VTechWorks staff will be away for the winter holidays starting Tuesday, December 24, 2024, through Wednesday, January 1, 2025, and will not be replying to requests during this time. Thank you for your patience, and happy holidays!

Browsing by Author "Morris, Brenton Alexander"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Thermomechanical Modeling of Oxidation Effects in Porous Ultra-High Temperature Ceramics
    Morris, Brenton Alexander (Virginia Tech, 2021-06-23)
    The effects of oxidation in the thermomechanical response of porous titanium diboride have been investigated. An in-house quasi-static material point method tool was used to perform two -dimensional plane strain simulations on unoxidized hexagonal representative volume elements (RVEs) with macroporosity volume fractions of 10%, 40% and 70% to establish a baseline for the response due to geometric effects. Compressive strains of up to 30% were applied at room temperature. The 10% and 40% RVEs showed shear banding and subsequent shear failure of the inter-pore struts, while shear banding in 70% RVE weakened the struts, which lead to buckling failure. A snapshot oxidation model was then applied to the hexagonal RVEs in place of a transient, diffusion-based oxidation solver. Compressive strain simulations were performed on RVEs with oxide layers ranging from 5 to 50 μm. In RVEs with porosity of 40% or higher, oxide percolation in the struts reduced the effective elastic modulus and compressive strength, though further oxidation beyond the percolation point did not have a significant impact. Ramped and cyclic thermal loads were applied and the damage due to thermal expansion coefficient mismatch at the oxide-substrate interface decreased as the oxide layer was increased. Finally, the snapshot oxidation modeling approach was applied to large porous RVEs derived from micro-computed tomography images of titanium diboride foam. The effective elastic modulus decreased by 47% when the 5 μm layer was applied due to many thin, flexible struts becoming fully oxidized. Subsequent oxidation did not have a significant impact on the thermomechanical response.