multiscale modeling solid mechanics

Hello all,

Why is there no body force considered in the equilibrium equations of the RVE in the homogenization technique?

The overall response of the RVE is obtained by solving the RVE boundary value problem under prescribed boundary conditions (either traction or displacement BC) without considering the body force. 

I am looking for introductory-level papers/texts on multiscale modelling of solids. Please suggest some titles which give introduction alongwith a summary about the latest advances in this field. I will be thankful for your suggestions.

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