Novel distributed strain sensing in polymeric materials

Abstract

Monitoring the state of strain throughout an entire structure is essential to determine its state of stress, detect potential residual stresses after fabrication, and also to help to establish its integrity. Several sensing technologies are presently available to determine the strain in the surface or inside a structure. Large sensor dimensions, complex signal conditioning equipment, and difficulty in achieving a widely distributed system have however hindered their development into robust structural health monitoring techniques. Recently, carbon nanotube forests were spun into a microscale thread that is electrically conductive, tough, and easily tailorable. The thread was integrated into polymeric materials and used for the first time as a piezoresistive sensor to monitor strain and also to detect damage in the material. It is revealed that the created self-sensing polymeric materials are sensitive to normal strains above 0.07% and that the sensor thread exhibits a perfectly linear delta resistance-strain response above 0.3%. The longitudinal gauge factors were determined to be in the 2-5 range. This low cost and simple built-in sensor thread may provide a new integrated and distributed sensor technology that enables robust real-time health monitoring of structures.

Piezoresistive Response of Integrated CNT Yarns under Compression and Tension: The Effect of Lateral Constraint

“…Figure 8 shows a comparison of the relative resistance change-strain curves of both the free CNT yarn [12] and the constrained CNT yarn of this study. There is a significant difference in the piezoresistive responses of the constrained and unconstrained CNT yarns [29]. For the samples tested to a maximum strain of 0.1 % at a strain rate of 0.003 min -1 , the gauge factors of the constrained yarns under pure bending and pure tension are approximately 15.2 and 2.7, respectively (Figure 8a) compared to 0.1 obtained for the free CNT yarn.…”

Localized Detection of Damage in Laminated Composite Materials Using Carbon Nanotube Yarn Sensors

“…The response of laterally constrained yarns is being determined and will be used to predict the response of the yarn sensors that are integrated in polymeric and composite materials. This piezoresistive characteristic of the CNT yarn is being used for sensing purposes and provide real time monitoring of the structural health of a polymeric or composite material through resistance measurements [10][11][12][13].…”

“…More critically, they fail to achieve damage detection without altering the microstructure of the composite material. An alternative method of strain monitoring and damage detection that may offer the advantages of the previously mentioned methods without their drawbacks consists of the use carbon nanotube (CNT) yarns [5][6][7][8][9] that are intricately integrated into the fiber reinforcements of composite materials [10][11][12][13][14]. The concept is that CNT yarns are integrated in a laminated composite material forming a continuous sensor circuit, and their inherent piezoresistive sensitivity would capture small amounts of strain within the host material [10][11][12][13].…”

Strain Gauge Sensor Comprised of Carbon Nanotube Yarn: Concept and Modeling

“…Carbon nanotube (CNT) yarns are micron-size fibers that contain thousands of intertwined carbon nanotubes in their cross sections and exhibit piezoresistance characteristics that can be tapped for sensing purposes [1,2]. The use of strain gauge sensors composed of CNT yarn may offer a feasible and practical measurement of strain in polymeric and composite materials [3][4][5]. Piezoresistive strain gauge sensors are typically made of a piezoresistive membrane layer attached to a flexible substrate layer.…”