Publications

10/04/2024

Isogeometric homogenization of unidirectional nanocomposites with energetic surfaces

Authors : DU, Xiaoxiao CHEN, Qiang CHATZIGEORGIOU, George MERAGHNI, Fodil WANG, Wei ZHAO, Gang
Publisher : Springer Science and Business Media LLC
The present work aims to propose an interface-enriched isogeometric analysis strategy for predicting the size-dependent effective moduli and local stress field of periodic arrays of nanosize inhomogeneity. The proposed framework allows for an exact representation of the curved boundary of inhomogeneity inside the matrix due to the representation of the geometry of repeating unit cells for microstructured materials with nonuniform rational B-splines. The energetic surface was characterized by the Gurtin-Murdoch model, and it was incorporated into the proposed framework by introducing additional surface energies linked to the bulk elements neighbouring the interface. The surface-enhanced isogeometric homogenization method was verified through comparisons with existing solutions found in the literature. It is demonstrated that the proposed framework enables the satisfaction of higher-order continuity of the displacement fields, leading to smooth and accurate predictions of the stress fields and homogenized moduli of nanocomposites, without encountering the convergence problems associated with conventional finite-element methods in the literature.
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05/04/2024

Comparing failure tests on pharmaceutical tablets: Interpretation using experimental results and a numerical approach with cohesive zone models

Authors : MAZEL, Vincent GIRARDOT , Jeremie KOPP, Jean-Benoit MOREL, Stéphane TCHORELOFF, Pierre
Publisher : Elsevier BV
The mechanical strength is an important quality attribute of pharmaceutical tablets. It can be determined using different failure tests like the Brazilian test or the three-point bending test. Nevertheless, literature shows that different failure tests often give conflicting values of tensile strengths (TS), which are generally calculated using the maximum stress criterion as a failure criterion. This work started from the hypothesis that these discrepancies are in fact due to the application of this criterion which is not suited to study pharmaceutical tablets, first due to heterogeneity of the stress distributions during the tests and second due to the quasi-brittle nature of pharmaceutical tablets. As an alternative, a numerical fracture criterion which is known to be well-suited for quasi-brittle solids (cohesive zone model, CZM) was used and calibrated using experiments. Using this approach, the breaking forces obtained numerically were shown to be in fair agreement with the experimental ones. Above all, the numerical results made it possible to catch the trends when comparing the different failure tests one to another. Especially, the model made it possible to retrieve the factor 2 between the TS obtained by three-point bending and by diametral compression found in the literature.
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04/04/2024

Physical aging and its effect on mechanical properties of toughened PLA films

Authors : RUELLAN, Alexandre ANDRE, Jérémy SAELICES JIMENEZ, Lidia GUINAULT, Alain DUCRUET, Violette DOMENEK, Sandra SOLLOGOUB, Cyrille
Publisher :
Physical aging plays an important role in determining the long terms performance of polymers, especially PLA, whose Tg is close to ambient temperature. Considering long term performances, PLA/PHBV/PODC blends are the most promising materials for the toughening of PLA. Indeed, for these blends significant improvement in the strain at break was observed, along with a limited depression of the Young modulus and the stress at yield in comparison to neat PLA, as well as animproved thermal stability.
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03/04/2024

AI-based Text Generation for Semantic Search Robustness : Application to Defence

Authors : FENDZI, Claude CARRON, Bruno GADEK, Guillaume
Publisher : IEEE
One of the biggest challenges in successfully applying Artificial Intelligence (AI) in the Defense sector is the availability of trustful domain specific data to train AI models on. These data have to be generated and collected from the real world or acquired through realistic scenarios simulations and validated by operation specialists or domain experts. In real world applications, most of the time these data are classified and difficult to access. Then only a handful coming either from unclassified documents or simulation / realistic scenarios can be made available. In this article, we discuss how Generative AI can be used to generate intelligence-oriented textual data that are semantically similar to a “ground truth” database. The methodology is applied in the frame of the EDIDP AI4DEF project, focusing on one of the use cases, Request for Information (RFI) semantic similarity detection in a database. We expose how a limited corpus has been enriched with noisy AI-generated data. The performances and the robustness of the AI model have been monitored to be kept similar before and after the data augmentation, while a human-in-the loop qualifies the AI-generated data.
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03/04/2024

Investigation of the effect of morphological and crystallographic textures on the ductility limits of thin metal sheets using a CPFEM-based approach

Authors : ZHOU, Shuai BEN BETTAIEB, Mohamed ABED-MERAIM, Farid 
Publisher : Elsevier BV
The current contribution investigates the effect of some relevant microstructural parameters (specifically, morphological and crystallographic textures) on the ductility limits of polycrystalline aggregates using the Crystal Plasticity Finite Element Method (CPFEM). The polycrystalline aggregates are assumed to be representative of thin metal sheets and their macroscopic behavior is determined from that of their constituent single crystals on the basis of the periodic homogenization technique. The single crystal behavior is described by a finite strain elastoplastic framework in which the plastic flow rule obeys the classical Schmid law and plastic deformation is solely attributed to the slip on the crystallographic slip systems. The CPFEM is implemented within and in connection with ABAQUS/Standard finite element code. The ductility limits are predicted by the Rice bifurcation theory where strain localization is detected when the macroscopic acoustic tensor becomes singular. Three grain morphologies (namely, cube, random, and elongated morphology) and three initial crystallographic textures (namely, cube, random, and copper orientation) are considered to investigate the effect of morphological and crystallographic textures on the onset of plastic strain localization. The numerical results indicate that the effect of initial crystallographic texture is much more pronounced than that of grain morphology on the predicted ductility limits. In addition, the impact of grain size and sheet thickness are thoroughly analyzed. The research reveals that the trends of the predicted ductility limits are strongly dependent on the size effects.
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02/04/2024

A physically-based mixed hardening model for the prediction of the ductility limits of thin metal sheets using a CPFE approach

Authors : ZHOU, Shuai BEN BETTAIEB, Mohamed ABED-MERAIM, Farid 
Publisher : Elsevier BV
An advanced Crystal Plasticity Finite Element (CPFE) approach is developed to accurately predict the ductility limit strains of thin metal sheets. This method uses polycrystalline unit cells to represent the metal sheets at the macroscopic level. The macroscopic behavior of these unit cells is determined based on that of the constituent single crystals using the periodic homogenization multiscale scheme. At the single crystal scale, the constitutive framework follows a finite strain rate-independent formulation, with the flow rule governed by the Schmid law. The evolution of the single crystal yield surface is described through a physically based mixed hardening model, where isotropic hardening is characterized by a dislocation density-based formulation, while kinematic hardening is described by the nonlinear Armstrong–Frederick model. The unit cell ductility limit strains are predicted by the Rice bifurcation criterion. The reliability of the mixed hardening model in accurately reproducing mechanical behavior is confirmed through simulations of uniaxial tension/compression loading. Then, the developed computational strategy is used to investigate the impact of key microstructural hardening parameters on the initiation of localized necking under linear strain paths. The numerical predictions reveal the significant influence of these parameters on the formability of thin metal sheets. Additionally, the analysis of ductility limits under non-linear strain paths demonstrates a strong dependency of the numerical predictions on strain path changes. The numerical predictions obtained by the developed CPFE multiscale strategy are compared with experimental results from the literature. In summary, the proposed approach provides a reliable tool for accurately predicting the ductility limits of thin metal sheets, offering valuable insights for engineering applications.
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29/03/2024

Smart actuators based on electroactive fluorinated polymers: relationship between molecular organization and electroactive response

Authors : ZANCHI, Sara ROLAND, Sébastien LE GOFF, Lena THUAU, Damien MARGERIT, Pierre REBILLAT, Marc ILIOPOULOS, Ilias TENCÉ-GIRAULT, Sylvie
Publisher : Eccomas proceedia/Dept. of Mechanical Engineering & Aeronautics University of Patras
Electroactive polymers (EAP) show a change of properties (size, shape, temperature…) when an electric field is applied. Poly(vinylidene fluoride-ter-trifluoroethylene-ter-chlorotrifluoroethylene) P(VDF-ter-TrFE-ter-CTFE) terpolymers have been extensively studied since the 2000s and they found various applications in organic printed and flexible electronics, such as smart actuators. They exhibit different electroactive properties depending on the CTFE content. For %CTFE = 0, copolymers are ferroelectric and piezoelectric at room temperature (RT), while terpolymers are relaxor-ferroelectric and electrostrictive at RT for %CTFE > 6%. On the top of the processing conditions, the chemical composition (%CTFE) have a strong impact on the crystalline structure and morphology, and consequently on the electroactive properties. Unimorph actuators with two different chemical compositions were studied by in-situ Wide Angles X-Ray Scattering (WAXS) and by measuring their macroscopic deformation under an increasing electric field (up to 110 V/µm). These techniques were used to extract their electromechanical coefficients (��31 and ��31) at the macroscopic scale and to relate the crystalline scale to the macroscopic properties. By comparing the evolution of the crystalline unit cell dimensions and of the macroscopic strain of the actuator under an electric field, interesting information on the mechanisms involved were deduced and will be discussed.
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29/03/2024

Deformation bands and alteration in porous glass-rich volcaniclastics: Insights from Milos, Greece

Authors : LEROY, E. CAVAILHES, T. ANGUY, Yannick SOLIVA, R. ROTEVATN, A. GABORIEAU, Cécile
Publisher : Elsevier BV
Deformation bands in porous volcaniclastics are little studied structural heterogeneities despite their relevance for constraining the modalities of deformation development and related fluid-rock interactions in volcanic areas. We document a dense network of normal-sense Deformation Bands (Normal-sense Compactional Shear Bands (NCSBs) affecting upper Pliocene felsic glassy tuffites in Milos, Greece. NCSBs probably formed between 300 and 500 m of burial depth, in response to NE-SW directed extension which is related to volcanic rift development in the area. They accommodate mm-to m-shear-offsets, trend either N105 ± 10° or N070 ± 10°, and show mutual cross-cutting relations. The NCSB fault rock is made of ultracataclasite in which the cataclastic mechanisms have affected both the mineral fraction and the volcanic glass. Minerals are fractured along their cleavages whereas pumices are interestingly fractured along their vesicles. The development of chemical alteration (dissolution and cementation) essentially into the ultracataclasite is expressed through glass-hosted corrosion gulfs and smectites filling the intergranular porosity. These observations support that NCSBs preferentially retained water, have been the seat of greater fluid flow, and are the locus of ongoing phyllosilicate self-sealing in the vadose zone. A significant decrease (up to one order of magnitude) in porosity is measured within the studied NCSBs.
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29/03/2024

Influence of the loading regime on the uniaxial compressive behaviour of density graded Citrus Maxima peel

Authors : LE BARBENCHON, Louise
Publisher : Elsevier BV
To conceive more efficient protective structures, it is possible to draw inspiration from natural structures. However, the origin of the mechanical absorption properties of natural structures is not always clear. Among the multitude of existing natural structures, the density graded peel of the Citrus Maxima was studied in this work to characterize its mechanical behaviour under uniaxial compression, from the quasi-static regime to the dynamic regime. The resulting behaviour is very different from a classical foam behaviour as no linear part is observed for small strains. Furthermore, the mechanical behaviour is deeply influenced by the loading regime: a stair-case response appears under dynamic loading.
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29/03/2024

Significant four-phonon scattering and its heat transfer implications in crystalline Ge2Sb2Te5

Authors : GHOSH, Kanka KUSIAK, Andrzej BATTAGLIA, Jean-Luc
Publisher : American Physical Society (APS)
We systematically demonstrate the temperature-dependent thermal transport properties in crystalline Ge2Sb2Te5 via first-principles density functional theory informed linearized Boltzmann transport equation. The investigation, covering a wide temperature range (30–600 K), reports the emergence of an unusual optical-phonon-dominated thermal transport in crystalline Ge2Sb2Te5. Further, a significant contribution of four-phonon scattering is recorded which markedly alters the lattice thermal conductivity. Therefore, the combined effect of cubic and quartic phonon anharmonicity is seen to navigate the underlying physical mechanism and open up intriguing phononic interactions in Ge2Sb2Te5 at high temperature. Irrespective of three- and four-phonon processes, umklapp is seen to prevail over normal scattering events. Consequently, four-phonon scattering is found to notably reduce the lattice thermal conductivity of Ge2Sb2Te5 to 28% at room temperature and 42% at higher temperature. This quartic anharmonicity further manifests in the breakdown of T−1 scaling of thermal conductivity and challenges the idea of a universal lower bound to phononic thermal diffusivity at high temperature. The faster decay of thermal diffusivity compared to T−1 is rationalized encompassing the quartic anharmonicity via a modified timescale. These results invoke better understanding and precision to the theoretical prediction of thermal transport properties of Ge2Sb2Te5. Concomitantly, this also triggers the possibility to explore the manifestations of the lower bound of thermal diffusivity in materials possessing pronounced four-phonon scattering.
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