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5
Cross-cutting Issues and Challenges
This chapter expands on the key lightweighting topics introduced in Chapter 1 based on the discussion in that
chapter and the assessments in Chapters 2-4.
5.1 DIFFERENT PRIORITIES, SIMILAR CHALLENGES
The preceding three chapters illustrate the point made in Chapter 1 and Table 1-1: that the key considerations
that drive lightweighting differ markedly across vehicles for land, sea, and air transport. For instance, for ground
vehicles, survivability is paramount to protecting the warfighter (see Chapter 4); performance attributes such as
speed, maneuverability, and payload capacity are secondary. Furthermore, in today’s combat environment, opera -
tional supportability related to fuel use and vehicle maintenance is viewed as less critical, although the vulnerability
of logistics support is a concern. The priorities for naval ships differ. For example, design of the new class of littoral
combat ship (LCS) is driven principally by performance (especially speed and maneuverability) and survivability
(see Chapter 3). Operational supportability is generally secondary, although replacement of steels with aluminum
alloys has implications for joining (see Box 5-1), fatigue, and repair. For aircraft, weight plays critical roles in
both performance and operational supportability. It relates directly to propulsion and lift requirements, and hence
to payload, range, speed, and fuel consumption. Survivability plays a secondary role overall, but a major role in
the design of fighters and attack aircraft.
A summary assessment of lightweighting considerations for each medium—air, sea, and land—is given in
Table 5-1. It illustrates that the use of metrics for design optimization relative to weight is most refined and mature
for aircraft, and much less so for ground vehicles and maritime vessels. Future materials opportunities include
high-strength steels, as well as more exotic materials such as titanium. As discussed in Chapter 2, composites are
already used extensively in aircraft; they are also of interest for maritime applications.
Although the relative importance of lightweighting and attributes differs across the spectrum of military
vehicles, lightweighting of all types of vehicles is hindered by at least two common barriers.
First, the time required to develop and certify new materials and process technologies generally exceeds
that required for development and certification of a military vehicle. For example, it can take as long as 10 to 20
103
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104 APPLICATION OF LIGHTWEIGHTING TECHNOLOGY TO MILITARY AIRCRAFT, VESSELS, AND VEHICLES
Box 5-1
Joining
The ability to join materials and structures together is fundamental to the construction of both military and
civilian vehicles and their underlying structures, and perhaps presents the biggest challenge to the economical
production of assembled multimaterial structures and complete vehicles while ensuring the complete integrity
of the structures and vehicles. The challenge for doing this rapidly is becoming greater as new materials are
introduced, requiring an expanded range of new joining techniques that are compatible with predominantly
steel, aluminum, or composites vehicle chassis in military air, sea, or ground applications. Revolutionary
improvements in joining can open new opportunities for weight and/or cost savings but need to be taken to
the next level of advancement so that many promising technologies can be evaluated or confirmed and engi-
neers can confidently specify their use. Joining techniques for major military body structure materials should
be addressed in collaboration with the supply industry or through industry consortia.
There is a need for military manufacturers to evaluate and adopt adhesive bonding (which is growing
in use in commercial automotive sectors) in combination with spot welding (known as weld bonding) or in
combination with riveting (known as rivbonding). These technologies are being used increasingly for joining
aluminum in some production situations, although it is generally necessary to have surface pretreatment
to provide adhesive bond strength and durability.
A critical industry need exists to establish parameters and performance targets for assessing imple-
mentation readiness for such joining techniques as laser welding (e.g., continuous joining with reduced
heat-affected zones), thermal drilling, and friction stir welding for assembling newer alloys of magnesium,
aluminum, and advanced high-strength steel. The services need to work closely with manufacturers to
define R&D projects involving real parts or performance conditions, in order to enhance the designers’
confidence in these technologies.
Concurrent with joining technology developments, new non-destructive evaluation and inspection
techniques are essential for developing manufacturing and assembly techniques and then for confirming
the integrity of assemblies, vehicle structures, and systems in production. This is especially critical as lower-
modulus materials are introduced and material thickness is reduced, thereby requiring that the integrity
of the materials and joints consistently and economically meet the design targets for strength, stiffness,
durability, and crashworthiness.
years to develop and implement a new advanced materials system.1,2 Consequently, new materials and process
technologies must be suitably mature at the time of preliminary design to ensure that the target vehicle will indeed
be manufactured within the required timeframe; otherwise, sometimes-costly risk mitigation strategies must be
implemented. Here, “maturity” encompasses the establishment of an adequate, stable supply of materials as well
as the manufacturing capability to produce useful forms of these materials in order to ensure that the capability
exists for streamlined insertion of lightweight materials into designs.
Second, the current acquisition process for military vehicles is expensive and lengthy. 3 Examples include
the F-22 Raptor (19 years)4 and the F-35B (9 years, although not a function of technical barriers). 5 The time and
1 Leo Christodolou, “Accelerated Insertion of Materials,” DARPA presentation to the NRC committee on ICME, November 20, 2006, avail -
able at http://www7.nationalacademies.org/nmab/CICME_Mtg_Presentations.html.
2 Materials Genome Initiative for Global Competitiveness, white paper and initiative prepared by the ad hoc Interagency Group on Advanced
Materials, National Science and Technology Council, T. Kalil and C. Wadia, June 2011.
3 See, for example, the NRC, 2011, Evaluation of U.S. Air Force Preacquisition Technology Development , Chapter 2, pp. 33-61, Washington,
D.C.: The National Academies Press.
4 Andrew McLaughlin. 2006. “F-22A Raptor—No Longer a Fair Fight,” Australian Aviation, April, pp. 55-61. Available at http://www.
ausairpower.net/AA-Raptor-0406.pdf. Last accessed June 21, 2011.
5 Bill Sweetman. 2011. “F-35B Put on Probation; New Bomber to Go.” Aviation Week, January 7.
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105
CROSS-CUTTING ISSUES AND CHALLENGES
TABLE 5-1 Summary Assessment of Lightweighting Considerations
Summary Assessment
Air Sea Land
General Considerations (Transport and Tactical) (Non-nuclear Vessels) (Tactical Vehicles)
Have explicit metrics been Yes—extensive and General, gross-level General, gross-level metrics:
developed and used for weight mature: metrics: • otal weight limits
T
optimization? • Component level • otal weight
T
• System level • eight distribution
W
• ubsystems—engines,
S
auxiliary power units,
and so on
Primary benefits of lightweighting • verall system
O • peed, maneuverability
S • uel use and associated
F
performance—range, • tability
S logistics
speed, payload, • ransportability
T • peed, maneuverability
S
maneuverability • ransportability
T
• upport cost—fuel use
S
Primary challenges of • ost and technical
C • oining, structural
J • urvivability—weight of
S
lightweighting maturity of advanced health monitoring armor
materials • urvivability and
S • dvanced lightweight
A
damage tolerance armor
• ost for mass volumes
C • ystems integration
S
of lightweight
materials
Future materials opportunities • omposite materials
C • igh-strength steels
H • S
teels
(not including armor applications) • itanium
T • luminum
A • A
luminum
• omposites
C • M
agnesium
• T
itanium
expense involved stem from extensive validation and certification requirements for new materials and processes
as well as exhaustive testing of full-scale systems. Because the consequences of failure are severe, the principal
decision makers tend to be risk-averse.
It is broadly recognized that the time to bring these technologies to fruition can be accelerated, and the
prospects for attaining optimal designs enhanced, through the use of systems engineering design, 6 enabled by the
unprecedented computational power at the disposal of the DoD. This approach also enables design for flexibility
and adaptability. That is, since many legacy systems remain in service well beyond the initial targets of useful
service life and often encounter new requirements or threats, new systems are ideally based on designs that allow
modifications to be made when necessary after design and certification. Modifications can range from adding or
replacing armor in land vehicles, as described in Chapter 4, to replacement of individual components as lighter
(or otherwise improved) versions become available. The flexibility to accept such modifications would require
consideration during the initial design of the vehicle external structure and the internals. Such flexibility could
also result in improved maintainability as well as easier sustainment of legacy vehicles.
Specifically, the implementation and broader use of comprehensive materials models, as embodied by inte -
grated computational materials engineering (ICME), need to be integrated with systems design and optimization
6 See,for example, NRC, Pre-Milestone A and Early-Phase Systems Engineering, pp. 1-13, Washington, D.C.: The National Academies Press.
Also see reports and other resources available through the Defense Acquisition University website, at http://www.dau.mil.
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106 APPLICATION OF LIGHTWEIGHTING TECHNOLOGY TO MILITARY AIRCRAFT, VESSELS, AND VEHICLES
analyses. This would ensure the consideration of potential new materials and enable analytic assessment of system
benefits at an early stage of product development, as well as guide the selection and focus for new materials devel -
opment. This is especially critical for lightweighting materials technology, because integration of the materials
with design and configuration would be extremely important. The process could be further accelerated through
greater use of advanced technology demonstration programs (see Chapter 1), which allow pursuit of technologies
that have higher risk but the potential for higher pay-off.
A third common barrier is that there is limited availability of some materials critical to lightweighting, or the
materials are prohibitively costly. Moreover, the specialized manufacturing capabilities needed to create some of
these materials, or to form them into useful structural shapes, are, in some cases, in short supply.
5.2 SYSTEMS ENGINEERING DESIGN
5.2.1 Approaches and Trade Spaces
As discussed in Chapter 1, systems engineering design requires consideration of many (often conflicting)
requirements for vehicle performance and functionality. It is broadly recognized as being essential to optimization
over the system trade space (which defines how changes in one aspect of a system, such as in the type and amount
of a material used, or the structural form of a component, affect all other aspects), based on the interrelationships
among material technology, structural forms, and performance (as well as costs). The task can be extraordinarily
complex.
Optimization7 of a military vehicle requires clear definitions of the performance metrics—top speed, range,
survivability under prescribed threats, and operating costs being common examples—as well as the weighting of
these metrics (to establish their importance relative to one another). The optimization process thus requires under -
standing of the operational trade space: that is, how changes in one aspect of a system—the type and amount of
material used in a component or its structural form—affect all relevant performance indices. In some cases, multiple
benefits can accrue. Lightweighting, for example, can lead to increased fuel efficiency (assuming no change in
functional requirements), increased vehicle range, and increased payload capacity. It can also be used to enhance
survivability by use of additional armor without necessarily changing the overall vehicle weight. However, these
changes can also be accompanied by increased acquisition costs, which can take precedence over life-cycle costs
in procurement.
Although the systems engineering approach has been successful in recent military vehicle projects, a number
of barriers prevent it from taking full advantage of the potential for lightweighting to improve system attributes:
• As discussed earlier in this chapter and throughout the report, the timeline for materials development
exceeds the timeline for product development, preventing or significantly delaying the incorporation of
new materials.
Material development and optimization have not been an explicit part of the system optimization process.8
•
The biggest impediments to this are the time, cost, and risk of material development and certification. 9
Consequently, optimization can be performed only over the domain of certified materials.
7 “Optimization” is certainly the ideal goal of systems engineering, but practitioners recognize that, in complex military systems, which typi -
cally have hundreds of requirements and numerous subsystems, optimization in the truest mathematical sense is not feasible due to difficulties
in defining clear objective functions across the many interacting constraints. In this context, the committee uses the word “optimization” to
mean state-of-the-art optimization strategies to design best possible system using realistic constraints.
8 Michael Winter, P&W, “Infrastructure, Processes, Implementation and Utilization of Computational Tools in the Design Process,” presenta -
tion to the NRC committee on ICME, March 13, 2007, available at http://www7.nationalacademies.org/nmab/CICME_Mtg_Presentations.html.
9 See, for example, G.L. Hahn et al., “Accelerated Insertion of Materials—Composites,” presentation, 34th SAMPE Conference, 2002; and
Z. Lui, P. Witte, J. Ceisel, and D.N. Mavris, “An Approach to Infuse Manufacturing Considerations into Aircraft Structural Design,” 56th
SAMPE Conference, May 2011.
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CROSS-CUTTING ISSUES AND CHALLENGES
• The current military procurement and acquisition process, whereby portions of vehicle systems are subcon-
tracted to different vendors, can lead to sub-optimization at the subcontract level, or even to development
of non-optimized subsystems, if systems engineering processes are not adequately followed or enforced.
• Explicit performance metrics and their weightings are ill-defined, especially in ground vehicles.
• The computational design tools used today for systems engineering and optimization by the DoD and origi-
nal equipment manufacturers (OEMs) do not generally include comparable analytical materials design
and behavior models. Development and integration of such comprehensive materials models (ICME) with
other systems analysis tools offers the potential to accelerate prototyping (especially preacquisition phase
prototyping) as well as make it possible to conduct rapid studies of the trade space. Such tools would
also result in better selection and evaluation of the most critical lightweighting materials technologies for
future investment.
The implementation and broader use of comprehensive materials models, as embodied by ICME, would have
to be integrated with systems design and optimization analyses. This approach would ensure the consideration of
potential new materials and enable analytical assessment of system benefits at an early stage of product devel -
opment, as well as guide the selection and focus for new materials development. This is especially critical for
lightweighting materials technology, since integration of the materials with design and configuration would be
extremely important.
5.2.2 Integrating ICME into Systems-Level Design and Optimization
As noted in Chapter 1, the statement of task encompasses the design of components, structures, and vehicles.
This goes beyond the use of lightweight or otherwise advanced materials, extending to how materials are arranged
and topologies optimized. Many of the innovations in lightweight construction are concerned with putting the mate-
rial where it is most beneficial. Advances in system design and topology can yield improvement in performance
even absent the incorporation of new materials.
Hardware design is an iterative process that starts with a set of specifications and functional requirements from
which a designer must develop a conceptual design establishing the overall form of the hardware to be designed.
The conceptual design needs to be optimized to best satisfy the specifications and functional requirements. Then
the design must trade off structural concepts and topologies, materials, manufacturability, service environments,
and so on.
Structural topology is an important area of research and is an integral element of the systems-level design
approach discussed in this report. An example of the approach can be found in, “Materials Selection Combined
with Optimal Structural Design: Concept and Some Results.”10 In this article the authors link materials data from
the Cambridge Material Selector (CMS) with a design optimizer (the Multipoint Approximation method with
Response Surface fitting, or MARS) to produce a final design for an automobile structural component. Figure 1
of the article, shown here as Figure 5-1, illustrates the approach.
In this approach, material and performance indices are derived on the basis of performance targets, standards
and other regulatory requirements, and load analyses. The authors used the CES for preliminary material selec -
tion. To optimize the structure of the component, the authors developed a system based on MARS combined with
MSC.MARC FEA code w9x.11 Because the material selection was considered as a multiobjective optimization,
a compound objection function was used as shown at the bottom of Figure 5-1. The final choice of material can
then be made on the basis of minimization or maximization of the compound objective function, depending on
the problem to be solved.12
Fundamental advances in structural topology are being made in both the United States and Europe that could
10 N.S. Ermolzeva, K.G. Kaveline, and J.L. Spoormaker. 2002. “Materials Selection Combined with Optimal Structural Design: Concept and
Some Results.” Materials and Design, Vol. 23, Issue 5, August, pp. 459-470.
11 Ibid.
12 Ibid.
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108 APPLICATION OF LIGHTWEIGHTING TECHNOLOGY TO MILITARY AIRCRAFT, VESSELS, AND VEHICLES
FIGURE 5-1 An approach to combining materials selection with structural optimization. SOURCE: N.S. Ermolzeva, K.G.
Kaveline, and J.L. Spoormaker. 2002. “Materials Selection Combined with Optimal Structural Design: Concept and Some
Figure 5-1.eps
Results.” Materials and Design, Vol. 23, Issue 5, pp. 459-470.
bitmap
contribute greatly to the lightweighting of military and civilian vehicles. An example is the work at Johns Hopkins
University on topology optimization, a computational method for optimizing the design of structural systems as
well as the design of multifunctional materials.13 Recent work at the University of Notre Dame has investigated
structural topology optimization for blast mitigation in ground vehicles. 14 These tools and techniques are being
used in the private sector,15 but the technology is still a long way from being fully developed.
Accelerating the development of improved analytical tools for doing structural topology optimization would
improve the speed and fidelity of the conceptual design phase. This research needs to be fully integrated into the
overall systems-level analyses for efficient development of lightweighting solutions.
5.2.3 Design for Flexibility and Adaptability
Because the functional requirements placed on military vehicles may change over their service lives, adaptabil-
ity and flexibility are important considerations when the vehicles are designed. However, designing for flexibility
can lead to bloated systems as more features and capabilities are added. Indeed, in some sense, designing for flex -
ibility is the antithesis of lightweighting. Additionally, flexibility often means compromising the performance goals
for any one specific application. An example of this dilemma is the Joint Strike Fighter (F-35): it was designed to
suit all of the services and, as a result, is heavier than originally desired. 16
13 See, for example, J.K. Guest and J.H. Prévost, 2006, “Optimizing Multifunctional Materials: Design of Microstructures for Maximized
Stiffness and Fluid Permeability,” International Journal of Solids and Structures, Vol. 43, Issues 22-23, November, pp. 7028-7047; A.
Asadpoure, M. Tootkaboni, and J.K. Guest, 2011, “Robust Topology Optimization of Structures with Uncertainties in Stiffness—Application to
Truss Structures,” Computers & Structures, Vol. 89, Issues 11-12, June, pp. 1131-1141; and E. Lund, 2009, “Buckling Topology Optimization
of Laminated Multi-material Composite Shell Structures,” Composite Structures, Vol. 91, Issue 2, November, pp. 158-167.
14 J.C. Goetz, H. Tan, J.E. Renaud, and A. Tovar. 2009. “Structural Topology Optimization for Blast Mitigation Using Hybrid Cellular Au -
tomata.” Proceedings of the 2009 Ground Vehicle Systems Engineering and Technology Symposium. August 28-20, Troy, Mich.
15 See, for example, “Study of Topography Optimization on Automotive Body Structure,” presentation by Rajan R. Chakravarty, General
Motors, at the SAE World Congress & Exhibition, Detroit, Mich., April 2009.
16 In 2004, it became apparent that the STOVL (Short Take-Off Vertical Landing) variant of the Joint Strike Fighter was exceeding its weight
targets to such an extent that it might be unable to accomplish its mission. A team was assembled to find ways to reduce its weight, which
was done primarily by reducing its mission requirements. For example, an original design specification to carry two internal air-to-ground
weapons in the 2000-pound class was changed to two weapons in the 1000-pound class, providing a 2000-pound weight reduction. See E.L.
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109
CROSS-CUTTING ISSUES AND CHALLENGES
A concept of flexibility embraced by the services is that of “multifunction structure plus,” wherein structural
components perform additional functions. Examples include the Army’s use of structural batteries embedded
within armor systems,17 the Navy’s advanced enclosed mast system (see Chapter 3), and the Air Force’s use of
composites for both damage resistance and electromagnetic environment protection (see Chapter 2). Another area
that aircraft manufacturers are considering involves lightning strike protection. Currently, because of the poor
electrical conductivity of the polymer resins used in the composites, conducting metallic meshes must be added.
Emerging technologies to embed carbon nanoparticles in the resin may raise the conductivities to the requisite
levels and obviate the need for the mesh material in advanced composites. This could also yield additional benefits
in the out-of-plane stiffness and strength.18
5.3 INSERTION OF LIGHTWEIGHTING MATERIALS AND TECHNOLOGIES
5.3.1 Timeline for Technology Development and Insertion
As discussed in Chapter 1, the time required to develop and certify materials generally exceeds that required
for product development and certification. The time can range widely—from a few years for derivative materials
on an expedited schedule to a decade or longer when a new class of material is under development or where new
infrastructure is required to produce the material or structure.19 The major challenge is to shorten the timeline for
materials development and bring it in line with that for product development.
This challenge is made more difficult by the mandates of the rigorous, gated 20 approaches taken for devel-
opment and certification of major engineering systems, which require that the maturity of new technologies be
relatively high by the time critical system architecture decisions are made—typically when detailed design is initi -
ated. New technologies that are not sufficiently mature at this stage are excluded from consideration unless backup
configurations are carried along for risk mitigation. Unacceptably high levels of risk could be incurred if system
architecture, design, or capability is critically dependent on a new technology, and failure to bring that technol -
ogy to fruition results in significant design changes, compromises to system attributes, or delays in production.
Many companies and DoD agencies use the technology readiness level (TRL) assessment process, and the
corresponding manufacturing readiness level (MRL) scale, for assessing and describing the maturity of materials
and processing technology and the readiness of the corresponding manufacturing technologies and processes.
The TRL scale and its definitions of maturity levels—originally proposed for use by NASA in the late 1980s and
detailed in the Defense Acquisition Guidebook21—are summarized in Table 5-2. Definitions for the corresponding
MRLs, which were developed and aligned with the TRL definitions somewhat later, are also shown. The TRL and
corresponding MRL gate definitions are very consistent in scope and intent. In fact, through TRL-7 and MRL-7,
the MRL gate exit criteria require that the corresponding TRL gate criteria be met as a condition of MRL gate
completion.
When the TRL assessment approach is applied to materials and process development, the timeline and typical
decision gates appear as illustrated in Figure 5-2. Two gates are often critical: TRL-3 (and MRL-3), where deci -
Palmer, 2008, “F-35 Lightning II News: Weighing the F-35,” F-16.net, March 16, available at http://www.f-16.net/news_article2784.html.
Last accessed May 26, 2011.
17 AMPTIAC Quarterly, Vol. 8, No. 4, 2004.
18 See for example, (1) B. Wang, R. Liang, C. Zhang, P. Funches, and L. Kramer, 2003-2004, “Investigation of Lightning and EMI Shield -
ing Properties of SWNT Buckypaper Nanocomposite,” Final Report, May 1, 2003-October 31, 2004, available at http://handle.dtic.mil/100.2/
ADA430333’; (2) T.W. Chou, L. Gao, E.T. Thostenson, Z. Zhang, and J-H Byun, 2010, “Review: An Assessment of the Science and Technol -
ogy of Carbon Nanotube-based Fibers and Composites,” Composites Science and Technology, Vol. 70, No.1, January, pp. 1-10; and (3) K.
Kalaitzidou, H. Fukushima, and L. Drzal, 2010, “A Route for Polymer Nanocomposites with Engineered Electrical Conductivity and Percola -
tion Threshold,” Materials, Vol. 3, pp. 1089-1103, available at http://www.mdpi.com/1996-1944/3/2/1089.
19 NRC. 2004. Accelerating Technology Transition: Bridging the Valley of Death for Materials and Processes in Defense Systems. Washing-
ton, D.C.: The National Academies Press. Available at http://www.nap.edu/catalog.php?record_id=11108.
20 Gated technology developments programs specify criteria that must be met before a project can advance through a “gate” from one de -
velopment stage to the next.
21 Defense Acquisition Guidebook, available at https://akss.dau.mil/dag/DoD5000.asp?view=document&rf=GuideBook\IG_c10.5.2.asp.
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110 APPLICATION OF LIGHTWEIGHTING TECHNOLOGY TO MILITARY AIRCRAFT, VESSELS, AND VEHICLES
TABLE 5-2 Technology and Manufacturing Readiness Levels and Maturity Descriptions
TRL or MRL
TRL Maturity Description MRL Maturity Description
Level
Basic principles observed and Basic Manufacturing Implications
1
reported I dentified
Technology concept and/or
2 Manufacturing Concepts Identified
application formulated
Technology Development Phase
Analytical and experimental
Manufacturing Proof of Concept
3 critical function and/or
Developed
Pre -Acquisition
characteristic proof of concept
Component and/or breadboard
Capability to produce the technology in a
4 validation in laboratory
laboratory environment
environment
Component and/or breadboard Capability to produce prototype
5 validation in relevant components in a production relevant
environment environment
System/subsystem model or Capability to produce a prototype system
6 prototype demonstration in a or subsystem in a production relevant
relevant environment environment
Capability to produce systems,
System prototype demonstration
7 s ubsystems, or components in a
in an operational environment
production representative environment
Acquisition Phase
Actual system completed and
Pilot line capability demonstrated; Ready
8 qualified through test and
to begin Low Rate Initial Production
demonstration
Low rate production demonstrated;
Actual system proven through
9 C apability in place to begin Full Rate
s uccessful mission operations
Production
Full Rate Production demonstrated and
10 Not defined
lean production practices in place
SOURCE: Defense Acquisition Guidebook and DoD/MRL Manufacturing Readiness Level (MRL) Deskbook, version 2.0,
May 2011.
sions to invest in comprehensive development and validation occur, and TRL-6 (and MRL-6), where materials,
processes, and manufacturing readiness are considered sufficiently mature for use. This level of maturity is usually
required for a technology to be included in the detailed design phase of a product or system.
For major DoD systems, development and acquisitions must adhere to Defense Acquisition Management
System requirements. Three key milestones defined in this process relate to technology introduction. These mile -
stones, illustrated in Figure 5-3, are defined by DoDI 5000.02:
1. Milestone A: approval of entry into the Technology Development (TD) phase;
2. Milestone B: approval of entry into the Engineering and Manufacturing Development (EMD) phase; and
3. Milestone C: approval of entry into the Production and Deployment (P&D) phase.
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CROSS-CUTTING ISSUES AND CHALLENGES
Technology
Mature for
Product
Commitment
Scale
-up,
Component &
Demo Basic Concept & Proof of System Level
Specimen &
1 2 3 4 5 6
Processes
Physical Benefits Concept/ Lab Validation or
Sub-
Characterization
Principles Identified Tests Prototype
component
& Validation
Lab Tests
Period of Highest
Process Reviews Development Investment
and Gates
Duration: Extensive (many years)
FIGURE 5-2 Typical technology readiness level (TRL) gates for development of materials and processes. The time period may
Figure 5-2.eps
vary widely, from around 2 years for derivative materials to >5 years for critical structural materials or when significant new
materials systems or infrastructure are associated with the technology. Gate 3 is typically where significant investment and
specific application focus begin. TRL-6 and MRL-6 are usually required prior to program initiation or product commitment.
SOURCE: Adapted from B.A. Cowles and D. Backman, 2010, “Advancement and Implementation of Integrated Computational
Materials Engineering (ICME) for Aerospace Applications,” a white paper sponsored by the Air Force Research Laboratory,
AFRL-RX-WP-TP-2010-4151, March, available at http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.
pdf&AD=ADA529049.
FIGURE 5-3 Defense acquisition system-level milestones. SOURCE: Department of Defense, Defense Acquistion Guidebook,
Figure 5-3.eps
Instruction 5000.02, December 8, 2008.
bitmap
Perhaps the most important considerations regarding the relationship between technology readiness and these
key system-level milestones are these:
• Technology and manufacturing maturity levels are required to be at TRL-6 and MRL-6, respectively, at or
before Milestone B, when engineering and manufacturing development for the product or system begins.
• The Technology Development phase, which begins at Milestone A, must have sufficient scope, resources,
and time to mature candidate technologies to TRL-6/MRL-6 before program initiation at Milestone B.
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112 APPLICATION OF LIGHTWEIGHTING TECHNOLOGY TO MILITARY AIRCRAFT, VESSELS, AND VEHICLES
The implications of this requirement are significant. If the time, cost, or risk of maturing a new materials
or processing technology prevents achievement of TRL-6, and/or MRL-6, by the time of program initiation at
Milestone B, then it is likely that the technology will not be included in the system development. If it is included,
some level of risk mitigation activity will be required. Risk mitigation activities may be significant depending on
the impact the technology is expected to have on the system architecture, design, or capability.
The Technology Development phase is critical for both selection and maturation of technologies. This is
especially true for lightweighting materials and related technologies, since—as described in this report—taking
full advantage of lightweighting requires integration of such materials and technologies at the system level. This
requires consideration of technologies and their potential impact well before Milestone B, and a commitment for
their development and maturation before the detailed design phase and program initiation. An excellent discussion
of the need for strategic selection of technologies, and this recurring issue of “bridging the valley of death” for
technology insertion, can be found in the recent NRC report Evaluation of U.S. Air Force Preacquisition Technol-
ogy Development22 (discussed in Chapter 1 of this report).
A generic representation of a gated product or system development process is shown in Figure 5-4. This
expands the first part of the DoD graphic in Figure 5-3 slightly, in order to better illustrate the activities that occur
from Milestone A (preacquisition technology development) into the acquisition phase where Milestones B and C
occur.
The alignment of technology and manufacturing development with the product or systems development process
is illustrated in Figure 5-5. Although the timelines for specific technologies and the programs themselves may vary
widely, it is apparent that accelerating the materials and processes development cycle is critical. Technologies not
already at TRL-3 (MRL-3) would likely have a difficult time being considered, even in the concept optimization
phase. Moreover, higher levels of maturity would be expected or required before commitment of a materials tech -
nology to preliminary design activities. For technologies and design approaches with significant implications for
system integration, such as materials and processes for lightweighting, benefits and impacts would best be assessed
during the concept initiation phase—very early in the product development process, and early in the Technology
Development phase of the Defense Acquisition process.
Ideally, technology development and product or system development would be interactive from inception of
both phases. In such an ideal state, product concepts would influence technology (including materials) develop -
ments, beginning at the conceptual (and low- maturity) stage, and analysis of potential materials and their capabili -
ties would be passed back to the concept initiation activities for product development. This loop would be iterated
and refined to guide both product and materials/technology development—including the selection of appropriate
technologies for investment. This is illustrated in Figure 5-6.
Then, again ideally, an accelerated materials and processes development and certification process would
begin, in time to meet requisite maturity levels by the start of Program Initiation, corresponding to Milestone B
and detailed design. Future materials and process technologies will require reductions in the time, cost, and risk
of development and certification. Regardless of whether such an idealized process could be supported in practice,
it is clear that accelerating the design, development, and insertion of new materials and manufacturing processes
is critical to future products and systems. This is especially true for lightweighting materials technologies, which
would be best selected and assessed as part of an integrated systems development process.
The next section discusses some approaches to better integrating the development of materials technologies
with development of entire systems. The committee believes that ICME offers significant potential to enable
improved materials design, accelerated development, and reduced risk for insertion. In addition, the capability to
analytically describe materials in a manner compatible with processes for design and concept optimization will
be essential to having these materials considered and integrated at the earliest stages of product development.
22 NRC. 2011. Evaluation of U.S. Air Force Preacquisition Technology Development. Washington, D.C.: The National Academies Press.
Available at http://www.nap.edu/catalog/13030.html.
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CROSS-CUTTING ISSUES AND CHALLENGES
Generic Product or System Development
Based on Integrated Product Deployment Process IPD
-
Product
Concept
Concept Preliminary Validation/ EIS,
Design &
0 Optimization 1 2 3 Certification 4 Production& 5
Initiation Design Initial
Support
Validation
Program
Process Reviews Launch Period of Highest
and Gates Development Investment
A B C
Defense Acquisition Milestones
FIGURE 5-4 Generic gated product or system development process. Gate 2 is a key gate: it corresponds to defense acquisition
Figure 5-4.eps
process Milestone B, program initiation, where TRL-6 and MRL-6 maturity levels are required. The time to advance from gate
2 to gate 4 can vary widely: from perhaps 2 years for a derivative system to more than 10 years for a complex major system.
SOURCE: Adapted from B.A. Cowles and D. Backman, 2010, “Advancement and Implementation of Integrated Computational
Materials Engineering (ICME) for Aerospace Applications,” a white paper sponsored by the Air Force Research Laboratory,
AFRL-RX-WP-TP-2010-4151, March, available at http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.
pdf&AD=ADA529049.
Technology
Material and Process Technology Development Mature for
Technology Readiness Level Gated Process - TRL Product
Commitment
Commitment
Scale-up,
Component &
Concept &
Demo Basic Proof of System Level
Specimen &
1 2 3 4 5 6
Processes
Benefits
Physical Concept/ Lab Valida on or
Sub-
Characteriza on
Iden fied
Principles Tests Prototype
component
& Valida on
Lab Tests
P eriod
Period of Highest
Process Reviews Development Investment
and Gates
Dura on: Extensive (many years)
Note: MRL and TRL gates align through TRL/MRL-7
Generic Product or System Development
Based on Integrated Product Deployment Process - IPD
Product
Concept
Concept Preliminary Valida on/ EIS,
Design &
0 1 2 3 4 Produc on & 5
Op miza on
Ini a on Design Cer fica on
Ini al
Support
Valida on
Program
Process Reviews Launch Period of Highest
and Gates Development Investment
A B C
Defense Acquisi on Milestones
FIGURE 5-5 How technology readiness for materials and processes relates to product and system development. SOURCE:
Adapted from B.A. Cowles and D. Backman, 2010, “Advancement and Implementation of Integrated Computational Ma -
terials Engineering (ICME) for Aerospace Applications,” a white paper sponsored by the Air Force Research Laboratory,
AFRL-RX-WP-TP-2010-4151, March, available at http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.
pdf&AD=ADA529049.
Figure 5-5 corrected
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117
CROSS-CUTTING ISSUES AND CHALLENGES
Figure 5-8.eps
FIGURE 5-2-2 Forecast and measured cumulative distribution of ultimate tensile strength (UTS) for Ferrium S53.
Inset represents the goal of forecasting variation validated at the 10 heat level of MMPDS specification from data on
bitmap
3 heat level of AMS specification. SOURCE: G.B. Olson. 2011. “Computational Materials Design: Making CyberSteel
Fly.” Northwestern University & QuesTek Innovations LLC. Evanston, Ill. April 6. Available at http://www.transportation.
northwestern.edu/docs/2011/2011.04.06.BAC_Olson_Presentation.pdf. By permission from QuesTek Innovations LLC.
during all stages of development to the processability conditions viable at the largest required scale of ingot
production. The approach successfully demonstrated the complete elimination of the scaleup component of al-
loy development—each scale ingot (from 3 lb to 15,000 lb) was produced with the required microstructure and
properties the first time, without the usual multiple iterations to find a processable composition at each scale.
Figure 5-2-2 illustrates the simulation. Design of this alloy went from a clean sheet of paper to flight qualifi-
cation in just 8.5 years. The developers stated that this could have been accomplished in 5 years if support had
been continuous. The project’s sponsor estimated a cost savings of $50 million relative to traditional empirical
development of the Strategic Environmental Research and Development Program.2
1G.B. Olson, 1997. “Computational Design of Hierarchically Structured Materials,” Science, Vol. 277, No. 5330, pp. 1237-1242. See also C.J.
Kuehmann and G.B. Olson. 2009. “Computational Materials Design and Engineering,” Materials Science & Technology, Vol. 25, No. 4.
2DoD-EPA-DOE. 2003. Strategic Environmental Research and Development Program (SERDP) Bulletin, Winter, No. 15, p. 6.
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118 APPLICATION OF LIGHTWEIGHTING TECHNOLOGY TO MILITARY AIRCRAFT, VESSELS, AND VEHICLES
Box 5-3
ICME Example: Development of Superalloy GTD262 at GE
GE was one of the three companies that carried out a DARPA-AIM project, which facilitated the adoption
of the AIM/ICME approach inside the company. During the AIM project, extensive testing was performed on
the reliability of thermodynamic databases in predicting phase stability in multicomponent superalloys,1 which
resulted in a rigorous assessment of the fidelity level of thermodynamic data for several key phases.
A GE-funded project was initiated in 2002 and executed by both GE Global Research and GE Energy
to replace tantalum (Ta), a critical refractory element subjected to high risks of supply and price disruptions,
in superalloy GTD222, which was widely used in nozzles and vanes in GE power generation gas turbines.
Using the AIM/ICME approach, especially by integrating computational thermodynamic predictions of phase
equilibria with GE’s materials property models and databases, Jiang and his collaborators designed four alloys
with niobium (Nb) replacing Ta and with modifications to the concentrations of other elements to optimize and
balance key properties and producibility.2 Laboratory-scale tests were performed on those four Ta-free alloys
for mechanical properties, oxidation resistance, weldability, and castability. The best of the four alloys doubled
creep-resistance performance; other properties remained comparable to those of the Ta-bearing GTD222. It
was subsequently subjected to an industrial-scale production trial (Figure 5-3-1) and successfully passed the
qualifications without any technical hurdles. The new alloy was named GTD262; it was successfully introduced
into GE power generation gas turbines starting in 2006, and it is experiencing much wider adoption today.
The first key lesson learned from this project is that reliable thermodynamic databases are essential to
the design of multicomponent alloys and that fidelity tests are required to increase the confidence level for the
predictions in specific regions of compositions. High-confidence thermodynamic predictions not only eliminated
several of the experimental iterations that are usually needed to obtain the right alloy compositions (GTD262
was designed without even a second round of experimental trials), but also eliminated the long-term thermal
exposure experiments that are generally required to test the propensity to form detrimental phases. GTD262
was developed and introduced in about 4 years from concept to industrial production (including design property
data gathering) at less than 20 percent of the typical alloy development cost, which is very likely a record in
both speed and cost in insertion of a new alloy into a gas turbine.
The second key lesson is that integration of thermodynamic predictions with property predictions from
physics-based models and regression-based property databases is vital to the balance of properties. GE’s
proprietary models and internal databases played an important role in the development of GTD262. More
widely applicable, physics-based, but experimentally validated microstructure and property models as well as
higher-fidelity databases (especially thermodynamic databases with higher accuracy and wider compositional
validity) are badly needed for the development of new alloys whose compositions differ vastly from those of
existing alloys.
Early engagement with production/application teams at GE Energy in terms of multiple design goals and
manufacturability has contributed significantly to the rapid and smooth transition from laboratory to produc-
tion, which was another important lesson learned from the prior DARPA-AIM project. The rapid development
of GTD262 is the first successful landmark that has helped establish within GE the credibility of computational
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119
CROSS-CUTTING ISSUES AND CHALLENGES
FIGURE 5-3-1 A production trial gas turbine nozzle made up of a new superalloy, GTD262. SOURCE:
Courtesy of the General Electric (GE) Company. 5-2-1.eps
Figure
bitmap
alloy design and its associated methodologies, models, and databases. GE teams have since successfully de-
signed and deployed into GE products new superalloys at similar high speed and low cost as a result of using
the same AIM/ICME approach, which has now firmly established a vital role in new alloy development at GE.
1J.-C. Zhao and M.F. Henry. 2002. “CALPHAD—Is It Ready for Superalloy Design?” Advanced Engineering Materials, Vol. 4, No. 7, pp. 501-508.
2L. Jiang, J.-C. Zhao, and G. Feng, 2005, “Nickel-Containing Alloys, Method of Manufacture Thereof,” and articles derived therefrom, World
Patent Application WO2005056852, filed on September 29, 2004, published on June 23, 2005; U.S. Patent Application 20100135847, filed on
October 21, 2009, published on June 3, 2010.
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120 APPLICATION OF LIGHTWEIGHTING TECHNOLOGY TO MILITARY AIRCRAFT, VESSELS, AND VEHICLES
FIGURE 5-7 Schematic illustration of relationships between time and length scales for the multiscale simulation methodology.
SOURCE: Adapted from T.S. Gates, G.M. Odegard, S.J.V. Frankland, and T.C. Clancy, 2005, “Computational Materials: Multi-
scale Modeling and Simulation of Nanostructured Materials,” Composites Science and Technology, Vol. 65, pp. 2416-2434.
strength of the composites, micromechanics and three-dimensional failure models are used, based on additional
data from coupon-level testing. The models can be used to tune toughness qualitatively based on resin chemistry,
but they are not yet quantitatively predictive (see Chapter 3 for additional details). The length scales over which
modeling is required are illustrated in Figure 5-7.
A significant gap arises between molecular-level modeling and the modeling of final structural properties of
the composite based on continuum assumptions. A major difficulty arises in the prediction of the local properties
of the polymer near the fiber and nanoparticle interfaces as a function of resin chemistry and processing condi -
tions. (Complexities of the modeling challenges are illustrated in Figure 5-8.) Another difficulty is that even the
relative dispersion of nanoparticles within a resin/composites cannot be predicted as a function of particle type,
size, and processing. Yet, since these composites are systems of interfaces with nearly all polymer existing in
the neighborhood of interacting surfaces (fiber and/or nanoparticle), these local polymer properties are critical.
Therefore, traditional composite modeling theories based on fiber layup must use coupon-level properties from
unidirectional specimens in order to build up properties of the composites. Finally, although prediction of stiffness
of composites based on traditional continuum and micromechanics modeling theories is well developed, predictions
of more challenging properties, such as strength, toughness, and ballistic performance, need significant attention.
Thus, while progress is being made, the existing gaps in modeling preclude the goal of being able to predict a
composite system’s properties based purely on knowledge of the individual constituents and the processing history.
Significant progress in implementing composites as tailored lightweight solutions in a wide variety of structural
applications will require the ability to design the material composition and processing to obtain desired properties.
5.4 TRANSITION OF LIGHTWEIGHTING TECHNOLOGIES INTO FIELDED SYSTEMS
Introduction of new technologies into complex systems typically requires significant experimental testing
from the level of materials to coupons to components to subsystems. While modeling can accelerate this process,
ultimately the new technology must be tested in field conditions as part of a complete system. Because light -
weight materials are often considered a risk in terms of strength and fatigue life, many new technologies are first
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121
CROSS-CUTTING ISSUES AND CHALLENGES
Figure 5-10.eps
FIGURE 5-8 Representative volume element for modeling a nanotube-reinforced composite of polyethylene. SOURCE: T.S.
Gates, G.M. Odegard, S.J.V. Frankland, and T.C. Clancy, 2005, “Computational Materials: Multi-scale Modeling and Simula -
bitmap
tion of Nanostructured Materials,” Composites Science and Technology, Vol. 65, pp. 2416-2434.
incorporated into legacy platforms in non-critical, secondary components. For example, as discussed in Chapter 2,
polymer composites were incorporated in aircraft air intake components before being used in primary structures
such as wings and fuselage. In other cases such as lightweight ballistic and blast protection for ground vehicles,
new ceramic and composite plates were simply bolted or adhered onto existing doors and undercarriages in place
of steel. Designing systems to facilitate selection from many component options, depending on function and
availability (e.g., the “A+B” approach described in Chapter 1), can speed up the adoption of new technologies.
For much greater leaps in system capability, however, the use of advanced technology demonstrations 26 can
bring together interdisciplinary teams that strive for revolutionary advances (see Chapter 1 and Box 5-2). ATDs
can be characterized as relatively large scale both in resources and complexity and as enabling enhanced military
operational capability, operator/user involvement from planning to final documentation, testing in a real and/or
synthetic operational environment, a finite schedule (e.g., 3-4 years), and the need to meet mutually agreed upon
cost, schedule, and objective performance baselines such that there is a rapid transition to deployment.
The recent revision to the Defense Acquisition Guide, through DOD Instruction 5000.02, actually calls for
ATDs in the preacquisition phase of development—that is, before Milestone B, in the technology development
phase. This would seem to be a good opportunity to integrate ICME methods to accelerate design and development
of prototypes for ATDs, especially for lightweighting materials and their integration with structural requirements
and design configurations.
ATDs offer an important opportunity to use system engineering and design optimization and it would be wise
to take maximum advantage of this opportunity. To ensure that this is done, ATDs should use a gated approach
to development that includes all of the requirements that an actual, fielded system would have to meet. Although,
because it is an ATD, not all of these requirements would need to be validated by test, there should be clear direc -
tion as to how the requirement would be met in a production vehicle. Additionally, where feasible, ICME tools
can be used in ATDs to accelerate the early stages of design and optimization and to improve the robustness of
the final hardware.
ATDs have potential to be very good vehicles for evaluation of lightweighting concepts, especially integrated
materials and configuration concepts. ICME investment, especially related to lightweighting materials technolo -
26 Note that ATDs are but one process for facilitating the transition from technology development to deployment. For others, see (for example)
the list at http://www.onr.navy.mil/en/Science-Technology/Directorates/Transition/Technology-Transition-Initiatives-03TTX.aspx. Some of
these other initiatives may also provide opportunities to develop and transition lightweighting materials and designs.
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122 APPLICATION OF LIGHTWEIGHTING TECHNOLOGY TO MILITARY AIRCRAFT, VESSELS, AND VEHICLES
gies, would facilitate success through accelerated assessment and analytical prediction of new material behavior.
This would enable an ATD (or prototype) to be designed and manufactured with reduced risk and on an acceler-
ated schedule.
As noted in Chapter 4 in the discussion of the JLTV competitive prototyping program, and of virtual proto -
typing, such a step—to try out new materials and new designs for lightweighting in terms of their effects on other
attributes—could be considered in the “pre-ATD” or “pre-prototyping” stage. The design solutions that look the
most favorable could then progress to the ATD stage or physical prototyping stage.
ATDs have brought about revolutionary military vehicles. For example, UAVs, advanced ship configurations,
and lightweight vehicles are technologies that emerged from ATD projects begun in the 1990s. But not every ATD
has proven to be a resounding success. Lightweight transport vehicles for the Army proved to be vulnerable to
IEDs and assault weapons because of inadequate armor,27 and UAVs suffered from poor ground station interfaces
and required inordinate maintenance. Some of the problems encountered with these vehicles can be attributed in
part to their hasty introduction into service, despite their having been intended as demonstration vehicles only.
Evidently the protocols used to “graduate” ATDs from demonstrators to fielded systems proved inadequate. 28 An
excellent set of recommendations for bridging the gap between ATDs and fielded systems is detailed in a previous
NRC report.29
5.5 MANUFACTURING AND MAINTENANCE TECHNOLOGIES
THAT FACILITATE LIGHTWEIGHTING
Despite the fact that the United States has been the innovator of virtually all major manufacturing technolo -
gies for defense products in the post–World War II era, there is widespread realization that the competitiveness
of the U.S. manufacturing industry has declined over the last 20 years. One consequence is that the U.S. defense
industry has had to rely more on global manufacturers for supply of raw materials, intermediate goods, and many
niche products.30
The ability of the DoD to “lightweight” will be dependent to some extent on the preservation and nurturing of
the domestic manufacturing base. It would also benefit significantly from a parallel commercial base for air, sea,
and land transport systems. Parallel markets would have the effect of reducing risk across all stages of technol -
ogy and manufacturing readiness and reducing associated costs. This trend has indeed been observed historically,
wherein the “knowledge spillovers” from the commercial sector have resulted in military systems with longer
service lifetimes.
While advances have been made in reducing raw material cost through DoD efforts (e.g., the Title III Program
on National Defense Industrial Resources Preparedness), the secondary processing methods for many newer mate -
rial candidates or product forms have not matured and are relatively undeveloped compared with those for steel
(e.g., see Table 5-3). For example, robust manufacturing processes for fabricating complex structural components
from continuous-fiber-reinforced composites have not yet achieved the rates and consistency of steel stamping.
Titanium is also recognized as a leading candidate material for lightweighting, but its viability for broad use
is questionable because of high acquisition costs and risks associated with its availability. Since no single military
application will raise demand for such materials to support and sustain production levels, there is a need to lever-
age demand with the commercial industry.
It is important to note that investments in fundamental research that leads to exciting new materials typically
27 Dick Engwall, “First Army ACAT-1 Program TRL Review Including MRL Critique,” briefing to NDIA Manufacturing Commmittee Meet -
ing, November 2008. This briefing includes some excellent suggestions on how to change the current paradigm.
28 Stew Magnuson. 2010. “New Truck to Show the Way for Acquisition Reforms.” National Defense Magazine. August. Available at http://
www.nationaldefensemagazine.org/archive/2010/August/Pages/NewTruckToShowTheWayforAcquisitionReforms.aspx.
29 NRC. 2003. Use of Lightweight Materials in 21st Century Army Trucks. Washington, D.C.: The National Academies Press. Available at
http://www.nap.edu/catalog.php?record_id=10662.
30 See, for example, RAND Corporation, 2004, “High Technology Manufacturing and US Competitiveness,” March 20, papers at http://www.
innovationpolicy.org/consolidating-the-multitude-of-reports-callin; and NRC, 1999, Defense Manufacturing in 2010 and Beyond, Washington,
D.C.: National Academy Press, pp. 12-15.
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CROSS-CUTTING ISSUES AND CHALLENGES
do not translate to commercial products or military application for many decades because the R&D on the scalable
processing of the material into functional forms follows at a much later stage. Accelerated use of new materials
requires parallel investments in manufacturing process R&D.
A critical need in the overall readiness of fielded combat systems is the “determination of remaining usable
life and the quantitative prediction (i.e., prognosis) of future operating capability.” This would mitigate the “fear
of failure” in the war theater and give commanders the “ability to adaptively manage and deploy combat systems
that might otherwise be removed from service.”31 In simple cost terms, extending the service life of a component
with a conservative 6-year life by 2 years reduces the cost of that component by 25 percent. There are also signifi -
cant operational benefits. A good example of this is the (now-canceled) Future Combat System (FCS) program. 32
Here the requirements for reliability and operational availability were to be met by employing a prognostics-based
approach to maintenance, allowing decisions to be made to replace critical parts vulnerable to failure just before
they fail or before an upcoming mission. Such condition-based maintenance (CBM) approaches are becoming
more widespread within U.S. industry and the U.S. military.
“A complete CBM system requires the integration of a variety of hardware and software components,” 33 as
demonstrated by an ongoing project titled “Light Amphibious Vehicles—Sense and Respond Logistics Phase I,
II, III, IV,” organized by the National Center for Manufacturing Sciences under its Commercial Technologies for
Maintenance Activities.34 The platform itself, with monitoring and communications equipment onboard, senses
vehicle health information and alerts the crew to vehicle status. The data are shared wirelessly with operations
in the immediate vicinity. Remote technicians can then provide real-time guidance to on-site personnel about
maintenance decisions.
The initial phases of this project have demonstrated that early warning has reduced maintenance cycle time by
approximately 50 percent and increased fleet-wide operational availability by 7 percent. Maintenance cost avoid -
ance exceeded $22 per mile based on overall preventive maintenance monitoring, and the vehicles are expected to
see an overall 14 percent increase in mean time between failure. These improvements should continue to increase
as further testing and optimization proceed.
5.6 AVAILABILITY OF LIGHTWEIGHTING MATERIALS
As noted in Chapter 1, two cornerstones of lightweighting are (1) low- or reduced-density, high-specific-
performance35 alloys, and (2) fiber-reinforced composite materials. A summary of the most important of these
materials and their current status is provided in Table 5-3, which also includes high-strength steels, because even
modest improvements in steel strength can have a large impact due to the large amounts of steel used in military
vehicles. Some alloys, such as those based on aluminum, are readily available. They are used widely in industry
in sufficiently large volumes to support the operations of multiple suppliers.
Magnesium is a structural metal used only in low volumes because conventional processing of magnesium
sheet is expensive and limited in availability and industrial capacity. Magnesium alloys, and components based
on wrought magnesium, have not found widespread commercial or military use. Consequently, neither the United
States nor Europe currently has adequate capabilities for producing these alloys or manufacturing magnesium
components on a large scale. Domestic production capabilities that had previously been established have been
31 This section is drawn from information at http://www.acq.osd.mil/log/mpp/cbm+_related_links.html.
32 The Future Combat Systems program was the Army’s principal modernization program. U.S. Defense Secretary Robert Gates announced
in April 2009 that he was killing the vehicle portion of the Army’s $160 billion Future Combat Systems. FCS was originally envisioned as “a
program that would create a group of brand-new super-brigades and outfit them with next-generation, hyper-connected vehicles and gear.” See
Kris Osborn, 2009, “FCS Is Dead; Programs Live On: U.S. Army to Dissolve Flagship Acquisition Effort,” Defense News, May 18, available
at http://www.defensenews.com/story.php?i=4094484.
33 See http://www.acq.osd.mil/log/mpp/cbm+_related_links.html.
34 “CTMA is a collaboration between the National Center for Manufacturing Sciences (NCMS), its member companies, and the DoD.
Under a historic Cooperative Agreement between NMCS and OSD (L&MR) MPPR, NMCS and its member companies co-sponsor technol -
ogy development, deployment, and verification with DoD organic maintenance activities.” Excerpted from http://www.acq.osd.mil/log/mpp/
cbm+_related_links.html. See that website for more information.
35 Specific performance (e.g., strength) is performance divided by density.
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124 APPLICATION OF LIGHTWEIGHTING TECHNOLOGY TO MILITARY AIRCRAFT, VESSELS, AND VEHICLES
TABLE 5-3 Current Status of Lightweight-Enabling Structural Materials
Manufacturing
Material Applications Material Availability Capability Cost
Magnesium Thick sections for Limited domestic Manufacturing High compared with
armor supply capability for thick aluminum
sections is lacking
Titanium Structures, armor, Adequate Inability to join thick Very high compared with
seawater systems sections steel, aluminum, and
magnesium
Organic matrix Ship superstructures Some limitation on Limited domestic Competitive
composites Airframes and aero- fibers, especially capability for large-
engines domestically sections fabrication
Land vehicle structure Lack of repair/joining
Peripherals to metal structure
Ceramic matrix Aircraft engines Very limited domestic Limited sources Extremely high
composites High-temperature sources of fibers, Manufacturing
structures low capacity technology not
(predominantly mature
Japanese)
Metal matrix Aircraft, engine Limited sources for Very limited sources Very high compared with
composites: (a) Fiber structure fiber-reinforced and technologies base metal alloys
reinforced Ship superstructure metal matrix
composites (MMCs)
Metal matrix Land vehicle structure, Limited sources for Limited sources and High compared with base
composites: (b) peripherals wrought MMCs technologies metal alloys
Particulate reinforced
Laminated ceramic Transparent armor Extremely limited Laboratory-level Extremely high
structures (laboratory-level capability
only)
High-strength steels Lightweight High High Low
automotive
structures
discontinued or the companies have gone out of business. This contraction in capability is due in large part to
the excess production of magnesium in China and Russia during the 1980s and 1990s, the “dumping” of excess
magnesium into U.S. markets, and the resulting global price reductions. 36
Nevertheless, there have been some encouraging developments recently in processing for improvements in
strength and toughness, making these materials even more competitive with aluminum and steel. For example,
Nanomag TTMP—a processing innovation that is eco-friendly and produces ultra-fine-grain magnesium sheet—
has led to significant improvements in strength and toughness, making these materials even more competitive
with aluminum and steel.37 In addition, there have been developments in equal channel angular processing that
36 G.J.Simandl, M. Irvine, and J. Simandl. 2007. “Primary Magnesium Industry at a Crossroads?” Light Metal Age, April, pp. 32-35.
37 Nanomag TTMP is a new technology developed by Thixomat, Inc., and the University of Michigan for injection molding of magnesium
sheet forms. See J. Huang, T. Arbel, L. Ligeski, J McCaffrey, S. Kulkarni, J. Jones, T. Pollock, R. Decker, and S. LeBeau, 2010, in Magnesium
Technology, Warrendale, Pa: TMS; and R. Decker, J. Huang, S. Kukarni, and J. Jones, 2010, in Materials Science Forum, Vol. 654-656, pp.
574-579.
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CROSS-CUTTING ISSUES AND CHALLENGES
have demonstrated dramatic improvements in ductility.38 Also, some new alloys have been developed that have
very high strengths.39
Titanium alloys have long been used in aircraft and propulsion structures. They exhibit superior specific
strength and elevated temperature capability relative to steels, without compromising specific stiffness. Titanium
alloys are readily formable into sheet and bar forms and can be forged at elevated temperatures. However, for
aerospace grades, the cost of titanium alloy is typically several times that of steel or aluminum alloys. A 2001
assessment revealed, “Just accounting for the extraction and processing costs to produce ingot, titanium is ~30
times more expensive per pound than steel and ~6 times that of aluminum. The cost gap for titanium widens when
fabricating components and structures.” 40 The extensive use of titanium in aerospace vehicles is testament to the
cost premium on lightweighting that the industry can bear. Although significant weight benefits could be achieved
through the use of titanium alloys in land vehicles and ships, their high cost and a somewhat limited production
capability severely restrict their use in these areas.
Carbon fibers have been used extensively as reinforcements in polymer matrix composites. These fibers have
been central to the development of composite airframes for the Boeing 787 and Airbus 380 aircraft. Nonethe -
less, there are now fewer suppliers of carbon fiber than there were a decade ago. In addition, there are few fiber
manufacturers today making the high-modulus and ultra-high-modulus fibers that will likely be in greatest demand
in future DoD programs. Furthermore, there is not much spare fiber production capacity. The latter deficiency
was made clear, for instance, in the worldwide shortage of carbon fiber that followed large-scale efforts in Japan
to seismically retrofit all bridge and elevated roadway supports with wound carbon fiber braces, 41 following the
Hyogoken-Nambu earthquake in 1995. The availability and sourcing of high-performance carbon fibers has been
a long-term concern for the DoD; the National Defense Authorization Act has, on two occasions (2001 and 2005),
directed the Secretary of Defense to prepare an assessment for the Committees on Armed Services of both the
House and the Senate.42
The limited availability of high-temperature silicon carbide fibers presents a more dire problem. These are
being investigated primarily as reinforcements in ceramic matrix composites for aircraft engines and future high-
performance military applications such as rocket nozzles and scramjets. The available volume of these composites
is currently small, and there is no large-scale manufacturer of these fibers outside Japan. The maximum tempera -
ture capabilities of these silicon carbide fibers are also limited (to about 1300-1400°C, depending on service life).
Continued and sustained development of new fibers will be necessary to reach the targeted temperature capabilities
(above 1500°C).
Polycrystalline oxide fibers, based on sol-gel derived alumina and mullite, have been developed by 3M Com -
pany under joint funding with DARPA for use in high-temperature ceramic composites. Although the temperature
capabilities (1100-1200°C) of current state-of-the-art oxide fibers are well below the target, these fibers have found
commercial application as reinforcements for aluminum alloy cables for power transmission, displacing steel-core,
aluminum-braided power cables.
The availability of polymer-based fibers used in armor, such as Kevlar, is of less concern. Kevlar is very widely
used in a variety of commercial applications that do not depend on DoD support. Furthermore, the manufacturer
(DuPont) is an exceptionally large, domestic company. Another fiber—based on highly oriented, high-molecular-
weight polyethylene and sold under the trade names Dyneema (DSM) and Spectra (Honeywell)—exhibits very
low density (less than 1 g/cm3) and exceptional strain-to-failure, or percent elongation before breaking (2.9 to 3.5
38 W. Kim, C. An, Y. Kim, and S. Hong, 2002, Scripta Materialia, Vol. 47, pp. 39-44; Y. Yoshida, K. Arai, S. Itoh, S. Kamado, and Y. Kojima,
2005, Science and Technology of Advanced Materials, Vol. 6, pp. 185-194; and T. Mukai, M. Yamanoi, H. Watanabe, and K. Higashi, 2001,
Scripta Materialia, Vol. 45, pp. 89-94.
39 K.Y. Zheng, J. Dong, X.Q. Zeng, and W.J. Ding, 2008, Materials Science and Engineering A, Vol. 489, p. 103; B. Smola, I. Stulíkova, F.
von Buch, and B.L. Mordike, 2002, Materials Science and Engineering A, Vol. 324, p. 113; and S.M. He, X.Q. Zeng, L.M. Peng, X. Gao, J.F.
Nie, and W.J. Ding, 2007, Journal of Alloys and Compounds, Vol. 427, p. 316.
40 B. Hurless and F.S. Froes. 2002. “Lowering the Cost of Titanium.” AMPTIAC Quarterly, Vol. 6, No. 2. Available at http://ammtiac.alion -
science.com/pdf/AMPQ6_2ART01.pdf. Last accessed June 21, 2011.
41 T. Ogaata and K. Osada. 2000. “Seismic Retrofitting of Express Bridges in Japan.” Cement and Concrete Composites, Vol. 22, pp. 17-27.
42 “Polyacrylonitrile (PAN) Carbon Fibers Industrial Capability Assessment, OUSD (AT&L) Industrial Policy,” October 2005. Available at
http://www.acq.osd.mil/ip/docs/pan_carbon_fiber_report_to_congress_10-2005.pdf.
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126 APPLICATION OF LIGHTWEIGHTING TECHNOLOGY TO MILITARY AIRCRAFT, VESSELS, AND VEHICLES
percent).43,44,45 This fiber shows considerable promise for composites in armor systems. Yet the full potential of
these fibers has yet to be realized in commercial products. Theoretical considerations and laboratory-scale dem -
onstrations indicate that strength elevations of more than 50 percent could be achieved in the next generation of
commercial fibers. This goal will require a robust research effort and sustained resources to bring it to fruition. See
Section 5.3.3 for an example of the challenges involved in modeling the behavior of polymer composite materials.
Finally, although high-strength steels may not immediately be recognized as materials for lightweighting, the
design of new steel compositions with even modest strength improvements (10 to 20 percent), combined with design
optimization and manufacturing innovations, can have significant impact in creating lighter structures. The benefits
are derived in part because of the large use of steels in military vehicles. However, the lack of availability of new
steels and of large-scale production remains an impediment to their wider use in military vehicles and components.
5.6.1 Design Expertise in the Process Industry Sectors
From 1998 to 2008, the U.S. Department of Energy’s Office of Industrial Technologies (renamed the Industrial
Technologies Program, ITP) partnered with trade organizations representing the nine energy-intensive industries
on which the branch has focused its R&D portfolio in order to identify common needs, concerns, and visions for
long-term investment and partnering:46 Elaborate roadmaps for new technology development were created with
each of the nine industry groups, of which the five groups relevant for the current NRC lightweighting study are
aluminum, glass, steel, metal casting, and chemicals. These roadmaps identified near-, mid-, and long-term R&D
priorities, performance targets, and programs to advance the state of these “industries of the future” with the aim
of strengthening U.S. capabilities and efficiencies in the supply of these base materials to domestic manufacturers.
Each roadmap generated grand challenges that have resulted in numerous internal R&D and cross-industry
collaborations involving leading material suppliers, which in turn generated a great deal of material and design
knowledge that is in the private and public domains. The respective trade associations—e.g., the Aluminum Asso -
ciation, Steel Industry Market Development Institute, Glass Manufacturers Association, and American Chemical
Society—have archived and disseminated much of the information through project reports. Such vital information
can be drawn upon by military manufacturers to initiate new R&D in design, manufacturing, and demonstration
of system-level lightweighting solutions. Examples of high-priority material and processing research include: 47
• Computer design tools;
• High-temperature materials, including refractories;
• Casting, advanced forming, and tool and die materials;
• Databases and process modeling;
• Joining and welding;
• Coating properties, processing, and applications;
• Mold and die filling;
• Ceramic and composite reliability and performance data;
• Erosion- and corrosion-resistant materials and coatings;
• Materials for sensors; and
• Separation methods, recycling, waste, and by-product treatment.
43 Keith McDaniels, R.J. Downs, Heiner Meldner, Cameron Beach, and Chris Adams. 2009. “High Strength-to-Weight Ratio Non-
Woven Technical Fabrics for Aerospace Applications.” Cubic Tech Corporation, Mesa, Ariz. Available at http://www.cubictechnology.com/
Technical%20Fabrics%20for%20Aerospace%20Applications.pdf.
44 “A Constitutive Model for DYNEEMA UD Composites,” available at http://www.iccm-central.org/Proceedings/ICCM17proceedings/
Themes/Materials/HIGH%20PERFORMANCE%20FIBRES/D6.9%20Iannucci.pdf. Accessed October 21, 2011.
45 Honeywell Spectra Fiber 1000 Product Information Sheet. Available at http://www51.honeywell.com/sm/afc/common/documents/PP_
AFC_Honeywell_spectra_fiber_1000_Product_information_sheet.pdf.
46 DOE-EERE, OIT, 2000, Program Plan for Fiscal Years 2000 Through 2004, Industrial Materials of the Future , July; NRC, 2000, Mate-
rials Technologies for the Process Industries of the Future: Management Strategies & Research Opportunities , Washington, D.C.: National
Academy Press.
47 Richard Silberglitt and Jonathan Mitchell. 2001. Industrial Materials of the Future (IMF) R&D Priorities. Rand Corporation study for NREL.
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127
CROSS-CUTTING ISSUES AND CHALLENGES
5.7 CONCLUSION
Despite the seemingly disparate considerations in lightweighting of the full spectrum of military vehicles,
important commonalties are evident. Future policies and investment strategies that are founded in these commonal -
ties should yield the greatest impact on lightweighting of future military vehicles.
Furthermore, with the enormous magnitude of military operations and associated costs, such strategies are
expected to have a broad impact on national concerns that extend beyond the military: notably, the sustainability
of fossil fuel use at present levels, the balance of trade, and domestic employment opportunities.
