The bulk of morphing airframe technology research over the past several decades has been geared toward commercial and military aircraft and rotorcraft platforms, but implementation has proven difficult due to complicating factors such as scalability, repeatability, reliability, weight, and cost. This review report looks at these and other emerging technologies with respect to projectiles, where many of these factors are relaxed. Projectiles are distinct from other types of munitions such as missiles, rockets, and bombs due to their cylindrical initial body conditions, lack of onboard propulsion and therefore cruise velocity, relatively small size, relatively low cost, and the extreme shock event at gun launch. Despite these challenges, projectiles are single-use systems with short flight durations, which decreases the reliability and repeatability constraints that have limited the implementation of morphing concepts on full-scale aircraft. These characteristics make projectiles an ideal platform for emerging morphing concepts, especially when factoring in the desire for range extension, maneuverability, and mission flexibility. This report reviews previously implemented and emerging morphing strategies, including smart materials, morphology-dependent structures, and fluid-driven actuators such as shape memory alloys, piezoelectric actuators, macro-fiber composites, active polymers, compliant structures, periodic cellular structures, bistable composites, inflatable structures, pressurized artificial muscles, and soft actuators.
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