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3 Lightweighting Maritime Vehicles
Pages 61-84

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From page 61...
... For example, see Sections 3.5.3 Marine Corps Expeditionary Fighting Vehicle and 3.5.4 High-Strength Steel in Aircraft Carriers.
From page 62...
... Current and planned Department of Defense (DoD) maritime assets include a number of platforms that could be improved with lightweight structural materials.
From page 63...
... DoD maritime platforms typically occurs at the design stage, because it is very difficult to retrofit large structural elements on complex ships. In particular, materials dramatically influence all aspects of a ship's life cycle, and so the selection of materials for lightweighting ships must come early in the design process.
From page 64...
... The design process begins with a detailed understanding of the loads that the ship will experience over its lifetime and how the structure will respond to those loads. A fairly good understanding of how mild steel ship structures perform in the ocean exists, but novel materials generally require larger design safety factors because of the more limited knowledge base on their performance.
From page 65...
... ; and • Avoid galvanic corrosion by isolating aluminum from steel. In a presentation to the committee, Robert Sielski outlined the following research needs required to advance aluminum ship construction: material property and behavior; structural design; structural details; welding and fabrication; joining aluminum to steel; residual stresses and distortion; fatigue design and analysis; fire protection; vibration; performance metrics, reliability, and risk assessment; maintenance and repair; structural health monitor ing; and emerging technologies.10,11 The largest identified knowledge gap is in the area of fatigue properties and fracture toughness, particularly dynamic fracture toughness.12 As shown in Figure 3-2, technological advances that reduce fatigue crack growth are needed to promote greater use of aluminum hulls for lightweighting.
From page 66...
... Material Availability Large ships use a massive quantity of structural material and can affect market availability of precursor and finished materials. This is especially true when novel, high-performance materials are used, such as the T700 carbon fiber for the DDG 1000 deckhouse.
From page 67...
... Development of new recycling technologies is expected as wind turbine blades that were designed to last for 20 years reach the ends of their life spans. 3.2.3 High-Strength Steel High-strength steel plate constitutes increasing portions of the hull structure in modern warships, surface combatants, and submarines for weight reduction, better stability, increased payload, increased mobility, and survivability.
From page 68...
... 2003. "Residual Stresses and Distortions in Lightweight Ship Panel Structures." Northrop Grumman Ship bitmap Systems, Technology Review Journal, Vol.
From page 69...
... Parasitic weight is added to hull structures in order to achieve thermal insulation, structural fire protection, and corrosion and bio fouling resistance. Developing material systems that incorporate all these functions will not only lightweight the ship but also decrease required manufacturing and maintenance labor.
From page 70...
... Use of composites will allow the Navy to reduce topside weight, platform signature and to integrate apertures into the structure. 21 According to Barry Heaps, Northrop Grumman Shipbuilding program manager/director DDG-1000 Deckhouse, carbon fiber was used instead of E-glass because "the structural load requirements for the .
From page 71...
... 3.3.4 Outfitting Reducing the weight of DoD maritime platforms by lightweighting outfitting elements is generally beyond the scope of this report but it is instructive to look at opportunities as part of the overall ship design process. Composites have been used for piping, pump housings, ventilation ducts, ladders, gratings, electrical enclosures, shafts, and foundations.
From page 72...
... Aluminum ship construction costs are being driven down by the greater use of specialty extrusions, such as stiffened panels and weld joint products shown in Figure 3-7. The Navy Metalworking Center reports that the Lockheed Martin Team Littoral Combat Ship design makes extensive use of stiffened aluminum panels for construction of the ship's superstructure.
From page 73...
... Indeed the initial Littoral Combat Ship incurred cost overruns by both vendors due to failures to effectively use earned value management procedures required of major defense contractors. 28 Warships typically have more significant outfitting requirements than commercial vessels of the same tonnage, which increases cost and management complexity.
From page 74...
... Many high-speed ship designs rely on complex hull structures that are not readily available for struc tural inspection, such as catamaran and surface effect ship hulls. Visual inspection is further hampered by thermal insulation or structural fire protection that covers hull plating and internal framing.
From page 75...
... Thus, new materials are introduced via a cautious and time-consuming process, which accounts for the Navy's excellent safety record but is a deterrent to introducing new materials for lightweighting. Two Designs -- Aluminum and High-Strength Steel -- for Littoral Combat Ships 35 3.5.2 The Navy started the Littoral Combat Ship (LCS)
From page 76...
... If the Navy's follows its 30-year shipbuilding plan for 55 sea-frames and 64 mission packages, the LCS would be one-sixth of the Navy's total fleet. Because of the likelihood of cost-effective upgrades to replace mission modules, the platform -- which is not easily upgraded -- assumes greater prominence as a determinant of life-cycle costs and vessel retirement.38 3.5.3 Lightweighting the Marine Corps Expeditionary Fighting Vehicle While Maintaining Survivability Figure 3-9 shows the expeditionary fighting vehi cle (EFV)
From page 77...
... . SOURCE: CAPT Mike Good, Program Manager LCS Mission Modules, "Littoral Combat Ship (LCS)
From page 78...
... 45 Participants: PEO Aircraft Carriers; Naval Surface Warfare Center, Carderock Division; Naval Sea Systems Command; Northrop Grum man Shipbuilding-Newport News; Navy Metalworking Center; Arcelor-Mittal Steel; DDL Omni Engineering; Puget Sound Naval Shipyard; and Navy Joining Center.
From page 79...
... The project focused on developing lightweight The accomplishment of the LASS project in fire protection and lightweight deckhouses, among fire protection systems for aluminum and composite others, reflects a conscientious effort by Scanconstruction. "Typical weight reduction when using dinavian countries to address the technological aluminum or FRP composites have been over 50 per challenges and develop commercial opportunicent compared to a conventional steel design, and cost ties for their lightweight, composite shipbuilding analysis has demonstrated possible payback times of 5 expertise.
From page 80...
... A lack of robust design tools acquisition process, Halter Marine delivered its first for the redesign limited the lightweighting potential Mark V 18 months later, and all 20 were delivered of carbon fiber construction.
From page 81...
... The lack of robust design tools posed a challenge, which was met in part by AEWC's development of a method for testing wave impact on alternative structures and laminates. According to Maine Marine Manufacturing's president and CEO, David Packhem Jr., the carbon fiber/epoxy resin/foam core Mark V "is actually 50 percent stronger and slightly lighter than its aluminum predecessor, and we expect that Navy testing will confirm that we've been able to reduce transmission of slamming loads."52 The composite Mark V is shown in Figure 3-12.
From page 82...
... Meloling, Figure 3-14.eps "Advanced Enclosed Mast/Sensor (AEM/S) System," SSC San Diego Biennial Review, August 2001.
From page 83...
... At present, cost and survivability are the overriding factors constraining further use of lightweight materials on military maritime platforms. The committee reached the following conclusions about lightweighting maritime platforms: • The impetus for lightweighting smaller ships and boats is either to meet speed targets or to meet an imposed transportability requirement.
From page 84...
... 84 APPLICATION OF LIGHTWEIGHTING TECHNOLOGY TO MILITARY AIRCRAFT, VESSELS, AND VEHICLES • Perceived combat threats and their concomitant vessel requirements are constantly changing, which poses a challenge to a 10- to 20-year design cycle for new technology integration on ships that often are expected to last 40 years. • The design process for U.S.


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