On the Evaluation of Stress Triaxiality Fields in a Notched Titanium Alloy Sample via Integrated DIC

Abstract : This paper presents a coupled experimental/numerical procedure to evaluate triaxiality fields. Such a type of analysis is applied to a tensile test on a thin notched sample made of Ti 6-4 alloy. The experimental data consist of digital images and corresponding load levels, and a commercial code (Abaqus) is used in an integrated approach to Digital Image Correlation (DIC). With the proposed procedure, samples with complex shapes can be analyzed independently without having to resort to other tests to calibrate the material parameters of a given constitutive law to evaluate triaxili-ties. The regularization involved in the integrated DIC procedure allows the user to deal with experimental imperfections such as cracking of the paint and/or poor quality of the speckle pattern. For the studied material different hardening postulates are tested up to a level of equivalent plastic strain about three times higher than those achievable in a tensile test on smooth samples. Different Finite Element discretizations and model hypotheses (i.e., 2D plane stress and 3D simulations) are compared. 1 Introduction In the design of turbo-engines, it is required to ensure safety margins between the operating conditions and burst. A criterion, which is based upon the calculation of the average hoop stress, was proposed by Robinson [1] and is used to estimate the burst speed of disks. In the case of complex geometries and material models, this criterion is not accurate enough. Today's trend is to try to reduce safety margins by relying on local burst predictions where finite element simulations are performed to take into account precisely both the complex geometry of actual disks and the constitutive model of the material [2, 3].
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Journal of Applied Mechanics, American Society of Mechanical Engineers, 2015, 82 (7), pp.4030457. 〈10.1115/1.4030457〉
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Dominik Lindner, Florent Mathieu, François Hild, Olivier Allix, Cuong Ha Minh, et al.. On the Evaluation of Stress Triaxiality Fields in a Notched Titanium Alloy Sample via Integrated DIC. Journal of Applied Mechanics, American Society of Mechanical Engineers, 2015, 82 (7), pp.4030457. 〈10.1115/1.4030457〉. 〈hal-01166848〉

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