Extracting material data for superplastic forming simulations

Q.H.C. Snippe, Vincent T. Meinders

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Abstract

In subatomic particle physics, unstable particles can be studied with a so-called vertex detector placed inside a particle accelerator. A detecting unit close to the accelerator bunch of charged particles must be separated from the accelerator vacuum. A thin sheet with a complex 3D shape prevents the detector vacuum from polluting the accelerator vacuum. Hence, this sheet should be completely leak tight with respect to gases. To produce such a complex thin sheet, superplastic forming can be very attractive if a small number of products is needed. This is a forming process in which a sheet of superplastic material is pressed into a one-sided die by means of gas pressure. In order to develop a material model which can be used in superplastic forming simulations, uniaxial and biaxial experiments are necessary. The uniaxial, tensile, experiments provide information about the one-dimensional material data, such as the stress as a function of equivalent plastic strain and strain rate. These data are extracted from the experiments by using inverse modeling, i.e. simulation of the tensile experiment. To fit these curves into a general material model, three parts in the uniaxial mechanical behavior are considered: initial flow stress, strain hardening and strain softening caused by void growth. Since failure in superplastic materials is preceded by the nucleation and growth of cavities inside the material, the void volume fractions of the tested specimens were also observed. A very important factor in this research is the study of the permeability of the formed sheet with respect to gas. If internal voids start to coalesce, through-thickness channels will start to form, thereby providing a gas leak path. To study the twodimensional behavior, including the gas leakage, bulge experiments were performed. Within these experiments, circular sheets were pressed into a cylindrically shaped die. From these experiments it followed that the plastic straining is dependent on an applied backpressure during the forming stage. This backpressure can postpone cavity nucleation and growth.
Original languageUndefined
Title of host publicationIDDRG International Congress 2009, 1-3 july 2009, Golden Colorado, USA
EditorsB.S. Levy, D.K. Matlock, C.J. van Tyne
Place of PublicationGolden, USA
PublisherColorado School of Mines
Pages737-748
ISBN (Print)978-0-615-29641-8
Publication statusPublished - 1 Jun 2009
EventInternational Deep Drawing Research Group annual conference, IDDRG 2009 - Golden, United States
Duration: 1 Jun 20093 Jun 2009

Conference

ConferenceInternational Deep Drawing Research Group annual conference, IDDRG 2009
Abbreviated titleIDDRG 2009
CountryUnited States
CityGolden
Period1/06/093/06/09

Keywords

  • METIS-260108
  • IR-68552

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