Plastic behavior of aluminum-killed steel following plane-strain deformation
- PDF / 869,661 Bytes
- 9 Pages / 603.28 x 788 pts Page_size
- 86 Downloads / 249 Views
I.
INTRODUCTION
SEQUENTIAL stamping operations are often used for sheet forming in the automotive industry. These operations produce multiple strain paths in a given element of the stamping which can in turn affect the hardening behavior, flow rule, and ultimate ductility of that element. A knowledge of the changes undergone during the multiple strain path is essential for accurate mathematical modeling of the stamping operation. Polakowski and Mostovoy ~'2 observed gross strain softening and "wavy" flow curves after changing deformation paths. The effect was similar for polycrystalline copper, iron and several iron alloys, and copper alloys (70/30 brass, e.g.). The apparent softening and wavy flow were correlated with the appearance and propagation of localized strain zones similar to LiJder's bands. Contrary to L~ider's banding, the effect could not be produced by an intermediate aging treatment, nor was the effect composition-dependent. Large stress transients were observed for some alloys which do not exhibit strain-aging. Pascoe3compared tensile and compressive work-hardening curves of an HSLA steel in rolling (RD) and transverse (TD) directions after a rolling direction tensile prestrain of 3 to 5 pct. The subsequent stress-strain curves in both directions showed an increased yield stress, followed by reduced work hardening rate and reduced total elongation. The coaxial strain paths showed sharper yield behavior than the 90 deg rotation paths. In 1973, Ghosh and Backofen, 4 using two-stage strain path tests, identified two kinds of mechanical behavior relating biaxial prestrain to subsequent uniaxial tensile curves. The ferritic type (aluminum-killed steel, e.g.) shows a higher subsequent tensile yield stress after biaxial straining, and this differential increases for larger prestrains. The nonferritic type (70/30 brass, e.g.) shows premature yielding in subsequent tension, with the effect enhanced at larger prestrains. Commercially pure aluminum, 1100-0, was intermediate, showing only small effects of strain path R.H. WAGONER, formerly Staff Research Scientist, General Motors Research Laboratories, is now Associate Professor, Department of Metallurgical Engineering, The Ohio State University, 116 West 19th Avenue, Columbus, OH 43210. J.V. LAUKONIS is Staff Research Scientist, Physics Department, General Motors Research Laboratories, Warren, MI 48090-9055. Manuscript submitted August 2, 1982.
METALLURGICALTRANSACTIONS A
changes. Although not specifically discussed, the subsequent stress-strain curves showed reduced work hardening in steel, enhanced work hardening in brass, and little change in aluminum. Therefore, in each case, the subsequent flow curve tended to rejoin the unprestrained flow curve. Subsequent two-stage strain path tests have been performed in a tensile-tensile mode (45 deg and 90 deg major strain axis rotation) for Cu, 5 brass, 5 several AI alloys, 5'6 and steel.5'7 The results have generally followed a single pattern: a high subsequent yield stress is followed by a low workhardening ra
Data Loading...
