Material characterisation for analyses of titanium sheet metal forming

Detta är en avhandling från Luleå : Luleå tekniska universitet

Sammanfattning: New demands and opportunities for simulation driven product development, that today's finite element (FE) technology allow for, exists in modern industry. Full applicability, in which decisions based on numerical evaluations and predictions, require accurate material parameters and of course accurate modelling of remaining features. To describe the deformation of a certain material a variety of material models are available (e.g. constitutive equations, models for anisotropy, creep, phase transformation and microstructure evolution) which all contain model parameters that have to be determined. Often, different material models require specific types of experimental methods to determine its material model parameters. For example, the parameters in a constitutive equation may require a different type of experiment e.g. compression tests at certain strain rates compared to a creep model which may require another type of test method under strain rates valid for creep. The objective of this thesis is first to establish an experimental foundation and comprehension on the thermo-mechanical behaviour of the titanium alloys Ti-6Al-4V but foremost Ti-6242, and to procure a good understanding of the possibilities and difficulties of used testing methods. Furthermore, experimental data are used both to obtain constitutive material model parameters trough force and displacement from elevated temperature compression tests by use of inverse modelling, and in finite element analyses for validation and prediction by analyses of sheet metal forming. Elevated temperature compression tests on cylindrical specimens are used for both Ti-6Al-4V and Ti-6242, revealing many interesting characteristics of these alloys. The experimental data are then used to estimate material parameters of different constitutive equations and used in initial predictions of sheet metal forming of Ti-6242. Cold and hot sheet metal forming tests of Ti-6242 is performed in order to evaluate suitable sheet metal forming processes for the alloy. Process parameters are studied and the tests functions as validation tests for the correlation of numerical models.

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