Electrical resistivity as a measure of change of state in substrates: Design, development and validation of an automated system

doi:10.1016/j.measurement.2010.09.040

Measurement

Volume 44, Issue 1, January 2011, Pages 159-163

https://doi.org/10.1016/j.measurement.2010.09.040 Get rights and content

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 development 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. Measurements 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 damage. 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.

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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Citation Excerpt :
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Electrical resistivity as a measure of change of state in substrates: Design, development and validation of an automated system

Abstract

Introduction

Section snippets

Methods

Calibration

Conclusions and recommendations

Materials Today

Composites Part B: Engineering

Construction and Building Materials

Cement and Concrete Composites

Measurement

Materials Letters

Carbon

Piezoresistive cement-based materials for strain sensing

Journal of Intelligent Material Systems and Structures

Composite Materials: Science and Applications