used by the industry when constructing composite parts for aircraft. e FAA also provides guidance directly to industry through Advisory Circulars (ACs). AC 20-107B sets forth an acceptable means for manufacturers to comply with 14 CFR regarding airwor- thiness type certification requirements for aircraft structures that involve fiber-reinforced materials. It also includes informa- tion on material and process control, manufacturing, structural bonding, environmental considerations, protection of structure, generating design values, structural details, proof of structure for static strength and fatigue and damage tolerance, as well as repair, inspection, crashworthiness, fire protection, flammability, thermal issues and lightning protection 9 . is AC was most recently updated in 2009. However, because the industry is constantly evolving, the next revision is not too far down the road. Tech Center test fleet These FAA flight test aircraft, located at the William J. Hughes Technical Center, function as an R&D testbed and are used for the purpose of evaluating navigational systems, communications systems and flight loads. Source | FAA Composite and metallic structures must conform to the same performance- based standard of safety.

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