PSI - Issue 14

Sukamal Adhikary et al. / Procedia Structural Integrity 14 (2019) 127–133 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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Compaction of powder mixture involves reduction of volume and re-arrangement of particles of the initial charge mass due to compression. It is followed by consolidation of the charge mass through formation of inter particulate bond during the consolidation phase to facilitate compaction as observed by Odeku (2007), Mohan (2012), and Antikainen (2003). During compression of the charge mass, the particles rearrange under low applied load and reduce the interparticle distance. The finer particles accommodate in the voids between larger particles. This results in increase in density with increase in applied load. As the applied load increases, the voids minimize, leading to increase in surface of contacts between particles which result in higher frictional forces and resistivity to compaction. As the applied load is further increased, plastic/elastic deformation of the particles occur along with fragmentation of the particles. However, with the change in shape of the particles, the contact areas progressively increase and so also the resistance to compaction as observed by Odeku (2007) and Mohan (2012). Thus, a state is reached when even with further increase in applied load, compaction is not manifested with increase in density as is observed with an applied load of 9 tons for the charge mass mixture of 100 gm. The compacting phenomenon is also validated through SEM images. Images at Fig 4 (a) to (f) represent the microstructure of the MTV pellets formed with applied load of 1 ton, 3 tons & 5 tons respectively and captured at 50X [Fig. 5(a), (b) & (c)] & 1600X [Fig. 6(a), (b) & (c)] magnified images. The images reveal the following two facts:  The inter particles distance progressively reduced and compaction increased with increase in applied load from 1 ton to 5 tons. This is ratified by reduction of void spaces depicted as dark regions in Fig 5(a), (b) & (c).  The particle size of magnesium progressively decreased with increase in load owing to fracture/permanent deformation of the magnesium particles with applied load as evident in Fig 6(a), (b) & (c) with 1600X magnification. Both these factors have led to increase in density with increase in applied load. However, there would always be a physical limit to which any given charge mass could be compacted with progressive increase of load. The maximum density is obtained as 1.663 gm/cc at an optimal applied load of 8 tons. There has been a slight decrease in density of the pellets to 1.649 gm/cc even when the applied load was increased to 9 tons from 8 tons which may be construed as experimental error.

Fig. 5(a) Magnification 50X, load 1ton (b) Magnification 50X, load 3 tons (c) Magnification 50X, load 5 tons

Fig. 6(a) Magnification 1600X, load 1ton (b) Magnification 1600X, load 3 tons (c) Magnification 1600X, load 5 tons

The practically calculated results of density variation with charge mass (Fig. 4) highlight that the density progressively increased with the increase in the weight of pellets. The increase in density is however, in the second place of decimal. Maximum density of 1.587 gm/cc is recorded for a L/D ratio of nearing unity and for a charge