Abstract
Dynamic tensile extrusion (DTE) tests with the strain rate order of ~105 s−1 were conducted on coarse grained (CG) Cu and ultrafine grained (UFG) Cu. ECAP of 16 passes with route Bc was employed to fabricate UFG Cu. DTE tests were carried out by launching the sphere samples to the conical extrusion die at a speed of ~475 m/sec in a vacuumed gas gun system. UFG Cu was fragmented into 3 pieces and showed a DTE elongation of ~340%. CG Cu exhibited a larger DTE elongation of ~490% with fragmentation of 4 pieces. During DTE tests, dynamic recrystallization occurred in UFG Cu, but not in CG Cu. In order to examine the DTE behavior of CG Cu and UFG Cu under very high strain rates, a numerical analysis was undertaken by using a commercial finite element code (LS-DYNA 2D axis-symmetric model) with the Johnson – Cook model. The numerical analysis correctly predicted fragmentation and DTE elongation of CG Cu. But, the experimental DTE elongation of UFG Cu was much smaller than that predicted by the numerical analysis. This difference is discussed in terms of microstructural evolution of UFG Cu during DTE tests.
Highlights
The dynamic tensile extrusion (DTE) technique is a newly developed mechanical test [1]
Soft-recovered fragments of coarse grained (CG) and ultrafine grained (UFG) Cu after DTE are shown in Fig. 1a ; the conical fragments are the remnants remained in the DTE die
CG Cu was fragmented into 4 pieces while UFG Cu was fragmented into 3 pieces
Summary
The dynamic tensile extrusion (DTE) technique is a newly developed mechanical test [1]. In the case of cubic CG metals (i.e. Cu and Ta), recrystallization hardly occurred during DTE significant adiabatic heating is expected in association with high strain rate deformation (usually higher than 105 s-1).
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