Abstract:A new non-quadratic orthotropic yield function is developed in the present paper. It does not have those limitatioins which existing non-quadratic anisotropic yield functions have> such as being usable only for the plane stress problems and in-plane isotropic sheet metals, and that the directions of principal stress or the exponent in yield function can not be arbitrary, etc. Furthermore all of the material constants involved in this yield function can be determined by performing only uniaxial tension test.
    This yield function contains three new parameters, of which each one is present for one principal plane of anisotropy.Their values can be, generally, selected to equal 3. Other methods to determine the value of these parmeters are discussed and given in this paper.
    From the regression estimate for the yield stress in five directions of several kinds of titanium metal sheet,it is obtained that the suitable value of exponent in yield function for titanium sheets is 6 or 8. This is confirmed from the use for several plastic deformation problems of titanium sheets.

Key words: orthotropy   triaxial stress   yield function