Electrical resistivity as a measure of change of state in substrates: Design, development and validation of an automated system Dong Le a , Vijay Vaidyanathan a,⇑ , Shailesh Vidhate a , Jaycee Chung b , Nandika D’Souza a a University of North Texas – College of Engineering, Denton, Texas, USA b Global Contour, Ltd., Rockwall, Texas, USA article info Article history: Received 28 May 2010 Received in revised form 15 September 2010 Accepted 22 September 2010 Available online 27 September 2010 Keywords: Structural health monitoring Electrical resistance measurement NERAC Damage abstract Intrinsically smart structural composites are materials, which can perform function such as sensing strain, stress damage or temperature. Electrical resistance could potentially serve as an indicator of structural well-being or damage in the structure. To this end, the devel- opment of an automated resistance measurement system is desired. An automated nodal electrical resistance acquisition circuitry (NERAC) was designed, and interfaced to a laptop for measurement of electrical resistance/impedance from the substrate of interest. Mea- surements were carried out using DC/AC method with four-point probe technique. Baseline reading before damage was noted and compared with the resistance measured after dam- age. The device was calibrated and validated on three different substrates: PVDF samples, composite panels and smart concrete. Results conformed to previous work done on these substrates, validating the effective working of the NERAC device. Change of state of the substrate, after damage was assessed by measurement of resistance/impedance. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Intrinsically smart structural composites are materials, which can perform function such as sensing strain, stress damage or temperature [1]. These materials exhibit piezo- resistivity with sufficient magnitude which allows the materials to sense their own strain and damage [2,3].A structural composite, which is itself a sensor, is said to be self-sensing [4,5]. In this class of materials are several ce- ment-matrix and polymer matrix materials. Using embedded devices such as optical fibers one can monitor damage in structural material composites. How- ever, the embedded technique has some drawbacks – high cost of sensors and equipment, poor durability of the sensor, limited functional volume and degradation of mechanical properties of the material due to embedding of the sensor. Given these drawbacks, the use of self- sensing materials to monitor strain and damage, assumes significance. The self-sensing ability of a composite mate- rial such as the carbon fiber polymer matrix has been shown through measurement of the electrical resistance/ resistivity of the system [6]. Thus, there is a need for the development of simple, reproducible methods using com- pact, state-of-the-art electronics that would facilitate the measurement of resistance for self-sensing of composite materials. Electrical resistance or resistivity could poten- tially serve as an indicator of damage in materials. McCar- ter and Vennesland [7] have shown the effectiveness of in situ monitoring of concrete structures to determine con- crete resistivity. Basheer et al. demonstrated the use of resistance/resistivity to determine the extent of chlorine ion penetration in concrete. This is significant because chlorine ion penetration results in the deterioration of con- crete due to cracking and spalling [8]. The most common technique of measuring the resis- tance/resistivity of a semiconductor material is by using a four-point collinear probe [9,10]. Our previous research using the four-point probe on composite structures, dem- onstrated proof of concept for a compact, easy to use nodal resistance measurement system. In addition, it was shown 0263-2241/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.measurement.2010.09.040 ⇑ Corresponding author. Address: A 160 E, UNT Discovery Park, 3940 N. Elm, Denton, TX 76207, USA. Tel.: +1 940 565 4203; fax: +1 940 369 8570. E-mail address: vijay.vaidyanathan@unt.edu (V. Vaidyanathan). Measurement 44 (2011) 159–163 Contents lists available at ScienceDirect Measurement journal homepage: www.elsevier.com/locate/measurement