Tech Talk Blog

The design of an adhesive bond may be simple or complicated depending on the adhesives function. For optimum performance of the materials and adhesive, some general principles should be considered:

1. Stress in the direction of maximum strength
2. Maximize bonding surface
3. Adhesive applied uniformly
4. Adhesive is thin and continuous
5. Minimize stressed areas

It is important to know the duration, direction and load of the forces being applied to designed joint. Most adhesives used for structural purposes are relatively strong in shear. Conversely, these same adhesives have relatively low adhesive strength in tensile or peel.

The design of the bond line should take into consideration the forces that occur when the device is under load. A simple lap shear bond has peel forces at the ends while the center observes little stress.

For lap joints loaded in tension, the load is transferred predominantly by shear stresses in the adhesive layer. If the adhesive was loaded uniformly then

ta = [ P / (Lb) ]

Where:

1. ta         is the adhesive shear stress
2. P          is the load
3. L          is the overlap length
4. b          is the width

The next post will expand on this discussion and provide more details about shear bonds under stress…

But if you can’t wait – look to our Video Learning Center for more information right now!