  In this article we propose to add stress-energy tensor to the Einstein
equations, assuming that the matter-energy and the metric space-time is nothing
but a continuous medium with some elastic properties. We first give a general
expression of the stress tensor which is linearly related to the strain tensor.
Then, we give the particular expression of the stress tensor for a spatially
homnogeneous and isotropic cosmological medium. After that we derive the
modified Friedmann equations. In first approximation, we end up with the usual
term $\Lambda g_{\mu\nu}$ , where the cosmological constant
$\Lambda=K\varepsilon$ is related with the bulk modulus K and the relative
variation of volume (dilatation). Then we derive corrections to the standard
model in second approximation, which depend on these two new parameters.
