THERMAL-STRESS WAVE AND SPALLATION INDUCED BY AN ELECTRON-BEAM

Thermal stress wave and spallation in aluminium alloy exposed to a hig h fluency and low energy electron beams are studied theoretically. A s imple model for the study of energy deposition of electrons in materia ls is presented on the basis of some empirical formulae. Under the str ess wave induced by energy deposition, microcracks and/or microvoids m ay appear in target materials, and in this case, the inelastic volume deformation should not vanish. The viscoplastic model proposed by Bodn er and Partom with corresponding Gurson's yield function requires modi fication for this situation. The new constitutive model contains a sca lar field variable description of the material damage which is taken a s the void volume fraction of the polycrystalline material. Incorporat ion of the damage parameter permits description of rate-dependent, com pressible, inelastic deformation and ductile fracture. The melting phe nomenon has been observed in the experiment, therefore one needs to ta ke into account the melting process in the intermediate energy deposit ion range. A three-phase equation of state used in the paper provides a more detailed and thermodynamical description of metals, particularl y, in the melting region. The computational results based on the sugge sted model are compared with the experimental test for aluminium alloy , which is subjected to a pulsed electron beam with high fluency and l ow energy. (C) 1997 Elsevier Science Ltd.