John Podhiny
Senior Research Engineer
Education
B.E., Mechanical Engineering, Villanova University, May 2000
M.E., Mechanical Engineering, Villanova University, December 2004
Experience
Mr. Podhiny joined MR&D in May of 1999 as a summer intern and accepted a position as a full-time engineer shortly after his graduation in May 2000. During his time at MR&D, he has worked on a variety of projects involving ceramic matrix composites (CMCs), carbon fiber composites, and oxide-oxide composites. These programs have involved advanced finite element modeling as well as calculation and correlation of composite material properties using fundamental micromechanics.
On his most recent program, a finite-element-based mathematical model was developed to predict the thermal response and structural performance of Space Shuttle leading edge damage that has been repaired using NOAX. Mr. Podhiny was responsible for writing the thermal and structural material subroutines, UMATHT and UMAT, that define the material behavior. The thermal subroutine calculates the effective thermal properties of NOAX based on phase fractions, defines any required heat source terms, calculates the mass loss of each phase based on equations derived from TGA testing, and updates phase fractions accordingly. The primary output of interest from the thermal analysis includes transient temperature distributions and phase fractions for the entire NOAX repair. These results are entered directly into the subsequent structural analyses, where UMAT is used to calculate effective elastic properties and strengths, perform a linear elastic thermal stress analysis, and provide failure predictions for all NOAX elements. Failed elements are then plotted visually for assessment. Current correlation results for six arcjet test specimens are promising in terms of both thermal results and failure predictions.
Another recent program involved the analysis and design ceramic matrix composite (CMC) wing leading edges cooled by embedded metallic heat pipes. The tasks under this program included extensive micromechanics calculations for the candidate CMC wing surface materials, as well as numerous trade studies to assess the effects of material choice and geometric parameters on the thermal and structural performance of the system.
Mr. Podhiny is currently working on an finite element based integrated durability model that will provide life and failure predictions of CMC components based on the surrounding environment. Factors such as temperature, partial pressure of oxygen, and time history of these quantities will all be included to provide an estimate on the usable life of the CMC component.