Biaxial inspection of adhesive bonds

When it comes to the properties of structural adhesives — including shear strength and tensile strength — stress tests are conducted on double-tube samples. The samples have a layer thickness of only a few millimeters, and they’re tested by applying tension or torsion.

In other words, a double tube sample is an experimental design for testing structural adhesives. These two thin-walled tubes are attached to the adhesive for testing. Here, the relative movements of the parts that connect by a tube are measured as a function of the applied force and the torsional moment. 

Now, as a result, a displacement occurs until the adhesive bond breaks in micrometers. To determine how stiff the adhesive bond is, this displacement is measured and it is so small that it doesn’t even go into the millimeter range. It’s just a submicrometer. In order to get the accurate value, Micro-Epsilon capacitive sensors are used for measurement. Precisely three capacitive sensors are connected via a capaNCDT 6500 capacitive controller with DL6530 demodulator module. Since there are no contact points in the measurement, it can be easily decoupled from axial and torsional displacement.