Bonding Measurements

Surface coatings whether, automotive or industrial adhesives, insulative foams like those used in refrigeration systems, or other coatings, cladding or plating modify the stresses of the substrate surface. This surface tension is developed through the crosslinking process a term describing the chemical bridging that occurs in bonding adjacent structures. In the event of adhesive or insulative foams the process of “curing” is the development of polymerization or crosslinking within the adhesive and with the surfaces that they come in contact. The stresses on the surface increase with increasing crosslinking and increasing stiffness at the surfaces and in the adhesive layer.

Improving Bond Measurements: Characterizing Bond Strength

The proprietary bond strength measurement technology developed by Resonic and utilized through the ARIS product line measures bonding integrity across a broad spectrum of conductive surfaces and bonding materials. The technique provides multidimensional information providing more than just the damping of the acoustic vibrations as they are absorbed at the interface of the bonding agent to the substrate. This is the typical measurement process of conventional contact type ultrasonic measurements. The unique ability to measure the stresses at the surface that are generated during the building of adhesive or coating related crosslinking makes the Resonic method superior as it senses not only the intimate contact typical of conventional ultrasonic methods it also senses the stresses generated by the building of the crosslinking processes. The Resonic method provides additional dimensions to bond measurement capability including the unique ability to see through the bond to the bond on the underlying substrate surfaces.

Attributes of the new Method

Two aspects of the use of EMAR make it superior to other measurement methods one being the ability to concentrate the acoustic vibration at discrete depths from the surface to the substrate centerline. This give the ability to detect the actual stresses created during the crosslinking process by isolating the surface damping effect from the stress gradient effects that extend away from the from the surface. Additionally, unique property of the non-contact sensor is the generation of controlled shear waves providing a practical, sensitive stress measurement capability, up to 9 times the actual strain in the substrate, this is not attainable with conventional UT methods.

Application of ARIS

ARIS uses non-contact designed specifically for use in EMAS measurements. These do not require any wet or dry couplants, they can see through surface treatments such as paints and can scanned across the surface at speed. They also can be configured as an array so larger areas can be scanned with a single pass. Currently the system is configured as a small bench top unit intended for use in the production and lab environments.

Case Study: Silicone RTV with Oil Contamination

The data in each plot are signal measurements taken over 10 hours as the RTV cures
The Blue Oil 1 plot is the amplitude response with an oil film applied to the bottom of the aluminum substrate surface.
The Orange Clean plot is the amplitude response for clean mating surfaces.
The Yellow Oil 2 plot is for oil contamination applied to the bottom substrate surface.