Vargas-Martinez, Juan C.

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    Tortuosity index based on dynamic mechanical properties of polyimide foam for aerospace applications
    (MDPI, 2019-06-07) Flores-Bonano, Sugeily; Vargas-Martinez, Juan C.; Suárez, O. Marcelo; Silva-Araya, Walter; College of Engineering; Department of Materials Science and Engineering
    The determination of a reliable tortuosity index is lacking in the aerospace industry. Therefore, a methodology is formulated via direct and indirect characterization methods of a fluid-filled porous media. Chemical, thermal, and mechanical characterization was performed to the PolyuMAC(TM) polyimide foam. Tortuosity was measured considering a pressure difference as the resistivity variable, rather than electrical resistivity or molecular diffusivity, as proposed on previous models. This is an empirical establishment of the tortuosity index considering the correlation among hydraulic and structural dimensionless parameters obtained through the Buckingham’s Pi theorem. The behavior of the polyimide was studied for samples of different lengths compressed at 30%, 60%, and 90% of its original length on the foaming direction. Results show that, porosity, sample length, and fluid viscosity are relevant for the insulation performance of the material. Regression analysis produced a significant statistical model fit to the data correlated from the dimensionless parameters for each dynamic compression series.
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    Fabrication of porous metals via selective phase dissolution of an Al-Cu alloy
    (2018-06-01) Vargas-Martinez, Juan C.; Suárez, O. Marcelo; College of Engineering; Hernández, Arturo; Quintero, Pedro; Perez, Nestor; Department of Mechanical Engineering; Cardona, Nelson
    Through free corrosion in sodium hydroxide, a new porous material was successfully fabricated by removing a single phase of the aluminum-copper alloy. This selective phase dissolution was performed for the eutectic composition of the aluminum-copper binary system and additionally for two hypereutectic compositions. The porosity of the material depends on the microstructure formed in the solidification process. For this, several solidification methods were analyzed in order to define the most convenient in terms of uniformity and refinement in the pore and ligament sizes. The concentration of the solution was determined by observing the effectiveness of the process during and after the corrosion, when the 10% v/v aqueous solution of sodium hydroxide was used better results were observed. The porosity was calculated after the selective dissolution through analysis of images obtained from a scanning electron microscope. In addition, the average pore and ligament size was measured for each composition. Finally, the effectiveness of the process was verified using x-ray diffraction, which showed that under the proposed methodology there was complete removal of one of the phases of the alloy.