Seattle, Wash --October 27, 2003-- Many new materials and processes were introduced and discussed at AeroMat 2003, the ASM Aerospace Materials conference held in Dayton, Ohio, June 9-12.

This article discusses several of these presentations, and also includes other reports about aerospace materials developments.

The Boeing 7E7 structure will include several varieties of composites, such as graphite/epoxy and graphite/titanium composites.

Boeing selects graphite composites for 7E7 structure

Over the past two years, a team made up of more than a dozen aerospace companies has investigated advanced composites and new aluminum alloys as possible materials for the Boeing 7E7 built by the Boeing Commercial Airplane Co., Seattle, Wash.. Graphite combined with a toughened epoxy resin has reportedly been selected as the primary material for the wing and fuselage. The wings will also include titanium matrix composites reinforced with graphite fibers.

According to Boeing senior VP Mike Bair, "Composites offer us a variety of advantages, including better durability, reduced maintenance requirements, and increased potential for future developments." He added that generally accepted assumptions that composites would weigh significantly less and cost significantly more than aluminum were found to be not universally true. "The aluminum companies did a great job of offering new alloys that were about as light as the composite materials, and the composite companies made a lot of progress on cost," he said. Boeing is also conducting developmental work on embedding sensors in the 7E7 structure to detect impacts and monitor structural integrity.

Boeing is said to be making excellent progress on the development of the 7E7, and continues to be on track to seek authority to offer the airplane later this year. Two family members are being considered for the 7E7: a basic version that seats about 200 passengers in a tri-class configuration, and a stretch version that would accommodate up 250 passengers in tri-class seating. The 7E7 will have a range of 7200 to 8000 nautical miles (13,300 to 14,800 kilometers).

The 7E7 will have the best fuel efficiency of any wide-body aircraft and will have the smallest sound "footprint," with the quietest takeoffs and landings in its class.

For more information: Lori Gunter, Boeing Commercial Airplanes, Seattle, WA 98124; tel: 425/ 294-1722; Web site: www.boeing/ commercial.com.

Aluminum-beryllium alloy cuts weight in satellite parts

An aluminum-beryllium alloy containing 40% beryllium that provides significant weight savings over conventional material was discussed in a paper by Charles Pokross and Warren Haws of Brush Wellman, Cleveland, Ohio, at AeroMat 2003. Titled "Advanced Manufacturing Techniques of Aluminum-Beryllium Alloys," the paper reported the results of recent developments in the manufacture of aluminum-beryllium alloys.

If aluminum-beryllium materials are substituted for aluminum in the same design, the part will weigh less. However, if the design takes into account the higher modulus of the aluminum-beryllium alloy, the amount of material needed can also be reduced.

Recent work in friction stir welding and electron beam welding shows promise that a weld with greater than 80% of parent metal strength can be achieved. All work reported is based on simple joints of two plates, typically 0.125 to 0.250 in. (3.2 to 6.4 mm) thick. Work is continuing in electron beam welding to make more sophisticated joints.

Near-net-shape extrusions of AM 140 made via conventional aluminum technology such as spider dies were also examined. Net shape extrusions with alloys containing 20 to 30% beryllium showed good distribution of the beryllium phase in the part.

Because of high strength and low density, AM 140 would be a good choice for aerospace applications such as skins for satellites, fittings, and brackets. Several such parts are being investigated by various aerospace companies, but have not flown yet. However, battery sleeves, brackets, and electronic packages made of AM 162 (an Al-Be alloy with 62% beryllium) have been in use on satellites for many years.

For more information: Charles Pokross, Brush Wellman Inc., 14710 West Portage River South Road, Elmore, OH 43416-9502; tel: 419/862- 4126; fax: 419/885-8424; e-mail: charles_pokross@brush-wellman.com; Web site: www.brushwellman.com.

High-strength aluminum alloy designed for forging

"Alcoa's New High Strength Forging Alloy 7085," by Ralph Sawtell, Alcoa Forged Produicts, Cleveland, Ohio, was presented at AeroMat 2003. It was a discussion of the latest developments in the high- strength alloy that was introduced in 1997. The alloy was designed to provide an excellent combination of properties regardless of section thickness. Product forms and tempers are currently at various stages of development, as shown in Table 1.

Although the 7085 composition resides in the vicinity of other 7XXX alloys (Table 2), it has very unique characteristics. Aluminum 7085-T7652 die forgings are in production for commercial aircraft. In addition, specifications are pending for 7085-T7452 die forgings, as development is complete and material is well characterized (Table 3). AMS and MIL-HDBK-5 specifications are in process.

Table 1 - Aluminum alloy 7085 resistance to SCC

Table 2 - Composition of aluminum alloy 7085, wt%

Table 3 - Minimum mechanical properties of 7085 and 7050

Aluminum 7085-T74 die forgings are also under development, and process development is to be completed this year. These die forgings are designed for an, optimum balance of properties and residual stress.

For more information: Ralph Sawtell, Alcoa Forged Products, Cleveland, OH 44105; tel: 216/ 641-4532; fax: 216/641-4122; e-mail: Ralph.sawtell@ alcoa.com. Circle 297

Orbital space plane to launch to the Space Station

The Boeing Orbital Space Plane (OSP) is shown with the Resource Module attached. The Resource Module connects the OSP to an expendable launch vehicle, such as the Delta IV, for launch to the International Space Station in low earth orbit. The Orbital Space Plane will be a multipurpose spacecraft that can perform crew rescue vehicle and crew transfer vehicle missions for the space station. Its structure is to be composed of lightweight metallic and composite materials, and the outside panels will be composites. It will be compatible with current expendable rockets and future reusable launch vehicles, and will seat four to six people.

The X-47 A "Pegasus" is a company-funded, experimental, one-of-a- kind unmanned aircraft designed and built by Northrop Grumman Space Technology, Redondo Beach, Calif., to demonstrate aerodynamic qualities suitable for autonomous flight operations from an aircraft carrier as part of the company's Naval Unmanned Combat Air Vehicle (UCAV-N) program. Shaped like a kite, Pegasus was built largely with composite materials. The air vehicle measures 27.9 ft (8.50 m) long with a nearly equal wingspan of 27.8 ft (8.47 m).

For more information: Northrop Grummanm, One Space Park, Redondo Beach, CA 90278; tel: 310/812-4321; Web site: www.st.northropgrumman.com.

For more information: NASA Marshall Space Flight Center, Huntsville, AL 35812; Web site: www.msfc.nasa.gov.

Advanced aluminum aircraft structures

A strategic development initiative aimed at redefining the cost and weight performance of advanced metallic structures has been announced by Alcoa, Pittsburgh, Pa. The Alcoa 20-20 initiative will provide a 20% weight reduction and 20% lower cost for metallic aircraft components, a goal that is to be reached in a building- block approach over the next 20 years.

"Alcoa's 20-20 initiative is focused on two objectives. The first is to shift current thinking about the cost and weight performance of metallics. The second is to develop new generations of innovative metallic structures that will help our customers break existing paradigms associated with manufacturing built-up structures," says William F. Christopher, President of Alcoa's Aerospace, Automotive, and Commercial Transportation business group.

Mr. Christopher said that the initiative responds to the needs of aircraft manufacturers to design, engineer, and manufacture products capable of meeting the requirements of the world's airlines for aircraft that are more affordable. Such aircraft must also enable lower operating and maintenance costs, and must be compatible with current infrastructure.

With the Alcoa 20-20 initiative's building-block approach, advanced metallic components can be first applied and validated on smaller-size structures. After establishing the material's reliability, component size may then be enlarged, and the number of applications broadened. This lower-risk approach allows aircraft manufacturers to make a phased transition to the new metallic alloys.

New aluminum-lithium alloys are being designed for service in the structure of the cryotank for the Space Shuttle and other spacecraft applications.

One of the 20-20 components displayed for the first time at the Paris Air Show is a prototype fuselage skin built of Alcoa's new 6013 aluminum alloy and produced with advanced welding and forming techniques. Its reinforcing ribs also were produced from new 6000- series alloys, and they were attached by a laser wel\ding process. The completed skin was given its curved shape through age / creep forming, a novel process in which the skin is shaped under high temperature, then held in position for several hours. The resulting prototype fuselage skin is lighter in weight, stronger, and corrosion-resistant, while providing excellent damage- tolerance characteristics.

In addition, the 6000-series alloy may be joined by the automated laser welding process. Welding eliminates the need for many individual fasteners, which have to be installed in holes that are manually drilled during production.

Aluminum-Lithium alloys at AeroMat 2003

Several papers covered the latest developments in aluminum- lithium alloys. The following abbreviated abstracts provide a sampling of the information presented.

"An Update on C458 Al-Li"

The 1.8 Li content and consequently the 0.0945 lb/in^sup 3^ density of C458, along with its higher modulus and good strength and toughness at ambient and cryogenic temperatures, make it an attractive alloy for single and multiple use cryogenic tankage and unpressurized structures for space launch and operational vehicles.

A major effort during the past year was directed towards establishing a production capability for C458 plate. Alcoa established a production ingot casting capability under Air Force Research Laboratory and NASA's Space Launch Initiative (SLI) sponsorship. Three heat lots of material were rolled so that the criteria for S-basis allowables could be met for AMS specifications. Lot acceptance testing showed that the strength and toughness values equaled and exceeded those from the earlier Air Force program when the alloy was developed. The details of this effort and the results achieved were described.

This paper was prepared by Henry Babel, The Boeing Company, Seattle, Wash.; and Roberto J. Rioja, Alcoa, Inc., Alcoa Technical Center, Pa.

For more information: Dr. Henry Babel, The Boeing Co., Huntington Beach, CA 92647-2099; tel: 714/896-1391; fax: 714/372-1866; e-mail: henry.w.babel@boeing.com.

'Origin and Effect of Delaminations on Al-Li Cryotank Structures"

Delaminations observed on the surface of CT fracture toughness K^sub Ic^ specimens of aluminum-lithium alloys led to a research program aimed at resolving under what conditions these delaminations took place, and their relevance to performance and structural integrity.

First the appearance of delaminations on aluminum alloys was discussed. Then constraint factors leading to their formation were presented, and results from tensile tests with varied constraints were reviewed. In addition, results from fatigue testing at constant values of the stress intensity factor were discussed in terms of the critical values needed for the nucleation of delaminations on fracture surfaces. Finally, results were reviewed in terms of the structural performance requirements of a cryotank.

This paper was prepared by D. N. Wells, NASA Marshall Space Flight Center, Huntsville, Ala.; and G. Bray, M. B. Heinimann, and R. J. Rioja, Alcoa, Inc., Alcoa Technical Center, Pa.

For more information: Roberta Rioja, Alcoa, Alcoa Technical Center, PA 15069-0001; tel: 724/337-2096; fax: 724/337-1323; e- mail: Roberto.rioja@alcoa.com.

"Delamination Behavior in Al-Li Alloy C458"

Early generation Al-Li alloys exhibited a tendency to delaminate normal to the short transverse direction, and this was a factor that limited their aerospace applications. However, the tendency for delamination has been substantially reduced in the latest generation of Al-Li alloys. The improvements in the mechanical behavior of Al- Li alloys coupled with their compatibility with welding processes has enabled 2195 to be specified as the material for the latest Space Shuttle cryotank. Additional Al-Li alloys such as C458 and L277 are being considered for future generation spacecraft cryotanks.

Improvements in alloy design have resulted in improved fracture toughness values for C458 compared to previous generation Al-Li products. As a result, the through-thickness stresses encountered under plane strain conditions during cracking may be potentially greater in C458 than in Al-Li alloys with lower fracture toughness values. This has resulted in the observation of delamination cracking during fracture toughness testing of high toughness C458. Results were presented to quantify and model the stress conditions necessary for the occurrence of delamination at room temperature in C458. This information will be useful for designing cryotanks to avoid delamination during service.

This paper was prepared by R. Bush and I. Moreno, U.S. Air Force Academy, USAF Academy, Colo.

For more information: Dr. Ralph Bush, U.S. Air Force Academy, CO 80840; tel: 719/333-7940; fax: 719/333-2944; email: Ralph.bush@usafa.af.mil.

"Thermal exposure effects on Properties of Al-Li alloy Plate Products"

As most aerospace structural hardware is weight sensitive, a reusable cryotank will be designed to the limits of the mechanical properties. Therefore, this effort was designed to establish the effects of thermal exposure on the mechanical properties and microstructure of one relatively production-mature alloy, and two developmental alloys: C458 and L277.

Tensile and fracture toughness behavior was evaluated after exposure to temperatures as high as 300[degrees]F (150[degrees]C)for up to 1000 hrs. Microstrucrural changes were also evaluated to correlate with the observed data trends. The ambient temperature parent metal data showed an increase in strength and reduction in elongation after exposure at lower temperatures. Strength reached a peak with intermediate temperature exposure, followed by a decrease at the highest exposure temperature. Characterizing the effect of thermal exposure on the properties of Al-Li alloys is important to defining a service limiting temperature, exposure time, and end-of- life properties.

This paper was prepared by S. Shah, NASA Marshall Space Flight Center, Huntsville, Ala.; J. Wagner, NASA Langley Research Center, Hampton, Va.; and H. Babel, The Boeing Company, Huntington Beach, Calif.

For more information: Sandeep R. Shah, Marshall Space Flight Center, Huntsville, AL 35812; tel: 256/544-0836; fax: 256/5444809; e- mail: sandeep.r.shah@nasa.gov.

"Aging Optimization of Aluminum-Lithium Alloy C458 for Application to Cryotank Structures"

Compared with aluminum alloys such as 2219, which is widely used in space vehicles for cryogenic tanks and unpressurized structures, aluminum-lithium alloys possess attractive combinations of lower density and higher modulus, along with comparable mechanical properties. These characteristics have resulted in the success of the aluminum-lithium alloy 2195 (Al1.0 Li-4.0 Cu-0.4 Mg-0.4 Ag-0.12 Zr) for the Space Shuttle External Tank, and the consideration of newer U.S. aluminumlithium alloys such as L277 and C458 for future space vehicles. These newer alloys generally have lithium content less than 2 wt%, and their composition and processing have been carefully tailored to increase the toughness and reduce the mechanical property anisotropy of the earlier generation alloys such 2090 and 8090.

This paper was prepared by B.J. Sova, K.K. Sankaran, H. Babel and B. Farahmand, The Boeing Company, Seattle, Wash.; and Roberta J. Rioja, Alcoa, Inc., Alcoa Technical Center, Pa.

For more information: Roberta Rioja, Alcoa Technical Center, Alcoa Center, PA 15069-0001; tel: 724/337-2096; fax: 724/3371323; e- mail: Roberto.rioja@alcoa.com.

"Fatigue Crack Growth Rate and Fracture Toughness Comparison of Several Aluminum Lithium Alloys with 2219-T87"

Aluminum lithium alloys 2195-T8, L277-T8, and C458-T8 were studied for space and aircraft applications. These alloys and their static and fracture properties were compared with the conventional 2219-T87 alloy at room and cryogenic temperatures.

Static properties of aluminum lithium alloys were superior to the 2219-T87. Results of laboratory tests indicated that modulus of elasticity, material yield, and ultimate tensile strength values of aluminum lithium alloys exceeded those of 2219 aluminum.

Because life assessment of space vehicles is an important issue to consider when designing structural components, both material fatigue crack growth rate (da/dn versus DK) as well as surface crack and plane strain fracture toughness (K^sub Ie^, and K^sub Ic^) must be analyzed.

Fracture properties of 2195-T8, L277-T8, and C458-T8 alloys were evaluated at room temperature and in liquid nitrogen, and results were compared with 2219-T87 alloy. Fatigue crack growth rate data in all cases were found with no difficulty, based on the ASTM-E647 Standards.

However, interpretation of through-fracture toughness K^sub Ie^, was difficult to make based on the conventional ASTM-E740. Therefore, a new approach was introduced that will be able to estimate the K^sub Ie^, value based on the structural thickness, initial flaw size, and load magnitude.

For more information: Bob Farahmand, The Boeing Company, Huntington Beach, CA 92647; tel: 714/896-3477; fax: 714/934-1795; e- mail: bob.farahmand@boeing.com.

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