data = SpecimenRawData1; %polyeth_stress_relax
data = table2array(data);
time = data(35:end,1);
strain = (data(35:end,2) ./ 80.6) - .0011; %unitless
stress = data(35:end,3) ./(12.85 * 2.75); %MPa

fit = polyfit(strain(1:4), stress(1:4), 1);
sigma0 = stress(2);
epsdot = .02/60;

relaxtime = data(3973:end,1);
strain_r = strain(3938:end);
stress_r = stress(3938:end);

K = fit(1) %UNRELAXED MODULUS OF ELASTICITY [MPa]
eta = stress_r(1)/epsdot%MPa-s
tou = eta/K %1/s

figure(2)

Erel = K .* exp(-(relaxtime)/tou);
plot(relaxtime, Erel), xlabel('Time relaxed (s)'), ylabel('Relaxed Modulus (MPa)'), title('Stress Relaxation of Polyethylene for $\dot{\epsilon}$ = .002/min', 'Interpreter','latex')