The Importance of Joint Design
Holding it all together
In gluing anything together, several factors have to be taken into account.
Notwithstanding the obvious factors such as the materials being glued, the actual gluing process required for manufacturing and the overall performance expectations for the glued joint, the design of the joint is an often forgotten about element.
There are several factors which industrial designers have to consider, in the design of a joint on an object. From an adhesives viewpoint, the main factors are physical, manufacturing and end user.
When our specialists are called upon to specify an adhesive for a new application, we must evaluating all of them as in use, glued joints can be exposed to several forces, the three foremost being tensile stress, shear stress and finally peel stress.
- What is tensile stress? If we glue two blocks of wood together, grab both ends and try to pull them apart, the stress in pulling them apart is balanced across the whole of the glued area.
- What is shear stress? With the same two blocks of glued wood, if we try to pull one block up and one block down, we are pulling parallel to or along the adhesive bond and, where the bond is in pure shear mode, the stress is again spread over the entire bond area. However, because bonded parts flex, the part may deform, thereby creating shear stress & peel stress (more about this below).
- What is peel stress? This stress is largely concentrate at one edge of a joint, rather than being spread throughout the joint. When at least one substrate is flexible, it can “peel” away from the other substrate, such as gluing a piece of flexible PVC to rigid wood. With peel stress, the stress tends to be much higher at the edge of the joint and this stress travels from the edge of the joint, back through the bond. The amount of peel stress that can occur, depends on the stiffness of both the materials being glued and the flexibility of the adhesive.
In working with our customers, on the design of the joint area, our engineers aim to create joint designs which work in the favour of adhesives.
- For example, we always prefer joints which offer tensile and shear stress, rather than peel stress.
- We prefer joint designs where more of the bond area, works against the stress which acts on the bond.
- Finally, we always aim to eliminate regions within the joint, where stress may accumulate.
As Ireland’s only indigenous research based manufacturer and distributor of industrial adhesives and sealants, our services to industry go far beyond the supply of adhesives. From the design concept to mass production, our technical staff are with you all of the way.