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Christian Thaulow - One of the best experts on this subject based on the ideXlab platform.

  • a study on determining true stress strain curve for anisotropic materials with rectangular tensile bars
    International Journal of Solids and Structures, 2001
    Co-Authors: J Odegard, O P Sovik, Christian Thaulow
    Abstract:

    Abstract Recently, a method has been proposed for determining material true stress–strain curve with rectangular tensile bars up to localized necking. In the proposed method, material true stress–strain curve can be directly calculated from the load versus thickness Reduction (at the minimum cross-section) curve. The method was established based on the finite element (FE) analysis for isotropic materials. In this study, this method has been extended for materials with isotropic elastic properties but anisotropic plastic properties. Two cases, transverse anisotropy and planar anisotropy, have been considered. Hill’s anisotropic material model implemented in abaqus was applied for the study. More than 30 three-dimensional FE analyses of rectangular specimens with different anisotropy value, hardening exponent and cross-section aspect ratio have been carried out. It is shown that the relation between thickness Reduction and total Area Reduction of a given cross-section is influenced by material plastic anisotropy. It is, however, found that the anisotropic effect on the thickness–Area Reduction relation can be normalized by the width to thickness strain increment ratio r, and a modified thickness–Area Reduction relation is proposed and numerically and experimentally verified. One practical problem in tensile test is that it is difficult to predict the necking location. In this regard, a study on the sensitivity of initial notch geometry has been carried out. It is found that for a fixed initial notch radius, the percentage of error is approximately equal to the percentage of initial width Reduction. The accuracy of using large initial width Reduction can be improved by using large notch radius.

  • determining material true stress strain curve from tensile specimens with rectangular cross section
    International Journal of Solids and Structures, 1999
    Co-Authors: Zhiliang Zhang, Mons Hauge, J Odegard, Christian Thaulow
    Abstract:

    Abstract The uniaxial true stress logarithmic strain curve for a thick section can be determined from the load–diameter Reduction record of a round tensile specimen. The correction of the true stress for necking can be performed by using the well-known Bridgman equation. For thin sections, it is more practical to use specimens with rectangular cross-section. However, there is no established method to determine the complete true stress–logarithmic strain relation from a rectangular specimen. In this paper, an extensive three-dimensional numerical study has been carried out on the diffuse necking behaviour of tensile specimens made of isotropic materials with rectangular cross-section, and an approximate relation is established between the Area Reduction of the minimum cross-section and the measured thickness Reduction. It is found that the Area Reduction can be normalized by the uniaxial strain at maximum load which represents the material hardening and also the section aspect ratio. Furthermore, for the same material, specimens with different aspect ratio give exactly the same true average stress–logarithmic strain curve. This finding implies that Bridgmans correction can still be used for necking correction of the true average stress obtained from rectangular specimens. Based on this finding, a method for determining the true stress–logarithmic strain relation from the load–thickness Reduction curve of specimens with rectangular cross-section is proposed.

Clemens Von Birgelen - One of the best experts on this subject based on the ideXlab platform.

  • first report of edge vascular response at 12 months of magmaris a second generation drug eluting resorbable magnesium scaffold assessed by grayscale intravascular ultrasound virtual histology and optical coherence tomography a biosolve ii trial sub s
    Cardiovascular Revascularization Medicine, 2019
    Co-Authors: Alexandre Hideokajita, Hector M Garciagarcia, Michael Haude, Michael Joner, Jacques J Koolen, Huseyin Ince, Alexandre Abizaid, Ralph Toelg, Pedro A Lemos, Clemens Von Birgelen
    Abstract:

    Abstract Introduction and objective The edge vascular response (EVR) remains unknown in second generation drug-eluting Resorbable Magnesium Scaffold (RMS), such as Magmaris. The aim of the study was to evaluate tissue modifications in the RMS edges over time, assessed by different invasive imaging modalities. Methods The patients treated with the device were assessed by optical coherence tomography (OCT), grayscale intravascular ultrasound (IVUS), and virtual histology IVUS at baseline and 12 months. The EVR study performed a segment- and frame-level analysis of the 5 mm segments proximal and distal of the actual RMS. Results The segment-level grayscale IVUS (n = 10), virtual histology IVUS (n = 10), and OCT (n = 18) analysis did not show any significant changes after 12 months, except for a fibrous plaque Area (FPA) Reduction of 0.5mm2 (p = 0.017) in the proximal segment compared to baseline. In the frame-level analysis, IVUS evaluation revealed a vessel Area decreased 2.80 ± 1.43 mm2 (p = 0.012) and 2.49 ± 1.53 mm2 (p = 0.022) in 2 proximal frames. This was accompanied by plaque Area Reduction of 0.88 ± 0.70 mm2 (p = 0.048) and a FPA decreased by 0.63 ± 0.48 mm2 (p = 0.004) in one proximal frame. In 1 distal frame, there was a dense calcium Area Reduction of 0.10 ± 0.12 mm2 (p = 0.045), FPA and fibrous fatty plaque increased 0.54 ± 0.53 mm2 (p = 0.023) and 0.17 ± 0.16 mm2 (p = 0.016), respectively. By OCT, there was a lumen Area decrease of 0.76 ± 1.51 mm2 (p = 0.045) in a distal frame. Conclusion At 12 months, Magmaris EVR assessment does not show overall significant changes, except for a fibrous plaque Area Reduction in the proximal segment. This could be translated as a benign healing process at the edges of the RMS. Summary The edge vascular response (EVR) remains unknown in second generation drug-eluting absorbable metal scaffolds (RMS), such as Magmaris. Patients treated with the device were assessed by multi invasive imaging modalities [i.e. optical coherence tomography (OCT), grayscale intravascular ultrasound (IVUS), and virtual histology IVUS] evaluating the tissue changes over time in the segment- and frame-level analysis of the 5 mm segments proximal and distal of the actual RMS. As a result, after 12 months, Magmaris EVR assessment does not show overall significant changes, except for a fibrous plaque Area Reduction in the proximal segment, translating a benign healing process at the edges of the RMS.

J. Scheibert - One of the best experts on this subject based on the ideXlab platform.

  • Finite deformations govern the anisotropic shear-induced Area Reduction of soft elastic contacts
    Journal of the Mechanics and Physics of Solids, 2020
    Co-Authors: J. Lengiewicz, M. De Souza, M. Lahmar, C. Courbon, D. Dalmas, S. Stupkiewicz, J. Scheibert
    Abstract:

    Solid contacts involving soft materials are important in mechanical engineering or biomechanics. Experimentally, such contacts have been shown to shrink significantly under shear, an effect which is usually explained using adhesion models. Here we show that quantitative agreement with recent high-load experiments can be obtained, with no adjustable parameter, using a non-adhesive model, provided that finite deformations are taken into account. Analysis of the model uncovers the basic mechanisms underlying anisotropic shear-induced Area Reduction, local contact lifting being the dominant one. We confirm experimentally the relevance of all those mechanisms, by tracking the shear-induced evolution of tracers inserted close to the surface of a smooth elastomer sphere in contact with a smooth glass plate. Our results suggest that finite deformations are an alternative to adhe- sion, when interpreting a variety of sheared contact experiments involving soft materials.

Alexandre Hideokajita - One of the best experts on this subject based on the ideXlab platform.

  • first report of edge vascular response at 12 months of magmaris a second generation drug eluting resorbable magnesium scaffold assessed by grayscale intravascular ultrasound virtual histology and optical coherence tomography a biosolve ii trial sub s
    Cardiovascular Revascularization Medicine, 2019
    Co-Authors: Alexandre Hideokajita, Hector M Garciagarcia, Michael Haude, Michael Joner, Jacques J Koolen, Huseyin Ince, Alexandre Abizaid, Ralph Toelg, Pedro A Lemos, Clemens Von Birgelen
    Abstract:

    Abstract Introduction and objective The edge vascular response (EVR) remains unknown in second generation drug-eluting Resorbable Magnesium Scaffold (RMS), such as Magmaris. The aim of the study was to evaluate tissue modifications in the RMS edges over time, assessed by different invasive imaging modalities. Methods The patients treated with the device were assessed by optical coherence tomography (OCT), grayscale intravascular ultrasound (IVUS), and virtual histology IVUS at baseline and 12 months. The EVR study performed a segment- and frame-level analysis of the 5 mm segments proximal and distal of the actual RMS. Results The segment-level grayscale IVUS (n = 10), virtual histology IVUS (n = 10), and OCT (n = 18) analysis did not show any significant changes after 12 months, except for a fibrous plaque Area (FPA) Reduction of 0.5mm2 (p = 0.017) in the proximal segment compared to baseline. In the frame-level analysis, IVUS evaluation revealed a vessel Area decreased 2.80 ± 1.43 mm2 (p = 0.012) and 2.49 ± 1.53 mm2 (p = 0.022) in 2 proximal frames. This was accompanied by plaque Area Reduction of 0.88 ± 0.70 mm2 (p = 0.048) and a FPA decreased by 0.63 ± 0.48 mm2 (p = 0.004) in one proximal frame. In 1 distal frame, there was a dense calcium Area Reduction of 0.10 ± 0.12 mm2 (p = 0.045), FPA and fibrous fatty plaque increased 0.54 ± 0.53 mm2 (p = 0.023) and 0.17 ± 0.16 mm2 (p = 0.016), respectively. By OCT, there was a lumen Area decrease of 0.76 ± 1.51 mm2 (p = 0.045) in a distal frame. Conclusion At 12 months, Magmaris EVR assessment does not show overall significant changes, except for a fibrous plaque Area Reduction in the proximal segment. This could be translated as a benign healing process at the edges of the RMS. Summary The edge vascular response (EVR) remains unknown in second generation drug-eluting absorbable metal scaffolds (RMS), such as Magmaris. Patients treated with the device were assessed by multi invasive imaging modalities [i.e. optical coherence tomography (OCT), grayscale intravascular ultrasound (IVUS), and virtual histology IVUS] evaluating the tissue changes over time in the segment- and frame-level analysis of the 5 mm segments proximal and distal of the actual RMS. As a result, after 12 months, Magmaris EVR assessment does not show overall significant changes, except for a fibrous plaque Area Reduction in the proximal segment, translating a benign healing process at the edges of the RMS.

J Odegard - One of the best experts on this subject based on the ideXlab platform.

  • a study on determining true stress strain curve for anisotropic materials with rectangular tensile bars
    International Journal of Solids and Structures, 2001
    Co-Authors: J Odegard, O P Sovik, Christian Thaulow
    Abstract:

    Abstract Recently, a method has been proposed for determining material true stress–strain curve with rectangular tensile bars up to localized necking. In the proposed method, material true stress–strain curve can be directly calculated from the load versus thickness Reduction (at the minimum cross-section) curve. The method was established based on the finite element (FE) analysis for isotropic materials. In this study, this method has been extended for materials with isotropic elastic properties but anisotropic plastic properties. Two cases, transverse anisotropy and planar anisotropy, have been considered. Hill’s anisotropic material model implemented in abaqus was applied for the study. More than 30 three-dimensional FE analyses of rectangular specimens with different anisotropy value, hardening exponent and cross-section aspect ratio have been carried out. It is shown that the relation between thickness Reduction and total Area Reduction of a given cross-section is influenced by material plastic anisotropy. It is, however, found that the anisotropic effect on the thickness–Area Reduction relation can be normalized by the width to thickness strain increment ratio r, and a modified thickness–Area Reduction relation is proposed and numerically and experimentally verified. One practical problem in tensile test is that it is difficult to predict the necking location. In this regard, a study on the sensitivity of initial notch geometry has been carried out. It is found that for a fixed initial notch radius, the percentage of error is approximately equal to the percentage of initial width Reduction. The accuracy of using large initial width Reduction can be improved by using large notch radius.

  • determining material true stress strain curve from tensile specimens with rectangular cross section
    International Journal of Solids and Structures, 1999
    Co-Authors: Zhiliang Zhang, Mons Hauge, J Odegard, Christian Thaulow
    Abstract:

    Abstract The uniaxial true stress logarithmic strain curve for a thick section can be determined from the load–diameter Reduction record of a round tensile specimen. The correction of the true stress for necking can be performed by using the well-known Bridgman equation. For thin sections, it is more practical to use specimens with rectangular cross-section. However, there is no established method to determine the complete true stress–logarithmic strain relation from a rectangular specimen. In this paper, an extensive three-dimensional numerical study has been carried out on the diffuse necking behaviour of tensile specimens made of isotropic materials with rectangular cross-section, and an approximate relation is established between the Area Reduction of the minimum cross-section and the measured thickness Reduction. It is found that the Area Reduction can be normalized by the uniaxial strain at maximum load which represents the material hardening and also the section aspect ratio. Furthermore, for the same material, specimens with different aspect ratio give exactly the same true average stress–logarithmic strain curve. This finding implies that Bridgmans correction can still be used for necking correction of the true average stress obtained from rectangular specimens. Based on this finding, a method for determining the true stress–logarithmic strain relation from the load–thickness Reduction curve of specimens with rectangular cross-section is proposed.