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.

 

[oswaler]

Hello,

Thank you for your question. To calculate the maximum shear stress in an adhesive joint, you will need to consider the shear force and the cross-sectional area of the joint. The equation you mentioned, stress = F/A, is correct. However, the value of the force (F) should be the maximum force that the joint can withstand before failure.

In this case, you are correct in assuming that the force will be parallel to the joint and not perpendicular to it. This is because shear stress is defined as the force applied parallel to a surface divided by the area of that surface. In your experiment, the force will be applied parallel to the adhesive joint, so you can use the equation stress = F/A to calculate the maximum shear stress.

It is important to note that the maximum shear stress may not be the same as the average stress. The average stress is calculated by dividing the total force applied by the total area of the joint. This may not accurately represent the stress distribution within the joint. To calculate the maximum stress, you may need to use more advanced equations, such as the one you mentioned: stress = VQ/Ib, where V is the shear force, Q is the first moment of area, I is the moment of inertia, and b is the width of the joint.

In your experiment, using 0.05 inch sheets of cardboard as the joint material may not accurately represent the behavior of a real adhesive joint. The properties of the adhesive and the surfaces being joined will also play a significant role in determining the maximum shear stress. It is important to consider all of these factors when conducting experiments and interpreting the results.

I hope this helps answer your question. If you have any further inquiries, please do not hesitate to ask. Thank you.