Ref HAL: hal-02163717_v1
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Since 2004, the wooden panel of the “Mona Lisa” painting by Leonardo da Vinci has been studied by an internationalresearch group of scientists [1,2] and several experimental campaigns have been carried out to understand itscharacteristics and provide information for the Artwork's conservation [3]. Among these, the implementation of its"digital twin" is here presented as a fundamental step for its conservation. Indeed, this digital twin is providing a deeperunderstanding of the mechanical characteristics of the panel, and after it has been accurately calibrated, it will providethe means for evaluating the stress states which the Artwork undergoes when the surrounding climatic conditions vary.Moreover, it will allow to evaluate in a non-invasive way the effects produced on the Artwork by any changes of itsframing conditions, including the internal stresses or the external forces that it can bear without damage.The implementation of the digital twin, through a Nelder-Mead optimization scheme, starts from the definition of theshape of the Artwork, through optical methods [4], and the identification of the boundary conditions, through anexperimental campaign based on the use of a film sensitive to pressure [5]. During the whole year, while exhibited inthe conditioned display case, the panel continuously tends to deform, due to the slight variations in the surroundingenvironment. Its mechanical behaviour is automatically monitored and recorded every 30 minutes by an ad hocequipment placed close to its back face: four miniature load cells (located at the four corners) measure the forces pressingit against the frame, and three displacement transducers measure its deflection at mid height. Finally, a method is heredescribed to compare two different framing conditions, through the numerical computation of point-by-point stress anddeformation differences, in order to provide information for optimizing settings and constraints to Conservators.

Ref HAL: hal-02160283_v1
DOI: 10.1073/pnas.1901160116
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Capillary effects, such as imbibition drying cycles, impact the mechanics of granular systems over time. A multiscale poromechanics framework was applied to cement paste, which is the most common building material, experiencing broad humidity variations over the lifetime of infrastructure. First, the liquid density distribution at intermediate to high relative humidity is obtained using a lattice gas density functional method together with a realistic nanogranular model of cement hydrates. The calculated adsorption/desorption isotherms and pore size distributions are discussed and compare well with nitrogen and water experiments. The standard method for pore size distribution determination from desorption data is evaluated. Second, the integration of the Korteweg liquid stress field around each cement hydrate particle provided the capillary forces at the nanoscale. The cement mesoscale structure was relaxed under the action of the capillary forces. Local irreversible deformations of the cement nanograins assembly were identified due to liquid–solid interactions. The spatial correlations of the nonaffine displacements extend to a few tens of nanometers. Third, the Love–Weber method provided the homogenized liquid stress at the micrometer scale. The homogenization length coincided with the spatial correlation length of nonaffine displacements. Our results on the solid response to capillary stress field suggest that the micrometer-scale texture is not affected by mild drying, while nanoscale irreversible deformations still occur. These results pave the way for understanding capillary phenomena-induced stresses in heterogeneous porous media ranging from construction materials to hydrogels and living systems.

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Ref HAL: hal-02153545_v1
DOI: 10.1080/19648189.2019.1623082
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The development of tools, using a micromechanical approach, predicting the macroscopic behaviour of heterogeneous materials such as concrete, requires the knowledge of their microstructures (geometrical properties of phases), the behaviour of phases and the interaction laws between phases. This study is focused on a numerical modelling of a local shear test on a cement paste-aggregate composite using a cohesive zone model with the objective to identify the behaviour of the cement paste-aggregate interface. The computations use a 3D finite element modelling of the composite, using a cohesive law at the interface between the two phases. The cohesive model mimics the behaviour of the well-known interfacial transition zone. This work presents a methodology for the identification of cohesive law parameters at different stages of hydration and for different confining stresses using experimental results.

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Ref HAL: hal-02153495_v1
DOI: 10.1103/PhysRevE.99.062903
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Using the contact dymanics method together with the finite element method, we simulate the uniaxial compression of assemblies of elastic cylinders. The numerical model accounts for finite deformations of the particles through the neo-Hookean constitutive equation and solid friction between the particles. A quantitative comparison with experiments carried out with centimetric rubberlike cylinders, with local deformations of the particles determined by image correlation, is proposed. We show that the simulations accurately capture the details of both the microstructure and the macroscopic behavior of the real granular system, demonstrating the relevancy of the numerical approach.

Commentaires: This work was partially supported by Labex NUMEV (ANR-10-LABX-20)

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Ref HAL: hal-02137074_v1
DOI: 10.1186/s13662-019-2126-0
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By using the asymptotic analysis method as regards two-scale convergence we derive the effective behavior of a fine mixing of piezoelectric material and piezomagnetic material. It can be shown that an electromagnetic coupling arises only when each phase is connected and the interface is electrically and magnetically impermeable.

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Ref HAL: hal-02143278_v1
DOI: 10.1016/j.otsr.2019.02.018
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Background: Surgical site infection is reputed to be infrequent in anterior cervical spine surgery. Data on pathophysiological mechanism and risk factors are sparse. The relationship between local site infection and pharyngoesophageal perforation is unclear. The present study aimed: (1) to estimate the incidence of surgical site infection in anterior cervical spine surgery, (2) estimate the incidence of associated pharyngoesophageal perforation, and (3) suggest a decision-tree for early management of this twofold issue. Hypothesis: Although with very low incidence, anterior cervical spine surgical site infection and pharyn-goesophageal perforation are frequently associated. Material and methods: A 2-center retrospective study included all anterior cervical spine surgeries between January 1, 2007 and December 31, 2016. Data were provided by the two medical information departments. Patients undergoing anterior revision surgery on the cervical spine were included. Files were analyzed to determine whether the revision surgery was secondary to surgical site infection. Results: In total, 1475 patients with anterior cervical spine surgery were identified: 1180 in center A (80%) and 295 in center B (20%). The rate of revision surgery for surgical site infection was 0.34% (5/1475). There were 3 cases of pharyngoesophageal perforation (0.2%). Discussion: The incidence of revision surgery for anterior cervical spine surgical site infection was comparable to rates in the international literature (0.07-1.6%). An association between surgical site infection and pharyngoesophageal perforation was frequent, but not statistically significant. This complication is extremely serious, requiring urgent multidisciplinary management. Level of evidence: IV, retrospective study.

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Ref HAL: hal-02143259_v1
DOI: 10.1016/j.otsr.2019.01.017
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Background: CT analysis of arthroscopic subtalar arthrodesis rarely finds complete fusion. The aim of the present study was to determine, at 12 months' follow-up of arthroscopic subtalar arthrodesis: (1) CT fusion ratio, (2) functional results, and (3) the correlation between the two. Hypothesis: Incomplete fusion ratio does not impair the result of arthrodesis. Materials and methods: A continuous series of 22 arthroscopic subtalar arthrodeses was assessed at 12 months' follow-up. The procedure used a posterior approach without bone graft, with stabilization by 2 compression screws. Clinical assessment comprised of a numerical analog pain scale (NAS, AOFAS and SF12) scores. Satisfaction was assessed on an NAS and on Odom's criteria. CT analysis at 12 months determined the posterior subtalar joint fusion ratio. Results: At follow-up, 2 patients showed non-union (9.1%). Among the 20 patients with fusion (91%), fusion was complete (> 67 •) in 16 (72.7%) and partial (34-66%) in 4 (18.2%). Mean fusion ratio at 12 months was 77.7% ± 14.8 (range, 36-98%). Functional gains () were: pain NAS 4.8 ± 2 (range, 1-10) and AOFAS score 31.1 ± 14 (range, 10-59). Mean satisfaction score was 8 ± 2.5 (range, 3-10). There were no significant correlations between fusion ratio and any clinical or satisfaction scores. Conclusion: Although clinical gain was systematic, functional and satisfaction scores were independent of whether subtalar fusion ratio was partial or complete. Level of evidence: IV, retrospective study.

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