Smart Materials: Ceramic Sensors application in SHM

Sabavoon Fazli, MSc. Candidate, Civil and Material Engineering Department, University of Illinois at Chicago
Michael J. McNallan, PhD, Professor ,Civil and Materials Engineering Department, University of Illinois at Chicago

INTRODUCTION EXPERIMENT
Infrastructures such as offshore structures, bridges structures, building structures, high- PZT based transducers are mostly are common type of transducers used in SHM In this part we evaluate results from a study which have assessed damages and
speed railway infrastructure, petroleum industry structures should meet safety, durability, application, because it is chemically inert and exhibits high sensitivity and low load history of rock samples using PZT and FBG sensors. The rock samples were
serviceability and sustainability requirement for a long-term operation. During its long term
service, the structure may be deteriorated in its performance slowly, or be damaged hysterias behavior. These sensors are usually used as point based sensors in subjected to different loading situation and the damages were monitored by PZT
severely and even collapse in severe condition. Structural Health Monitoring (SHM) systems different NDE methods, or as an arrayed map in 2D or 3D configuration to patches and FBG sensors. The experiment set up is shown in following figure.
provides a way to evaluate the safety and durability of a structure during its service life, to measure the strains. In addition it can be patched to structure where online
ensure its serviceability and sustainability. A SHM system consists of sensors, data monitoring is desired. Figure below show a typical piezoelectric transducer.
acquisition and transmission systems, database for effective data management and health
diagnosis (including data processing, data mining, damage detection, model updating,
safety evaluation and reliability analysis).
Data acquisition and transmission system is important for an accurate and effective
diagnosis. Sensors basically are materials that demonstrate different characteristics when
they are exposed in different situation. Various sensing technologies are developed for
monitoring of fatigue, corrosion, and seismic damages including piezo-electric ceramic,
optical fiber Bragg Grating , gas ceramic sensors , shape memory alloy and etc. In this work
we introduced piezoelectric ceramic based and fiber optic based sensors and their
application. Finally we have assessed their application in Rocks and Underground Structures
monitoring.

FIBER OPTIC SENSOR Figure 3: Experiment Configuration, sample and sensors location
PIEZOELECTRIC CERAMICS Fiber optic sensors (FOS) have generated a great interest among NDE researchers
due to their small size, immunity to electromagnetic and radio frequency
interferences. These sensors were first developed in 1980s. FOSs are susceptible
Piezoelectric consist of Greek word piezo meaning pressure and materials that to change in light intensity received by detector and the change in light intensity
exhibit electric current when they undergo mechanical deformation, or vice versa would cause fiber loss due to scattering, absorption or bending. Fiber Bragg
are called piezoelectric materials. In non-centrosymmetric crystals such as quartz grating (FBG) was introduced to provide absolute measurement. FBGs provide
(SiO2 ) Lithium Niobite (LiNbO3) PZT (Pb(Zr1-x Tiy)O3) , electric dipoles would occur wavelength measurement independent of overall system of light and only
when they undergo mechanical deformation. Figure 1 present schematic behavior depended on strain and temperature effects acting on senor.
of piezoelectric materials.

Figure 1: Damages and sensors after failure, b) strains identification resulting from FBGs, c) shift in peak frequency of PZT patch resulting damages

CONCLUSIONS
Figure 2: a) FBG sensor configuration, b) FBG behavior mechanism, c) Multiple sensing points existing in a single fiber.

Figure 1: a) Schematic Piezoelectric materials behavior under different mechanical loading, b) Zincite(ZnO4) crystal, and its behavior B grating
Fiber Bragg 2neff is wavelength selective filter and only reflects signals that have
under loading correspondent wavelength twice as period multiple by its effective refractive index
follows equation. FBG sensors can exist both as transducers for point The above experiment show a high similarity between results taken from PZT and
When piezoelectric based sensors exposed to stress field, it generate proportional sensing and as wire for 2-D and 3-D testing. Because of FGBs can be easily FBG sensors in low load cycles, and PZT had better performance .
embedded inside structure and provide measurement for long time without
charges in response that can be . The response normally measured with following After failure no debounding between PZT patches and specimen was observed.
equation significant fiber loss, they have been used extensively in bridges, dams, and nuclear
facilities. Significant debonding occurred between the rock surface and the FBG sensor
prior to specimen failure.
One of various composition available for producing FBGs is Zr-EDF material which
Where [D] (C/m2) is electric displacement vector, [S] the second order strain PZT and FBG sensor show long-term durability and fast dynamic response, low
produced by co-doping Zirconia oxide in silica fibers which have excellent cost, negligible aging, and are immune to ambient noise.
tensor, [E] (V/m) the external electric field vector, [T] (N/m3) the stress tensor. In mechanical strength and are chemical corrosion resistance as well as being non-
addition, [T] (F/m) is second order of dielectric permittivity tensor, [dd] (C/N) and hygroscopic, making them highly compatible with conventional silica fibers and have In real world online monitoring practice of different type of sensors for data
[dc] are third order of piezoelectric strain coefficient tensor and [sE] is the fourth acquisition is suggested.
relatively stable performance
order elastic compliance tensor under constant electric tensor. This equation
signifies the complex nature of piezoelectric behavior of materials such as PZT and
quartz.