Stress is an unavoidable part of life. We all experience it in one way or another, and we all have ways of coping with it.
However, product designers and engineers must manage a very distinct type of stress – the force applied to adhesive bonds. While today’s innovative adhesives and tapes are viable alternatives to mechanical fasteners, bonding strength must be considered to ensure optimal performance and durability. In this article, we’ll cover common types of stress that affect adhesive, along with tips for material selection.
Types of stress on adhesive
When you adjoin two or more materials together, the adhesive can be a weak point of the component. Depending on the design and orientation of the product, the adhesive can be impacted and potentially weakened by several types of stress, including:
Sheer stress – Pull is parallel to the bond; stress is distributed across the entire bond pane.
Tensile stress – Pull is perpendicular to (and away from) the bond; stress is distributed across the entire bond area.
Cleavage stress – Stress between two rigid substrates that is concentrated on one edge of the bond area while the opposite edge does not experience stress.
Peel stress – Stress pulls on one edge of a bond area; assembly includes at least one flexible substrate.
Compression – The opposite of tensile stress; the force is perpendicular and across the bond plane but is aimed toward the bond area.
*Images courtesy of 3M
If stress on an adhesive can’t be reduced or avoided, it’s best to ensure that the force is evenly distributed across the bonding area – not concentrated on an edge line.
Another way you can combat the effects of stress is by selecting an adhesive that’s strong enough for your application. The most common adhesive attributes we’re asked about during materials selection are shear strength and peel strength.
What is shear strength?
Shear stress measures the adhesive’s ability to withstand shear stress, either vertically or horizontally. During a torsion test, an increasing shear load is applied until the adhesive fails or tears. The shear strength of adhesive can be influenced and reduced by the condition of the substrate, especially corrosion.
What is peel strength?
The peel strength is measured in adhesives and tapes used on flexible materials, often used in medical packaging, films, labels, consumables, and other products. Testing involves determining the average load per unit width of bond line required to separate the adhered materials with a separation angle of 180°. In addition to peak peel load, other important characteristics to know include average peel strength and peel strength variability.
Three ways to improve adhesive strength
If adhesive integrity is a critical need for your application, there are a few areas to consider to ensure your bond is as strong and reliable as possible.
- Improve the design – The design can help or hinder the adhesive’s strength. For example, a reinforced or optimized corner joint can redistribute some of the cleavage stress into shear or compression stress – resulting in a stronger bond.
- Consider surface energy – Substrates have varying surface energy, influencing how adhesive will flow on and adhere to the surface. For example, liquid will spread easily on a substrate with high surface energy (such as metal or glass). On the other hand, liquid will be more likely to bead on materials with low surface energy (such as LSE plastics, certain rubbers, and more). Understanding the substrate surface energy and how the adhesive will wet out is vital for material selection.
- Compare adhesive bond strength – Here is where expert materials selection can make or break (quite literally) your product. Adhesives are available in a wide range of strengths, including pressure-sensitive and acrylic adhesives.
Manufacturing partner for adhesives
As you can see, there isn’t a one-size-fits-all solution for maximizing the strength of adhesive or tape in your product. That’s why the best route is to work with an experienced manufacturing partner with experience in this specialty application.
At Tapecon, we provide expert materials selection for adhesives and can test options with your desired substrates. We also have close relationships with leading material suppliers, giving you access to the most advanced bonding products and technologies on the market. Finally, we put your adhesive plan into action by custom-making your tape or component using an array of converting techniques.
Let’s make something great
With over 100 years of manufacturing experience, Tapecon works with product teams to solve challenges, create products, and enhance lives. Learn more about our materials selection expertise.