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Evolution of Structures
Published in Stuart R. Stock, MicroComputed Tomography, 2019
Superplastic forming (very high strains in certain alloys without rupture of the starting material) is finding application in aerospace and automotive fields. Superplastic deformation is generally limited by strain-induced cavitation leading to fracture. Using synchrotron microCT, Martin et al. found that the number of cavities per unit volume vs strain (∼1 < ε < ∼1.7) in AA5083 followed model predictions and observed developing cavity linkage (Martin, Blandin et al. 2000a, Martin, Josserond et al. 2000b). Pore evolution from rolling of an Al-6Mg alloy was studied with lab microCT, and the authors demonstrated that the highly tortuous pores would be difficult to detect in polished sections (Youssef, Chaijaruwanich et al. 2006). The tortuous pores spheroidized during homogenization, and accelerated centerline intrapore coarsening observed during initial, low-reduction-ratio rolling passes was attributed (through finite element modeling) to local tensile conditions, a counterintuitive but not unreasonable result (Youssef, Chaijaruwanich et al. 2006).
Applications, Challenges, and Future Scope
Published in B. Ratna Sunil, Surface Engineering by Friction-Assisted Processes, 2019
Superplasticity can be defined as the ability of a material which can undergo large amounts of deformation, for example, more than 200% without failure [1–3]. A higher level of formability is possible with super-plastic forming by which complex shaped structures can be produced. For the past two decades, superplastic forming has attracted great attention in the metal forming field to produce near net shape structures at low cost. Automobile and aerospace industries are the two important areas where superplastic forming helped to produce low weight high strength superplastic structures at a relatively lower cost. Grain size is one of the crucial factors dictates the level of superplasticity. In addition to grain size, high angle grain boundary, the presence of very fine secondary phase particles at the grain boundaries to arrest the grain growth are the other favoring factors which promote superplasticity. Grain boundary sliding is the important mechanism in superplastic forming.
Evolution of Structures
Published in Stuart R. Stock, MicroComputed Tomography, 2018
Superplastic forming (very high strains in certain alloys without rupture of the starting material) is finding application in aerospace and automotive fields. Superplastic deformation is generally limited by strain-induced cavitation leading to fracture. Using synchrotron microCT, Martin et al. (2000a, b) found that the number of cavities per unit volume versus strain (~1 < ε < ~1.7) in AA5083 followed model predictions and observed developing cavity linkage. Pore evolution from rolling of an Al–6Mg alloy was studied with lab microCT, and the authors demonstrated that the highly tortuous pores would be difficult to detect in polished sections (Youssef et al., 2006). The tortuous pores spheroidized during homogenization, and accelerated centerline intrapore coarsening observed during initial, low-reduction-ratio rolling passes was attributed (through finite element modeling) to local tensile conditions, a counterintuitive but not unreasonable result (Youssef et al., 2006).
Material model calibration for superplastic forming
Published in Inverse Problems in Science and Engineering, 2019
In summary, all three versions of the calibrated SV-sinh model and the Nazzal model with show the onset of localized thinning with increasing strain rate. These models would be suitable to minimize the final forming time of a superplastic forming process, by finding a pressure profile that forms the part faster, subject to some minimum allowable thickness. An optimization algorithm that uses the material model calibrated in this paper would naturally avoid pressures that deform the part too quickly, since this would lead to localization [15].