6. Experimental test of composite with sensor wire

A cured composite sample with integrated sensor was tested using an Instron test machine and the oscilloscope was connected to sensor lids. Uniaxial tensile testing machine and oscilloscope were used simultaneously to correlate the mechanical behavior of the composite specimen with the electrical response of the strain sensor wire. Three experimental tests were performed to confirm the reproducibility of the results. In addition, electrodes were attached at both ends of the specimen to provide better connection. Then, the specimen was placed in the tensile machine and test was performed, Figure 5. As a result, the stress-strain behavior of composite specimen with resistance profile of the sensor was obtained.

nanoparticle grains, or aggregates less than one micro-meter in size, Figure 6. SEM characterization of the coated untwisted yarn showed uniform coating with some minute discontinuities and defects and also confirmed that the Ag thin film coating consisted of deposition of nanoparticles of silver. Regardless of the imperfections in the Ag film coating in some filaments, it did not seem to affect the electrical

SEM characterization of the Ag thin film-coated untwisted yarn: (a) shows the uniform coating with some minute discontinuities and defects in the coating and (b) confirms that the Ag thin film coating on the nylon

Nanotechnology and Development of Strain Sensor for Damage Detection

DOI: http://dx.doi.org/10.5772/intechopen.82871

Three tensile tests of piezo-resistive sensor wire were performed. The Young modulus and yield strength of the tested samples were about 1348.5 and 20.13 MPa, respectively. The stress-strain behavior of untwisted coated yarn is shown in Figure 7a. Stress and electrical response of the untwisted yarn are plotted simultaneously in Figure 7b. The resistance was changed at the same time as the failure started to initiate, and, as the test progressed, the resistance increased gradually when the number of fractured filaments was increased. Ultimately, when the untwisted yarn was fractured completely, the resistance went to maximum value.

After tensile test, fractured samples were studied using SEM technique, and it appeared that there were two distinct morphologies. Some filaments exhibited a clean ductile failure in which both the coating and the fiber showed a clean cut; however, other filaments showed a pull-out of the coating or flaking off, Figure 8.

The results were very encouraging, and piezo-resistive flexible sensor was

conductivity.

Figure 6.

7.2. Experimental testing

7.2.2 Damage modes

103

7.2.1 Electromechanical response

surface consisted of deposition of nanoparticles of silver.

responding very well to any change in load.

Figure 5.

Composite sample mounted on test frame for mechanical test. Sensor lids are connected to the oscilloscope.
