Use of Lightweight Materials in 21st Century Army Trucks (2003) / Chapter Skim
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2. New Materials and Processing Opportunities
2. New Materials and Processing Opportunities
Pages 27-54
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From page 27... ...
The structural elements of a truck are divided into the following three categories: · Frame: The primary structural element in all current military trucks is a steel frame that runs the length of the vehicle; the engine, drivetrain, suspension, and truck bed are all attached to the frame; · Secondary structural elements: The secondary structural elements are the parts of the truck that carry passengers and cargo—for example, the cab and the cargo bed. Although these elements may account for a significant portion of the vehicle's weight, they do not provide the essential strength or stiffness of the truck; and Structural drivetrain: This category includes driveshafts, the suspension, the steering mechanism, and braking components.
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From page 28... ...
Such an instance might involve the use of a modestly different architecture or different joining methods. For example, the replacement of a truck's steel frame rails with hydroformed tubes would require changes in several other design aspects and would thereby open up opportunities for materials substitutions.
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From page 29... ...
The design of Army trucks should include a minimum-weight study as the final step in the design process. As is often done with commercial vehicles, a minimum-weight, optimal-shape design study should be performed on a vehicle after the preliminary designs, including the selection of lightweight materials, are complete.
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From page 30... ...
Sand, lost wax, and lost foam castings can be done by hand at low fixed tooling costs. These processes are amenable to the low production volumes commonly associated with military tactical trucks.
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From page 31... ...
Low production volumes can enable the use of more expensive materials provided that tooling and fabrication costs are minimized. For example, for Freightliner trucks and Panoz roadsters, the use of superplastic aluminum alloys is favored over the less expensive (and higher strength)
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From page 32... ...
The insertion of composite materials into Army vehicles must therefore be accompanied by new repair manuals and the training of Army personnel in these new procedures. Careful handling and storage of composites is also necessary, because their properties are sensitive to the presence of surface flaws.
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From page 33... ...
Under these constraints, the approach pioneered by Ashby and described above in the subsection "Component Shape" can be used to identify appropriate materials options.6 The basis of the Ashby materials selection process is the use of quantitative performance indices, or mathematical functions of service requirements, geometric parameters, and materials properties. The higher the performance index, the better suited a material is for a particular job, with the part weight needed to reach a given level of performance typically inversely related to its performance index.
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From page 34... ...
failure by elastic buckling or plastic compression; collapse load and length specified, section area free Plate loaded externally or by self weight in bending; stiffness, length, width specified, thickness free Plate loaded in-plane; failure by elastic buckling or plastic compression; collapse load, length and width specified, thickness free Rotating disks, flywheels energy storage specified Cylinder with internal pressure elastic distortion, pressure and radius specified; wall thickness free Spherical shell with internal pressure elastic distortion, pressure and radius specified, wall thickness free E/p of/p G~2/p of2/3/p EY2/p o~/3/p E~2/P or/P El/3/p C74/2/p E1/3/P of/p of/p E/p ot/P E/(1 - v) p ot/P NOTES: To minimize cost, use the above criteria for minimum weight, replacing density p by Cp, where C is the cost per kilogram.
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From page 35... ...
load, length specified, section area free Torsion bar or tube torque, length specified, section area free Beam loaded externally or by self-weight in bending; stiffness, length specified, section area free Column (compression strut) failure by elastic buckling or plastic compression; collapse load and length specified, section area free Plate loaded externally or by self weight in bending; stiffness, length, width specified, thickness free Plate loaded in-plane in tension; collapse load, length and width specified, thickness free Rotating disks, flywheels energy storage specified Cylinder with internal pressure elastic distortion, pressure and radius specified; wall thickness free Spherical shell with internal pressure elastic distortion, pressure and radius specified, wall thickness free Kl~P KIC,4/3/p KIC 2,3yp KIC2/3/P K,C,4/5/p K,C,4/5/p K,c2/3/P KIct4/5/p K,C.~2/P KIC 2,3yp KI>P KIC2/P K,,ip KIDNAP K,,:/p K1c2/p Kic /(l-vJp K~c2/(l-v~p NOTES: To minimize cost, use the above criteria for minimum weight, replacing density p by Cp, where C is the cost per kilogram.
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From page 36... ...
To minimize energy content, use the above criteria for minimum weight, replacing density p by q p where q is the energy content per kilogram. KEY: E = Young's modulus; of = failure strength; p = density; r1 = loss coefficient.
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From page 37... ...
In addition, stress corrosion cracking caused by the presence of in-service residual stresses has limited the use of magnesium alloys in commercial vehicle applications. However, potential applications in the near future include castings for transmission casings or transfer cases, and magnesium 37
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From page 38... ...
Significant advances have been made in the development of superplastic aluminum alloys and superplastic forming of automotive structures in compositions near alloy 5083.9 in Superplastic aluminum sheet 7Body-in-white (BIW) refers to all body structural components, the roof panel, and subframes, but not the closure panels.
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From page 39... ...
For both truck cabs and cargo beds, aluminum's resistance to normal atmospheric corrosion can provide significant life-cycle cost savings in terms of corrosion prevention and repair. However, good engineering design must be exercised to avoid galvanic couple effects, which could produce significant corrosion problems.
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From page 40... ...
and innovative manufacturing processes (such as tailor welded blanks and hydroformed tube structures and roof panels) to reduce the average thickness of steel sheet used for a typical automobile body.
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From page 41... ...
Corrosion resistance must therefore be considered in any materials selection process for Army trucks. Other Commercially Available Technologies Metal Matrix Composite Brake Rotors and Drums Brake rotors and drums are generally made from cast iron, but recent research has focused on the use of lighter-weight, aluminum-based metal matrix composites and ceramics for braking surfaces.
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From page 42... ...
It might be possible to use higher-strength aluminum alloys to manufacture larger-diameter aluminum driveshafts for use in military trucks. Such aluminum driveshafts could result in a net weight savings.
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From page 43... ...
Selective use of advanced, commercially viable materials such as aluminum, magnesium, MMCs, and polymer matrix composites (PMCs) could be advantageous in the medium term.
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From page 44... ...
In the commercial automotive and truck industries, there has been a proliferation of a wide variety of high-strength martensitic steel alloys and fabrication methods that are strong candidates for application in future Army trucks. Through the use of dual-phase steel alloys (such as DP600 for frame rails, cross members, suspension components, and wheels)
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From page 45... ...
A pee rlitic UHCS can lead to higher wire strengths than those of conventional eutectoid composition steels.~9 Aluminum Alloys Aluminum offers the greatest potential for weight reduction in truck bodies, but it also requires the use of different construction techniques. Aluminum space frames have been the subject of much research and development in the past decade, owing to the need to improve strain rate sensitivity (i.e., crash performance)
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From page 46... ...
Specific improvements in aluminum fabrication technology and cost reduction that would accelerate the medium-term use of aluminum alloys in future Army trucks include the following: . Reduction in sheet raw material prices (e.g., by way of continuous casting)
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From page 47... ...
Provided that significant improvements can be achieved in feedstock quality, die-casting processing and handling, cost reduction, and structural quality, die-cast and wrought magnesium alloys (e.g., ZK60 and AZ31) have a number of potential component applications in military trucks, including the following: · Body and closure components for door and hood inner panels, support modules, A and B pillars, and roof-opening panels; · Powertrain components for transmission, transfer case and cover, and engine block (brackets, mountings, housings, oil pan, covers)
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From page 48... ...
Early commercial successes include the castable-aluminum MMCs, marketed under the trade name of Duralcan, using SiC particulate reinforcement, and wrought products that use alumina (Altos) particulate reinforcement.
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From page 49... ...
Processing and machinability data, for example, could be made available to everyone. Polymer Matrix Composites Polymer matrix composites with fiberglass or carbon filaments have already been demonstrated and applied in limited production volumes on Army trucks.
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From page 50... ...
Newer, more recyclable engineering and structural thermoplastic resins, such as cyclic thermoplastic polyesters, are strong candidates for component applications in the medium to long term. The Army should leverage the experience of the commercial automotive industry and other military services in the development, application, and demonstration of PMC and lightweight armor materials.
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From page 51... ...
efforts are under way at suppliers such as Oshkosh Truck Corporation and Stewart and Stevenson and at other Army research facilities. LONG-TERM OPPORTUNITIES Long~term opportunities are defined at the beginning of this chapter as those that would result from changes in the basic truck paradigm and would thereby enable the use of radically different materials.
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From page 52... ...
The use of titanium alloys has been limited by their high cost relative to that of steels and aluminum alloys, the high rate of waste in production, and difficulty in machining and welding. Recent developments in processing technologies, such as single-melt cold hearth electron beam melting and plasma-arc melting, however, have reduced the cost of titanium feedstock significantly.
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From page 53... ...
The anticipated future growth of MMC components and less harsh operating environments are expected to result in the greater use of sensors integrated in vehicle components to serve this function. Combined with these advances, there is a need to bring Army depots abreast of new maintenance technologies (NDE, repair, and manufacturing)
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