Developement of an electrically conductive elastomer for sensorising yacht window bonding
Arvid Witkabel, Hochschule Bremen
Adhesive bonding is a special process defined in DIN EN ISO 9001:2015-11 as a process that cannot be tested to guarantee a quality of 100% with non-destructive tests.
In naval architecture adhesive bonding plays a vital role in the installation of glazings.
The glazing in cruise ships and large yachts place an important role in the final aesthetic of the vessel. A constant increase in the demand of window panes with edge lengths above 10 m is linked to complex requirements of the adhesive bonds that support said glazing, yet the quality control of the installation is based on superficial observations and installation guidelines based on experience and manufacture specifications.
At present windows are not taken into consideration for the structural integrity when designing a ship and are instead considered voids. Therefore, additional stiffeners are required to compensate for these voids in the hull.
To combat the current lack of experience with the behaviour and requirements of glazing of this size, this thesis aimed to develop an electrically conductive elastomer for the continuous sensorization of yacht window bonds. To accomplish this, the SMP Merbenit SF50 already used in ship glazing was filled with various conductive filler materials and subjected to a number of tests including tensile, compression, shear and dynamic tests.
During preliminary tests 24 infill compositions using 5 different filler materials were tested for elasticity, conductivity (DC) and workability (mixing and application). Out of the 24 infill compositions, 8 were selected for further analysis. The selected infills were a copper powder used at two different infill-percentages as well as copper microfibres and an iron-aluminium compound powder tested at three different infill percentages each.
To measure conductivity an alternating current was applied to the samples during the compression and dynamic test in uniaxial load and the impedance measured. In a first attempt the compression was conducted stepwise where at each stop the impedance was measured for a range of different frequencies. This setup was selected as the impedance measuring device was the only dedicated impedance measuring device available at the time. As the aim was for continuous measurements, the test setup was later changed to an oscilloscope with a wave-function generator.
For this second iteration the force-way measurements and voltage-time measurements were aligned and the impedance calculated.
With the measurements an attempt at relating the deformation and applied force to the calculated impedance was done. While no final composite could be produced that can be used in a real-world application already as the measured signals were noisy due to multiple factors, the results are promising for future research in this field, as a correlation between impedance and deformation/applied force was found for some of the tested composites even with measured noise.
In future research these interfering signal sources need to be addressed, additional composites tested and sample sizes increased significantly for proper statistical analysis. By decreasing the applied AC frequency, for example, from the here used 2kHz some of the interference sources can be mitigated as the signal has more time to stabilize before polarity is reversed again.
