I want to calculate the maximum shear stress, that two surfaces joint by a single lap joint, would be able to take. I am going to suspend one surface from a rigid supoort and then put the force on the other surface downwards using weights. I am assuming that material will be able to take the stress before the joint breaks up. My question is that, for max. shear stress, do i still use stress = F/A ? or something like stress = VQ/Ib. I posted this question because I think the Force here is parallel to the joint and NOT perpendicular to it. Note that the surfaces are merely 0.05 inch sheets of cardboard. Also, would that give me the max. stress or the avg. stress? and if its just the avg. stress, what should i do to calculate max. stress???? Thnx in advance.