On the Parameter Identification of Polynomial Anisotropic Yield Functions

Abstract

Nonquadratic anisotropic yield functions have been developed in recent years for many lightweight automotive sheet metals. Realization of the improved performance of these advanced anisotropic yield functions depends in part on a careful calibration of their material constants via simple mechanical tests. This paper describes a novel approach on the parameter identification of plane–stress polynomial anisotropic yield functions by recasting them in a special form in terms of two principal stresses and one loading orientation angle. Independent mechanical tests for the parameter identification can thus be classified according to the plane stress state and the in-plane loading orientation, respectively. Parameter identification options have been examined in detail for a fourth-order homogeneous polynomial anisotropic yield function using the proposed approach. Some new insights have been gained on the permissible types and the number of independent mechanical test measurements per type that are needed for fully calibrating the material constants of the fourth-order yield function. The use of equal biaxial plastic strain ratio instead of equal biaxial yield stress makes the experimental calibration of the yield function more feasible as only simple in-plane uniaxial tension and out-of-plane compression tests of sheet metal samples are required.