Documents / Official release
This Defense Intelligence Reference Document, DIA-08-0912-008, is dated 12 January 2010. It was prepared by the Defense Warning Office's Acquisition Support Division at the Defense Intelligence Agency as one of a series of FY 2009 technology reports under the Advanced Aerospace Weapon System Applications program. It reviews materials for launch vehicles, space vehicles and reusable rocket engines, including aluminum alloys, polymer and metal matrix composites, titanium and nickel alloys, and titanium aluminides. It concludes that newer materials and integrated design could improve on the space shuttle.
From the source: Release of 2026-09-18 Incident: 1/12/10, Las Vegas, Nevada. Released with redactions. This document is a Defense Intelligence Reference Document (DIRD), a technical reference format used by the Defense Intelligence Agency (DIA) to capture baseline knowledge on a specific topic for later analytic use. DIRDs are best understood as reference and synthesis products rather than as original research. It is one of 38 DIRDs produced under the Advanced Aerospace Weapon System Applications Program (AAWSAP) between 2009 and 2011. Because AAWSAP’s scope permitted a broad range of supporting topics, not every DIRD in the series directly concerns aerospace systems or future threat assessment. The following summary reflects the DIRD’s scope and framing at the time of writing and should not be read as implying current validation of the concepts discussed. This DIRD surveys the structural materials needed for advanced aerospace platforms and argues that material choice cannot be separated from overall vehicle design, because launch vehicles, space vehicles, reusable systems, and propulsion hardware each face different temperature, durability, weight, and manufacturing constraints. The report reviews a range of candidate material classes, including advanced aluminum alloys; polymer-, aluminum-, and titanium-matrix composites; titanium alloys; nickel-base alloys; refractory metals; ceramic-matrix composites; carbon-carbon composites; and titanium aluminides. It emphasizes that balancing performance against practical limits such as fabrication methods, cost, inspection, contamination control, and service environment remains a major challenge. Its overall conclusion is that many promising materials exist, but their usefulness depends on application-specific tradeoffs and on closer integration of material selection with design and manufacturing, with some systems judged to be more valuable targets for development than others.
UNCLASSIFIED/ /POI': OPPlelAL l:ISE 8PtLY
leaving voids. This limitation makes it difficult to use many thermoplastic resins that
are otherwise attractive because they are recyclable and have much longer shelf
lives than thermosets (epoxies). Another, more obvious limitation of RTM is
component size. This is in part because weaving of very large fiber preforms is
challenging and requires a very large weaving machine. It also requires a large
injection mach ine capable of multiple injection sites to ensure the complete
infiltration necessary to avoid formation of voids.
In practice, there are several significant challenges associated with manufacturing large
PMC structures today. Among these, perhaps the most significant are manufacturing
cost and the difficulty associated with making large, nonaxisymmetric components.
Large axisymmetric components that can be produced by winding tows of pre-preg are
clearly possible today, as demonstrated by the Boeing 787 fuselage whose section is
shown in Figure 2. For other shapes, because the load-bearing capability of PMCs
depends on the transfer of externally imposed loads to the strong, stiff fibers, joints
that intersect the principal load path become problematic. This is because the fibers
and, as a direct consequence, the load path are discontinuous, requiring local section
size adjustments to offset this local structural inefficiency. Thus, achieving the most
structurally efficient use of PMCs requires monolithic structures with continuous fibers.
In large structures, this is at best a challenge. Even in the Boeing 787's PMC fuselage,
mechanically fastened joints are used to connect adjacent barrel sections. In the
fuselage, as in any cylindrical pressure vessel, the principal stresses are hoop stresses
stemming from pressurization during flight. However, the compromise in structural
efficiency is minimized by the circumferential orientation of the joints. Although these
bolted joints add weight, the overall structural efficiency of the PMC structure is still
better, albeit considerably more expensive, than a longitudinally and circumferentially
stiffened Al structure. The circumferential joints also create discontinuous longitudinal
crack paths that improve the structure's damage tolerance. Some of the added expense
of the PMC fuselage stems from the use of Ti alloy fasteners because of the galvanic
coupling issues that would accompany Al or steel fasteners.
For other applications, which are limited by different material properties, the PMC
system can be tailored to optimize structural performance. This is possible because
both the matrix and the fiber can be independently selected. Moreover, the fiber
"architecture" (fiber orientation, weave geometry, and fiber volume fraction) can be
varied spatially to optimize load-bearing capability under complex stress states. For
example, again drawing on recent applications in commercial aircraft, the fan blades of
the large, high-bypass-ratio turbofan engine {GE90) produced by General Electric for
the Boeing 777 are made from PMCs. The limiting design consideration for these fan
blades is resistance to bird strikes. To optimize the PMCs' impact resistance, a medium
modulus, high-tensile-strength carbon fiber was selected in combination with a
thermoplastic toughened epoxy matrix. Furthermore, the fiber architecture was set to
optimize the bending strength under the impact of a bird. The GE90 fan blades are
produced by hand layup and are quite costly to produce. In the 10-plus years that
these fan blades have been in service, not a single unscheduled engine removal related
to the PMC fan blades has occurred. The competitive fan blade technology for B-777-
class engines is hollow Ti, which is used by both Pratt & Whitney and Rolls Royce. By all
informal accounts, these blades are cost intensive. This example supports the unwritten
rule that the pathways leading to high-performance, high-value structures typically are
5
UNCLASSIFIED/ ,sroR. OFFl&IAL W&li 8Ptllf Not linked to a story yet.
Official release, from the pursue collection. The PDF is mirrored here; the original link is above. 27 pages are in the text index: search them above, or from the library's search.