Navy

Higher-impact shaped charges

Orientations in the microstructue of the shaped charge liner allow for tunability of the jet and better distribution of impact loads without adding mass or size

Military Technology

Marines use three M2A4 shaped charges to create holes for continued excavation. The liner is on the inside of the cone.

A shaped explosive charge is designed to focus the energy of the explosion to achieve more blasting, cutting, or excavating than could otherwise be done with bulk explosives alone. A shaped charge is usually cylindrical with a detonator at one end and a hollow cavity at the other. The cavity focuses gaseous detonation products resulting in an intense localized force known as a “jet”. The shaped charge cavity is lined with thin metal, glass, or ceramics and is referred to as the “liner”. Effectiveness of a shaped charge can be related to characteristics of the jet, as the jet works by pushing target material out of its way and forming an entry hole in the target. During the explosive event a generated shock front interacts with the liner under extreme temperature and pressure incorporating the liner material into the jet accelerating at 13,000 m/s. Thus, the liner material becomes the impactful force. The characteristics of the liner material are very important and microstructure – grain size and shape, distribution of inclusions, and crystal orientation – of the material is key.

Shaped charge performance is typically a function of jet length. Jet length is the stretch of elongated, coherent liner material flowing from a detonation of a shaped charge. Jet elongation is a function of the ability of the material to yield and demonstrate stable flow under high-strain rate. Leveraging this knowledge, Navy researchers have developed a method of forming a liner in which large and small grain microstructures can be oriented to optimise the force loading of the explosion. Liner material with large grains oriented at shallow angles to the direction of an oncoming shock front distribute the load away from the directly impacted surface area. Conversely, material with small grains oriented with essentially the opposite relative angles deform dramatically and locally at an impacted area. Without a pre-aligned structure, energy is lost. Liners constructed with heavy cold working in the direction of the liner contour will perform the most successfully and the Navy has patented this method.

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