Research Activities

The Nondestructive Evaluation Laboratory at Michigan State University is home to one of the premier facilities in the country to conduct research across a broad spectrum of electromagnetic and ultrasonic nondestructive evaluation techniques ranging from magnetostatic through quasistatic and microwave frequencies. The laboratory is also equipped with instrumentation to carry out these measurements simultaneously in order to conduct data fusion studies. Faculty in the research group has been at the forefront in developing methods and solution to a variety of forward and inverse problems in the field. NDE systems and software developed by NDEL are used in industry extensively. The research group is also involved in the development of high-end instrumentation and has successfully transferred technology for manufacturing eddy current instruments and acoustic microscopes to companies in Japan.

Model Assisted Inspection Methods for Aging Aircraft

The objectives of this project are: 1) to develop advanced signal processing algorithms for the interpretation of giant magnetoresistive (GMR) sensor data, 2) to develop model based inversion algorithms for GMR inspection data obtained from aircraft structures, and 3) to determine the feasibility of the employing these algorithms for meeting future vehicle health monitoring requirements.

Nondestructive Evaluation of Sprayed on Foam Insulation (SOFI) Using Terahertz Waves

The objective of the project is to improve the effectiveness of the terahertz inspection of the Sprayed on Foam Insulation (SOFI) of the space shuttle external tank by developing advanced signal processing tools. Specifically, the research group is involved in developing computational models for simulating continuous wave and pulsed terahertz (THz) imaging systems for inspecting SOFI. Model as well as system based techniques are being developed for inverting THz image data. The latter approach involves the development of signal processing algorithms for interpreting the data. The project is funded by NASA.

Model Based Data Fusion Algorithms

Nondestructive testing involves the application of an appropriate form of energy to a test specimen. A snapshot of the material/energy interaction process is then taken using a transducer and analyzed to determine the state of the specimen. The nature of the information that can be extracted is a function of several factors including the type of energy employed, characteristics of the excitation signal, including its amplitude, frequency and/or wavelength. Specific choices of these factors can provide different “shades” of information. It is therefore logical to expect that one would be able to garner more complete information concerning the state of the specimen by combining information from multiple sensors that provide complementary segments of data. This project involves the development of data fusion algorithms that build on models of the associated physical processes. We propose to investigate the use of q and inverse–q transforms to map data from a heterogeneous sensor environment to a common physical format. As an example, the q-transform can be employed to map diffusive fields, such as those generated by eddy current probes, onto equivalent propagating wave fields generated by sensors that rely on wave phenomena such as ultrasonic NDT sensors. The project is being carried out in collaboration with faculty at the University of Cassino, Italy.

Development of a Fully Automated System for the Analysis of Eddy Current Data

This Electric Power Research Institute (EPRI) sponsored project involves of the development of a fully automated system for the analysis of eddy current data obtained from steam generator tube inspection. Ensuring the integrity of steam generators is critical for the safe and proper operation of nuclear power plants. Eddy current techniques provide a fast and efficient method for performing steam generator inspection. The data comes from a variety of probes such as bobbin coil, rotating pancake/plus point probes and array probes. The challenge associated with the need for analyzing vast amounts of data generated during the inspection process has contributed to a growing level of interest in automatic methods for the detection and characterization of various types of tube degradation. This project involves development of algorithms and software for the automatic analysis of steam generator tube eddy current probe data. Algorithms for processing bobbin, rotating pancake/plus-point and array probes have been developed. The approach employs a wavelet basis function neural network for sizing the defect. Wavelet basis networks use a multi-resolution approach to map the measured signal onto the defect space. These networks are designed to reconstruct the three-dimensional defect profile of volumetric defects. The software has been beta tested successfully at a number of nuclear power plants.

High Resolution Material Characterization Using Eddy Currents and Ultrasound

Inconel alloys are commonly used in nuclear power plants, and structures (such as steam generator tubing) made of these materials are exposed to high temperatures and pressures, ultimately resulting in cracking and corrosion. The objective of this research is to develop techniques for determining the condition of Inconel samples using multiple NDE techniques. Eddy current and ultrasonic inspection of samples (with corrosion, heat treatment and cracking) will be carried out and the resulting data analyzed using multiparameter analysis methods to determine whether these inspection techniques may be used to successfully characterize these materials.

Development of a Data Analysis Tool Box for Aviation Applications

This Federal Aviation Administration (FAA) project involves of the development of a data analysis tool box for aviation applications. Inspection data from aircraft structures are corrupted by noise and artifacts that are characteristic of the part geometry. For instance, data from wheel inspections is vastly different from engine slot inspection data. This project involves the development of signal processing and analysis algorithms for analyzing eddy current and ultrasonic signals. The objective is to embed these analysis algorithms in commercial NDE inspection systems used by the aviation industry.

Development of Finite Element Models for Simulating Magneto-Optic Inspection

This FAA funded project calls for the development of finite element models for simulating magneto-optic inspection (MOI) of aircraft structures. MOI methods have shown considerable promise in detecting corrosion and second layer cracking. The method allows large area coverage and produces analog images of the corrosion damage. The model predicts the magnitude of the magnetic flux associated with the eddy currents. The computational model is being used by industry for determining the probability of detection (POD) of critical flaws in structures and also for optimizing the design parameters of the magneto-optic sensor and system.

Detection of Outlet Strut Fracture in Bjork-Shiley Prosthetic Heart Valves

The objective of this project is to build prototype units of one catheter-based and one noninvasive system for detecting outlet strut fractures in Bjork-Shiley prosthetic heart valves. The catheter-based method employs two large excitation coils placed on each side of the valve to generate a uniform, time varying field in the neighborhood of the heart valve. The field generated by the induced eddy currents in the outlet strut. These eddy currents, in turn, generate a field which perturbs the uniform field established by the external excitation coils. The perturbation in the field, or more specifically, the perturbation in the gradient of the field in the vicinity of the strut is measured using a catheter-mounted gradiometer to determine the condition of the strut. Studies conducted using a full scale prototype unit has shown that the valves can be classified with 100% accuracy using this approach.

The noninvasive method relies on the use of the electromagnetic acoustic transduction techniques (EMAT) to vibrate the valve in situ within the heart. Prior studies have indicated that the vibration modes associated with an intact and a fractured strut are different and can be exploited for diagnosing the condition of the heart valve. The excitation frequency is swept over the range of frequencies normally associated with single leg separated (SLS) and intact valves. The resonant modes are derived from acoustic signals generated by the vibrating outlet strut which are detected using one or more microphones that are acoustically coupled to the chest of the patient. The signals are analyzed to calculate the vibration modes and hence determine if the strut is fractured or otherwise. Studies conducted using a small scale prototype unit has shown that the valves can be classified with 100% accuracy using the EMAT approach. A clinical scale prototype unit for conducting human studies is being constructed.

Magnetic Flux Leakage Method for the Inspection of Natural Gas Transmission Pipelines

Model and signal processing algorithms for the classification, compensation and characterization of MFL signals are being developed. Additionally, finite element models simulating the inspection tool and capable of predicting 3D leakage field profiles have been developed. The finite element simulation models are being employed to optimize inspection tool design and for training inverse models. The compensation systems can compensate for signal distortion introduced as a result of variations in tool velocity and pipeline magnetic permeability variations. The classification algorithms can be used for separating flaw signals from other benign artifacts such as those introduced by valves, tees and welds. The predicted flaw profile is made use of to calculate the maximum allowable operating pressure for the pipe using finite element stress analysis models.

X-ray, Microwave and Terahertz Tomography Systems

The research group is engaged in the development of novel tomographic imaging systems. The systems do not require a 180° scan of the object under test. Test results obtained to date indicate that the system offers performance levels that are far superior to those obtained using limited angle tomography systems. X-ray systems can be used to obtain tomographic images of cargo laden trucks at border crossings. The terahertz tomography systems can be employed for screening passengers at airports and other secure locations.

Analysis of Ultrasonic Inspection Data from Submarine Hulls

The objective of this project is to develop a knowledge-based ultrasonic inspection system (KBIS) for inspecting steel welds in submarine hulls. A key element of the KBIS system is a neural network classifier that is trained to classify a discontinuity as slag, porosity, lack of fusion or a crack. The software has been integrated into the commercial ABB Amdata ultrasonic inspection system and has been tested and validated for use by the U.S. Navy at locations including the Puget Sound Naval Shipyard, the Electric Boat Corporation and General Dynamics.

Quantitative Characterization of Fretting Damage in Aircraft Turbine Disk

The objective of this project is to develop NDE methods for quantitatively characterizing surface damage in turbine disks and components in difficult-to-access locations in aging airframes. The project involves a combination of new sensor design and the development of texture analysis, feature extraction and classification algorithms.

Rotating Magnetic Field Probes for the Detection of SCC in Gas Transmission Pipelines

Conventional magnetic flux leakage inspection tools are insensitive to axially oriented colonies of gas pipeline stress corrosion cracks. This project explored the feasibility of applying a rotating magnetic field (RMF) probe for detect stress corrosion cracks in pipelines. The study involves the development of a finite element model for studying the underlying physical processes as well as the design, construction and testing of an experimental prototype unit.

Single Frequency Eddy Current Instrument

A single frequency PC compatible single board eddyscope for industrial use was designed, developed and tested. All functions on the board can be controlled via a computer using a custom designed, Microsoft Windows compatible software package. The board was designed to accommodate absolute, differential and transmit/receive eddy current probes. The excitation frequency can be set anywhere over the range 100Hz to 3MHz in increments of 0.01 Hz and the system gain can be adjusted up to 80dB. Balancing is accomplished automatically through software. A programmable eighth order low pass filter, implemented in hardware is available on board. In addition to the hardware based filter, low, high and bandpass digital filters can be implemented via software to process the signals. Other functions such as rotation, scaling and biasing are implemented via software. The board can be interfaced with mechanical scanners. The software package includes state-of-the-art signal/image processing as well as pattern recognition algorithms for signal enhancement, restoration, segmentation and classification. The software package can be custom designed to accommodate the needs of specific industries. As an example, the software package embedded in systems for the nuclear industry could include algorithms for the automatic analysis of steam generator tube eddy current probe data. The system was designed in 1993 and the technology was transferred to Takano in 1994. The system incorporated state-of-the-art technologies and offered many features that were not available in eddyscopes on the market at that time.

High Resolution Scanning Acoustic Microscope

The project involved the design, development, construction and testing of a high resolution acoustic microscope. A 220 MHz ultrasonic pulser/receiver was designed and developed as part of the effort. The pulser/receiver unit could be used as a stand-alone instrument controlled through the front panel. Alternately, the instrument can be controlled remotely through a personal computer. The pulse repetitive frequency can be set anywhere from 500Hz to 125 kHz using either an internal clock or triggered via an external source. A choice of 16 preset energy levels together with the ability to choose three different peak amplitudes is offered. The damping level can be set between 10 and 1000 ohms. The receiver gain (7-70 dB), attenuation (0-63dB) and damping (10 -1000 ohms) can be set via the front panel or remotely from a computer. A number of filter and signal rectification options are available to the user.

The acoustic microscope is interfaced to a personal computer which is equipped with a suite of user friendly, state-of-the-art pattern recognition as well as signal/image processing packages. Powerful 2D and 3D computer graphics packages for displaying and manipulating images are included. The software package includes algorithms for controlling an X-Y-Z mechanical scanner. The software is capable of detecting the boundaries of the test specimen, conduct a scan with the desired spatial resolution and display the processed c-scan image automatically. The signal/image processing package can subsequently be used to extract information of interest to the user.

The resolution of the microscope is better than 5 micrometers. The instrument has been used to study the structure of metallic as well as ceramic components.

The scanning acoustic microscope system was designed in 1992 and the technology was transferred to Takano in 1993. As in the case of the single frequency eddyscope, the acoustic microscope system incorporated state-of-the-art technologies and offered many features that were not available in acoustic microscopes on the market at that time.