MECHANICAL AND FRACTURE-BEHAVIOR OF POROUS MATERIALS

The elastic moduli of porous materials represented as a combination of spherical, cylindrical or disk shaped holes or solid elements was calculated using a self consistent method. A yield criterion could be found by stating that the elastic distortion energy evaluated with these moduli was equal to a critical value. Another yield criterion could be approximated from the results of finite elements computations using the homogenization technique. These criteria possess the same homogeneity as the yield criterion of the dense material. The fracture toughness of syntactic foams could be explained by the local stress distribution in the glass spheres. In the case of ductile porous nickel the COD at initiation decreased as the fracture strain. This material exhibited a large tearing modulus whose decrease when the porosity was increased could be taken into account by the damage parameter. Fatigue crack propagation rates could also be rationalized with the use of the damage parameter and by reducing the surface of the material to be fractured.