Theory Manual Version 3.4
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Section 5.6: Reactive Damage Mechanics Up Section 5.6: Reactive Damage Mechanics Subsection 5.6.2: Free Energy Density and Stress

### 5.6.1 Bond-Breaking Reaction

The reactive damage mechanics framework was first described in [58]. It is used to model damage in an elastic solid as a reaction that transforms intact (elastic) bonds into broken bonds, Here, is the material associated with bonds ( for intact bonds and for broken bonds). The material is modeled as a constrained mixture of these two constituents . Whereas intact bonds may store free energy, broken bond sustain none. This framework assumes that isothermal conditions prevail. Thus, any heat generated by the dissipative damage reaction must be radiated from the continuum to preserve a constant temperature. In an isothermal framework, the free energy density is also equal to the strain energy density.
The referential mass density of the solid mixture is (mass of solid per volume in its referential, stress-free configuration), which remains constant throughout an analysis. The material associated with intact bonds has an apparent mass density while that associated with broken bonds is such that the mixture mass balance is satisfied by
Section 5.6: Reactive Damage Mechanics Up Section 5.6: Reactive Damage Mechanics Subsection 5.6.2: Free Energy Density and Stress