Yuri Alexeyevich Plotnikov

Defect characterization in multi-layered conductive components with pulsed eddy current

Capabilities of the Pulsed Eddy Current (PEC) method to perform in-depth scanning have been successfully demonstrated for hidden corrosion detection. In the present work, a drive pulse and the response is analyzed in terms of Fourier Transform to understand the scope of material penetration with PEC. Variations of the drive pulse shape can be an effective technique to control the depth of penetration of conductive materials. An observation time interval and a sampling rate are the components that can be used for “in-depth slicing” of conductive media. Two-dimensional scanning of multi-layered structures such as aircraft skin structures with a PEC probe provides detection of subsurface defects. Experiments have been performed on aluminum panels with flat bottom holes. An image processing routine is applied to reconstruct geometry of the component from a series of eddy current images obtained with a two-dimensional scanner. A problem of accurate reconstruction of the internal geometry of the component under test is considered. The advantages and limitations of the technique are discussed.

Quantitative evaluation of discrete failure events in composites using infrared imaging and acoustic emission

We describe the successful synchronization of thermal imaging with acoustic emission to observe and characterize for the first time the thermal responses of discrete fiber breaks and matrix cracks in composite panels under load in real time. These events can be accurately described by ideal buried point and line thermal sources.

Subsurface Defect Detection in Metals with Pulsed Eddy Current

The eddy current (EC) method is traditionally used for open surface crack detection in metallic components. Subsurface voids in bulk metals can also be detected by the eddy current devices. Taking into consideration the skin effect in conductive materials, a lower frequency of electromagnetic excitation is used for a deeper penetration. A set of special specimens was designed and fabricated to investigate sensitivity to subsurface voids. Typically, flat bottom holes (FBHs) are used for subsurface defect simulation. This approach is not very representative of real defects for eddy current inspection because the FBH depth extends to the bottom of the specimen. Two‐layer specimens with finite depth FBHs were fabricated and scanned with conventional EC of variable frequency. Sensitivity and spatial resolution of EC diminish with flaw depth. The pulsed EC approach was applied for flaw detection at variable distance under the surface. The transient response from multi‐layer model was derived and compared to exp...

Lateral heat flow method for thickness independent determination of thermal diffusivity

A pulsed transient thermography method is described where a high-intensity light pulse is used to heat a long, uniform stripe on the surface of a plate. A high spatial resolution, high frame rate focal plane array infrared camera is used to monitor surface temperature. We explain the theoretical model and data analysis framework used to experimentally determine all three thermal diffusivity components from the temperature measurements. The analysis does not require any fitting to the temperature profile and is based on the creation of thermal time-of-flight (tof) images from the temperature data and the relationship between tof and the distance from the stripe edge. The in-plane components of thermal diffusivity are obtained without the need for thickness information. Experimental validation of this procedure was carried out using anisotropic carbon fiber reinforced polymer composites.

Eddy current sensor for in-situ monitoring of swelling of Li-ion prismatic cells

In-situ monitoring an on-board rechargeable battery in hybrid cars can be used to ensure a long operating life of the battery and safe operation of the vehicle. Intercalations of ions in the electrode material during charge and discharge of a Lithium Ion battery cause periodic stress and strain of the electrode materials that can ultimately lead to fatigue resulting in capacity loss and potential battery failure. Currently this process is not monitored directly on the cells. This work is focused on development technologies that would quantify battery swelling and provide in-situ monitoring for onboard vehicle applications. Several rounds of tests have been performed to spatially characterize cell expansion of a 5 Ah cell with a nickel/manganese/cobalt-oxide cathode (Sanyo, Japan) used by Ford in their Fusion HEV battery pack. A collaborative team of researchers from GE and the University of Michigan has characterized the free expansion of these cells to be in the range of 100×125 microns (1% of total cell...

EDDY CURRENT INSPECTION OF COMPONENTS WITH COMPLEX GEOMETRIES

Eddy current (EC) technique is a common inspection method for the detection of open surface cracks and subsurface anomalies. While manual EC inspection is quite reliable on parts with flat (or large curvature) surfaces and parts with consistent subsurface geometry, EC inspection of parts having more complicated surface and subsurface profiles has to rely on automated scan/data collection and post‐processing. Examples of the structures with complex geometries are aircraft engine rotating parts and multi‐layer aircraft structures (lap joints). Data collection for such structures, in most cases, can be performed by using multiple scans of a single sensor EC probe with multi‐frequency excitation. To improve productivity of the inspection, arrays of EC sensors are applied during inspection for surface flaws. In this work, the flexible ECAP (EC array probe) with sensitivity to the cracks of variable orientations is presented. To resolve the complex subsurface geometry of the aircraft skin, pulsed excitation is ...

A LOW‐POWER WIRELESS SENSOR NETWORK FOR MONITORING THE MICROCRACK INITIATIONS IN AEROSPACE COMPOSITES

A low power wireless sensor network was developed to monitor the microcrack events in aerospace composites. The microcracks in the composites mostly result from a stress loading or temperature and/or humidity cycles. Generally, a single microcrack is too small to be detected by conventional techniques such as X‐ray or ultrasonic C‐scan. The whole developed sensor network is aimed to capture the released acoustic signals by the microcracking events in real time. It comprises of a receiving station as well as a series of sensor nodes. Each sensor node includes two acoustic emission transducers as well as two signal amplification and data acquisition channels. Much of our development effort has been focused on reducing the power consumption of each node and improving the detection reliability for each event. Each sensor node is battery‐powered and works in a sleep mode most of time. Once a microcrack is initiated in the composite, the acoustic signal triggers the node and wakes it up. The node will then reac...

RESIDUAL STRESS MEASUREMENT USING RECTANGULAR SPIRAL COILS

Shot peening process provides compressive residual stress within a depth of about 150∼200 um from the surface. It has been demonstrated that multi‐frequency eddy current measurement can be effectively used for the residual stress estimation on Ni‐based superalloys. In order to measure the stress profile over the entire compressive zone, the probe needs to work in a wide frequency range from 0.1 MHz to above 50 MHz. Due to its wide bandwidth and high precision fabrication process, spiral coils fabricated on flexible substrate using photolithographic technology are good candidate for this task It is useful to develop a coil model in order to optimize coil design, minimize liftoff effect and maximize coil gauge factor. In this work, a 3D analytical model was used to simulate rectangular spiral coil response on a half‐space conductor. The results were compared with commercial available 3D finite element software and experimental results. The analytical model was also used to simulate 4‐point calibration proce...

Novel thin temperature and expansion sensors for li-ion battery monitoring

This paper introduces a combined temperature and displacement sensor for new measurements of physical parameters which can inform multi-physics based models of Li-ion batteries. These flexible sensors can be placed directly on the cell to measure intercalation effects which can improve battery state estimation. The sensors were characterized on individual Panasonic cells and subsequently, packaged into a 76 cell Ford Focus hybrid electric vehicle (HEV) pack, which was cycled for 5000 equivalent miles. Results showed improvement in temperature estimation capability with the combination of sensor and model. However, the low expansion of the hard cased cells limited utility of the eddy current sensors.

Development of an electromagnetic imaging system for well bore integrity inspection

State-of-the-art imaging technologies for monitoring the integrity of oil and gas well bores are typically limited to the inspection of metal casings and cement bond interfaces close to the first casing region. The objective of this study is to develop and evaluate a novel well-integrity inspection system that is capable of providing enhanced information about the flaw structure and topology of hydrocarbon producing well bores. In order to achieve this, we propose the development of a multi-element electromagnetic (EM) inspection tool that can provide information about material loss in the first and second casing structure as well as information about eccentricity between multiple casing strings. Furthermore, the information gathered from the EM inspection tool will be combined with other imaging modalities (e.g. data from an x-ray backscatter imaging device). The independently acquired data are then fused to achieve a comprehensive assessment of integrity with greater accuracy. A test rig composed of sev...