Shear stress calculation for adhesive

[sonani_deepak]

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.

 

[PhanthomJay]

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.

The shear stress in your case, with the force parallel to the plane, is just F/A. The shear stress formula VQ/It applies primarily to beams subject to bending stresses, in which case this is the max stress in the beam, while the average stress may be approximated by V/A. But back to the case at hand, for your glued surface subject to shear without bending, it is common practice to consider the shear stress, F/A , as the average and max shear stress, that is, a uniform shear stress distribution across the entire glued surface. In actuality, the shear stress tends to concentrated higher in the area closer to the load application, but such max stresses are generally not considered in design, since the F/A formula works out quite well.