Comparing Two Damage Models Under Shear Stress

Baldi, Antonio; Francesconi, Luca; Medda, Andrea; Bertolino, Filippo

doi:10.1007/s11340-013-9715-8

Cited by 7 publications

(6 citation statements)

References 23 publications

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“…Most of the time, this solution is acceptable, but sometimes the ability to better describe the boundaries of the area of interest is a significant improvement (see Fig. 2 for an example [2]). Thus, to fully exploit the potentiality of the mesh approach in describing the active region, we opted for removing the ''rectangular elements'' constraint; however, this choice poses two problems: the obvious one is the requirement for a general (simple) procedure for the identification of normalized coordinates in a general quadrilateral, because the shape of elements is no longer rectangular, the second being that the obvious solution, i.e.…”

Section: And 'mentioning

confidence: 99%

“…7 shows the corresponding mesh when no refinement is performed; to allow simple identification of the displacement field, all speckles inside a 200 pixel-wide border were disabled; moreover, to ensure that the code worked properly, the origin was moved to (250, 250), thus the speckled area includes a 50-pixel-large border. 2 In both analyses, the initial element size was set to about 20 Â 10 3 pixels whereas the minimum allowed element size for h-adaptivity was 225 pixels.…”

Section: Synthetic Imagesmentioning

confidence: 99%

“…Equation (2) involves two unknowns (V x and V y ), thus it is not possible to estimate the displacement field unless a second condition is specified. The most common solution to this problem, the Lucas-Kanade formulation [10], assumes a predefined displacement field-usually an affine transformation-and locally minimizes, in the least-squares sense, the differences between the reference and target images over a small region.…”

Section: Introductionmentioning

confidence: 99%

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Assessment of h-refinement procedure for global digital image correlation

Baldi

Bertolino

2015

Meccanica

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Digital image correlation (DIC) is a noninterferometric optical technique able to measure bidimensional\ud (tri-dimensional in its stereo version) displacement fields by comparing two images acquired before and after motion. In its standard formulation, the measurement is performed by comparing a small subset of pixels in the two images, looking for the best set of parameters that minimize a given error function under the assumption of an affine displacement field. This procedure is performed in several points of the image so as to allow the reconstruction of the full displacement field by interpolating the various independent samplings. Global DIC formulation avoids the a posteriori interpolation by describing the displacement field\ud with a finite-element-like mesh: the resulting minimization is global because the fitting parameters\ud (usually the nodal displacements) are shared by neighbor elements; thus the standard deviation of\ud displacements is lower. However, the new formulation raises the problem of the identification of the optimal\ud mesh. A possible solution to this problem is the adaptive mesh refinement. This work proposes a\ud simple h-refinement approach for global DIC and analyses its performance using both synthetic and\ud experimental data

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Section: And 'mentioning

confidence: 99%

Section: Synthetic Imagesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Assessment of h-refinement procedure for global digital image correlation

Baldi

Bertolino

2015

Meccanica

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“…The expanding use of finite elements (FE) meshes in digital image correlation (DIC) algorithms is explained by their ability to be coupled with numerical models. The interaction of measurement and simulation becomes fast and friendly, as both kinematic fields are defined at the nodes of the same mesh.…”

Section: Introductionmentioning

confidence: 99%

Noninvasive multilevel geometric regularization of mesh‐based three‐dimensional shape measurement

Colantonio

Chapelier

Bouclier

et al. 2020

Numerical Meth Engineering

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Summary Finite element stereo digital image correlation (FE‐SDIC) requires a crucial calibration phase in which the initial CAD needs to be updated to fit the actual shape of the specimen. On the one hand, the use of a FE mesh facilitates the coupling of measurements with simulation tools, while on the other hand, it provides a unique, fine description of both the geometry and the displacement, which often makes the shape measurement problem highly ill‐posed. As a remedy, we propose a hybrid isogeometric‐FE strategy that can measure a shape in terms of spline functions while considering as an input and output the analysis‐suitable FE mesh. Making use of the appealing spline refinement procedures and of Bézier‐based operators, multilevel smooth spline discretizations are built concurrently with the initial FE subspace and related to the multiscale images used for the initialization of the shape measurement. It results in a geometrically sound regularization which provides a spline parametrization of the optimal shape along with its FE twin. A noninvasive implementation from an existing FE‐SDIC code is also detailed. The performance of the proposed method is assessed on real images and comparisons are made with other published techniques to prove its efficiency.

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“…Therefore, the damage models applied in finite element models of shear tests should be composed of the stress triaxiality and the Lode's angle parameter. The comparisons of damage models based on the introduced key parameters was done for the Gurson-Tvergaard-Needleman's model in [4] and for the Lemaitre and Wierzbicki-Xue' model in [5]. The evaluation, calibration and validation of the damage models implemented in finite element shear tests is often carried out in experimental pure tensile conditions [4], digital image correlation tests [5] and in micro-double shear test coupled with simultaneous nanoindentation test [6].…”

Section: Introductionmentioning

confidence: 99%

Numerical And Experimental Analysis Of Fracture Of Athrombogenic Coatings Deposited On Ventricular Assist Device In Micro-Shear Test

Kopernik¹,

Milenin²,

Kąc³

2015

Archives of Metallurgy and Materials

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The Polish left ventricular assist device (LVAD -RELIGA EXT) will be made of thermoplastic polycarbonate-urethane (Bionate II) with deposited athrombogenic nano-coatings: gold (Au) and titanium nitride (TiN). Referring to the physical model, the two-scale model of LVAD developed in the previous works in the authors' finite element code is composed of a macro-model of blood chamber and a micro-model of wall: TiN, Au and Bionate II. The numerical analysis of stress and strain states confirmed the possibility of fracture based on localization of zones of the biggest values of triaxiality factor. The introduction of Au interlayer between TiN and polymer improved the toughness of the connection, and increased the compressive residual stress in the coating what resulted in reduction of stress and strain close to the boundary between substrate and coating.However, the proper design of multilayer wall of the medical device requires the introduction of the real stress and strain states in the deposited coatings. The characteristics of TiN nano-coating such as residual stress, material model and fracture model were determined in the previously completed studies such as experimental and numercial nanoindentation tests, profilometry studies and in situ SEM's micro-tension tests.The experimental in situ SEM's micro-shear test was performed in the present paper and the corresponding numerical model of the test was also developed, and then, interpreted. The critical strains taken from experiment and considered as the effective strains in the model of test are the values which are the function of triaxiality factors for the tested samples. The developed in the authors' FE code model of multilayer wall of VAD enriched with critical strain determined in the present paper enables prediction of fracture.Keywords: micro-shear test, finite element method (FEM), fracture, ventricular assist device (VAD), titanium nitride (TiN), gold (Au) Polska lewa komora wspomagania pracy serca (LVAD -RELIGA EXT) zostanie wykonana z termoplastycznego poliwęgla-no-uretanu (Bionate II) z naniesionymi atrombogennymi powłokami: złota (Au) i azotku tytanu (TiN). W odniesieniu do modelu fizycznego, dwuskalowy model komory LVAD opracowany we wcześniejszych pracach w autorskim kodzie elementów skończonch jest złożony z modelu makro czaszy krwistej i z mikro-modelu ściany: TiN, Au i Bionate II. Analiza numeryczna stanów naprężenia i odkształcenia potwierdziła prawdopodobieństwo pękania poprzez zlokalizowanie stref o największej wartości współczynnika naprężenia trójosiowego. Wprowadzenie międzywarstwy złota pomiędzy TiN i polimer poprawiło wytrzymałość tego połączenia i powiększyło ściskające naprężenie własne w powłoce, co doprowadziło do redukcji naprężenia i odkształcenia blisko granicy pomiędzy podłożem i powłoką.Jednakże, właściwy projekt wielowarstwowej ściany urządzenia medycznego wymaga wprowadzenia rzeczywistych stanów naprężeń i odkształceń w naniesionych powłokach. Charakterystyki powłok TiN takie jak naprężenie własne, model materiału i model pęk...

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Comparing Two Damage Models Under Shear Stress

Cited by 7 publications

References 23 publications

Assessment of h-refinement procedure for global digital image correlation

Assessment of h-refinement procedure for global digital image correlation

Noninvasive multilevel geometric regularization of mesh‐based three‐dimensional shape measurement

Numerical And Experimental Analysis Of Fracture Of Athrombogenic Coatings Deposited On Ventricular Assist Device In Micro-Shear Test

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