Hydrocode and microstructural analysis of explosively formed penetrators

Sridhar Pappu, University of Texas at El Paso

Abstract

Issues in simulation modeling, materials and high-energy explosives have been the three areas of research that have had the most impact on warhead technology. The present study focused on the materials issues and simulations and the relationship between the two in the case of Explosively Formed Penetrators (EFPs). ^ Tantalum (Ta), Armco iron (Fe) and oxygen-free high conductivity copper (OFHC Cu) EFPs were characterized using optical and transmission electron microscopy and microhardness testing, in order to understand the complex deformation mechanisms operating under the high strains (up to 300%) and high strain rates (of the order of 104 – 105 s–1 ) the EFPs are subjected to. Whereas dynamic recovery (DRV) was the dominant mechanism in Ta, Cu was characterized by complete dynamic recrystallization (DRX) and associated shear banding. Fe, on the other hand, showed features common to both Ta and Cu. It must be noted that Ta and Fe have a BCC crystal structure and Cu has a FCC crystal structure. Also, the melting point for Ta is 3020°C compared to 1539°C for Fe and 1083°C for Cu. Extensive twinning (Neumann banding) occurred in Fe on shock wave interaction with the liner. Subsequent deformation caused the twins to deform, stretch and fragment, akin to the shaped charge jet formation and fragmentation process. This process resulted in the formation of DRV and DRX structures and shear bands. This shows that twinning, DRV, DRX and shear band formation are mechanisms not quite independent of each other, at least in the EFP regime. ^ Validations of the AUTODYN-2D hydrocode were performed in the case of each material not only considering the geometrical factors (which is the general practice) but also using microstructures and microhardness data. Plastic strain and temperature contour plots were correlated with observed microstructures, and microhardness maps matched with computer generated yield stress plots. It was shown that although both the Zerilli-Armstrong and Johnson-Cook strength models predicted the final EFP shapes fairly well, they showed stark differences in the yield stress predictions. Whereas Zerilli-Armstrong model predictions were better for Ta and Johnson-Cook for Fe, both models were equally good for Cu. ^

Subject Area

Engineering, Metallurgy|Engineering, Materials Science

Recommended Citation

Pappu, Sridhar, "Hydrocode and microstructural analysis of explosively formed penetrators" (2000). ETD Collection for University of Texas, El Paso. AAI9997674.
http://digitalcommons.utep.edu/dissertations/AAI9997674

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