Strain distribution analysis in ring upset forging and hot-rolling by photoplasticity

Abstract

Photoplasticity was used to determine the three-dimensional strain distribution in upset forged rings and in hot rolled bars. A 70 percent rigid Laminac mixed with 30 percent flexible Laminac polyester resin which simulates aluminium deformed at 425/sup 0/C, was used in the strain analysis. A good correlation was found between the neutral radius determined graphically from the three-dimensional strain distribution along the mid-section of the ring plotted against the relative distance r - r/sub 0//R - r/sub 0/, and the neutral radius determined using Avitzur's mathematical solutions for compressed rings. However, as has been indicated for metals as well, the interfacial friction factor m determined by another Avitzur's relationship to the 70:30 Laminac rings was found, in certain instances, to be in excess of unity. This tends to invalidate his theoretical solutions for determining the interfacial friction factor, m. The ratio of the final width to the original width (which is equivalent to epsilon/sub x/ at the edge of the rolled block) increased with reduction, thereby supporting the theoretical prediction of Oh and Kobayashi for spread during rolling. Double-bulging was found to be less in 1-in. wide blocks than in 2-in. wide blocks. Uniform spread on both edges of themore » block of this size was found to exist at higher reductions either at a roll speed of 0.2 or 0.05 rpm. Plane-strain was found to exist only when the 2-in. wide blocks were rolled at 0.2 rpm either at lower or higher percentage reductions. The viscoelastic property of the 70:30 Laminac mixture still stands as a major problem in reaching a quantitative strain distribution in either the compressed rings or the rolled blocks. « less

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