Master of Science, The Ohio State University, 2011, Mechanical Engineering

The increase in using light weight alloys such as aluminum and magnesium sheet materials is accompanied by many challenges in forming these alloys due to their unique mechanical properties and/or low formability. Alternative forming operations, such as warm forming or sheet hydroforming, are potential solutions for the low formability problem of aluminum alloys. Identifying potential difficulties in forming these materials early in the product realization process is important to avoid expensive late changes. Finite Element (FE) simulation is a powerful tool for this purpose provided that the inputs to the FE model, including the flow stress data, are reliable. However, obtaining the flow stress under near production condition (state of stress, strain rate, temperature) may be challenging especially if the flow stress is required at elevated temperature for warm forming applications. In this study, elevated temperature biaxial Viscous Pressure Bulge (VPB) tests were conducted for Aluminum (AA 5182) and Magnesium (Mg AZ61 L) alloys and the resulting flow stress curves were obtained. Using the Surface Response Method that evaluates the error function gave the prediction of flow stress coefficients K, n and m that fit the Power Law Equation. Results of this work predict the flow stress data under a variable strain rate and thus cannot be directly compared with other results which were conducted under a constant strain rate. 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 light weight alloys to be used as an input to FE models. The sheet hydroforming with punch (SHF-P) process offers great potential for low and medium volume production, especially for forming: (1) lightweight sheet materials such as aluminum and magnesium alloys and (2) thin gage high strength steels (HSS). Aluminum and Magnesium alloys are being increasingly considered for au (open full item for complete abstract)

Committee: Taylan Altan Dr (Advisor); Jerald Brevick Dr (Committee Member) Subjects: Engineering; Mechanical Engineering; Metallurgy

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