Stresses on the substrate and bond
From low tack, repositionable and removable to very high strength, permanent bonding, adhesive tapes and films are available in a wide range of strengths. To ensure you are using the correct adhesive strength, it is important to understand the stresses, or load, the bond will be subjected to.
Consider the following:
✔ Does the application require a permanent or temporary bond? If temporary, must the tape remove cleanly (such as for masking, surface protection or temporary holding)?
✔ How much stress is the adhesive expected to take, and in what direction is the stress expected to be applied?
✔ Would a certain thickness be more appropriate than another?
✔ How will the tape be applied? By hand or machine?
✔ Will the bond be subjected to shock or vibration?
The answers to these questions will allow a tape manufacturer to specify a product for you, along with advice on the amount of tape and coverage needed.
As a rule, tapes perform better when the primary stress is tensile or shear. Most industrial applications involve a combination of stresses.
Tensile stress occurs when the pull direction is straight and away from the adhesive bond, and the pull is exerted equally over the entire joint.
Shear stress occurs when the pull direction is across the adhesive – or in parallel to the bonding surface – forcing the substrates to slide over each other.
Cleavage stress occurs when the pull concentrates at the one edge of the joint, exerting a prying force on the bond. The other edge of the joint is theoretically under zero stress.
All stress force images on this page supplied by 3M
Peel stress occurs when the pull concentrates along a thin line at the edge of the bond where at least one substrate is flexible. Once peeling has begun, the stress line stays out in front of the advancing bond separation.
Rule of thumb for joint design
Place basic stress in shear or tensile and minimise or eliminate cleavage and peel in the cases of:
- Lap joints
- Angle joints
- Butt joints
- Cylindrical joints
- Corner joints (e.g., sheet metal, rigid members)
- Stiffener joints.
Supplied by Nitto