Strain Gauge Installation Methods
How Strain Measurement Sensors are Applied to Test Specimens
Strain gauges can be installed on a wide range of test systems to evaluate strain, stresses and forces being generated.
Strain gauges are sensors used to measure strain and calculate stresses in mechanical systems. Because the strain gauge needs to experience the same strains as the part being measured, the installation process is extremely important in ensuring accurate and repeatable measurements.
There are two categories of strain gauges when it comes to installation: bonded strain gauges and welded strain gauges. Choosing which type of gauge to use depends highly on the application and environmental conditions during installation and testing.
Bonded Strain Gauges
Bonded strain gauges consist of a foil gauge mounted to a non-conductive backing material, such as polyimide or fiberglass. As their name implies, bonded strain gauges are bonded to the part to be measured using a stiff adhesive. Cyanoacrylate, otherwise known as super glue, is often used because of its quick drying time and stiffness when dry. Bonded strain gauges require specific surface preparation to ensure a clean surface prior to bonding. The surface preparation process generally includes sanding the surface with extra fine sandpaper, abrading the surface with a light acid, and then cleaning the surface with a neutralizer and a clean cloth to remove all residues.
Depending on the environmental conditions, additional care must be taken in the bonding process. For example, at low temperatures, cyanoacrylates may not cure properly, and the bond could be compromised. A similar situation can be found in high-humidity environments. If the environmental conditions are known, the bonding medium should be chosen based on the conditions to ensure an optimum bond.
Welded Strain Gauges
Welded strain gauges consist of foil gauges mounted to a non conductive backing material, which is in turn mounted to a thin steel sheet. A welded gauge can contain one or more matrices in varying orientations, such as a bi-axial gauge. The steel backing sheet can then be spot welded to the part to be measured. Small spot welds are applied around the perimeter of each gauge in order to provide consistent contact between the gauge and the part being measured.
Welded strain gauges can only be installed on ferrous metal parts. Less surface preparation is required when installing welded gauges. Preparation generally includes lightly grinding the surface of the part to be measured to remove any rust, paint, or scale, then lightly cleaning the surface to remove any loose residue. Welded gauges can be installed in just about any environmental condition, and also perform well in high-temperature applications where a bond could be compromised.
Strain gauges are invaluable tools used by engineers to measure strain, stresses and forces in systems, and require an installation process that is more complex than other types of sensors. To learn more about strain gauges, please read the article “An Introduction to Strain Gauges”.
Source
Vishay-Micromeasurements website and technical bulletins
