Biaxial inspection of adhesive bonds

In order to test the shear and tensile strength of structural adhesives, two tubes are bonded together (double tube sample) and clamped at the test bench. The adhesive layers between the tubes are only a few thenths of a millimeter thick while being charged with tension and/or torsion which slightly moves the samples. Measuring these very small displacements requires a very accurate and stable measuring system. The test set-up therefore includes three MicroEpsilon capacitive sensors, which are connected via a capaNCDT 6500 capacitive controller with DL6530 demodulator module. Using a special holder, the sensors are attached directly to the tube joining parts of the double tube sample. Two flat sensors with 2 mm measuring range measure the displacement in the axial direction and a cylindrical sensor measures the displacement by torsion. Due to the non-contact measuring technique used, it is easy to decouple axial displacement components and the torsion-induced displacement.