Mohammad Faisal Haider

Nonlinear anisotropic electrical response of carbon fiber-reinforced polymer composites

Composites materials are often subjected to multi-physics conditions in different applications where, in addition to mechanical loads, they also need to sustain other types of loads such as electrical currents. Composite materials have heterogeneous electrical properties at the local level that can be different at the global level. In this study, electrical response was measured to explore how different lamina orientation and electrical current density affect anisotropic electrical properties of composite. For in-plane study, current was applied up to 80 kA/m2 for both unidirectional and quasi-isotropic composite. In thickness direction, maximum current density was 6 kA/m2. As expected, electrical properties are indeed dependent on fiber architecture which acts as conduction path in the laminate, and also depends on progressive increase in current density. Anisotropic electrical behavior was measured experimentally and the threshold of nonlinear behavior due to high current was identified. Threshold current density for unidirectional composite in fiber direction and for quasi isotropic are, respectively, 48.14 ± 4.3% kA/m2, 56.06 ± 4.4% kA/m2. For off-axis fiber laminates, this threshold limit shifts from 34.36 ± 5.9% kA/m2 to a lower value of 17.95 ± 7.9% kA/m2 as the fibers are oriented away from the x axis. In thickness direction, this threshold limit is in between 2.56 and 3.80 kA/m2. The electrical-thermal responses were also studied experimentally with thermography tests and the results were compared to indicate damage. A 3D X-ray microscope has been used to visualize and quantify (down to 1 micron) such local material state changes due to electrical current.

Sensing capabilities of piezoelectric wafer active sensors in extreme nuclear environment

There is considerable demand for structural health monitoring (SHM) at locations where there are substantial radiation fields such as nuclear reactor components, dry cask storage canister, irradiated fuel assemblies, etc. Piezoelectric wafer active sensors (PWAS) have been emerged as one of the major SHM sensing technologies. In order to use PWAS to perform SHM in nuclear environment, radiation influence on sensor and sensing capability needs to be investigated to assure the reliability of the PWAS based method. Radiation may cause degradation or even complete failure of sensors. Gamma radiation is one of the major radiation sources near the nuclear source. Therefore, experimental investigation was completed on the gamma radiation endurance of piezoelectric sensors. The irradiation test was done in a Co-60 Gamma Irradiator. Lead Zirconate Titanate (PZT) and Gallium Orthophosphate (GaPO4) PWAS were exposed under gamma radiation at 100 Gy/hr rate for 20 hours. Electro-mechanical (E/M) admittance signatures and electrical capacitance were measured to evaluate the PWAS performance before and after every 4 hours exposure to gamma radiation. PWAS were kept at room temperature for 6 days after each 4 hours radiation exposure to investigate the effect of time on PWAS by gamma radiation. It was found that, PZT-PWAS show variation in resonance frequency for both in plane and thickness mode E/M admittance. Where, the changes in resonance amplitudes are larger for PZT-PWAS. GaPO4-PWAS E/M impedance/admittance spectra don’t show any reasonable change after gamma irradiation. A degradation behavior of electrical properties in the PZT-PWAS was observed. Capacitance value of PZT-PWAS decreases from 3.2 nF to 3.07 nF after exposing to gamma radiation for 20 hours at 100Gy/hour. This degradation behavior of electrical properties may be explained by the pinning of domain walls by some radiation induced effect. GaPO4-PWAS doesn’t show reasonable degradation in electrical properties. GaPO4 has good radiation endurance, although amplitude sensitivity is relatively low.

A Helmholtz Potential Approach to the Analysis of Guided Wave Generation During Acoustic Emission Events

This paper addresses the predictive simulation of acoustic emission (AE) guided waves that appear due to sudden energy release during incremental crack propagation. The Helmholtz decomposition approach is applied to the inhomogeneous elastodynamic Navier–Lame equations for both the displacement field and body forces. For the displacement field, we use the usual decomposition in terms of unknown scalar and vector potentials, U and H. For the body forces, we hypothesize that they can also be expressed in terms of excitation scalar and vector potentials, A and B . It is shown that these excitation potentials can be traced to the energy released during an incremental crack propagation. Thus, the inhomogeneous Navier–Lame equation has been transformed into a system of inhomogeneous wave equations in terms of known excitation potentials A and B and unknown potentials U and H. The solution is readily obtained through direct and inverse Fourier transforms and application of the residue theorem. A numerical study of the one-dimensional (1D) AE guided wave propagation in a 6 mm thick 304-stainless steel plate is conducted. A Gaussian pulse is used to model the growth of the excitation potentials during the AE event; as a result, the actual excitation potential follows the error function variation in the time domain. The numerical studies show that the peak amplitude of A0 signal is higher than the peak amplitude of S0 signal, and the peak amplitude of bulk wave is not significant compared to S0 and A0 peak amplitudes. In addition, the effects of the source depth, higher propagating modes, and propagating distance on guided waves are also investigated. [DOI: 10.1115/1.4038116]

Characterization of Piezo Electric Wafer Active Sensors After Exposure to High Temperature

Piezoelectric wafer active sensors (PWAS) at high temperature with reliable operation are desired for structural health monitoring. The PWAS may be generalized as an electromechanical system because of the incorporation of electromechanical coupling. The basic principle of SHM method by PWAS is to monitor variation in the electro-mechanical (E/M) impedance/ admittance signature. The operational temperature range of PWAS can be limited by the sensing capability of the piezoelectric material at elevated temperatures. Therefore stability of PWAS at high-temperature environments is of great interest for SHM. In such cases SHM can be done at room temperature or at relatively lower temperature. However, during service permanently bonded PWAS can be exposed to very high temperature. The traditional PWAS use piezoelectric materials Lead Zirconate Titanate (PZT) that have been attracted by researchers due to its enhanced sensing, actuation or both capabilities. This paper discusses properties relevant to sensor applications, including piezoelectric materials that are commercially available. For temperature dependence study PWAS were exposed to 50 0 C to 250 0 C with 50 0 C interval at around 2 0 C/min heating rate. E/M impedance/ admittance and different material properties such as, dielectric constant, dielectric loss, mechanical quality factor, P-E hysteresis loop, in plane piezoelectric constant were determined experimentally at room temperature after exposure to high temperature. The variation in E/M impedance and admittance signature and different material properties were obtained at each temperature. The piezoelectric material degradation was also investigated by microstructural and crystallographic study. INTRODUCTION Piezoelectric wafer active sensors (PWAS) have been used extensively for detecting damages and flaws in the structure in SHM [1], [2], [3], [4]. PWAS can be used for electromechanical (E/M) impedance/ admittance method for detecting damages. The (E/M) impedance/ admittance method has been utilized to determine the local dynamic characteristics of a PWAS bonded on a host structure for in situ ultrasonic inspection [3]. The basic principle of this non-destructive monitoring method is to monitor variation in the impedance/ admittance signature measured from the permanently attached PWAS to the host structure. PWAS use transduction of ultrasonic elastic waves into voltage and vice versa. Since a relationship exist between the mechanical impedance/ admittance of the host structure and the electrical impedance/ admittance of the PWAS, any change in the material state can be attained by measuring the coupled electro-mechanical impedance/ admittance. However there is a major problem when using (E/M) impedance/ admittance method by PWAS on host structures after exposure to high temperature. After exposure to high temperature the E/M impedance/ admittance method can lead to unsuccessful damage detection due to ambiguous change in the impedance/ admittance signature. Any change in the material state of PWAS due to crossing characteristic temperature limit can lead significant change in (E/M) impedance/ admittance. As a result, (E/M) impedance/ admittance of free PWAS after exposure to high temperature are important dynamic descriptor for characterizing the sensor prior to its installation on a structure. The thermal effect of PWAS after exposure to hightemperature environments such as dry cask storage canister, Proceedings of the ASME 2016 Pressure Vessels and Piping Conference PVP2016 July 17-21, 2016, Vancouver, British Columbia, Canada

Piezoelectric wafer active sensors under gamma radiation exposure toward applications for structural health monitoring of nuclear dry cask storage systems

Structural health monitoring (SHM) is in urgent need and must be integrated into the nuclear-spent fuel storage systems to guarantee the safe operation. The dry cask storage system (DCSS) is such storage facility, which is licensed for temporary storage for nuclear-spent fuel at the independent spent fuel storage installations (ISFSIs) for certain predetermined period of time. Gamma radiation is one of the major radiation sources near DCSS. Therefore, a detailed experimental investigation was completed on the gamma radiation endurance of piezoelectric wafer active sensors (PWAS) transducers for SHM applications to the DCSS system. The irradiation test was done in a Co-60 gamma irradiator. Lead Zirconate Titanate (PZT) and Gallium Orthophosphate (GaPO4) PWAS transducers were exposed to 40.7 kGy gamma radiation. Total radiation dose was achieved in two different radiation dose rates: (a) slower radiation rate at 0.1 kGy/hr for 20 hours (b) accelerated radiation rate at 1.233 kGy/hr for 32 hours. The total cumulative radiation dose of 40.7 kGy is equivalent to 45 years of operation in DCSS system. Electro-mechanical impedance and admittance (EMIA) signatures and electrical capacitance were measured to evaluate the PWAS performance after each gamma radiation exposure. The change in resonance frequency of PZT-PWAS transducer for both in-plane and thickness mode was observed. The GaPO4-PWAS EMIA spectra do not show a significant shift in resonance frequency after gamma irradiation exposure. Radiation endurance of new high-temperature HPZ-HiT PWAS transducer was also evaluated. The HPZ-HiT transducers were exposed to gamma radiation at 1.233 kGy/hr for 160 hours with 80 hours interval. Therefore, the total accumulated gamma radiation dose is 184 kGy. No significant change in impedance spectra was observed due to gamma radiation exposure.

Guided wave crack detection and size estimation in stiffened structures

Structural health monitoring (SHM) and nondestructive evaluation (NDE) deals with the nondestructive inspection of defects, corrosion, leaks in engineering structures by using ultrasonic guided waves. In the past, simplistic structures were often considered for analyzing the guided wave interaction with the defects. In this study, we focused on more realistic and relatively complicated structure for detecting any defect by using a non-contact sensing approach. A plate with a stiffener was considered for analyzing the guided wave interactions. Piezoelectric wafer active transducers were used to produce excitation in the structures. The excitation generated the multimodal guided waves (aka Lamb waves) that propagate in the plate with stiffener. The presence of stiffener in the plate generated scattered waves. The direct wave and the additional scattered waves from the stiffener were experimentally recorded and studied. These waves were considered as a pristine case in this research. A fine horizontal semi-circular crack was manufactured by using electric discharge machining in the same stiffener. The presence of crack in the stiffener produces additional scattered waves as well as trapped waves. These scattered waves and trapped wave modes from the cracked stiffener were experimentally measured by using a scanning laser Doppler vibrometer (SLDV). These waves were analyzed and compared with that from the pristine case. The analyses suggested that both size and shape of the horizontal crack may be predicted from the pattern of the scattered waves. Different features (reflection, transmission, and mode-conversion) of the scattered wave signals are analyzed. We found direct transmission feature for incident A0 wave mode and modeconversion feature for incident S0 mode are most suitable for detecting the crack in the stiffener. The reflection feature may give a better idea of sizing the crack.

Effects of Gamma Radiation on Resonant and Antiresonant Characteristics of Piezoelectric Wafer Active Sensors

This paper presents gamma radiation effects on resonant and antiresonant characteristics of piezoelectric wafer active sensors (PWAS) for structural health monitoring (SHM) applications to nuclear-spent fuel storage facilities. The irradiation test was done in a Co-60 gamma irradiator. Lead zirconate titanate (PZT) and Gallium Orthophosphate (GaPO4) PWAS transducers were exposed to 225 kGy gamma radiation dose. First, 2 kGy of total radiation dose was achieved with slower radiation rate at 0.1 kGy/h for 20; h then the remaining radiation dose was achieved with accelerated radiation rate at 1.233 kGy/h for 192 h. The total cumulative radiation dose of 225 kGy is equivalent to 256 years of operation in nuclear-spent fuel storage facilities. Electro-mechanical impedance and admittance (EMIA) signatures were measured after each gamma radiation exposure. Radiation-dependent logarithmic sensitivity of PZT-PWAS in-plane and thickness modes resonance frequency ð@ðf Þ=@ð logeRdÞÞ was estimated as 0.244 kHz and 7.44 kHz, respectively; the logarithmic sensitivity of GaPO4-PWAS in-plane and thickness modes resonance frequency was estimated as 0.0629 kHz and 2.454 kHz, respectively. Therefore, GaPO4-PWAS EMIA spectra show more gamma radiation endurance than PZT-PWAS. Scanning electron microscope (SEM) and X-ray diffraction method (XRD) was used to investigate the microstructure and crystal structure of PWAS transducers. From SEM and XRD results, it can be inferred that there is no significant variation in the morphology, the crystal structure, and grain size before and after the irradiation exposure. [DOI: 10.1115/1.4041068]