Optical measuring systems provide much more detail on the deformation of the blank in the bulge test than conventional contact height measuring systems. A significant increase in accuracy of the stress-strain curve can be achieved by fitting the surface to more complicated equations than the traditional spherical surface and by considering the local strain data to approximate the curvature for the midplane. In particular an ellipsoid shape is shown to be very accurate in describing the surface of the blank. Contact height measuring systems provide insufficient data to fit a surface to an ellipsoid shape and to establish local strain data. Pragmatic equations are proposed using the work hardening coefficient from the tensile test to approximate the same accuracy in stress-strain curves as obtained by optical measuring systems using the before mentioned evaluation method.
|Journal||Key engineering materials|
|Publication status||Published - 2013|