Overall properties of a soft porous material: Surface tension effects

The behavior of a porous material on which air-solid surface tension effects are not negligible is studied experimentally and theoretically. Overall properties were measured on mixtures of foams and pastes. Theoretical estimates were obtained in the framework of an upscaling approach. It was observed and predicted that the overall properties of the porous medium depend upon the deformability of the pores in the elastic regime whereas in the plastic regime, the porous medium yield stress is the same as the matrix yield stress. Deformability of the pores is accounted for by a capillary number defined as the ratio of the matrix elastic modulus to the pore capillary pressure in the linear regime and as the ratio of the matrix secant modulus to the pore capillary pressure in the non-linear regime. This non-linear capillary number tends toward zero when the plastic plateau is reached.