A B C D Fig. 10 — LSDYNA simulations of the setup. A — lw < lcoil; B — lw = lcoil; C — lw > lcoil; and D — determination of the collision angle . A C B D Fig. 11 — Simulation results showing the radial impact velocity and angle for samples with various orientations, simulated using a peak current of 500 kA at 20 kHz, working lengths of 10 and 7 mm, and coil widths of 10 and 15 mm. Each point represents a distance of 1 mm. teraction area between parent and flyer, and as the working length exceeds the coil width, the area of noticeable interaction segments into two bands, split by a zone of apparently less-disturbed, metallic bright material. Experimental Results – Varied Energy To ensure the results presented above could be applied to other charging energies, several working distances were selected for further analysis at higher and lower pulsing energies using the 15-mm coil. As the energy was changed for a given working length, the width of the interaction areas tended to increase or decrease in accordance with the charging voltage; however, the general interface characteristics seen in Fig. 5A and B (areas of debris, undisturbed areas, etc.) remained constant — Fig. 6A. At higher energies of 15.7 and 16.8 kJ (0.004 and 0.005 kWh), welding occurred for working lengths of 4 and 7 mm, respectively. Figure 7 shows metallographic analyses of these samples. The increase in welding length in accordance with the working length is apparent. For the 10-mm coil, a good weld could be obtained with a discharge energy of 11.5 kJ (0.003 kWh) and working length of 4 mm — Fig. 6B. At four positions around the part (45, 135, 225, and 315 deg), the peel test resulted in a failure in the aluminum base material. Welding experiments with an increased working length of 12 mm at the same energy failed. The specimen showed material failure in the form of cracks and spalling — Fig. 6C. Experimental Results – Deformation of the Flyer Part The visioplastic analysis showed that independent of the working length, the deformation behavior of the flyer tube is quite nonuniform — Fig. 8. The experiments were performed with the 15-mm coil at 11.5 kJ. The aluminum flyer tubes had a wall thickness s = 1.5 mm, and the initial standoff was 2.5 mm. For all working lengths, the highest elongation can be found close to the free edge of the flyer tube. A decrease of the elongation along the tube axis can be seen for all working lengths. Only for the experiments with an intermediate working length between 7 and 13 mm, a characteristic increase in elongation at 7 mm from the flyer edge can be observed. Results of Numerical Simulation In addition to using PDV measurements, numerical simulation results were validated by comparing the final flyer-parent interface given by numerical simulation with metallographic examinations — Fig. 9. The presented specimens are the same as shown in Fig. 7. The final collision angle, the length of the area in contact from the undeformed free edge to the position of the bend, and the flyer part wall thickness at the position of the bend were compared. All simulated parameters show acceptable accordance with the experimental results so that the numerical simulations were valid for the assessment of flyer deformation. As the purpose of WELDING RESEARCH 106-s WELDING JOURNAL / MARCH 2016, VOL. 95
Welding Journal | March 2016
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