Shock and Spall in the Low-alloy Steel AF9628

  • Christopher NeelEmail author
  • Sean Gibbons
  • Rachel Abrahams
  • Joel House
Research Paper


The shock and spall behavior of tempered AF9628, an ultra-high strength (UHSS) martensitic low-alloy carbon steel, is investigated using gun-driven, symmetric, planar impacts. The study utilized laser velocimetry to obtain transmitted wave velocity histories that were analyzed to obtain the Hugoniot Elastic Limit (HEL), the shock Hugoniot, and the spall strength. The work was limited to the stress range below 13 GPa (below the ε phase transition), and an HEL of 2.35 GPa and a spall strength of 6.8 GPa are reported. The HEL and spall strength of AF9628 are both above the typical values for inexpensive low-alloy steels, and only slightly below those for a much more expensive Aermet steel. The dynamic compressive yield strength (as calculated from the HEL) is only slightly higher than the quasi-static compressive yield strength when compared using a similar yield assignment convention, indicating a small, but positive, value of strain-rate sensitivity. The Hugoniot for AF9628, US = 0.67uP + 5.01 km/s, is in good agreement with other low-alloy martensitic steels for which data is available, and distinctly different than the Hugoniot for ferritic steels. The Hugoniot extrapolates to a bulk sound speed significantly higher than what is measured at ambient conditions, an incongruity that is unusual among metals and that the authors attribute to the unsteady nature of the shock waves generated in this work. Finally, it is suggested that there may be a relationship between dynamic compressive yield strength (calculated from the HEL) and dynamic tensile failure strength (the spall strength).


Steel AF9628 Shock Spall Hugoniot HEL bct Martensite 



The authors thank the gun team (Richard Davis, Adam White, and Jason Hipp) for careful execution of experiments, as well as Richard Harris and Captain Lawal Olawale for SEM and optical micrographs. Dr. Sarah Thomas, who provided data on 1018 steel, is also gratefully acknowledged.


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Copyright information

© This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply. 2019

Authors and Affiliations

  1. 1.Air Force Research Laboratory, Munitions DirectorateEglin AFBUSA

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