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 engineers 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 implementation 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.
5 Bill Sweetman. 2011. “F-35B Put on Probation; New Bomber to Go.” Aviation Week, January 7.