Electrical resistivity as a measure of change of state in substrates: Design, development and validation of an automated system
Introduction
Intrinsically smart structural composites are materials, which can perform function such as sensing strain, stress damage or temperature [1]. These materials exhibit piezoresistivity 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 cement-matrix and polymer matrix materials.
Using embedded devices such as optical fibers one can monitor damage in structural material composites. However, 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 material 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 compact, state-of-the-art electronics that would facilitate the measurement of resistance for self-sensing of composite materials. Electrical resistance or resistivity could potentially serve as an indicator of damage in materials. McCarter and Vennesland [7] have shown the effectiveness of in situ monitoring of concrete structures to determine concrete 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 concrete due to cracking and spalling [8].
The most common technique of measuring the resistance/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, demonstrated proof of concept for a compact, easy to use nodal resistance measurement system. In addition, it was shown that there was a significant difference (statistical confidence level of 95%) between resistance measurements from the composite substrate, before and after the infliction of damage. In the current study, our objective was to develop a deployable nodal electrical resistance acquisition circuitry (NERAC) hardware and post-processing analytical tools (software) to detect damage and strain in multifunctional materials (e.g., carbon fiber composite structure, carbon fiber mixed cement concrete, etc.)
Section snippets
Methods
The process of measurement of resistance from various substrates was divided into five stages:
- (a)
Design and development of microprocessor based system and its ancillary units.
- (b)
DC and AC methods of measurement.
- (c)
Calibration; and validation of system for various substrates.
Calibration
Standard resistances measured using the NERAC unit was compared to those measured using a frame of reference – a HP multi-meter. The % error was found to be less than 5%. Statistical analysis was performed to compare the resistance measurements made using NERAC unit to that of the resistance measured using an HP 1100 multi-meter. This was accomplished by performing, a ‘paired t-test’ [15] at a significance level of 0.05. The statistical analysis was done by using Microsoft® Office Excel
Conclusions and recommendations
Using resistance based measurements to assess damage in structural health monitoring holds great promise. Given the increasing use of composites and carbon nano-tubes in development and design of structures, the NERAC unit facilitates assessing damage in engineering structures where damage is likely to originate at the material level and then progress to component and system level. AC measurement with variable frequencies seems to offer the best route to using resistance/impedance to determine
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2017, Composite StructuresIndirect estimation of electrical resistivity by abrasion and physico-mechanical properties of rocks
2017, Journal of Applied GeophysicsCitation Excerpt :There is also a large variability in measuring the electrical resistivity of intact rocks, since it is sensitive to properties such as porosity, the amount of pore saturant, temperature, and pressure surface conduction (Roberts et al., 2001). DC and AC methods with a four point probe, i.e. Wenner measurements, are widely applied to measure the surface and volume resistance of rocks (Le et al., 2011). Similar site testing conditions can also be obtained in the laboratory by taking into consideration the conditions below.
Effects of coarse aggregates on the electrical resistivity of Portland cement concrete
2017, Construction and Building MaterialsCitation Excerpt :Unlike material compositions and maturity levels that cause microstructural differences, moisture content and temperature also affect concrete resistivity by influencing ion mobility, as well as ion-ion and ion–solid interactions [19,22,23]. Based on these observations, researchers have proposed employing the electrical characteristics of concrete for various sensing applications [12,17,22,27–40]. Although diffusive mass transport may not be fully interpreted by ionic conduction, many previous studies have indicated that electrical resistivity measurement could serve as a fast and economic alternative for assessing concrete resistance to chloride penetration [12,17,28,38,39].
Modification of four point method to measure the concrete electrical resistivity in presence of reinforcing bars
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