13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- regions. Figure 5. Engineering stress–strain curve with major strain images from ARAMIS system The DIC measurements in the linear-elastic region allow the determination of Young’s modulus E, and Poisson’s ratio ν. For the foam with a density of 301 kg/m3 (closer to a porous solid) the deformation bands tend to be less inclined. For a loading speed of 1 mm/min in Fig. 6 are shown the following: the current stage in the engineering stress-strain curve (here one in the plateau region is chosen), the vertical displacements and Mises strains in that moment, and the variation of the Mises strains along a vertical line taken in the middle of the specimen (figure upper-left) at different stages of loading – the one represented hereby being depicted by a red curve. In the last registered stage (the last curve) the foam deteriorates significantly – close to 100% – and the curve becomes discontinuous. Figure 6. Mises strains and vertical displacements in the plateau region 3. Numerical simulation Based on the statistical analysis of the closed cells microstructures the geometric parameters were determined and the 3D representative volume (RVE) of the foams was built. Two strategies were considered: a model based on tangent hollow spheres for low density foams (Fig. 7a), respectively a solid cube from which were extracted spheres for higher density foams (Fig. 7b). Polyurethane was considered the material for the cell walls with Young’s modulus Es=1600 MPa and Poisson’s ratio
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