School of Materials Science and Engineering
Georgia Institute of Technology

Anthony Fredenburg

Anthony Fredenburg is currently in his fourth year at Georgia Tech in pursuit of a PhD in Materials Science and Engineering. Graduating from North Carolina State University with a Batchelor’s degree in 2005, he came to GT to study the dynamic compaction of energetic powder mixtures and their potential application to structural energetic materials. In addition to researching/studying at GT during the academic years, Anthony has spent his summers working at Sandia National Labs in Albuquerque, NM performing experimental and computational work on the dynamic compaction of aluminum powders to form lightweight-high strength bulk nanostructured materials.

In the area of energetic materials, Anthony is characterizing the dynamic response of Ta + Fe2O3 and Ta + Bi2O3 thermite mixtures for structural energetic material applications. Specifically, the relationships of interest are the stress-volume and shock velocity-particle velocity response of initially porous thermite mixtures with thrust to determine the crush strength, the stress at which near full densification occurs, and the threshold for reaction initiation of powder mixtures. Densification and reaction characterization is carried out using instrumented parallel plate impact experiments on the 80 mm bore diameter single-stage light gas gun, and Taylor tests coupled with high-speed digital imaging on the 7.62 mm bore diameter gas-gun. In addition to experimental work, continuum and discreet particle level simulations are used to further understand the transient mechanisms occurring during compaction that lead to densification and reaction.

At Sandia Anthony has been working on a three year LDRD project that explores the possibility of using cold spray, dynamic compaction, and direct extrusion to form fully nanocrystalline bulk materials for light-weight structural applications. Initially, his research focused on the compaction of three different morphology partially nanocrystalline Al 6061 T6 machining chips formed through a modulation assisted severe plastic deformation machining process. Discreet particle level simulations of the various morphology particles were carried out to determine the effect of particle shape on compaction, where shape effects were found to be more pronounced at lower compaction stresses. Subsequently, powders with fully nanocrystalline Al 6061 microstructures were successfully consolidated to near full density, with compacts showing an almost two-fold increase in hardness over course-grained Al 6061 T6.

Nanocrystalline Al 6061 Project

Figure 1.

Portions of experimental microstructures of Equiaxed, Needle, and Platelet morphology machining chip powders to be used for input into computer simulations to examine shape effect on compaction behavior.

Figure 2.

Image showing vorticity localized at particle surfaces near shock front (y = 0.06 cm) for compaction of equiaxed machining chip.

Figure 3.

Radial cross-section of one capsule and surrounding fixture used in 3-capsule recovery experiments for recovery of bulk nanocrystalline samples.

Figure 4.

Dynamically consolidated and recovered nanocrystalline aluminum 6061 sample.

Figure 5.

Microstructure of dynamically consolidated Al 6061 showing nanocrystalline structure of compact.

Structural Energetic materials Project

Figure 6.

Experimental setup showing side view and front view of instrumented parallel plate impact experiments for measuring dynamic response of powder mixtures.

Figure 7.

Dynamic response of equivolumetric mixture of Ta + Fe2O3 powder mixture initially compressed to ~50 % theoretical density.

Figure 8.

Input gauge response for shot 0814 showing experimental stress trace overlayed with stress trace from tracer particle in half-symmetry and 1D continuum simulations.