Abstract
A servo-controlled multiaxial tube expansion testing machine was developed to measure the plastic deformation behavior of sheet metals under biaxial stress condition in a large strain range. The test material was an interstitial free steel sheet. The test specimen was fabricated by bending and laser-welding the sheet into a tube specimen with an inner diameter of 44.6 mm and a wall thickness of 0.7 mm. Many linear stress paths in the first quadrant of stress space were applied to the tubular specimens using the servo-controlled multiaxial tube expansion testing machine. Moreover, biaxial tensile tests using a cruciform specimen were also performed to precisely measure the deformation behavior in a small strain range following the initial yielding. True stress-true plastic strain curves, the contours of plastic work in stress space up to an equivalent plastic strain of 0.15, and the directions of plastic strain rates were successfully measured. The test material exhibited differential hardening. Moreover, forming limit strains and stresses were determined.
