An adhesive is a substance that is used for glueing different objects or materials to one another. These substances have been used for centuries and were traditionally made out of natural materials such as tar or beeswax. In modern times, the options have greatly expanded with the emergence of synthetic polymers.
When the link created by an adhesive is required to bear a load, the glue is referred to as a structural adhesive. The name is frequently used when talking about adhesives used in engineering where the joints created have lap shear strengths larger than 1MPa and frequently larger than 10MPa.
If an adhesive does not have a structural function, it may be called a sealant. The distinction between structural adhesives and sealants is not always very clear as it depends on the load borne by the final joint and its purpose. Pressure-sensitive adhesives (PSAs) often come as tapes and are most frequently used as sealants because they tend to creep under load. If joints are designed carefully, however, it is possible to prevent creep and iuse PSAs as structural adhesives.
There are several global standard tests that are used by the adhesive industry to support structural engineers in selecting the most appropriate adhesive for a given situation.
Examples of structural adhesives
Several adhesives can be classed as structural adhesives. For example, epoxies, anaerobics, phenolics, toughened acrylics, polyurethanes, cyanoacrylics and vinyl acetates are all considered structural adhesives.
Silicone systems are frequently considered sealants as their adhesive properties are limited and will only cure correctly if there is a gap of more than 1mm. However, silicone systems do adhere well to glass and are often used by the glazing industry and in the construction of fish tanks. Considering the pressures exerted on the glass walls of fish tanks, these systems would certainly be classed as structural.
Advantages of using structural adhesives
There are several advantages to using a structural adhesive rather than mechanical or fusion fastening. A metal bonding adhesive such as those available at http://www.ct1ltd.com/product-applications/metal-to-metal-adhesive/ is a lighter-weight solution compared to using nails or rivets. They may also be considered more appealing from an aesthetic point of view.
Structural adhesives can offer increased design options and generally require less machining than other solutions. The cost of using structural adhesives can also be much lower.