A testing procedure for measuring flow properties of powders is developed which makes it possible to use results from triaxial tests in the Jenike bin theory. For the elaboration of the results a numerical method is used, based upon the Warren Spring equation (τ/C)N = (σ + T)/T. In this equation σ and τ are the normal and shear stresses respectively, C and T the cohesion and tension, and N a curvature parameter. A constant K = C/T and a constant curvature parameter N are assumed for a material. The algorithm used is a least-squares method using Newton's zero finding technique. The solutions obtained by this procedure are not influenced by the initial estimates.
Eelkman Rooda, J., & Haaker, G. (1977). A testing procedure for triaxial tests and a numerical method for the calculation of powder flow properties. Powder technology, 16(2), 273-280. https://doi.org/10.1016/0032-5910(77)87013-7