Marciniak-Kuczynski and Nakajima tests of the dual-phase steel Docol 600DL have been carried out for a range of stress states spanning from uniaxial tension to equi-biaxial tension. The deformation histories of the specimens have been recorded by digital images, and the displacement and strain fields have been determined by post-processing the images with digital image correlation software. The fracture characteristics of the material are presented by means of the stress triaxiality, the Lode parameter and the equivalent strain. These parameters are evaluated on the surface of the specimens based on the optical field measurements and assumptions regarding the mechanical behaviour of the material. Additionally the minor versus major principal strains up to fracture are presented. It is found that the material displays a significantly lower ductility in planestrain tension than in uniaxial tension and equi-biaxial tension, and that it in the tests exposed to local necking undergoes large strains between the onset of necking and fracture. Fractographs of selected specimens reveal that fracture is due to growth and coalescence of voids that occur in localized areas governed by shear-band instability.
This paper presents experimental tensile test results obtained on flat aluminum magnesium alloy samples on a hard machine. The mechanical response, kinematic fields and acoustic emissions were simultaneously obtained in an experimental setup. Propagation instabilities associated with the Portevin-Le-Châtelier effect were observed as localized intense strain increment bands. Depending on the strain rate, A, B or C types were studied on the basis of stress drops, acoustic emission and strain fields. Then the band characteristics (position, orientation, width, thickness reduction, intensity, acoustic emission, principal strain direction) were presented in various strain rate conditions.
Sheet metal formability is traditionally described by the Forming Limit Curve were observed between the results reported by different laboratories. The main limitation of the standard method for detection of forming limits is that its application is limited to cases where a single local neck is formed in the metal sheet prior to fracture. In the case of multiple local necks, the samples are simply discarded. Furthermore, the standard method does not include any guidelines to distinguish the failure by local necking and direct failure by fracture. One of the advantages of DIC over the traditional etched-grid technique is that the former allows us to obtain not only the strain distribution but also its history.This allows for alternative methods for detection of forming limit strains. This paper introduces a DIC-based method which was specially developed to handle
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