a simulative and experimental approach toward … asme...robin james1 department of mechanical...

Robin James1

Department of Mechanical Engineering,University of South Carolina,

Columbia, SC 29208e-mail: [email protected]

Mohammad Faisal HaiderDepartment of Mechanical Engineering,

University of South Carolina,Columbia, SC 29208

e-mail: [email protected]

Victor GiurgiutiuDepartment of Mechanical Engineering,

University of South Carolina,Columbia, SC 29208


David LilienthalThe Boeing Company,Charleston, SC 29456


A Simulative and ExperimentalApproach Toward Eddy CurrentNondestructive Evaluation ofManufacturing Flaws andOperational Damage in CFRPCompositesThe manufacturing process of carbon fiber reinforced polymer (CFRP) composite struc-tures can introduce many characteristic defects and flaws such as fiber misorientation,fiber waviness, and wrinkling. Therefore, it becomes increasingly important to detect thepresence of these defects at the earliest stages of development. Eddy current testing(ECT) is a nondestructive inspection (NDI) technique that has been proven quite effectivein detection of damage in metallic structures. However, NDI of composite structures hasmainly relied on other methods such as ultrasonic testing (UT) and X-ray to name a fewand not much on ECT. In this paper, the authors explore the possibility of using ECT inNDI of CFRP composites by conducting simulations and experiments thereafter. Thisresearch is based on the fact that the CFRP displays some low-level electrical conductivitydue to the inherent conductivity of the carbon fibers. This low-level conductivity may permiteddy current pathways to cause the flow of eddy currents in the CFRP composites that canbe exploited for nondestructive damage detection. An invention disclosure describing ourhigh-frequency ECT method has also been processed. First, the multiphysics finiteelement method (FEM) simulation was used to simulate the detection of various types ofmanufacturing flaws and operational damage in CFRP composites such as fiber misorien-tation, waviness, wrinkling, and so on. Thereafter, ECT experiments were conducted onCFRP specimens with various manufacturing flaws using the Eddyfi Reddy eddy currentarray (ECA) system. [DOI: 10.1115/1.4044722]

Keywords: CFRP, composites, characteristic defects, manufacturing flaws, operationaldamage, misorientation, waviness, wrinkling, ECT, air-cored eddy current sensor,impedance, ECA, aerospace engineering, continuous and periodic condition assessment,damage classification, diagnostic feature extraction, eddy current, imaging, materialstesting, mechanical engineering, prognosis, sensors, ultrasonics

1 Introduction1.1 State of the Art. Carbon fiber reinforced polymer (CFRP)

composites are of extreme interest in the aerospace and automotiveindustries due to their light weight and high strength-to-weightratio. Structures manufactured using CFRP composites must bemade in a perfect state such that they do not introduce any danger-ous risks. The manufacturing process of CFRP structures can intro-duce significant manufacturing flaws such as fiber misorientation,fiber waviness, and wrinkling. Besides manufacturing flaws, theCFRP composite can also undergo operational damage during itsservice lifetime. These types of defects may lead to catastrophicfailures if they are not detected at the earliest stages of development.An assortment of nondestructive testing (NDT) methods exist

that can be used for damage detection in CFRP composites. Thespecific method used for testing for the presence of the damage isselected after considering the cost of inspection, time involved forinspecting the part, access to the composite part, and the potentialability of the inspection method to detect the presence, extent,and location of the damage. The simplest and most common

nondestructive testing method for CFRP composites is visualinspection [1], wherein the quality inspector uses flashlights, mag-nifiers, or borescopes for the initial detection of the damage. Ifvisual inspection arises suspicions, then detailed investigation isconducted to verify the presence of the damage using the cointapping method [2]. The coin tapping method involves using asmall and blunt object like a coin and tapping the composite andlistening for changes in the sound of the material, which indicatesthe presence of the damage. This method is clearly not very reliableand is extremely time consuming. Another possible technique fordamage detection is to use vibration-based methods. Vibration-based methods are used to measure the frequency response of com-posites. These methods can detect reduction in stiffness indamage-induced areas evenly distributed over the composite [3].A change in the natural frequencies is an indicator of stiffnesschange. This method is used widely for detecting low velocityimpact damage. Infrared thermography involves taking thermalimages of a composite, which can provide information about itsinner structure and information that differentiates the areas thatare damaged from the areas that are pristine. This method candetect the presence of voids, foreign inclusions, delamination, andimpact damage in relatively short time [4]. More recent applicationsof infrared thermography have been in the areas of thermoplasticwelding. In ultrasonic nondestructive evaluation and structural

1Corresponding author.Manuscript received March 29, 2019; final manuscript received August 25, 2019;

published online September 4, 2019. Assoc. Editor: Yuris Dzenis.

Journal of Nondestructive Evaluation, Diagnosticsand Prognostics of Engineering Systems

FEBRUARY 2020, Vol. 3 / 011002-1

Copyright © 2019 by ASME

Dow

nloaded from https://asm

edigitalcollection.asme.org/nondestructive/article-pdf/3/1/011002/6430403/nde_3_1_011002.pdf by Stanford U

niversity user on 25 October 2019

mailto:[email protected]




https://crossmark.crossref.org/dialog/?doi=10.1115/1.4044722&domain=pdf&date_stamp=2019-10-15

health monitoring, pulses of high-frequency sound waves generatedfrom piezoelectric transducers are transmitted into the compositematerial, and the time it takes for them to reflect back (timeof flight) is measured. This method allows the detection of disbondsand delaminations in the composite structures [5–8]. Amongelectromagnetic methods, microwave nondestructive evaluationmethods have begun to be explored and utilized for the detectionof corrosion damage precursors in Al-CFRP composites [9,10]and for the prediction and detection of low velocity impactdamage in aerospace composites [11,12]. High-resolution andwideband microwave synthetic aperture radar imaging [13] and amicrowave nondestructive testing system [14] have been developedfor damage detection in multilayered CFRP composite materials.The earliest application of eddy current (EC) testing of CFRP

composites was conducted by Owston [15] where he tried tomeasure the fiber volume fraction and fiber orientation. Later,Prakash and Owston [16] came up with an eddy current methodto determine the stacking sequence of a cross-ply CFRP compositeand to detect the presence of fiber wash during manufacturing.Dingwall and Mead [17] conducted eddy current inspection ofCFRP composites to determine local variations in fiber volume frac-tion at 10–12 MHz by adopting the principles developed by Prakashand Owston. In the same year, Carpenter and Stuhrke [18] adoptedthe use of eddy current techniques at NASA and encounteredproblems with its depth of penetration in metallic and compositematerials. In 1979, Phelps [19] introduced the application of eddycurrent testing (ECT) on graphite/epoxy composites for Boeingand suggested that ECT could be feasible for surface damage detec-tion using high-frequency probes in the range of 50–100 MHz.For a fundamental understanding of the behavior of eddy currentsin CFRP composites, Prakash [20] found that ECT can be usedon composites with a fiber volume fraction of 55% or greater.High fiber volume fraction in complex layups and chopped fibercomposites will ensure higher fiber-to-fiber contact, resulting inlower transverse resistivity. Vernon [21] developed the use ferritecup core probes for inspecting graphite epoxy composites in1987. This method was used for detecting the presence of brokenfibers. An optimized single-sided inspection was developed forhigh resistivity materials. Due to the extremely low conductivitiesof the CFRP composites, researchers [22] suggested modificationsto existing methods applied to metals and for exploring high fre-quencies in the range of 1–30 MHz for woven composites and10–500 MHz for unidirectional composites to detect fiber orienta-tions and large size delaminations. In 1995, Gros [23] conductedECT of CFRP helicopter panels followed by the visual data analysisto rapidly locate the damage using a probability of detection analy-sis approach. Pratap and Weldon [24] were the first researchers todevelop the anisotropic conductivity matrix for CFRP compositesto be used in pulsed electrical machines. This conductivity matrixhas been used extensively in numerical simulations of ECT.Mook et al. [25] described the fundamental approach to modelingof ECT of CFRP composites and the suitability of existing ECprobes toward CFRP composites. Gros et al. [26] have exploredthe use of multiple techniques to detect the presence of delaminationin a quasi-isotropic CFRP composite. The 3D eddy current mappingof the delaminated composite has been obtained, and a multi-sensordata fusion approach has also been explored.In recent years, extensive work has been done to understand the

phenomena of ECT in weakly conductive materials and how it canbe used to detect the presence of defects. A benchmark problemcalled the testing electromagnetic analysis methods (TEAM) work-shop problem 15: rectangular slot in a thick plate has been describedin Ref. [27], which involves an experiment where a circular air-cored coil is scanned, parallel to the x-axis, along the length of arectangular slot in an aluminum alloy plate. This model is used tovalidate ECT computational models. Mook et al. [28] used high-frequency eddy current sensors to characterize CFRP compositeswith various flaws such as fiber misorientation, delaminations,and cracks. The EC distribution was reconstructed from the mag-netic field in their work. Heuer and Schulze [29] claimed that

there is no efficient and reliable testing system for in-line and con-secutive manual inspections of raw carbon fiber materials and post-composited CFRP materials. The multifrequency ECT systemconsisting of a scalable 16-sensor demonstrator line array devel-oped at Fraunhofer IZF is used to detect missing carbon fiberbundles, fringes, missing sewing threads, and fiber misorientation.They were able to obtain high-resolution eddy current images ofvisible even weaving threads. Mizukami et al. [30] have proposeda specialized EC probe to detect in-plane and out-of-plane fiberwaviness in the unidirectional CFRP. The proposed EC probe candetect in-plane fiber waviness in a thin unidirectional CFRP com-posite at sufficiently high drive frequencies. Validity of their pro-posed method is verified through 3D finite element method(FEM). Cacciola et al. [31] have proposed a ferrite core EC probefor the nondestructive evaluation of CFRP composites. The effectof the ferrite core is analyzed in order to focus the magnetic fluxdensity on the investigated specimen. Eddy currents generated byhigh-speed ferrite core probe movement were investigated usingnumerical simulation applying an FEM approach. Machado et al.[32] have developed customized the eddy current NDT systemfor online inspection of unidirectional CFRP ropes. Characteristicsof the distribution and the flow of eddy currents in CFRP compos-ites have been described by Jiao et al. [33]. The complex eddycurrent data at high frequencies were used by Hughes et al. [34]to characterize the CFRP composites using the Radon-transformanalysis. Researchers have also explored the ECT of operationaldamage such as delaminations in CFRP composites using finiteelement analysis [35]. Despite the extensive research conductedby researchers in this field, ECT commercial systems are almostnonexistent due to the challenges in developing high-frequencyprobes and the inability of obtaining good depth of penetration todetect the presence of subsurface flaws in CFRP composites.

1.2 Objective of the Present Paper. After the manufacturingprocess, the CFRP retains some of the conductive properties of thecarbon fibers. These retained conductive properties of the carbonfibers in the CFRP composites create electrical pathways that canbe exploited using high-frequency ECT systems. In this paper,the authors pursue the development of an ECT method for detectingmanufacturing flaws and operational damage in CFRP composites.First, various multiphysics FEM simulations were conducted to

simulate the detection of various types of manufacturing flaws andoperational damage inCFRPcomposites using an air-cored eddy cur-rent sensor tomeasure changes in its complex impedance.Changes inthe complex impedance of the coil can bemeasured in the impedanceplane, and the Lissajous curve can be plotted to indicate the presenceof a defect. Subsequently, the experimental detection of manufac-turing flaws was pursued using the knowledge accumulated fromECT simulations. The specimens used in these experiments areboth in-house manufactured specimens and specimens supplied byThe Boeing Company with manufacturing flaws. The specimenswere subjected first to conventional ultrasonic testing (UT) in animmersion tank. Subsequently, the specimens were subjected toECT using an Eddyfi Reddy eddy current array (ECA) system.Results and findings described in this paper were also presented

as a conference paper [36], and an invention disclosure [37] cover-ing our novel findings has been forwarded to The Boeing Company.

2 Eddy Current Testing Simulation of CFRPComposites2.1 Eddy Current Testing Simulation Methodology.

COMSOL MULTIPHYSICS commercial code was used to perform the3D FEM simulations of the ECT process. In order to build confi-dence in the modeling approach, the TEAM Workshop Problem15 [27] was used, which offers the experimentally measured dataduring ECT of a rectangular slot in an aluminum plate. First, alift-off coil impedance plot was generated by simulating a lift-offscenario, which is similar to the lift-off curve that is obtained by

011002-2 / Vol. 3, FEBRUARY 2020 Transactions of the ASME

Dow




an EC device after which the NDT inspector manually adjusts thephase of the lift-off curve and makes the lift-off signal parallel tothe horizontal axis to calibrate the instrument. A similar procedurewas followed while conducting FEM simulations, and the phase ofthe lift-off curve obtained was adjusted to align it with the horizontalaxis. Subsequently, the ECT simulation of the TEAM WorkshopProblem 15 scenario was conducted to obtain an impedance plot.This plot was phase compensated to distinguish it from the lift-offcurve obtained earlier (similar to how themeasurements are recordedon an EC device by the NDT inspector). A good match is observedbetween the experimental results obtained [27] and the 3D FEM sim-ulations. The results obtained (Fig. 1) indicate that a similar simula-tion strategy for an anisotropic CFRP composite plate can be used.

2.2 Eddy Current Testing Simulation of CFRPComposites. An approach similar to the one described in theTEAM Workshop Problem 15 [27] at the end of Sec. 2.1 wasused to model the behavior of eddy currents due to an air-coredcoil placed on top of an eight-layer pristine CFRP composite withdifferent stacking sequences. Four distinct stacking sequenceswere used: unidirectional [0]8, cross-ply [0/90]2S, quasi-isotropic[0/+45/−45/90]S, and unidirectional [90]8. All the laminates con-sidered in this study had the same thickness, the difference beingonly in the orientation of the individual layers, which was per-formed in accordance with the prescribed stacking sequence. Thelift-off distance between the air-cored coil and the CFRP compositewas kept as 0.1 mm. Table 1 displays the characteristics of theair-cored eddy current coil, and Table 2 displays the characteristicsof the eight-layer CFRP composite used in the FEM simulations.Following the work of Pratap and Weldon [24] and Cheng et al.[38], a homogenized macroscopic approach was adopted by usinga conductivity tensor to represent an assumed homogenous

anisotropic conductivity for each lamina in a specific stackingsequence. Each lamina can be regarded as a homogeneous andanisotropic layer with a specific conductivity tensor [24]. The con-ductivity tensor [38] σn of the nth layer in the global coordinatesx, y, and z can be expressed as follows:

σn = RTn σRn =

σxx σxy 0σxy σyy 00 0 σzz

⎡⎣

⎤⎦ (1)

where

Rn =cos θn sin θn 0−sin θn cos θn 0

0 0 1

⎡⎣

⎤⎦ (2)

σ =σL 0 00 σT 00 0 σT

⎡⎣

⎤⎦ (3)

Equation (2) is the rotation matrix that transforms the principalcoordinates into the global x, y, and z coordinates. θn is the rotationangle of the nth layer according to the stacking sequence of thecomposite laminate under consideration. Equation (3) indicatesthe conductivity tensor with respect to the principal axes of thenth layer. In Eq. (3), σL is 20,000 S/m and σT is 20 S/m. Therefore,to model a specific layer in the composite, the orientation angle θnhas to be changed in the rotation matrix Rn to obtain the homo-geneous and anisotropic conductivity tensor of that particular layer.

2.3 Frequency Response of Air-Cored Eddy Current Coil.The frequency response of the air-cored coil was conducted byplacing the air-cored coil in a fixed lift-off position of 0.1 mmabove the pristine CFRP composites with different stackingsequences and by running a simulation in the frequency domainwith a frequency sweep from 0.1 kHz to 10 GHz in a log scale step-ping. The schematic of the simulation setup in which an air-corededdy current coil is placed over an eight-layer pristine CFRP com-posite is displayed in Fig. 2. The frequency response of the air-coredcoil above composite plates of different stacking sequences wasobtained as a Bode plot as shown in Fig. 3. It consisted of thelog-log plot of the magnitude and the phase plot of the compleximpedance varying with increasing frequency for different stackingsequences. From this plot, the real part of the impedance and theimaginary part of the impedance were obtained as functions offrequency as can be seen in Fig. 4. These two plots were combinedto obtain the coil impedance plot on a log-log scale, which clearlyidentified three distinct zones as displayed in Fig. 5. In zone 1, it isobserved that the real part of the coil impedance remains constantwith an increase in the frequency as the imaginary part of the coil

Table 1 Coil characteristics

Outerdiameter(mm)

Innerdiameter(mm)

Height(mm) Turns

Excitationcurrent (mA)

Lift-off(mm)

3.2 1.2 0.8 140 30 0.1

Table 2 Composite characteristics

Laminathickness(mm)

Numberof layers

Totalcompositethickness(mm)

Compositelength (mm)

Compositewidth (mm)

0.125 8 1 20 10

(a) (b)

Coil above slot edge

Initial coil position

Final coil position (pristine area)

Coil above slot edge

Initial coil position

Final coil position (pristine area)

Fig. 1 FEM simulation results of TEAM Workshop Problem 15: (a) coil impedance plot com-paring simulation and experimental results and (b) coil impedance plot with the lift-off curve


FEBRUARY 2020, Vol. 3 / 011002-3

Dow




impedance increases. In zone 2, it is observed that as the frequencyis increased, there is a linear relationship between the real part ofthe coil impedance and the imaginary part of the coil impedance.It is also observed that there is a clear gap in the coil impedance

between a unidirectional composite and other angle-ply composites.This zone is a zone of interest, and the frequencies in this zone canbe used to identify flaws such as fiber misorientation, fiber wavi-ness, and wrinkles. In zone 3, nonlinear effects seem to be arisingwith an increase in the coil frequency. This simulation was usefulin narrowing down the range of frequencies to conduct subsequentECT simulations using the air-cored EC coil on a CFRP compositeplate with simulated manufacturing flaws.

2.4 Fiber Misorientation Detection in a UnidirectionalCFRP Composite. A [0]8 unidirectional CFRP composite wasmodeled with a fiber misorientation domain in the second layer,and the air-cored EC coil was placed above it with a lift-off distanceof 0.1 mm to model the ECT detection of the simulated misorien-tation zone at a frequency of 800 kHz, which lies inside our zoneof interest obtained from the previous simulation. The misorienta-tion zone was assigned different misorientation angles (±45 deg,±60 deg, and 90 deg) by changing the orientation angle (θn) inthe rotation matrix (Rn), and the material properties for this zonewere calculated based on the conductivity tensor given byEqs. (1)–(3). Table 1 displays the properties of the air-cored EC

Air-coredEC coil

8-layerCFRP composite

Fig. 2 Frequency response of the air-cored EC coil: schematicconfiguration of the air-cored coil over eight-layer CFRPcomposite

Fig. 3 Frequency response of the air-cored EC coil: bode plot ofmagnitude and phase

(a) (b)

Fig. 4 Frequency response of the air-cored EC coil: (a) coil resistance (real part of imped-ance) plot and (b) coil reactance (imaginary part of impedance) plot for different stackingsequences for increasing frequencies

Zone 1

Zone 2

Zone 3

Dependence of coil impedance on frequency

Fig. 5 Frequency response of the air-cored EC coil: coil imped-ance plot for different stacking sequences for increasingfrequencies


Dow




coil, and Table 2 displays the properties of the unidirectional CFRPcomposite used in this simulation. Figure 6(a) displays theschematic configuration of the air-cored coil scanning over theeight-layer unidirectional CFRP composite with the fiber misorien-tation domain. The initial position of the coil is directly above themisorientation domain, and the coil is scanned in the longitudinaldirection along the length of the composite plate toward the finalposition of the coil in a line scan. Figure 6(b) displays the compen-sated coil impedance plot along with the lift-off curve. The lift-offcurve was obtained in a similar manner as described in Sec. 2.1for the case of the ECT of an aluminum plate with a rectangularslot. From the results obtained, it can be observed that as the air-cored eddy current coil is scanned from the top of the misorientationdomain (initial position of the coil) and toward a pristine location(final position of the coil), which is away from the fiber misorien-tation, the coil impedance begins to approach the origin of theLissajous curve where both the real and imaginary parts of theimpedance is zero (pristine area). It can also be observed thatthe magnitude of the impedance is directly proportional to theextent of the misorientation. This means that the tail or length ofthe damage curve in the impedance plot (Fig. 6(b)) will be longerfor higher misorientation angles and smaller for smaller angles.The effect of change in magnitude of the coil impedance can beobserved in the bar graph displayed in Fig. 6(c).

2.5 In-Plane Fiber Waviness Detection in UnidirectionalCFRP Composite. A scenario very similar to the one describedin the previous section was used to model the fiber waviness detec-tion in a [0]8 unidirectional CFRP composite. The fiber wavinesszone was divided into four equal subdomains and assigned misori-entation angles (θ) of 45 deg, 30 deg, −30 deg, and −45 deg to

simulate an in-plane fiber waviness. The schematic configurationof modeling the fiber waviness is displayed in Fig. 7 along withthe compensated coil impedance plot with the lift-off curve. Thelift-off curve was obtained in a similar manner as described inSec. 2.1 for the case of the ECT of an aluminum plate with a rect-angular slot. It can be observed that as the air-cored eddy currentcoil is scanned from the top of the fiber waviness domain (initialposition of the coil) toward a pristine location (final position ofthe coil) and away from the fiber waviness, the coil impedancebegins to approach the origin of the Lissajous curve where boththe real and the imaginary parts of the impedance is zero (pristinearea). It can also be observed that there is a sharp change in thedamage curve in the impedance plot when the coil is directly ontop of the edge of the fiber waviness domain (half of the coil isabove waviness domain and half of the coil is above the pristinearea). In a similar way, out-of-plane waviness was also modeledin the thickness direction by considering different subdomainswith different misorientation angles and was able to be detectedusing the air-cored coil [36].

2.6 Embedded Wrinkle Detection in Cross-Ply CFRPComposite. A [0/90]2S cross-ply CFRP composite was modeledwith an embedded wrinkle, and an air-cored coil was placedabove it to model the ECT detection of an embedded wrinkle.The embedded wrinkle was modeled as a noodle along the widthof the composite with an elliptical cross-section and assigned a con-ductivity tensor similar to the 90 deg laminas. The properties of theair-cored eddy current coil and the cross-ply CFRP composite aresimilar to the ones used previously. Figure 8 displays the schematicconfiguration of the air-cored coil scanning over the eight-layercross-ply CFRP composite with the embedded wrinkle domain

(a) (b)

(c)

Final posi�on of coil(Pris�ne area)

Ini�al posi�on of coil for +/- 45 deg

Ini�al posi�on of coil for +/- 60 deg

Ini�al posi�on of coil for 90 deg

Initial position of coil

Fig. 6 Fiber misorientation detection in a unidirectional CFRP composite: (a) schematic config-uration of the air-cored coil over the eight-layer unidirectional CFRP composite with fiber misori-entation, (b) the compensated coil impedance plot with lift-off, and (c) a change in the magnitudeof complex impedance due to different misorientation angles


FEBRUARY 2020, Vol. 3 / 011002-5

Dow




along with the compensated coil impedance plot with the lift-offcurve. The lift-off curve was obtained in a similar manner asdescribed in Sec. 2.1 for the case of the ECT of an aluminumplate with a rectangular slot. From the results obtained, it can beobserved that as the air-cored eddy current coil is scanned fromthe top of the embedded wrinkle domain (initial position of thecoil) and toward a pristine location (final position of the coil)away from the embedded wrinkle, the coil impedance begins toapproach the origin of the Lissajous curve where both the realand imaginary parts of the impedance is zero (the pristine area).In this way, the embedded wrinkle is detected.

2.7 Embedded Polymer Canyon Detection in Cross-PlyCFRP Composite. A scenario very similar to the one describedin Sec. 2.6 was used to model the embedded polymer canyon detec-tion in a [0/90]2S cross-ply CFRP composite. The embeddedpolymer canyon was modeled as a noodle along the width of thecomposite with a rectangular cross-section having a thickness thatranges from half of the first layer until half of the eighth layer. Itwas assigned the electric conductivity corresponding to epoxyresin. The properties of the air-cored eddy current coil and the cross-ply CFRP composite are similar to the ones used previously.Figure 9 displays the schematic configuration of the air-cored coil

(a) (b)


Ini�al posi�on of coilon top of the damage


Fig. 7 In-plane fiber waviness detection in a unidirectional CFRP composite: (a) schematic con-figuration of the air-cored coil over eight-layer unidirectional CFRP composite with fiber wavinessand (b) compensated coil impedance plot with lift-off

(a) (b)

Ini�al posi�on of coilon top of the damage



Fig. 8 Embedded wrinkle detection in a cross-ply CFRP composite: (a) schematic configurationof the air-cored coil over eight-layer unidirectional CFRP composite with embedded wrinkle and(b) compensated coil impedance plot with lift-off

(a) (b)

Ini�al posi�on of coil



Fig. 9 Embedded polymer canyon detection in a cross-ply CFRP composite: (a) schematic con-figuration of the air-cored coil over eight-layer unidirectional CFRP composite with embeddedpolymer canyon and (b) compensated coil impedance plot with lift-off


Dow




scanning over the eight-layer cross-ply CFRP composite with theembedded polymer canyon domain along with the compensatedcoil impedance plot with the lift-off curve. The lift-off curve wasobtained in a similar manner as described in Sec. 2.1 for the caseof the ECT of an aluminum plate with a rectangular slot. Fromthe results obtained, it can be observed that as the air-cored eddycurrent coil is scanned from the top of the embedded polymercanyon domain (initial position of the coil) and toward a pristinelocation (final position of the coil) away from the embeddedpolymer canyon, the coil impedance begins to approach the originof the Lissajous curve where both the real and imaginary parts ofthe impedance is zero (pristine area). In this way, it is possible todetect the presence of an embedded polymer canyon.

3 Experimental Eddy Current Testing of ThermosetCFRP Composites3.1 Manufacturing of Cross-Ply Composite With

EmbeddedWrinkle. A [0/90]6 cross-ply composite was manufac-tured using the CYCOM® 5320-1 epoxy resin system with theHexcel IM7 12 K fiber in a compression molding (hot press)machine with the manufacturer’s cure cycle. A wrinkle was intro-duced between the first and the second layer of the composite byrolling up prepreg into a noodle shape and aligning it with the0 deg fiber direction (Fig. 10). Experimental UT and ECT were con-ducted on this composite plate to determine if the embedded wrinklewas detectable.

3.2 Experiments on Cross-Ply CFRP Composite SpecimenWith Embedded Wrinkle

3.2.1 Ultrasonic Testing Immersion Tank Inspection. UTscans were conducted in the ultrasonic immersion tank on theCFRP composite specimen with the embedded wrinkle. A10 MHz, 1 in. focused, 0.375 in. diameter ultrasonic transducerwas used in the pulse-echo mode for conducting UT scans. Theexperimental setup is displayed in Fig. 11 with the compositeplate placed inside the immersion tank with the focused transducerscanning in the in-plane x–y direction. Postprocessing of the dataobtained from the ODIS software interface is able to provide aclear C-scan image, B-scan image, and A-scans in the pristineand wrinkled areas of the specimen as displayed in Fig. 12. Fromthis figure, it can be clearly observed that from the C-scan andB-scan images, there is strong reflection from the embeddedwrinkle. By comparing the A-scan signals, it can be clearly seenthat in the location with the embedded wrinkle, there is a clearreflection signal in between the front wall and the back wall ofthe composite plate.

3.2.2 Experimental Eddy Current Testing. Experimental ECTwas conducted on the [90/0]6 cross-ply composite specimen withembedded wrinkle using the Eddyfi Reddy ECA scanner connectedwith I-Flex probes. I-Flex probes are extremely flexible probes andcan be used for flat and curved surfaces. The I-Flex probes havemany small air-cored coils that operate as transmitters and receiversbased on the mode of operation that is chosen as can be seen inFig. 13. The long single-driver mode uses a combination of onetransmitter and three receivers that are further away from eachother, and the short double-driver mode uses a combination oftwo transmitters and two receivers that are close to each other.For our experiments, the short double-driver mode was used toincorporate equal number of transmitters and receivers. Figure 14displays the components of the experimental setup, which includesthe Eddyfi Reddy instrument and the two types of I-Flex probes thatwere used for the experiments. The first I-Flex probe had a centralfrequency of 250 kHz and a maximum frequency of 525 kHz with acoverage width of 56 mm. The second I-Flex probe had a centralfrequency of 500 kHz and a maximum frequency of 800 kHzwith a smaller coverage width of 34 mm. The four frequencies,250 kHz, 525 kHz, 500 kHz, and 800 kHz, were explored for thedetection of the embedded wrinkle in the cross-ply composite speci-men. The experimental setup consisted of Eddyfi Reddy and an

(a) (b) (c)

Fig. 10 Manufacturing of cross-ply composite with embedded wrinkle: (a) cure cycle, (b) prepreg layup, and (c) final compositeplate (355 mm×355 mm×1.5 mm) with embedded wrinkle

Fig. 11 Experimental setup for the ultrasonic immersion tankinspection


FEBRUARY 2020, Vol. 3 / 011002-7

Dow




I-Flex probe chosen from the two available probes as displayed inFig. 15.Eddy current testing experiments were conducted from the top

side and the bottom side of the CFRP specimen to see if the embed-ded wrinkle can be detected from both sides of the specimen.Figure 16 displays the results obtained from the top-side ECAscans for different probes and frequencies, and Fig. 17 displaysthe results obtained from the bottom-side ECA scans. From boththese figures, it can be observed that the embedded wrinkle canbe detected using all four frequencies from both sides of the plate

with subtle differences between different frequencies withreduced signal-to-noise ratio at higher frequencies.

3.3 Manufacturing of Cross-Ply Composite WithEmbedded Polymer Canyon. A [0/90]2S cross-ply compositewas manufactured using the CYCOM® 5320-1 epoxy resinsystem with the Hexcel IM7 12 K fiber in a compression molding(hot press) machine with the manufacturer’s cure cycle. Apolymer canyon was introduced between the first and the second

Fig. 12 UT immersion tank inspection results: (a) C-scan, (b) B-scan, (c) pristine area A-scan, and (d ) damaged area A-scan

Fig. 13 Modes of operation of I-Flex probes: (a) small air-cored coils in the I-Flexprobes, (b) long single-driver mode, and (c) short double-driver mode

Fig. 14 Components of the experimental setup for ECT: (a) Eddyfi Reddy, (b) first I-Flex probe with a coverage of 56 mm oper-ating at 250 kHz and 525 kHz, and (c) second I-Flex probe with a coverage of 34 mm operating at 500 kHz and 800 kHz


Dow




layer of the composite aligning a Teflon rod of 3 mm diameter withthe 90 deg fiber direction (Fig. 18). Experimental UT and ECT wereconducted on this composite plate to determine if the embeddedpolymer canyon was detectable.

3.4 Experiments on Cross-Ply Thermoset CFRP CompositeSpecimen With Embedded Polymer Canyon

3.4.1 Ultrasonic Immersion Tank Inspection. Similar to theprevious scenario, UT scans were conducted in the ultrasonicimmersion tank on the CFRP specimen with the embedded

polymer canyon. A 10 MHz, 1 in. focused, 0.375 in. diameter trans-ducer was used for conducting C-scans. The experimental setupis similar to the one displayed in Fig. 11 with the composite plateplaced in the immersion tank with the focused transducer scanningin the in-plane x–y direction. Postprocessing of the data obtainedfrom the ODIS software interface is able to provide a clear C-scanimage, B-scan image, and A-scans in the pristine and wrinkledareas of the specimen as displayed in Fig. 19. From the C-scanand B-scan images, the pristine area in the composite specimenand the area with the embedded polymer canyon can be clearlydifferentiated. From the A-scan signals, the reflection from theembedded polymer canyon in the waveform can be observed.

3.4.2 Experimental Eddy Current Testing. Experimental ECTwas conducted on the cross-ply [0/90]2S composite specimenusing the Eddyfi Reddy ECA scanner connected with I-Flexprobes. Similar to the previous scenario, the short double-drivermode was chosen, and four frequencies, 250 kHz, 525 kHz,500 kHz, and 800 kHz, were explored for the detection of theembedded polymer canyon in the cross-ply composite specimen.The experimental setup consisted of Eddyfi Reddy connected toan I-Flex probe chosen from the two available probes as displayedin Fig. 15.Eddy current testing experiments were conducted from the top

side as well as the bottom side of the CFRP specimen to see ifthe embedded wrinkle can be detected from both sides of the speci-men. Figure 20 displays the results obtained from the top-side ECAscans for different probes and frequencies, and Fig. 21 displays theresults obtained from the bottom-side ECA scans. From both thesefigures, it can be observed that as the frequency increases, the detec-tion of the embedded polymer canyon becomes easier and thesignal-to-noise ratio decreases.

3.5 Description of Wrinkled CFRP Composite SpecimensFrom the Boeing Company. Three wrinkled specimens weresupplied by The Boeing Company, namely wrinkle 1 specimen,wrinkle 2 specimen, and wrinkle 3 specimen. All the specimenshave 48 plies with wrinkle 1 and wrinkle 2 specimens being unsym-metrical composites and wrinkle 3 specimen being a cross-plyFig. 15 ECT experimental setup with the composite plate

Fig. 16 Top-side ECA scan of specimen with embedded wrinkle at (a) 250 kHz, (b) 525 kHz,(c) 500 kHz, and (d ) 800 kHz


FEBRUARY 2020, Vol. 3 / 011002-9

Dow




composite. The average total thickness of wrinkle 1 and wrinkle 2specimens was 8.84 mm. The average total thickness of wrinkle 3specimen was 8.27 mm. The L/d ratio (ratio of the width of thewrinkle to the depth of the wrinkle) of the wrinkle of these threespecimens is displayed in Fig. 22 along with high-resolution cross-sectional images of each specimen at 4800 dpi. The cross-sectionalscans are able to display the out-of-plane waviness caused by theembedded wrinkle and are also used to imply the clear meaningof the L/d ratio for the wrinkle of each specimen.

3.6 Experiments on Wrinkled CFRP Composite SpecimensFrom the Boeing Company

3.6.1 Ultrasonic Immersion Tank Inspection. Similar to theprevious scenarios, UT scans were conducted in the ultrasonicimmersion tank on the three wrinkled specimens. A 10 MHz,1-in. focused transducer was used for conducting the C-scans.The experimental setup is similar to the one displayed in Fig. 11

with the composite plate placed inside the immersion tank withthe focused transducer scanning in the in-plane x–y direction. Post-processing of the data obtained from the ODIS software interface isable to give a C-scan image, B-scan image, and A-scans in the pris-tine and wrinkled area of the specimen as displayed in Figs. 23–25.From the UT scans, it can be observed that the wrinkle in wrinkle

1 specimen was able to be detected, but the wrinkles in wrinkle 2and wrinkle 3 specimens, which are much wider, were not detectedvery well and give little evidence of the presence of embedded wrin-kles in these specimens.

3.6.2 Experimental Eddy Current Testing. Experimental ECTwas conducted on the three wrinkled composite specimens usingthe Eddyfi Reddy ECA scanner connected with I-Flex probes.Two types of I-Flex probes were used for the experiments similarto the earlier scenarios. Similar to the previous scenarios, theshort double-driver mode was chosen, and four frequencies,250 kHz, 525 kHz, 500 kHz, and 800 kHz, were explored for the

Fig. 17 Bottom-side ECA scan of specimen with embedded wrinkle at (a) 250 kHz, (b) 525 kHz,(c) 500 kHz, and (d ) 800 kHz

(a) (b) (c)

Fig. 18 (a) Cure cycle, (b) prepreg layup, and (c) final composite plate (355 mm×355 mm×1.5 mm) with embedded wrinkle


Dow




detection of wrinkles in each of the three specimens. The experi-mental setup consisted of Eddyfi Reddy connected to an I-Flexprobe chosen from the two available probes similar to the setup dis-played in Fig. 15.ECT experiments were conducted from the top side and the

bottom side of each specimen to see if the wrinkles can be detectedfrom both sides of the specimens. Figure 26 displays the resultsobtained from the top-side ECA scans for different probes and fre-quencies used on wrinkle 1 specimen, and Fig. 27 displays theresults obtained from the bottom-side ECA scans. Figure 28 dis-plays the results obtained from the top-side ECA scans for different

probes and frequencies used on wrinkle 2 specimen, and Fig. 29displays the results obtained from the bottom-side ECA scans.Figure 30 displays the results obtained from the top-side ECAscans for different probes and frequencies used on wrinkle 3 speci-men, and Fig. 31 displays the results obtained from the bottom-sideECA scans.The embedded wrinkles in both wrinkle 1 specimen and wrinkle

2 specimen were able to be detected at all frequencies using both theI-Flex probes. As observed in the previous ECA scanning results,increase in the frequency not only improves the detectability ofthe embedded wrinkle but also increases the noise in the images

Fig. 20 Top-side ECA scan of specimen with embedded polymer canyon at (a) 250 kHz,(b) 525 kHz, (c) 500 kHz, and (d ) 800 kHz



FEBRUARY 2020, Vol. 3 / 011002-11

Dow




obtained from the scanning. The embedded wrinkle in wrinkle 3specimen was unable to be detected from the top-side scan usingthe first probe but was partially detectable using the second probewith high noise. The embedded wrinkle in Wrinkle 3 specimenwas successfully detected using both the probes from the bottom-side scan. The results obtained clearly indicate that for these spec-imens, the UT scans were inconclusive in detecting the embeddedwrinkles and the ECA scans were able to detect the presence ofthe wrinkles more conclusively.

4 Summary, Conclusions, and Future Work4.1 Summary. In this paper, the TEAM problem 15 [27] was

used to validate the ECT simulation methodology, and a goodmatch between the simulation results and the experimental resultsfrom Ref. [27] was observed.The first set of simulations was conducted on CFRP composite

plates of different stacking sequences. The impedance was calcu-lated, and its frequency response was obtained over a wide

frequency range, 100 Hz–10 GHz. It was found that the imaginarypart of the coil impedance X(ω) varies almost linearly with the fre-quency when plotted on a log-log scale and is not effected due to theanisotropic material properties. It was also found that the real part ofthe coil impedance R(ω) has a much more interesting behavior,which can be separated into three zones: zone 1, in which the realpart of the coil impedance hardly changes with an increase in thefrequency; zone 2 (230 kHz–450 MHz), in which the real part ofthe coil impedance varies almost linearly with the frequency onthe log-log scale for the unidirectional layup but nonlinearly forthe other layups at the end of this zone, and zone 3, in which itvaries almost nonlinearly for all layups. Thus, it seems that zone2 is quite sensitive to the CFRP composite layup and, by implica-tions, to deviations/defects in the actual layup when comparedwith the layup prescribed in composite design specifications. Sub-sequently, ECT simulation was used to investigate the detectionsensitivity for various manufacturing flaws such as fiber misorien-tation, fiber waviness, embedded wrinkle, and embedded polymercanyon. It was found that these manufacturing defects inducechanges in the impedance response that could be used to detect

Fig. 21 Bottom-side ECA scan of specimen with embedded polymer canyon at (a) 250 kHz,(b) 525 kHz, (c) 500 kHz, and (d ) 800 kHz

Fig. 22 Specimenswith embedded wrinkles supplied by The Boeing Company: (a) wrinkle 1 spe-cimen, (b) wrinkle 2 specimen, and (c) wrinkle 3 specimen


Dow




such flaws in a production environment. This methodology wouldalso be applicable to operational damage.This work also involved a large number of experiments. Experi-

mental ECT scans were conducted on in-house manufacturedCFRP specimens with embedded wrinkle and a polymer canyonas well as on wrinkled specimens that were supplied by The BoeingCompany. Section 3 describes experimental ECT of several CFRPspecimens with built-in defects: University of South Carolina(USC)-embedded wrinkle specimen, USC-embedded polymercanyon specimen, and Boeing wrinkled specimens. First UTscans were performed in the ultrasonic immersion tank on all thespecimens, and then, Eddyfi Ready ECA scanning equipment and

I-Flex probes were used in the short double-driver mode with amaximum frequency of 800 kHz. It was found that ECT was ableto detect the flaws embedded in all specimens, in some situationseven better than ultrasonic scanning.

4.2 Conclusions. The correctness of our ECT simulation usingCOMSOL MULTIPHYSICS software was successfully verified using theTEAM Workshop Problem 15 of an aluminum plate with a rectan-gular slot; the changes in the coil impedance as it moves over therectangular slot toward a pristine region showed a good matchwith the experimental data.




FEBRUARY 2020, Vol. 3 / 011002-13

Dow




The frequency response plot indicated a zone of interest (zone 2)where there was a linear relationship between the real part of thecoil impedance and the imaginary part of the coil impedance withthe increasing frequency when plotted on the log-log scale. Thiszone indicated a significant change in the real part of the coil imped-ance with a stacking sequence, e.g., between a unidirectional com-posite compared with an angle-ply composite. This difference is

important for ECT detection of manufacturing flaws such as fibermisorientations, fiber waviness, wrinkling, etc. and can be extendedto the detection of operational damage.ECT simulation of CFRP composite plates with simulated

damages such as fiber misorientation, waviness, wrinkling, etc.indicated that the changes in coil impedance were sufficient toenable the detection of such manufacturing flaws; these impedance


Fig. 26 Top-side ECA scan of wrinkle 1 specimen at (a) 250 kHz, (b) 525 kHz, (c) 500 kHz, and(d ) 800 kHz


Dow




changes were observed as the coil was moved between the pristineand the flawed areas.Experimental ECT scans confirmed the capability of detecting

manufacturing flaws in specially built specimens. In these experi-ments, the authors investigated in-house manufactured CFRP spec-imens with an embedded wrinkle and with an embedded polymercanyon. The authors also investigated three wrinkled specimenswith out-of-plane waviness supplied by The Boeing Company.

The ECT experiments were compared with UT scanning tests per-formed in the immersion tank. The results demonstrated the capabil-ity of our Eddyfi Reddy system with I-Flex probes to detectmanufacturing flaws in CFRP composites.Based on the theoretical and experimental results presented in

this paper, it appears that ECT is a promising methodology fordetecting manufacturing defects in CFRP composites. In somecases, ECT was able to detect flaws that other nondestructive

Fig. 27 Bottom-side ECA scan of wrinkle 1 specimen at (a) 250 kHz, (b) 525 kHz, (c) 500 kHz, and(d ) 800 kHz



FEBRUARY 2020, Vol. 3 / 011002-15

Dow




inspection techniques, e.g., ultrasonics, were unable to detect. Theuse of ECT can also be extended toward the detection of the oper-ational damage in CFRP composites.

4.3 Future Work. The eddy current methodology and equip-ment currently existing for metals do not suit very well for CFRPcomposites. As shown by simulations described in this paper, theuse of eddy current testing in CFRP composites would be more

sensitive to hidden defects if performed at much higher drive fre-quencies than available in the current equipment used for metals.Thus, a sustained R&D effort seems necessary to explore the devel-opment of novel eddy current equipment and methodologies moresuitable for CFRP composites than those currently available formetals.Further work could be performed toward the practical application

of the research results presented in this paper by exploring the pos-sibility of eddy current nondestructive inspection to the operational




Dow




damage in CFRP composites. More computer simulations andequipment development could be conducted independently or incollaboration with an industrial partner.

AcknowledgementThe financial support of The Boeing Company (Grant No.

SSOW-BRT-W0915-0005; Funder ID: 10.13039/100000003) isthankfully acknowledged. The authors would also like to thankthe Ronald E. McNair Center for Aerospace Innovation andResearch for providing them the manufacturing facilities to manu-facture the composite specimens.

References[1] Bossi, R. H., and Giurgiutiu, V., 2015, Polymer Composites in the Aerospace

Industry, P. E. Irving and C. Soutis, eds., Woodhead Publishing, Sawston,Cambridge, pp. 413–448.

[2] Kim, S. J., 2008, “Damage Detection in Composite Composites Using Coin-TapMethod,” J. Acoust. Soc. Am., 123(5), p. 3064.

[3] Kessler, S. S., Spearing, S. M., Atalla, M. J., Cesnik, C. E., and Soutis, C., 2002,“Damage Detection in Composite Materials Using Frequency ResponseMethods,” Composites Part B Eng., 33(1), pp. 87–95.

[4] Meola, C., Boccardi, S., and Carlomagno, G. M., 2016, Infrared Thermographyin the Evaluation of Aerospace Composite Materials: Infrared Thermography toComposites, Woodhead Publishing, Sawston, Cambridge.

[5] D’orazio, T., Leo, M., Distante, A., Guaragnella, C., Pianese, V., and Cavaccini,G., 2008, “Automatic Ultrasonic Inspection for Internal Defect Detection inComposite Materials,” NDT Int., 41(2), pp. 145–154.

[6] Diamanti, K., and Soutis, C., 2010, “Structural Health Monitoring Techniques forAircraft Composite Structures,” Prog. Aerosp. Sci., 46(8), pp. 342–352.

[7] Raišutis, R., Kazys, R., Žukauskas, E., and Mazeika, L., 2011, “UltrasonicAir-Coupled Testing of Square-Shape CFRP Composite Rods by Means ofGuided Waves,” NDT Int., 44(7), pp. 645–654.

[8] Giurgiutiu, V., and Soutis, C., 2012, “Enhanced Composites Integrity ThroughStructural Health Monitoring,” Appl. Compos. Mater., 19(5), pp. 813–829.

[9] James, R., Kim, T. H., and Narayanan, R. M., 2017,, “Prognostic Investigation ofGalvanic Corrosion Precursors in Aircraft Structures and Their DetectionStrategy,” Nondestructive Characterization and Monitoring of AdvancedMaterials, Aerospace, and Civil Infrastructure 2017, Portland, OR, Mar. 25–29,Vol. 10169, p. 101690C.

[10] James, R., 2017, “Prognostic Investigation of Environmentally Assisted Damagein Aerospace Composite Materials and Its Detection Strategy,” Master’s thesis,Pennsylvania State University, State College, PA.

[11] James, R., Kim, T. H., Navagato, M. D., and Narayanan, R. M., 2017,“Modeling and Simulation of Environmental Impact Damage of AerospaceComposites and Its Detection Scheme,” Proceedings of 32nd American Societyfor Composites Technical Conference, West Lafayette, IN, Oct. 23–25,pp. 2363–2377.

[12] Narayanan, R. M., and James, R., 2018, “Microwave Nondestructive Testing ofGalvanic Corrosion and Impact Damage in Carbon Fiber Reinforced PolymerComposites,” Int. J. Microwaves Appl., 7(1), pp. 1–15.

[13] Kim, T. H., James, R., and Narayanan, R. M., 2017, “High-Resolution Nondestructive Testing of Multilayer Dielectric Materials UsingWideband Microwave Synthetic Aperture Radar Imaging,” NondestructiveCharacterization and Monitoring of Advanced Materials, Aerospace, and CivilInfrastructure 2017, Portland, OR, Mar. 25–29, Vol. 10169, p. 1016903.

[14] Kim, T. H., Navagato, M. D., James, R., and Narayanan, R. M., 2017, “Designand Performance of a Microwave Nondestructive Testing System for DamageAnalysis of FRP Composites,” Proceedings of 32nd American Society forComposites Technical Conference, West Lafayette, IN, Oct. 23–25 .

[15] Owston, C. N., 1976, “Eddy Current Methods for the Examination of CarbonFibre Reinforced Epoxy Resins,” Mater. Eval., 34, pp. 237–244.

[16] Prakash, R., and Owston, C. N., 1976, “Eddy-Current Method for theDetermination of Lay-Up Order in Cross-Plied Crfp Laminates,” Composites,7(2), pp. 88–92.

[17] Dingwall, P. F., and Mead, D. L., 1976, “Non-Destructive Inspection andVolume Fraction Determination of CFRP Using an Eddy Current Method,”Royal Aircraft Establishment Farnborough (United Kingdom), Report No.RAE-TR-76078.

[18] Carpenter, J. L., Jr., and Stuhrke, W. F., 1976, “NDE: An Effective Approach toImproved Reliability and Safety. A Technology Survey. [Nondestructive Testingof Aircraft Structures],” NASA, US, Report No. NASA-CR-134963.

[19] Phelps, M. L., 1979, Assessment of State-of-the-Art of In-Service InspectionMethods for Graphite Epoxy Composite Structures on Commercial TransportAircraft, Boeing Commercial Airplane Co, Seattle, WA.

[20] Prakash, R., 1980, “Non-Destructive Testing of Composites,” Composites, 11(4),pp. 217–224.

[21] Vernon, S. N., 1987, “Eddy Current Nondestructive Inspection of Graphite EpoxyUsing Ferrite Cup Core Probes,” Naval Surface Warfare Center, Silver Spring,MD, Report No. NSWC-TR-87-148.

[22] De Goeje, M. P., and Wapenaar, K. E. D., 1992, “Non-Destructive Inspection ofCarbon Fibre-Reinforced Plastics Using Eddy Current Methods,” Composites,23(3), pp. 147–157.

[23] Gros, X. E., 1995, “An Eddy Current Approach to the Detection of DamageCaused by Low-Energy Impacts on Carbon Fibre Reinforced Materials,” Mater.Des., 16(3), pp. 167–173.

[24] Pratap, B., and Weldon, W. F., 1996, “Eddy Currents in Anisotropic CompositesApplied to Pulsed Machinery,” IEEE Trans. Magn., 32(2), pp. 437–444.

[25] Mook, G., Köser, O., and Lange, R., 1997, “Non-Destructive Evaluation ofCarbon Fibre-Reinforced Structures Using High Frequency Eddy CurrentMethods,” Functionally Graded Materials 1996, Elsevier Science BV,New York, pp. 433–438.



FEBRUARY 2020, Vol. 3 / 011002-17

Dow




http://dx.doi.org/10.1121/1.2932812

http://dx.doi.org/10.1016/S1359-8368(01)00050-6

http://dx.doi.org/10.1016/j.ndteint.2007.08.001

http://dx.doi.org/10.1016/j.paerosci.2010.05.001

http://dx.doi.org/10.1016/j.ndteint.2011.07.001

http://dx.doi.org/10.1007/s10443-011-9247-2

http://dx.doi.org/10.30534/ijma/2018/01712018

http://dx.doi.org/10.1016/0010-4361(76)90018-5

http://dx.doi.org/10.1016/0010-4361(80)90428-0

http://dx.doi.org/10.1016/0010-4361(92)90435-W

http://dx.doi.org/10.1016/0261-3069(95)00025-9

http://dx.doi.org/10.1016/0261-3069(95)00025-9

http://dx.doi.org/10.1109/20.486530

[26] Gros, X. E., Ogi, K., and Takahashi, K., 1998, “Eddy Current, Ultrasonic C-Scanand Scanning Acoustic Microscopy Testing of Delaminated Quasi-IsotropicCFRP Materials: A Case Study,” J. Reinf. Plast. Compos., 17(5), pp. 389–405.

[27] Testing Electromagnetic Analysis Methods (T.E.A.M.). “Workshop Problem 15:Rectangular Slot in a Thick Plate: A Problem in Nondestructive Evaluation.”

[28] Mook, G., Lange, R., and Koeser, O., 2001, “Non-Destructive Characterisation ofCarbon-Fibre-Reinforced Plastics by Means of Eddy-Currents,” Compos. Sci.Technol., 61(6), pp. 865–873.

[29] Heuer, H., and Schulze, M. H., 2011, “Eddy Current Testing of Carbon FiberMaterials by High Resolution Directional Sensors,” Smart Materials, Structuresand NDT in Aerospace, NDT in Canada., Montreal, Quebec, Canada, Nov. 2–4.

[30] Mizukami, K., Mizutani, Y., Todoroki, A., and Suzuki, Y., 2016, “Detection ofIn-Plane and Out-of-Plane Fiber Waviness in Unidirectional Carbon FiberReinforced Composites Using Eddy Current Testing,” Composites, Part BEng., 86, pp. 84–94.

[31] Cacciola, M., Calcagno, S., Megali, G., Pellicano, D., Versaci, M., and Morabito,F. C., 2009, “Eddy Current Modeling in Composite Materials,” PIERS Online,5(6), pp. 591–595.

[32] Machado, M. A., Antin, K. N., Rosado, L. S., Vilaça, P., and Santos, T. G., 2019,“Contactless High-Speed Eddy Current Inspection of Unidirectional Carbon FiberReinforced Polymer,” Composites, Part B Eng., 168, pp. 226–235.

[33] Jiao, S., Li, J., Du, F., Sun, L., and Zeng, Z., 2016, “Characteristics of EddyCurrent Distribution in Carbon Fiber Reinforced Polymer,” J. Sens., 2016.

[34] Hughes, R. R., Drinkwater, B. W., and Smith, R. A., 2018, “Characterisation ofCarbon Fibre-Reinforced Polymer Composites Through Radon-TransformAnalysis of Complex Eddy-Current Data,” Composites Part B Eng., 148,pp. 252–259.

[35] Zeng, Z., Jiao, S., Du, F., Sun, L., and Li, J., 2018, “Eddy Current Testing ofDelamination in Carbon Fiber Reinforced Polymer (CFRP): A Finite ElementAnalysis,” Res. Nondestr. Eval., 29(4), pp. 199–211.

[36] James, R., Haider, M. F., Giurgiutiu, V., and Lilienthal, D., 2019, “Eddy CurrentNon-Destructive Evaluation of Manufacturing Flaws and Operational Damage inCFRP Composites,” Nondestructive Characterization and Monitoring ofAdvanced Materials, Aerospace, Civil Infrastructure, and Transportation XIII,Denver, CO, Mar. 3–7, Vol. 10971, p. 109711N.

[37] Giurgiutiu, V., James, R., Haider, M. F., and Lilienthal, D. A., 2018, “EddyCurrent Detection of Flaws and Damage in CFRP Composites,” USC-IPMO,Disclosure ID No. 1369.

[38] Cheng, J., Ji, H., Qiu, J., Takagi, T., Uchimoto, T., and Hu, N., 2015, “NovelElectromagnetic Modeling Approach of Carbon Fiber-Reinforced PolymerComposite for Calculation of Eddy Currents and Eddy Current TestingSignals,” J. Compos. Mater., 49(5), pp. 617–631.


Dow




http://dx.doi.org/10.1177/073168449801700502

http://dx.doi.org/10.1016/S0266-3538(00)00164-0

http://dx.doi.org/10.1016/S0266-3538(00)00164-0

http://dx.doi.org/10.1016/j.compositesb.2015.09.041


http://dx.doi.org/10.2529/piers090910070900


http://dx.doi.org/10.1155/2016/4292134


http://dx.doi.org/10.1080/09349847.2017.1304598

http://dx.doi.org/10.1177/0021998314521475

a simulative and experimental approach toward … asme...robin james1 department of mechanical...

Documents