I have a problem with cantalever beams, the beam is 1m long by 0.1m by 0.1m. A 10Kn force placed at the end of the beam deflecting it down. My lecturer simmulated the problem in Ansys and we all got to do it with him using more dense nodes and solutions to find a more refined answer of the deflection in y and principle stresses in x and y direction.

The results are clear from the program but we have been asked to calculate the theoretical values and compare. Deflection is okay i derived the equation

v = 1/EI(5000z^2-1666.67z^3)

this has given me an answer which is quite similar to the simulated. My question is how do i calculate the principle stresses. I have calculated the Bending stress using

Bending stress = My/ I

but i fear this is not what i need,because my values are very different. how do i relate bending stress to sigma (X) and sigma (y) or calculate them from the force and dimensions given?

Thanks

KJ