function [stress sigma_plastic sigma_viscous  mechanism] = stress_function_cellmat(Tg_0,T,Tg,eps_dot,eps)

k_b = 1.38064852E-23; % Boltzmann Constant

% ree-eyring data
v = 2.5E-27;
Q = 7.31E-19;
eps_dot_0 =  10E56;



% viscous flow data
eta_0 = 2.788E6;
C1 = 1.4;
C2 = 17.3;

T_Tg = T/Tg;

% calculate stresses for each regime corresponding to eps_dot and T/Tg

sigma_plastic = k_b*T_Tg*Tg_0/v*asinh(eps_dot/eps_dot_0*exp(Q/(k_b*T_Tg*(Tg_0)))); %no pressure dependency, can be added of course

sigma_viscous = 3*eps_dot*eta_0*exp((-log(10)*C1*(T_Tg-1)/(C2/Tg_0 + T_Tg -1)));

if T_Tg < 1
stress = sigma_plastic;
mechanism = 1;
elseif sigma_plastic <= sigma_viscous
 stress = sigma_plastic;
 mechanism = 1;
elseif sigma_plastic > sigma_viscous
    stress = sigma_viscous;
    mechanism = 2;
end