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Electromagnetic Expansion and Fragmentation of Hollow Aluminium 5052 Tube

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Document pages: 19 pages

Abstract: Electromagnetic forming is a high-speed formingtechnology by which hollow profiles can be compressed or expanded. It is donewith a pulsed magnetic field to apply Lorentz’ forces at electrically conductivematerial. Electromagnetic hollow tube expansion is limited by the fragmentationtendency. This work attempts to use a combination of analytical andcomputational approach to compute the net tangential stress during tubeexpansion. A simplified analytical framework to estimate the temporal evolutionof plastic stresses present in aluminium alloy AA5052 at low and high appliedmagnetic pressures is developed based upon dynamic imaging. The time resolvedimages captured using current synchronised high speed camera record the overalldimensional changes of the tube that is validated by multi-physics simulationof expansion process. Imaging of hollow tube expansions at two selected peakcurrents has been carried out at various current levels in the range 76 - 160kA. The direct visualisation of the increase in the tube diameter at twocurrent levels provided a comparison of the developing net tangential stressesin the hollow tube during the undamaged and fragmented expansion. Imaging oftube expansion also facilitates the estimation of the strain rate experiencedby the tube and was in the range of ~1700 s-1 to ~1200 s-1.The propensity of fragmentation was found to be due to the level and durationof generated tangential stresses above the yield stress during expansion of thealuminium tubes. Presented study provides a mean of exploiting the enhancedformability of aluminium alloys using electromagnetic forming.

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