L-218 Material Selection And Property-Processing Implications In Additive Manufactured Materials For Munitions

February 2020
Wade Babcock
Additive manufacturing (also referred to as AM) offers many opportunities in the munition design space to tailor bulk properties, such as spatially-variant composition, density, etc., with intent to subsequently affect macro behavior through changes in stress/strain profiles, variable burn rate, fracture progression, and other parameters.
 
With the introduction of any novel processing and manufacturing technology, new and very different material properties, flaws, and defects are also introduced. Historically this was seen with the introduction of welding in the early 20th century (heat affected zones, inclusions) that drastically changed the science of fracture and fatigue, as well as the introduction of lamellar and fiberreinforced composites 50 years later that created entirely new fracture, fatigue, creep, and crackgrowth
phenomenologies. The advent of microelectronics expanded materials science into new realms with layered micro- and nano-metallic films, deposition techniques, and incorporation of metals, semiconductors, and plastics, and introduced even more material failure, flaws, and defect creation.
 
The Munitions Safety Information Analysis Center (MSIAC, a North Atlantic Treaty Organization multi-national project office) provides a review of the types of materials currently being used in AM, the resultant material properties achieved, and the main issues that will face munitions science in utilizing these AM-created materials. This report describes the key issues, compares the materials possible, and provides assistance for practitioners who plan to employ AM in munitions. Published reports have already illustrated novel pin-cushion shaped flaws in AM metals and plastics that will significantly impact the ease of crack formation and propagation, independent of the material’s stress intensity factor (Kic). Additionally, many AM processes appear highly prone to creation of micro and macro-voids during material build-up dependent on rate of travel/deposition, input heat intensity, etc. This could be particularly deleterious to bulk sensitivity when used to create energetic materials.

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