the opposite direction and the second moment of area is large in
the in-plane bending direction. However, when the sheet metal is
bent in the U-bending manner, the warp appears because the bending
moments Mrs at the two sides are in the same direction and
the second moment of area is small in the out-of-plane bending
direction.
the initial value within the very wide range of 1% from 130 to
280 MPa. However, if the residual stress does not exist in the sheet
metal, i.e. rsmax = 0 MPa, the press should not be given to the sheet
metal without the residual stress as it could cause the warp in the
opposite direction.
5