In this paper, the micromechanism of dynamic ductile damage and fragmentation in porous metallic materials is studied. Firstly, the dynamic ductile damage is described by employing the hollow spherical micromechanical model with a viscoplastic assumption of the constitution of the matrix. Then the local inertial effect on the dynamic ductile damage is investigated by directly comparing the results of the evolution rule of damage parameter, i.e. the porosity of the material, with and without consideration of the inertial influence. It is shown that the effect of the inertia is negligible in comparison with that of the strain rate. Consequently, a simpler form of the dynamic evolution equation of porosity is employed in the energy description for local fragmentation in porous material, and the dynamic evolution of fragment size versus damage under external load is obtained. At last, the work-hardening effect on the dynamic ductile damage is compared with that of the strain rate(viscosity). It is still shown that the former is negligible in comparison with the latter. It is revealed from the present work that the quasi-static result of ductile constitutive equation such as Gurson's might be able to expand to the study of dynamic ductile mechanical behaviors of materials, just by replacing the relevant yield stress of the matrix with a strain rate dependent form.
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