A new thermo-mechanical damage model is constructed in the present contribution using a two-scale approach. The model is deduced from microstructures with microcracks evolving dynamically in a nominally brittle material and for which the fracture energy dissipated at the moving tips is converted to heat. The use of an homogenization method based on asymptotic developments leads to a damage evolution law coupled with the macroscopic thermoelasticity system. The obtained model accounts for inertial effects, thermo-elastic coupling and heat dissipation effects due to damage propagation. The local effective response of the model is analyzed with special emphasis on thermal evolutions. Strain-rate and microstructural size effects are illustrated. Cooling and heating regimes associated to damage initiation and propagation are identified and analyzed for different values of the model parameters. Results of numerical simulations for a compact compression test are presented and compared with the experimental data for temperature field measurements during rapid failure of PMMA samples. Good agreement is found between the model predictions and the measured thermal evolution.