Post necking characterisation for sheet metal materials using full field measurement

Marth, Stefan; Häggblad, Hans‐Åke; Oldenburg, Mats; Östlund, Rickard

doi:10.1016/j.jmatprotec.2016.07.036

Cited by 52 publications

(19 citation statements)

References 11 publications

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“…The strain tensor, obtained as described in previous subsection, was used to calculate the stress tensor by a radial return algorithm based on isotropic von Mises plasticity, as described by Marth et al (2016), but without using a stepwise modelling of the hardening relation. Instead of this stepwise modelling, the plastic work hardening of the materials was modelled with the Hollomon hardening law using the material parameter presented in Table 1.…”

Section: Evaluation Of Stress From Measured Strainmentioning

confidence: 99%

“…Strain and stress conditions can be calculated from fullfield measurements of displacement as shown by Marth et al (2016). In that work, incremental displacement fields were obtained from captured images during the experiments by the digital image correlation (DIC) technique, thorough reviewed by Hild and Roux (2006).…”

mentioning

confidence: 99%

“…The purpose of the present work was to extend these experiments with stress calculations using the method described by Marth et al (2016), to determine the strain and stress conditions at crack initiation. The calculated stresses were compared with stresses from FE simulations at the stage of crack initiation.…”

mentioning

confidence: 99%

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Strain and stress conditions at crack initiation during shearing of medium- and high-strength steel sheet

Gustafsson

Marth

Karlsson

et al. 2017

Int J Mech Mater Eng

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Background: Strain and stress conditions in sheet metal shearing are of interest for calibration of various fracture criteria. Most fracture criteria are governed by effective strain and stress triaxiality. Methods: This work is an attempt to extend previous measurements of strain fields in shearing of steel sheets with the stress state calculated from the measured displacement fields. Results are presented in terms of von Mises stress and stress triaxiality fields, and a comparison was made with finite element simulations. Also, an evaluation of the similarities of the stress conditions on the sheet surface and inside the bulk material was presented. Results: Strains and von Mises stresses were similar to the surface and the bulk material, but the stress triaxiality was not comparable. There were large gradients in strain and stress around the curved tool profiles that made the result resolution dependent and comparisons of maximum strain and stress values difficult. Conclusions:The stress state on the sheet surface calculated from displacement field measurements is useful for validation of a three-dimensional finite element model.

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Section: Evaluation Of Stress From Measured Strainmentioning

confidence: 99%

mentioning

confidence: 99%

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Strain and stress conditions at crack initiation during shearing of medium- and high-strength steel sheet

Gustafsson

Marth

Karlsson

et al. 2017

Int J Mech Mater Eng

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“…Moreover, the spatial resolution for deformation detection and strain calculation is limited by the surface feature dimensionality. Laser speckle photography [12] transgresses these limitations and is already used for tensile tests [13] as well as an in-process measuring method for the induced deformation during machining [14,15]. Speckle photography is physically limited only by Heisenberg's uncertainty principle and the respective measurement uncertainty limit can be derived with the Cramér-Rao bound [16,17].…”

Section: Introductionmentioning

confidence: 99%

Uncertainty and Resolution of Speckle Photography on Micro Samples

et al. 2020

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The efficient development of new materials with defined properties requires fast methods of testing low volumes of material, such as a high-throughput investigation of spherical metallic micro samples with varying compositions and structuring treatments. A classical material testing method for macro samples, the tensile test cannot be employed for analyzing the mechanical properties of spherical samples with diameters below 1 mm since there are currently no methods for holding and stretching them. A combination between the incremental electrohydraulic extrusion as stress actuation unit and the speckle photography as strain measuring method is presented for obtaining the required mechanical characteristics. Positive longitudinal strain is generated at stepwise extrusion through < 1 mm wide forming channels using a liquid punch and the deformation is observed in situ after each forming step at the interface between the micro sample and a transparent window integrated into the forming die. The occurring local strain fields with a lateral extension down to 100 µm and high gradients require displacement measurements with high lateral resolution over a large range of local dislocations between 0.1 and > 10 µm. It is unknown, whether the speckle strain measuring method is able to provide the necessary low uncertainty for the required resolution in the whole measuring range. Therefore, theoretical and experimental investigations of the deformation measurability using the speckle correlation method are presented, showing that local displacements up to 10 µm can be measured with a spatial resolution between 3 and 10 µm depending on the displacement size. The dominant effect influencing the measurement uncertainty for displacements at this high spatial resolution is the speckle noise, resulting into measurement uncertainties of less than 100 nm. Hence, speckle photography is shown to be applicable for tensile test on micro samples.

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“…DIC can be used to determine the contour and displacement field of an object under loading in both two and three dimensions. If DIC is combined with the finite element method (FEM), a powerful tool in obtaining optimized material properties based on rather simple material tests becomes available [3].…”

Section: Introductionmentioning

confidence: 99%

On the Material Characterization of an Aluminium Alloy Using Different Specimens and Identification Methods

Thomesen

Hopperstad

2018

The 18th International Conference on Experimental Mechanics

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Abstract:The validity of material properties obtained from uniaxial tension tests using different specimen types and measurement techniques is investigated in this paper. Four different specimen geometries were tested, including round axisymmetric and rectangular flat samples of different sizes. This gave a significant variation in both size and shape of the specimens. The specimens were strained in tension to fracture, and different measurement techniques were applied to measure the deformation of the specimens during loading. This involved an extensometer, a laser micrometre, digital image correlation (DIC) and edge tracing. Cauchy stress versus logarithmic strain curves were obtained from the experimental data, and little spread was seen between the different test series. The data were further used to calibrate a work-hardening relation for the material, and it was found that the fitted curves differed mainly for strains beyond diffuse necking.

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Post necking characterisation for sheet metal materials using full field measurement

Cited by 52 publications

References 11 publications

Strain and stress conditions at crack initiation during shearing of medium- and high-strength steel sheet

Strain and stress conditions at crack initiation during shearing of medium- and high-strength steel sheet

Uncertainty and Resolution of Speckle Photography on Micro Samples

On the Material Characterization of an Aluminium Alloy Using Different Specimens and Identification Methods

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