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In this article we propose to add stress-energy tensor to the Einsteinequations, assuming that the matter-energy and the metric space-time is nothingbut a continuous medium with some elastic properties. We first give a generalexpression of the stress tensor which is linearly related to the strain tensor.Then, we give the particular expression of the stress tensor for a spatiallyhomnogeneous and isotropic cosmological medium. After that we derive themodified Friedmann equations. In first approximation, we end up with the usualterm $\Lambda g_{\mu\nu}$ , where the cosmological constant$\Lambda=K\varepsilon$ is related with the bulk modulus K and the relativevariation of volume (dilatation). Then we derive corrections to the standardmodel in second approximation, which depend on these two new parameters.

Th\'eorie des champs des contraintes et d\'eformations en relativit\'e  g\'en\'erale et expansion cosmologique: Theory of stress and strain fields in  general relativity and cosmological expansion