Adhesives and tapes offer unique benefits compared to welds and mechanical fasteners, without sacrificing strength. Learn how adhesive bond strength is tested and measured, and the many factors to consider when choosing an adhesive for an application.
With each of the mechanisms of adhesion playing a role in performance, adhesion scientists investigate the strength of an adhesive bond to determine its ability to perform in an application.
Measuring the “work of adhesion” for a given bond helps to determine the strength of an adhesively bonded assembly. The most common way to measure this is to pull an adhesive bond apart. The force needed to pull the bond apart allows engineers to understand how the adhesive will perform in an application.
Adhesive strength is the interfacial strength between adhesive and substrate, and usually the most important consideration when designing a strong adhesive bonded assembly. However, adhesive strength is not the only factor critical to creating an effective bond. Even when using the world’s toughest adhesive, a bond will fail if the adhesive does not bond to the surface of the substrate.
Cohesive strength is the internal strength of an adhesive - the ability of the adhesive to hold itself together under stress. The higher the cohesive strength, the stronger the adhesive. Cohesive strength is determined by the chemical composition of the adhesive. The strength of adhesives covers a wide range, from pressure sensitive adhesives to structural epoxy and acrylic adhesives.
It’s important to consider the specific types of stress that will act on an adhesive joint. Common stresses include shear, cleavage, peel and tensile. Knowing the magnitude and frequency of the stresses your application will be subjected to is helpful in choosing the adhesive with the best cohesive strength for the task at hand.
Surface energy is a physical property of the surface of a material that determines whether an adhesive will make intimate contact. On a material with high surface energy, a liquid will wet out or spread out on the surface; on a material with low surface energy, the liquid will resist flowing and bead up. An adhesive must wet out the substrate to provide a bond.
To choose the proper adhesive, it’s important to understand the surface energies of all the substrates in your assembly, and how well the adhesive will wet out each one. Surface cleanliness must also be considered as some adhesives require a high degree of substrate cleanliness.
The Science of Adhesion Educational Series is designed to be a comprehensive introduction to Adhesion Science and the use of tapes and adhesives in design applications. Visit the Science of Adhesion to view all articles or choose from the selected topics below.