New Yield Function

The equation for the yield function is

The yield function provides continuous yield under both tensile and compressive loads. For a material with no prior plastic deformation, the first yield surface is a point at the origin which denotes the stress free state. The hardening parameter a is zero at this point. As the load increases, the surfaces harden and the material deforms plastically until in the limit of the plastic strain trajectory tending to infinity, the final failure surface corresponding to a = 1 is reached.

Details of parameters and parameter determination procedures are in Dube (2004). The new yield function was developed to provide a comprehensive solution to the issues that were detected (Dube, 2004) with the HiSS yield function of Desai (2001). The problems with HiSS arise as unlike the new yield function, the HiSS function does not start at the origin of the stress axes. Only the final yield surface, in terms of R, b, and g is the same for both functions. For the new function, yield surfaces that govern deformation from zero stress through to the final failure start at the origin and expand in under both tensile and compressive loading, unlike HiSS, where all surfaces start at J1=-3R.