I am using Abaqus UMAT subroutine to model wear damage between two contacting steel surfaces. I need to get the absolute maximum shear stress as it is a function of my wear damage model. I have tried using a utility routine called CALL SPRINC to get the 3 principal stresses ( σ 1,2,3). Since abs max shear stress = (σ1- σ 2)/2, ( σ 1- σ 3)/2, (σ 2- σ 3)/2 (the numerically largest of these).

However, it gives me principal stresses for each number of element and increment (which are thousands or maybe more than that), and I do not know how to assign the values to different variables in order to calculate the abs max shear stress using the eq. above. How do I assign the values in different variables?

I have also tried using the trigonometry (with the calculation of discriminant) to solve the cubic formulation to get the principal stresses manually but there is an error in trying to run the program as follow: The executable standard.exe aborted with system error code 1073741676.

1. Is there any way to directly get the abs max shear stress in UMAT subroutine?

2. How do I assign principal stress values in different variables?

Thank you!