In this case, uniaxial bending and neglectable normal forces, you can just use P_M1 and divide it by the section modulus W = t²/6. By that, you get the stress in the outer fibers of the shell.
If the stress distribution is more complex, you can use the von Mises stresses. They return the maximum stresses in the upper part of the shell. The lower part has unfortunately be computed by yourself. (Maybe we add this in a future version.) But this is only necessary if the moments and the normal forces do not have the same sign:
sigma_1_bot = -m/W + n/thick
sigma_2_bot = -m/W + n/thick
sigma_3_bot = -m/W + n/thick
vMises_bot = sqrt(sigma_1_bot² + sigma_2_bot² - sigma_1_bot * sigma_2_bot+3 * sigma_3_bot²)
02_K!-Shell_mod.gh (33.9 KB)
I added this in your definition. They all yield approx. the same stress for this problem. Related to your other question you have to check your input regarding the units. The Young’s modulus of the material is interpreted as kN/m². You have either change the unit by right-clicking the component or adapt the rest of the model. Or just use the standard material component, where you can define a custom Young’s modulus matching the 240.