Doctor of Philosophy (PhD), Ohio University, 2022, Mechanical and Systems Engineering (Engineering and Technology)

In this study, it was hypothesized that graphene aluminum alloys can be engineered for improved bulk electrical properties by establishing a form of coherency with aluminum valance and graphene π electrons. To this end, the effects of graphene concentration and process parameters were assessed, and thus shown that improvements in the electrical performance of bulk aluminum alloys is possible. Al/graphene composites were manufactured under varying thermo-mechanical process conditions with varying graphene content embedded into three different aluminum alloy systems, namely AA1100 (commercially pure, non-heat treatable), AA3003 (alloyed, non-heat treatable), and AA6101 (alloyed, heat treatable) alloys. Electrical conductivity and temperature coefficient of resistance were determined for the 10 - 12 AWG composite wires manufactured via solid phase processing techniques, hot extrusion and shear assisted processing and extrusion. Microstructural characterizations were performed through optical and scanning electron microscopy to identify the process-structure-property relationships for the composites. Results showed that hot-extruded AA1100 composites with 0.25 wt.% graphene showed the highest improvement of 2.32% in electrical conductivity as well as the TCR lower by 23.4% compared to control samples manufactured under similar conditions. Enhanced conductivity was seen in composites with higher semimetallic graphene while lower TCR was observed in samples with higher semiconductor graphene concentration. Extrusion pressures played a key role in the exfoliation and deformation of agglomerated graphene nanoparticle precursors. Second phase solubility was affected by hot pressing conditions, extrusion temperature and ShAPE parameters, and not the presence of graphene in the composite microstructures. On the other hand, graphene affected precipitation dynamics during aging of hot-extruded AA6101 composites. Finally, composite grain morphology and distribution as well as pre (open full item for complete abstract)

Committee: Frank Kraft (Advisor); Keerti Kappagantula (Advisor); Muhammad Ali (Advisor); Brian Wisner (Committee Member); Jay Wilhelm (Committee Member); Zaki Kuruppalil (Committee Member); Eric Stinaff (Committee Member) Subjects: Materials Science; Mechanical Engineering

Master of Science, The Ohio State University, 2009, Industrial and Systems Engineering

The increase in using Advanced High Strength Steel (AHSS) and aluminum sheet materials is accompanied by many challenges in forming these alloys due to their unique mechanical properties and/or low formability. Therefore, developing a fundamental understanding of the mechanical properties of AHSS, as compared to conventional Draw Quality Steel (DQS), is critical to successful process/ tools design. Also, alternative forming operations, such as warm forming or sheet hydroforming, are potential solutions for the low formability problem of aluminum alloys. In this study, room temperature uniaxial tensile and biaxial Viscous Pressure Bulge (VPB) tests were conducted for five AHSS sheet materials; DP 600, DP 780, DP 780-CR, DP 780-HY, and TRIP 780, and the resulting flow stress curves were compared. Strain ratios (R-values) were also determined in the tensile test and used to correct the biaxial flow stress curves for anisotropy. The pressure vs. dome height raw data in the VPB test was extrapolated to the burst pressure to obtain the flow stress curve up to fracture. Results of this work show that flow stress data can be obtained to higher strain values under biaxial state of stress. Moreover, it was observed that some materials behave differently if subjected to different state of stress. These two conclusions, and the fact that the state of stress in actual stamping processes is almost always biaxial, suggest that the bulge test is a more suitable test for obtaining the flow stress of AHSS sheet materials to be used as an input to FE models. An alternative methodology for obtaining the flow stress from the bulge test data, based on FE-optimization, was also applied and shown to work well for the AHSS sheet materials tested. Elevated temperature bulge tests were made for three aluminum alloys; AA5754-O, AA5182-O, and AA3003-O, using a special machine where the tools and specimen are submerged in a fluid heated to the required temperature. Several challenges were faced (open full item for complete abstract)

Committee: Taylan Altan (Advisor); Jerald Brevick (Committee Member) Subjects: Automotive Materials; Engineering; Industrial Engineering; Materials Science; Mechanical Engineering