AFRL Enhances Miniature Fragmentation Warhead Design

  • Published
  • By Munitions Directorate
  • AFRL/MN
EGLIN AIR FORCE BASE, Fla. --  AFRL completed a computational analysis effort supporting the design and evaluation of a miniature fragmentation warhead intended to provide warfighters with a lethal and readily deployable weapon system. AFRL engineers first designed and tested the device, which comprises an array of small fragments launched by an explosive charge. They subsequently provided the computational simulations needed for interpreting test results and improving design characteristics. The analysis has tremendously impacted the warhead design effort, exposing the physics behind the experimental test results and providing a much clearer path towards optimizing the device.

The analysis involved a two-step approach: researchers employed the CTH shock physics code to identify the fragments' deformation mode and then used EPIC shock physics code to simulate the fragments' bulk motion during fly-out. The two-part analysis accurately identified the deformation mode of recovered precut fragments; it also exposed an error in the assumption of precut fragment orientation. The presumed orientation (a result of postmortem fragment inspection) implied that a terraced design was a worthwhile option and, further, that changes in stacking could alleviate shortcomings in pattern uniformity. 

However, because the analysis revealed the fragments' true deformation behavior, it became clear that abandoning the terraced design option in favor of a shoulder-to-shoulder stacking configuration was warranted. The team's analysis techniques effectively captured the two stages of fragment fly-out behavior, as follows: (1) the shock wave first causes each individual fragment to expand into any available void (as revealed by the CTH calculations), and (2) the next phase involves the bulk motion of fragment fly-out (as more accurately represented by the EPIC results). The same analysis also explained the mechanism causing the outer rows of fragments to fly well wide of the main pattern. Further computations showed the effects of curvature on fragment fly-out, and analysis of this additional data accurately predicted the problem related to this curvature--specifically, that fragment pattern uniformity decreases as fragment pack assembly curvature increases.