Buzz Wincheski

Nondestructive evaluation using a reduced order computational methodology

This paper uses eddy current based techniques and reduced order modeling to explore the feasibility of detecting a subsurface damage in structures such as air foils and pipelines. To identify the geometry of a damage, an optimization algorithm is employed which requires solving the forward problem numerous times. To implement these methods in a practical setting, the forward algorithm must be solved with extremely fast and accurate solution methods. Therefore, our computational methods are based on the reduced order Karhunen-Loeve or Proper Orthogonal Decomposition (POD) techniques. For proof-of-concept, we implement the methodology on a 2-D problem and find the methods to be efficient and robust even with data containing 10 Furthermore, the methods are fast; our findings suggest we can reduce the computational time on average by a factor of 3000.

Real time computational algorithms for eddy-current-based damage detection

In the field of nondestructive evaluation, new and improved techniques are constantly being sought to facilitate the detection of hidden corrosion and flaws in structures such as aeroplanes and pipelines. In this paper, we explore the feasibility of detecting such damage by application of an eddy-current-based technique coupled with reduced order modelling. We begin by developing a model for a specific eddy current method in which we make some simplifying assumptions reducing the three-dimensional problem to a two-dimensional problem (we do this for proof of concept). Theoretical results are then presented which establish the existence and uniqueness of solutions as well as continuous dependence of the solutions on the parameters which represent the damage. We further discuss theoretical issues concerning the least squares parameter estimation problem used in identifying the geometry of the damage. To solve the identification problem, an optimization algorithm is employed which requires solving the forward problem numerous times. To implement these methods in a practical setting, the forward algorithm must be solved with extremely fast and accurate solution methods. In constructing these computational methods, we employ reduced order proper orthogonal decomposition (POD) techniques. This approach permits one to create a set of basis elements spanning a data set consisting of either numerical simulations or experimental data. We discuss two different algorithms for forming the POD approximations, a POD/Galerkin technique and a POD/interpolation technique. Finally, results of the inverse problem associated with damage detection are given using both simulated data with relative noise added as well as experimental data obtained using a giant magnetoresistive sensor. The experimental results are based on successfully using experimental data to form the POD basis elements (instead of numerical simulations), thus illustrating the effectiveness of this method on a wide range of applications. In both instances the methods are found to be efficient and robust. Moreover, the methods were fast; our findings demonstrate a significant reduction in computational time.

Response of Fe powder, purified and as-produced HiPco single-walled carbon nanotubes to flash exposure

The exposure of as-produced HiPCo single-walled carbon nanotubes (SWNTs) to a camera flash causes ignition, (oxidation) and subsequent coalescence of the Fe catalyst particles, while purified SWNTs do not respond to flashing. TEM and electron energy loss spectroscopy (EELS) analysis attribute the phenomena to the pyrophoric oxidation of Fe nanoparticles.

Microstructural, Magnetic Anisotropy, and Magnetic Domain Structure Correlations in Epitaxial FePd Thin Films With Perpendicular Magnetic Anisotropy

L10 order was optimized in FePd epitaxial thin films prepared using dc magnetron sputter deposition on MgO(001) substrates by investigating various growth temperatures. A series of films was grown at the optimal temperature with varying thickness and degree of chemical order to investigate the interplay between the microstructure, magnetic anisotropy, and magnetic domain structure. The experimentally measured magnetic domain size/period and magnetic anisotropy in this high perpendicular anisotropy system were found to be correlated following the analytical energy model proposed by Kooy and Enz that considers a delicate balance between the domain wall energy and the demagnetizing stray field energy.

Development of Giant Magnetoresistive inspection system for detection of deep fatigue cracks under airframe fasteners

A redesign of the NASA Langley Research Center developed Giant Magnetoresistive-based Rotating Probe System has been performed based upon experimental and finite element analyses. The resulting probe footprint has been greatly reduced without significantly affecting the depth of detection of the device. Electronics for the probe drive and signal detection circuitry have also been updated. The new electronics deliver variable phase outputs for drive and feedback signals and produces high gain at flaw detection frequencies. The complete system configuration is presented, along with results for the detection of fatigue cracks in sub-layer airframe components.

Deep flaw detection with giant magnetoresistive (GMR) based self-nulling probe

Giant magneto-resistive sensors provide a high sensitivity to low frequency magnetic fields. This, combined with an inherent small size, low cost, and low power consumption, make GMR sensors a good candidate for low frequency eddy current probe development. Previous research has shown that the incorporation of a GMR sensor in the NASA LaRC developed Self-Nulling Eddy Current Probe greatly enhances the low frequency detection capabilities of the device. Experimental results have shown the detection of a 1.4 cm long notch under up to 9 mm of unflawed aluminum. A limiting factor in this work appeared to be the increased background level with decreasing frequency. In order to improve the signal-to-noise ratio several techniques have been incorporated to reduce the background level and increase the signal-to-noise ratio. The incorporation of a gradiometric sensor, active feedback, and improved shielding have led to an enhanced detectability. In addition, image processing techniques have been explored to filter...

Study of the new eddy current non-destructive testing sensor on ferromagnetic materials

A new eddy current non-destructive testing (NDT) sensor developed at NASA Langley Research Center can accurately detect fatigue cracks and measure material and non-conducting coating thicknesses. This paper presents experimental and finite element modeling data on the characteristics of the sensor on ferromagnetic materials. Fatigue crack detection and lift-off characteristics in steel and aluminum are compared and discussed. >

Development of Very Low Frequency Self-Nulling Probe for Inspection of Thick Layered Aluminum Structures

Nondestructive evaluation technologies have recently been challenged to inspect thick, layered, conducting materials for fatigue and corrosion damage. Structures that fall into this class, such as airframe wings, pose significant difficulties for conventional inspection techniques. Reflections of ultrasound at layer boundaries cause serious problems for the application of ultrasonic inspection methods. Conventional eddy-current inspection techniques are also compromised due to the exponential decay of electromagnetic energy with depth into a conductor.

Application of Eddy Current Techniques for Orbiter Reinforced Carbon‐Carbon Structural Health Monitoring

The development and application of advanced nondestructive evaluation techniques for the Reinforced Carbon‐Carbon (RCC) components of the Space Shuttle Orbiter Leading Edge Structural Subsystem (LESS) were identified as a crucial step toward returning the shuttle fleet to service. In order to help meet this requirement, eddy current techniques have been developed for application to RCC components. Eddy current technology has been found to be particularly useful for measuring the protective coating thickness over the reinforced carbon‐carbon and for the identification of near surface cracking and voids in the RCC matrix. Testing has been performed on as manufactured and flown RCC components with both actual and fabricated defects representing impact and oxidation damage. Encouraging initial results have led to the development of two separate eddy current systems for in‐situ RCC inspections in the orbiter processing facility. Each of these systems has undergone blind validation testing on a full scale leadi...

Development and Application of Wide Bandwidth Magneto-Resistive Sensor Based Eddy Current Probe

The integration of magneto‐resistive sensors into eddy current probes can significantly expand the capabilities of conventional eddy current nondestructive evaluation techniques. The room temperature solid‐state sensors have typical bandwidths in the megahertz range and resolutions of tens of microgauss. The low frequency sensitivity of magneto‐resistive sensors has been capitalized upon in previous research to fabricate very low frequency eddy current sensors for deep flaw detection in multilayer conductors. In this work a modified probe design is presented to expand the capabilities of the device. The new probe design incorporates a dual induction source enabling operation from low frequency deep flaw detection to high frequency high resolution near surface material characterization. Applications of the probe for the detection of localized near surface conductivity anomalies are presented. Finite element modeling of the probe is shown to be in good agreement with experimental measurements.