I'm in the process of calculating my combined stress on an axle I am designing, I have calculated the bending and torsional stress, however I need to calculate the direct stress in the axle. In order to do this I need to know the axial thrust in my axle, I understand what axial force is but I am unsure what kind of factors need to be taken into consideration when determining what it will be? I understand that this isn't something which is answered by an equation and is something determined by my environment, design and function. The axle is designed for one wheel of a wheelchair, supported by 2 bearings and is manually driven at a max speed of 10mph. Not sure if this extra info helps or not. I think it may have something to do with when going around corners in the wheelchair will cause the most axial thrust but not sure on this either. Any help would be great and let me know if you need anymore information.