Experimental and finite element study of armature dynamics in helical magnetic flux compression generators.

摘要

Armatures are the key mechanical component and have significant influences on the performance of helical Magnetic Flux Compression Generators (MFCGs). However, the detailed understanding of the expansion and interaction behaviors of armatures in helical MFCGs has been not well reached and not systematically investigated. The ultimate objective of this dissertation is to systematically investigate the detailed behaviors of armatures in helical MFCGs by means of the finite element analysis and simulation.; The metallurgical observations on samples from the armatures show that the microstructural evolution during the armature expanding process is mainly caused by the rapid plastic deformation and the axial crack will be first initiated on the expanding armature.; The chosen material constitutive models and equations of state for the finite element analysis and simulation are verified by the explosive experiments. They are extensively used to explore the expansion and interaction behaviors of armatures in helical MFCGs. The following main conclusions are obtained: (1) There is a serious detonation end effect, which might cause an additional magnetic flux loss for the improper helical MFCGs' design. (2) The expansion angle of the armature in helical MFCGs varies with the post-detonation time and with the axial positions of the armatures. If the armature expansion angle is assumed to be a constant, its value should be the average expansion angle. (3) There is no the scaling effect on the expansion angle of the armature. The expansion angle is only a function of the densities of the armature and the explosive, and the armature wall thickness ratio. (4) The aluminum 6061-T6 armature is the best among five possible armature structures. (5) The crowbar has a locally significant influence in armature expansion behaviors. (6) During impacting process of the armature with the helical wires/insulators, most of the insulator material has been squeezed out of the contacting zone. However, some fragmented insulator materials are still trapped on the contacting zones. (7) The deformed core copper wire does not break down the adjacent insulator to contact the adjacent core copper wire. (8) The “turn-skipping” is mainly governed by the eccentricity of the armature with the stator, the armature wall thickness tolerance, the pitch of the helical coils and the armature expansion angle. The criteria for preventing the “turn-skipping” are provided.