An Analytical Model for Explosive Compaction of Powder to Cylindrical Billets through Axial Detonation

An analytical model, describing an explosive compaction process performed axially on a powder assembly of cylindrical geometry, is discussed. The powder is encapsulated in a cylindrical metal container surrounded by an explosive pad, which is detonated parallel to the major axis of the compact. The pressure generated in the powder is a function of the nature and the thickness of the explosive material as well as the powder characteristics. The model is based on the principle of shock propagation in powder aggregate and, the detonation as well as the refraction wave characteristics of the explosives. For the purpose of validation and illustration, this investigation considers the explosive compaction of aluminium powder particles for different explosive pad thicknesses. The model brings-out a closed-form solution for densification of powders. The density of the final powder compact depends on the pad thickness. Inadequate pad thickness leads to under compacted core, while higher pad thickness leads to melting at the core leading to over all low density. The optimum pad thickness of the explosive to produce the highest densification is thus determined using the model. The densification depends on the size of the powder particles also, since; the heat generated by the high pressure shock wave melts the surface of the powder particles depending on the specific heat, thermal conductivity and the latent heat of the powder material. The study essentially covers the effect of the explosive pad thickness and the particle size of the powder on densification. The analytical results are compared with a few experimental data and the comparison is found to be satisfactory.