Wireless sensing using piezo-ceramic transducers for structural health monitoring
Venu Gopal Madhav ANNAMDAS University of Pittsburgh, PA
Co-Authors: Yang Yaowen and Liu Hui [Nanyang Tech. Uni., Singapore]
SPIE 2009 San Diego
March/10/2009
Contents • Introduction • Experimental study on damage localization in beam • Experimental procedure • Results and discussion
• Wireless sensing system • Design of wireless sensing system • Validity test
• Conclusions Q&A
Introduction • OPTIMIZE: Smart material based SHM techniques have been extensively used and have attracted many researchers to study and develop new methods to OPTIMIZE engineering resources. • SELECTION: Among the different types of smart materials, PZT material is one of the most widely SELECTED. • APPLICATIONS: distributed vibration sensors, strain sensors, actuators, and pressure transducers. • PRINCIPLE: EMI EM admittance signature • SIGNATURES: function of the stiffness, mass and damping of the host structure, + Dimensions and orientation of the PZT transducer. • CHANGES: admittance signature presence of structural damages.
Introduction • POTENTIAL: great potential in damage detection. Objective Damage localization of aluminum beam using two PZT transducers a) Conventional EMI monitoring system b) Wireless sensing system 1. Success so far…. 2. Limitations…
Damage Localization In Beam • Conventional set up • Wayne Kerr 6420 impedance anlyzer, Agilent 34980A switch box, an interface cable and a personal computer with data acquisition software
Damage Localization In Beam • Specimen • An aluminium beam Length (mm)
Width (mm)
Thickness (mm)
Beam
400
40
2
PZT
10
10
0.3
Damage Localization In Beam • Experimental procedure • BASELINE: The aluminium beam with all holes fixed with bolts and nuts was considered as pristine state. • DAMAGE: Structural damage was incurred by taking out the bolt and nut at a particular location sayB1 or B11. • Signatures acquired from both PZT1 and 2 at damaged state were compared to those baseline signatures. • At each damage state, only ONE nut and bolt was removed. • LOCATION: damage location (MOTION) from one end to other end was studied. Location 1: removal
Location 3: removal at B3 and re-installing at B1
Damage Localization In Beam • Experimental results and discussion • In the experiments, the admittance signatures were recorded in the frequency range of 10-50 kHz as [PZT is more sensitive to incipient damage at lower frequency] • The scanning step was set to 0.1 kHz which is small enough to include the major peaks in the acquired signatures. • 400 FREQUENY ACQUITITION
Damage Localization In Beam • Experimental results and discussion • Conductance signatures obtained from PZT1 in 10-50 kHz and in 46-50 kHz,
Damage Localization In Beam • Experimental results and discussion • Conductance signatures obtained from PZT2 in 10-50 kHz and in 44-48 kHz
Damage Localization In Beam • Experimental results and discussion • For signatures obtained from PZT1, the dominant peak at damaged state shifts to the left of baseline, while the peak shifts to the right for signatures obtained from PZT2. • DAMAGE PZT1: PZT2: [PEAK SHIFTS]
Damage Localization In Beam • Experimental results and discussion • To have a better understanding of the signature changes in relation to the different damage locations, the Root Mean Square Deviation (RMSD) is chosen as a statistical damage index to analyze the experimental results quantitatively.
∑( y − x )
2
N
RMSD (%)
=
i
i
i =1
N
∑ x i =1
x 100
2
i
xi signatures obtained before (baseline) damage yi signatures obtained after damage incurred
Damage Localization In Beam • Experimental results and discussion • DAMAGE RMSD decreases • RMSD values calculated for results obtained from PZT1 in 10-50 kHz and in 40-50 kHz
Damage Localization In Beam • Experimental results and discussion • DAMAGE RMSD increases • RMSD values calculated for results obtained from PZT2 in 1050 kHz and in 40-50 kHz
location Vs RMSD value is established.
Damage Localization In Beam • Experimental results and discussion • RMSD is proportional to location of damage. • The changes of peak RMSD values are more consistent compared to the overall RMSD values. • The frequency range within which the dominant peak falls is more appropriate for damage localization using RMSD index in this case. 1. The RMSD values for PZT1 are generally larger than the ones of PZT2. This is consistent to the fact that all the damages are nearer to PZT1. 2. The RMSD value of H11 for both PZT1 and 2 are close which also confirms the fact that H11 is located near the center of the beam.
Wireless Sensing System • Design of Wireless Sensing System for EMI based SHM • The newly developed wireless sensing system is portable and relatively cheap compared to conventional impedance analyzer • The wireless sensing system consists of 1. Analog Device AD5933, 2. NXP LPC2136 microcontroller 3. Radio frequency (RF) transmitter (STR-30)/ receiver 4. Powered by 4 AA batteries.
Wireless Sensing System • Design of Wireless Sensing System for EMI based SHM • PZT is connected to the wireless sensing unit and admittance signatures are acquired and all the data are transmitted to a PC by the RF transmitter. • An STR-30 receiver is connected to PC via RS232-to-USB interface to receive data. • Data acquisition software is installed in the computer to control the whole sensing and data transmitting processes.
Wireless Sensing System • Design of Wireless Sensing System for EMI based SHM
Wireless Sensing System • Experimental Test for Validity • To examine the reliability of the designed wireless sensing system, experiments were carried out on the aluminium specimen which was used in the damage localization test previously. • Comparisons of signatures obtained for H1 state
Wireless Sensing System • 1) 2) 3) 4)
SUCCESS so far.. Wide band of acquisition [40 kHZ wide] Signature accuracy was satisfactory Size is reasonable small [less than A4 Size paper] Distance of about 100 m between transmission and receiving stations. Future plans 1. Increasing the band to 1 MHz range 2. Fine tuning to have 99% accurate signatures 3. To increase the distance to atleast 1 Km
100 m
Conclusions • Experimental study on damage localization of an aluminium beam with bolts and nuts is presented. 1. signatures were analyzed statistically using RMSD index in the frequency ranges of 10-50 kHz and 40-50 kHz [where dominant peak falls in]. 2. For both PZTs, RMSD value increases when damage approaches and vice versa. 3. The RMSD values calculated in the frequency range of 40-50 kHz is more appropriate in this study since the changes of RMSD values are more consistent. 4. PZT1 which is nearer to damage, generated larger RMSD values compared to PZT2 and when the damage is located at center of the beam, the RMSD values from two PZTs are approximately the same. 5. A newly developed wireless sensing system was presented. [Validity tests were conducted to examine the reliability of this sensing system and the results have shown reliability of the new system]
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