Theses and Dissertations



Whittington, Wilburn

Committee Member

Smith, Aaron

Committee Member

Hammi, Youssef

Committee Member

Rhee, Hongjoo

Date of Degree


Original embargo terms

Embargo 2 years

Document Type

Dissertation - Open Access


Mechanical Engineering

Degree Name

Doctor of Philosophy (Ph.D)


James Worth Bagley College of Engineering


Department of Mechanical Engineering


This work investigates the interactions between impact devices and material response in the realm of solid mechanics, utilizing explicit finite element analysis and experimental methods based on the split-hopkinson pressure bar. It focuses on understanding how tools like jackhammers use hammer strikes to generate pressure waves, then the wave is transferred through a chisel to materials such as rocks to cause fracture. The interaction between the wave and the rock is complex. Under dynamic loading the mechanical response of materials changes and significant losses occur due to reflections and inefficient pressure states. This research explores how chisel geometry can be optimized to control critical parameters influencing rock fracture, including stress state, pulse length, and peak pressure. The use of notches to influence the stress state, periodic boundaries to influence the pulse length and pressure amplification in tapers the increase the pressure showed an improvement in efficiency in jackhammers. Additionally, this work extends insights of the concept of pressure amplification in solids, to liquids inside tapered pipes, enhancing the understanding of phenomena like pulse pressure amplification in arteries and water hammer effects in piping systems. Two innovative contributions emerge from this work: a novel amplifier design for water cannons, improving these machines efficiency and showing promise for applications in water jet cutting and drilling, and a novel process for extruding nanocrystalline magnesium. This process leverages pressure amplification and impact-induced plastic shear deformations to refine crystal size, offering a new avenue for producing various nanocrystalline materials.

Available for download on Friday, May 15, 2026