calculating these data directly using the µCT images will be presented in this paper. This method based on finite element modeling is not a direct experimental measurement but is derived from the images of the real microstructure. Material and Methods Materials The material was produced using highly porous vitreous carbon foam (relative density * r S 0.98 – with ρ* the apparent density of the foam and ρ S the density of the constitutive material). This preform was produced from the pyrolysis of a polymer foam. Fig. 1-a and Fig. 1-b presents two secondary electron microscope (SEM) pictures respectively at low and high magnification of the porous vitreous carbon foam. Unfortunately this foam does not have sufficient mechanical and corrosive strength for shock absorber or fuel cell applications. the foam was thus densified by vapour deposition with pyrocarbon (PyC) or silicon carbide (SiC) using respectively propane and methiltrichlorosilane/hydrogen (MTS/H2) precursor [1-2-4-5] (Fig. 1-c). The deposition time was adjusted to obtain the desired thickness and thus the desired relative density. The final material is an open foam characterised by its relative density ρr and the number of pores per inch (ppi). In this paper only a PyC densified foam was analysed with a relative density and a cell size of 0.14 and 60 ppi respectively. (a) (b) (c) Fig. 1 : MEB pictures of he foam. (a) Magnification x50 to illustrate the mesoscopic morphology of the non densified foam. (b) and (c) Magnification x500 to illustrate the microscopic morphology of a ligament respectively before and after densification. Adapted from [1]. Fig. 2-a presents the stress/strain compression behavior of a 60 ppi foam densified with PyC up to a relative density of 0.14. The sample was placed between two plates. The superior plate is mobile and controlled in displacement. The device records the load (F) and displacement (l-l0), the stress ( 0 F S ) and the true strain ( 0 0 ln(1 ) l l l ) being calculated using S0 as the initial surface (S0=78.5 mm2) and l 0 the initial length of the sample (l0=10mm). This curve is in good agreement with the standard compression behavior of foams [3], as presented on Fig. 2-b. The different domains are highlighted with numbers. Firstly (1) the material exhibits a pseudo elastic behavior, in this part of the curve, or during unloading, the Young’s modulus is measured. The value is about 320 MPa. Then a crack appears and the load decreases (2) to reach a stable value often named the plateau (3). In this part the load is almost constant with some fluctuations around an average value. These perturbations are generally attributed to successive brittle failures corresponding to individual pores crushing. The average stress value of the plateau (σpl –estimated by an average of the values in this domain) is about 2 MPa, the plateau appearing for a strain higher than about 0.02 in the present case. In this domain the material 40
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