I write a uel subroutine for plane stress state using the method of Javier Bonet's book, "nonlinear xxxxxxx FEM static". The method is given in exercise 6.1 and 6.2. the question is "even the Residual and the tangent matrix are correct, the code can not work in abaqus for a uniaxial tension test. after several step, it diverges." Does anybody ever successfully code the plane stress probelm for incompressible neo-hookean model in abaqus? can anybody share the code or possible method to solve the problem?