Pressure stimulated voltage detection in manmade and geological materials

Archer, James William (2017) Pressure stimulated voltage detection in manmade and geological materials. Doctoral thesis (PhD), University of Sussex.

[img] PDF - Published Version
Download (10MB)

Abstract

This thesis investigates pressure stimulated voltages (PSVs) in manmade and geological materials using
a field capable and commercially viable electric potential sensor (EPS) technology. Sensing
technologies are of great importance for the structural health monitoring (SHM) of manmade and
geological structures and are critical for improving the health and safety of humans and infrastructure.
A wide variety of sensing technologies are needed to assess damage over structures. Work by others
involves measuring pressure stimulated electrical emissions (PSEs) (i.e. the study of pressure stimulated
voltage, electric field and current) that are related to acoustic emissions (AEs) in rock and cement mortar,
and also mechanical properties. Although these studies yield promising results, the measurement tools
(laboratory electrometers and electromagnetic emissions (EME) antennas) are not suitable for field use.
This is predominantly because of the need of Faraday shielding to reduce noise, plus the impracticalities
and high costs associated with using laboratory instruments for SHM. However, the EPS developed at
the University of Sussex is capable of measuring PSVs in rocks and is field capable.
In this thesis, PSVs in rocks and man-made materials were measured using two EPS variants. An
existing capacitively coupled sensor was used to measure high frequency (25.5 mHz to 750 kHz)
transient PSVs associated with cracking. In addition, a novel directly coupled smart EPS was developed
for monitoring low frequency (DC to 250 Hz) PSVs associated with applied stress. A signal conditioning
and data reduction procedure was developed for PSV emissions analogous to methods used for AE. A
new robust method for measuring PSV was established in which cylindrical material specimens were
instrumented with strain gauges, piezo transducers and EPSs to measure strain, AE and PSV respectively
and a force transducer was used to measure the applied load.
The results showed that PSVs were detected in a wide range of piezo and non-piezo rocks and for the
first time in concrete, in the range of millivolts (0.32 mV – 1180 mV). Faraday shielding the experiments
was not necessary as with other PSE monitoring technologies.
For oven dried materials there was some degree of correlation between PSV high frequency transient
signals and AE (i.e. cracking). Rocks had cross-correlation coefficients ranging from 0.13 to 0.86, and
the cross-correlation coefficient for concrete (0.24) was lower than most rock lithologies. Environmental
conditions and the stage of uniaxial deformation of materials influence PSV-AE cross-correlations.
Water or saline saturation of materials generally reduced the PSV-AE cross correlation coefficients.
During the cyclic loading of various rock lithology, a work hardening effect was observed in the PSV
emissions analogous to the well-known Kaiser and Felicity effect of AE. A likely reason for the PSV-AE
correlations is that PSVs are generated by the movement and separation of fresh charged fracture
surfaces. EPS could be a cost effective and more advanced technology for detecting cracking in
structures and in combination with piezo transducers, could be used to identify material deformation
stages.
There was a linear relationship between applied stress and DC/low frequency PSV in piezo rocks
(r2 = 0.84) but not non-piezo rocks (r2 = 0.0063). The piezoelectric effect of quartz is the most likely
generation mechanism behind the PSV-stress relationship. The novel, directly coupled, smart EPS is a
successful design as it has the necessary high input impedance and low noise characteristics for
measuring PSVs noninvasively at low frequencies. EPS could be the first non-invasive technology for
in-situ stress measurement in quartz bearing rocks; current methods involve disturbing the rock mass
and are expensive to implement.
In conclusion, the results show that the EPS-PSV measurement technique is viable for the SHM of rocks
and concrete. Although, factors such as material composition, environmental condition and type of
material deformation influence PSV characteristics and would need to be accounted for in real world
applications.
Future directions for the research would involve the development of a “real time” PSV event detection
system for long term monitoring of structures for SHM applications. Additionally, large scale testing of
different material samples in different environmental conditions and the testing of larger structures using
arrays of EPS would be necessary before commercialisation.
Future commercialisation could result in a restively coupled broadband monolithic semiconductor EPS
being developed for SHM to monitor PSVs associated with applied stress and cracking events
simultaneously. This would produce a more cost effective and advanced tool than existing technologies,
such as piezo transducers for monitoring AE and in-situ stress monitoring techniques.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Engineering and Informatics > Engineering and Design
Subjects: Q Science > QE Geology
T Technology > TA Engineering (General). Civil engineering (General) > TA0703 Engineering geology. Rock mechanics. Soil mechanics. Underground construction
T Technology > TK Electrical engineering. Electronics Nuclear engineering
Depositing User: Library Cataloguing
Date Deposited: 07 Dec 2017 08:01
Last Modified: 07 Dec 2017 08:01
URI: http://sro.sussex.ac.uk/id/eprint/71818

View download statistics for this item

📧 Request an update