is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. This is an author-deposited version published in: https://sam.ensam.eu Handle IDKeywords: Multi-scale microstructure Cellular material Cork agglomerate X-ray microtomography Mechanical behaviour a b s t r a c tThis study focuses on the microstructural aspects of a cork-based by-product known as agglomerated cork and its influence on the compressive mechanical behaviour. The material consists in granulates of a natural polymeric foam -cork -mixed together with a small quantity of a bio-sourced resin.Optical and scanning electron microscopy (SEM) are first used to investigate on the bead geometry and placement and interfaces arrangement. Then X-ray computed tomography allows to study the spatial arrangement of agglomerated cork microstructure and hence to complete and confirm 2D observations. 2D and 3D observations show a transverse anisotropic material which is confirmed by the mechanical tests. SEM pictures demonstrate an intricate and heterogeneous material. Microtomography confirms the presence of macroporosities between cork granulates having a mean volume around 0.1 mm 3 . Cork cell specific geometry is also confirmed. The volume of those cells lies around 10 −5 mm 3 . Finally quasi-static compression tests are run to establish a link between microstructure and mechanical behaviour thanks to digital image correlation (DIC). Cork agglomerate demonstrates strong strain localisation at its surface caused by its multi-scale structure.

The Discrete Element Method (DEM), also known as Distinct Element Method (DEM), is extensively used to study divided media such as granular materials. When brittle failure occurs in continuum such as concrete or ceramics, the considered media can be viewed as divided. In such cases, DEM offers an interesting way to study and simulate complex fracture phenomena such as crack branching, crack extension, crack deviation under coupled mode or crack lip closure with friction. The fundamental difficulty with DEM is the inability of the method to deal directly with the constitutive equations of continuum mechanics. DEM uses forcedisplacement interaction laws between particles instead of stress-strain relationships. Generally, this difficulty is bypassed by using inverse methods, also known as calibration processes, able to translate macroscopic stress-strain relationships into local force-displacement interaction laws compatible within DEM frameworks. However, this calibration process may be fastidious and really hard to manage. The presented work proposes to improve the Distinct Lattice Spring Model in order to deal with non-regular domains, by using Voronoi cells, which allows to completely fill the volume space of discrete domains. With this approach, the rotational effects must be included in the contact formulation, which enables the management of large rigid body rotations. This work also introduces a simple

The fracture behaviour of a semi-crystalline bio-based polymer was studied. Dynamic fracture tests on strip band specimens were carried out. Fracture surfaces were observed at different scales by optical and electron microscopy to describe cracking scenarios. Crack initiation, propagation and arrest zones were described. Three distinct zones are highlighted in the initiation and propagation zone: a zone with conical markings, a mist zone and a hackle zone. The conical mark zone shows a variation in the size and density of the conical marks along the propagation path. This is synonymous with local speed variation. Microcracks at the origin of the conical marks in the initiation zone seem to develop from the nucleus of the spherulites. In the propagation zone with complex roughness, the direction of the microcracks and their cracking planes are highly variable. Their propagation directions are disturbed by the heterogeneities of the material. They branch or bifurcate at the level of the spherulites. In the arrest zone, the microcracks developed upstream continue to propagate in different directions. The surface created is increasingly smoother as the energy release rate decreases. It is shown that the local velocity of the crack varies in contrast to the macroscopic speed. A

The grinding process is continuously adapting to industrial requirements. New advanced materials have been developed, which have been ground. In this regard, new abrasive grains have emerged to respond to the demands of industry to reach the optimum combination of abrasive-workpiece material, which allows for both the minimization of wheel wear and increased tool life. To this endand following previous experimental worksthe present study models in 3D the wear behavior of Sol-Gel alumina abrasive grain using Discrete Element Methods. It is established that the alumina behaves as a ductile material upon contact due to the effect of high temperature and pressure. This model reproduces the third body generation in the contact, taking into account the tribochemical nature of the wear flat, w hich i s the most h armful type o f wear i n the grinding p rocess. The evolution of the wear during a complete contact is analyzed, revealing similarities in the wear of white fused alumina (WFA) and Sol-Gel (SG) alumina. However, the SG abrasive grain suffers less wear than the WFA under the same contact conditions. The proposed wear model can be applied to any abrasive-workpiece combination.

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Since the beginning of the last decade, few examples of multifilament models for dry fabrics have been presented in literature. This work deals with the simulation of a single yarn subjected to transverse impact. Inspired by the models previously developed by other authors, a revisited form of Discrete Element Method has been adopted to perform microscopic analyses in a more efficient computational environment. Transverse impact analysis onto a single KEVLAR KM2 yarn has been performed using this approach. Truss elements have been adopted to discretize yarn filaments instead of heavy computational 3D finite elements. A good agreement with literature results has been achieved with an important reduction of computational resource. In the end, a proposed scale transition is discussed.

Mechanical strength is an important critical quality attribute for tablets. It is classically measured, in the pharmaceutical field, using the diametral compression test. Nevertheless, due to small contact area between the tablet and the platens, some authors suggested that during the test, the failure could occur in tension away from the center which would invalidate the test and the calculation of the tensile strength. In this study, the flattened disc geometry was used as an alternative to avoid contact problems. The diametral compression on both flattened and standard geometries was first studied using finite element method (FEM) simulation. It was found that, for the flattened geometry, both maximum tensile strain and stress were located at the center of the tablet, which was not the case for the standard geometry. Experimental observations using digital image correlation (DIC) confirmed the numerical results. The experimental tensile strength obtained using both geometries were compared and it was found that the standard geometry always gave lower tensile strength than the flattened geometry. Finally, high-speed video capture of the test made it possible to detect that for the standard geometry the crack initiation was always away from the center of the tablet.

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. This is an author-deposited version published in: https://sam.ensam.eu Handle ID