This article was downloaded by: [Zahra Dashtizadeh]On: 30 July 2012, At: 09:25Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Polymer-Plastics Technology and EngineeringPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/lpte20

The Use of Infrared Thermography in Detecting theDefects in Kenaf-Poly Urethane CompositesZahra Dashtizadeh a , Aidy Ali a , Khalina Abdan b & Mohammad Behmanesh ca Department of Mechanical and Manufacturing Engineering, UPM, Serdang, Malaysiab Department of Biology and Agriculture Engineering, UPM, Serdang, Malaysiac Department of Mechatronics Engineering, UCSI, Cheras, Kuala Lumpur, Malaysia

Version of record first published: 30 Jul 2012

To cite this article: Zahra Dashtizadeh, Aidy Ali, Khalina Abdan & Mohammad Behmanesh (2012): The Use of InfraredThermography in Detecting the Defects in Kenaf-Poly Urethane Composites, Polymer-Plastics Technology and Engineering,51:11, 1155-1162

To link to this article: http://dx.doi.org/10.1080/03602559.2012.671427

PLEASE SCROLL DOWN FOR ARTICLE

Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form toanyone is expressly forbidden.

The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses shouldbe independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly inconnection with or arising out of the use of this material.

The Use of Infrared Thermography in Detecting the Defectsin Kenaf-Poly Urethane Composites

Zahra Dashtizadeh1, Aidy Ali1, Khalina Abdan2, and Mohammad Behmanesh31Department of Mechanical and Manufacturing Engineering, UPM, Serdang, Malaysia2Department of Biology and Agriculture Engineering, UPM, Serdang, Malaysia3Department of Mechatronics Engineering, UCSI, Cheras, Kuala Lumpur, Malaysia

This paper explores the use of active thermography technique forKenaf-Polyurethane (PU) composites. Presently the industry isgoing toward environmental friendly materials, so investigating moremethods in quality control of products is an essential issue. Ther-mography has potential to detect the defects in-depth. The sampleswere manufactured by a hand lay-out method and use of a hot pressto produce the composites. This method proves that the defects ofKenaf-PU boards are dependent on the amount of fiber and the thick-ness of the boards. Non-destructive infrared thermography techniquehas the capability of detecting the defects in Kenaf-PU boards. Thisstudy demonstrates evidence that this method can investigate somedefects such as voids and kenaf fiber pulled out from its original placewith an accuracy of 90%.

Keywords Bio-composites; Kenaf; Natural defects; Non-destructive techniques; Quality control; Thermography

INTRODUCTION

The structural integrity of materials, components andstructures has to be assessed for quality control, safetyregulations and product specifications. Numerous testingtechniques have been developed for maintenance and con-dition monitoring. These techniques can be categorizedinto two main classes: destructive testing, based on fracturemechanics, and non-destructive testing which leaves theinspected component undamaged.

Infrared thermography is the mapping of isotherms overthe surface of a component using heat-sensitive devices. Aninfrared camera scans the surface of a component andrecords any changes in temperature. The presence of adefect appears as a cold or hot spot and can be rapidlylocated. Very often, the component inspected has to bepre-heated before inspection. Thermography is a non-contact method, which provides rapid visual qualitativeinformation about the structural integrity of a material. Itis used for condition monitoring of composite materialsand concrete and to check alignment of parts[1].

In numerically modelling the thermographic processassociated with an infrared (IR) technique we can affordinspectors the ability to predict subsurface defect infor-mation associated with a specific material configuration[2].Infrared thermography (IRT) provides colorful images ofspecimens where local changes in surface temperature indi-cate subsurface defects. Although thermography providescolorful images, it provides a clear linkage between the truesize of a defect and its thermographic image[3]. Non-destructive thermal evaluation (NDTE) of composite mate-rials engenders with it the responsibility to accurately predictsubsurface defect information without compromising struc-tural integrity[2]. Any object emits by radiation energyaccording to its surface temperature. Human eyes are struckby such energy only when the object is warm enough andemits in the visible band (0.4–0.8mm). In fact, we are ableto recognize the temperature during heating of a metal, whenit passes from red (720�C), to yellow, to white (1350�C).

For low temperature values falling in the infrared region,thermography provides us with artificial eyes and gives us achance to see invisible radiation [4]. An infrared (IR) systembasically includes a camera, equipped with a series ofchangeable optics, and a computer. The core of the camerais the infrared detector, which absorbs the IR energy emit-ted by the object (whose surface temperature is to be mea-sured) and converts it into electrical voltage or current [4].

Thermography method can be performed after themanufacturing process is complete (and before installationof the component occurs) or during the components lifecycle, referred to as in-situ health monitoring. Both meth-ods despite their inherently different requirements necessi-tate a fundamental understanding of the material andinspection protocol being undertaken [2].

The increasingly use of kenaf bio-composites and itsdemands for quality control during manufacturing processor in-situ during applications such as heat insulator, leadsto use of NDT such as infrared thermography. In theresearch work reported in this article, infrared thermographywas used for the detection of defects in kenaf-Polyurethane(PU) bio-composite boards. Different kinds of defects were

Address correspondence to Zahra Dashtizadeh, Departmentof Mechanical and Manufacturing Engineering, 43400 UPM,Serdang, Malaysia. E-mail: zdashtizadeh@gmail.com

Polymer-Plastics Technology and Engineering, 51: 1155–1162, 2012

Copyright # Taylor & Francis Group, LLC

ISSN: 0360-2559 print=1525-6111 online

DOI: 10.1080/03602559.2012.671427

1155

Dow

nloa

ded

by [

Zah

ra D

asht

izad

eh]

at 0

9:25

30

July

201

2

distinguished. The recorded thermal images and itsprocessing demonstrate the feasibility of implementing thistechnology in a quality control process.

Methodology

The bio-composites (Kenaf-PU) have been manufac-tured through hand-lay-out and hot press method. Bio-composites having three different weight contents (40=60,50=50 and 60=40 Kenaf=PU weight %) were manufactured.Then, the bio-composites were cut into three boards andeach board was sanded to reduce its thickness. Finally,there were nine type of samples with three different groupof weight percentage and three different group of thickness(4mm, 6mm and 9mm). In Table 1 it is demonstrated moreclearly.

To determine the effect of thickness, active thermogra-phy is used. Active thermography is the method in whichthe samples gain heat before inspecting by infrared camera.The samples were put in an oven to reach the desired tem-perature of 100�C, more than the 100�C, the samples wouldstart to burn from the edge, and less than this temperaturethe results of thermal image would not be able to detect thedefects. The samples were heat up to 2 minutes for eachspecimen before the infrared camera, brand FLUKETi45FT=HT, took the photos. This method of thermogra-phy is called active thermography. To ensure that the sam-ples reach the temperature of the oven a thermocouple is

used and the results are comparable with the temperaturegiven from thermography. Figure 1 demonstrates theprocedure of the experiment.

In the first step also the emissivity calibration has beendone. Thermography is very sensitive to emissivity. To findout the emissivity of the kenaf boards, a black color tape

TABLE 1Final sample dimensions

40% 50% 60%

Sample dimension A B C A B C A B C

LengthðmmÞWidthðmmÞ

ThicknessðmmÞ

24

35

120909

24

35

120906

24

35

120904

24

35

120909

24

35

120906

24

35

120904

24

35

120909

24

35

120906

24

35

120904

24

35

FIG. 1. The procedure of thermography.

FIG. 2. Thickness and fiber percentage effect. (Color figure available

online.)

TABLE 2Cut points and the represented colors

Point Color

Point 1 Red or white(the highest temperature)Point 2 YellowPoint 3 GreenPoint 4 BluePoint 5 Dark blue or purple (the lowest temperature)

1156 Z. DASHTIZADEH ET AL.

Dow

nloa

ded

by [

Zah

ra D

asht

izad

eh]

at 0

9:25

30

July

201

2

has been used to as a black body, then the temperature ofblack body and the other part is measured via thermalimage and the emissivity is calculated and that is:

e ¼ 0:92Then the camera is calibrated with the new emissivity.

Emissivity does not change for the 40%, 50% and 60%because the material is the same. Another calibration thathas been done through the camera is the ambienttemperature that was:

T ¼ 26�C

Finally, a SEM test was done to prove the thermographyresults. For SEM the samples were cut into small pieces,these pieces have been chosen carefully via thermal imagesthat each piece represents a color (and therefore a specifictemperature area) in the specimen to check why the thermalimage has so many different colors and each color is repre-senting what type of defect. To do so each specimen was cutwith the CNC machine (see Table 2). For each sample 5points have been chosen according to inhomogeneity thatwas in thermal images, and the SEM test has been done.

Definition of Healthy Part and Defected Part

Thermography principles indicate that any inhomogene-ities in thermal images are due to some kind of defect, sub-surface or surface defect. These inhomogeneities are shownby difference in colors of the thermal image. The hypothesishere is that the parts with the temperature near to the oventemperature should be the healthiest parts and as the tem-perature in other parts are far from the given temperaturethe defects should get worse.

A healthy part is defined as a part where the fibers andPU are in good combination together and fibers are notpulled out or break out from their place. Also the amount

of voids and air bubbles are negligible. The healthy partshould reach the given temperature in the oven since thereis no gap between the fibers and the PU, the energy of heatshould be able to move from one to another easily. This partshould be the white or red part in the thermal image, whichrepresents the highest temperature in the thermal image.

The defected parts are shown with other colors in thethermal image such as yellow, green, blue or purple, whichshould indicate the majority of defects as the temperature isless in the parts, the defects seem to be mostly voids andnot good combination between kenaf fibers and PU.

TABLE 3Thermocouple results

Percentage of Kenaf loading 40% 50% 60%

Sample thickness 4mm 6mm 9mm 4mm 6mm 9mm 4mm 6mm 9mmTemperature�C 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

FIG. 3. Position of 6mm board in the sample.

FIG. 4. Maximum temperature gain in 60 minutes. (Color figure

available online.)

USE OF INFRARED THERMOGRAPHY TO STUDY KENAF-PU DEFECTS 1157

Dow

nloa

ded

by [

Zah

ra D

asht

izad

eh]

at 0

9:25

30

July

201

2

RESULTS AND DISCUSSION

Thickness Effect

The samples were tested in three different thicknessgroups; these groups were 4mm, 6mm and 9mm thicknesssamples, for each 40%, 50% and 60% of kenaf fibers.Figure 2 presents thermal images for 40%, 50% and 60%.(The scale is chosen according to better color distribution).In this test, all parameters were kept constants such astemperature, time of heating up, and the amount of kenaffiber in samples, except the thickness. As can be seenclearly from the images in Figure 2, the difference in thick-ness causes different thermal images.

To ensure that the samples reach the desired tempera-ture as set at the oven a thermocouple is used to measurein situ temperature. The results are shown in Table 3.

According to the results shown in Figure 2, it can beseen clearly that in all cases 6mm thickness boards have

FIG. 6. SEM images for 50%, 4mm thickness. (Color figure available

online.)

TABLE 4Thermocouple results for considering the amount of fiber

40%,6mm 50%,6mm 60%,9mm

Temperature 101.34 103.87 104.21

FIG. 5. Chosen points in 50% kenaf sample. (Color figure available

online.)

TABLE 5Composite failure for 50%, 4mm thickness

Composite

Failure Voids

PU-

rich

zones

Fiber

bending

Misaligned

fibers

Fiber

pulled

out Delamination Crack

Point 1 �� ����� � � � – –

Point 2 �� ����� � � � ���� ���

Point 3 ��� ��� �� ��� � – �

Point 4 ��� �� � ���� � – –

Point 5 ���� � �� ����� ��� – –

1158 Z. DASHTIZADEH ET AL.

Dow

nloa

ded

by [

Zah

ra D

asht

izad

eh]

at 0

9:25

30

July

201

2

the most defects. This is due to the manufacturing method,since the 6mm sample is in the middle of the plate, there isonly two sides available for losing the air that is trappedinside, but for the 4mm and 9mm, there are three sides,as seen below (Fig. 3):

Voids and air bubbles are the most defects in the kenaffiber boards; this is the reason of their usage as insulators.Another reason for having the most defects in 6mmthickness is that during hot press PU that is liquid in thehigh temperature moves from the middle of the sample to

the sides therefore the amount of PU in 6mm is less thanin 4mm and 9mm, that causes not good binding betweenkenaf and PU in 6mm samples.

Also results determine that as the amount of fibersdecrease in the sample, it takes longer time to get to the certaintemperature, in other words the maximum temperature of40% kenaf is lower than 50% and 60% at the same time.The results of heating up the samples (6mm thickness) for 1hour in 105�Care shown inFigure 4, the pictures indicate thatthe maximum temperature of 40% sample is lower than 50%and the maximum temperature of 50% is lower than 60%.

Tmax;40% < Tmax;50% < Tmax;60%

Therefore as an insulator, 40% boards have betterapplication, since it takes longer time to get a certaintemperature. Also the results of in-situ thermocouple areshown in Table 4.

As it can be seen in Figure 4, the results are a bit differ-ent from thermocouple results, although the emissivitycalibration has been done, still the camera is not capableof determining the exact temperature .

SEM Results

Because the algorithm of the amount of defect wasrepeated in 40%, 50% and 60% kenaf samples, here theSEM results of 50% are presented. Figure 5 shows the ther-mal image of 50% kenaf with different thicknesses, and theSEM results are presented in Figures 6–8 for 4mm to 9mmthicknesses, respectively.

SEM results indicate that a higher temperature repre-sents PU in that point and as the temperature reduces inthe sample it means that the points have less PU and moreKenaf, this does not change with the percentage of Kenafin the specimens, because this algorithm has been repeatedfor 40%, 50% and 60% samples (Fig. 4):

In all thermal images white and red colors spots representthe highest temperature and in the yellow, green and bluespots, the temperature reduces respectively then dark purpleor black colors spots represent the lowest temperature. Here,points for SEM have been chosen according to the spottemperature; point 1 represents the highest temperature with

FIG. 7. SEM images for 50%, 6mm thickness. (Color figure available

online.)

TABLE 6Composite failure for 50%, 6mm thickness

Composite

Failure Voids

PU-

rich

zones

Fiber

bending

Misaligned

fibers

Fiber

pulled

out Delamination Crack

Point 1 �� ����� � � � – –

Point 2 �� ����� � � � ���� ���

Point 3 ��� ��� �� ��� � – �

Point 4 ��� �� � ���� � – –

Point 5 ���� � �� ����� ��� – –

USE OF INFRARED THERMOGRAPHY TO STUDY KENAF-PU DEFECTS 1159

Dow

nloa

ded

by [

Zah

ra D

asht

izad

eh]

at 0

9:25

30

July

201

2

white or red color in the thermal image. Point 2 is chosenfrom the yellow color part with a lower temperature as com-pared with point 1. Respectively point 3 is from the greencolor part, point 4 from blue color part and point 5 from darkblue or purple color part.

SEM results indicate that in the point 1 with white or redcolor the amount of PU is more than kenaf fibers and as thetemperature reduces the amount of PU decreases, thereforethe amount of fibers and voids increases. Therefore withcapturing a thermal image of kenaf-PU composite andhaving a blue color we can immediately result in havingvoid in the spot. Figures 9–13 summarize the results.

As the number of points increases from 1 to 5 thetemperature decreases and as Figures 6, 7, and 8 indicatethe two defects that can be easily detected by thermalimaging are the void and PU-rich zone that’s because theamount of these two are more than the others.

FIG. 8. SEM images for 50%, 9mm thickness. (Color figure available

online.)

TABLE 7Composite failure for 50%, 9mm thickness

Composite

Failure Voids

PU-

rich

zones

Fiber

bending

Misaligned

fibers

Fiber

pulled

out Delamination Crack

Point 1 � ����� � � � ���� –

Point 2 �� ����� � � � ���� –

Point 3 ��� ��� �� ��� ��� � –

Point 4 ��� ��� ��� ��� ��� � �

Point 5 ��� ��� ���� ��� � � �

TABLE 8Description of symbols

Symbol Description

� Very poor (1)�� Poor (2)��� Moderate (3)���� Fair (4)����� Excellent (5)

FIG. 9. Distribution of PU and voids in the samples. a) Distribution of

voids in the samples. b) Distribution of PU in the samples. (Color figure

available online.)

1160 Z. DASHTIZADEH ET AL.

Dow

nloa

ded

by [

Zah

ra D

asht

izad

eh]

at 0

9:25

30

July

201

2

So, as temperature decreases, the amount of fibersincreases, and the amount of voids also increases. The highamount of fiber in the specific part of the sample cause fiberbreak-out or fiber pulled out from its original place.

The thermal images indicate that in all cases 6mmthickness samples have more defects. SEM also determinedthat 6mm thickness has more inhomogeneity than 4mm and9mm thickness. From Figure 13 and Figure 14, it isdetermined that crack and delamination are the defects thatcannot be easily detected through thermography.

CONCLUSIONS

The purpose of this work was to test the feasibility ofinfrared thermography as an NDT&E technique usablein a quality control inspection process. As it was demon-strated, recording thermal images provides significantinformation about the defects that may appear on manu-facturing processes. Processing the images not only investi-gates the location of defects easier, but it also allows itsclassification. The latter is valuable information for qualitycontrol mechanisms. Actually, several types of defectshave been analyzed, leading to successful results support-ing the use of this technique. The following conclusionsare made:

� Thickness characterization has been done by thecamera and the results determine that the differentthickness in the same specimen makes a difference inthe thermal image and the 6mm thickness boards havemore defects, since it was taken from the middle of thesample which in this part during manufacturing moreair was trapped.

� Thermal images indicate that the amount of fiber playsan important role in the thermal images, since thethermal image of a 60% kenaf board is different froma thermal image of a 50% or 40% kenaf boards.

� Thermal images determine that with the constantthickness and time of heating the 60% kenaf boardget more temperature that 50% and 40%:

Tmax;40% < Tmax;50% < Tmax;60%

REFERENCES

1. Gros, X. E. 3-Non-destructive Testing Techniques. NDT Data Fusion,

Butterworth-Heinemann, Oxford, 1996, 43–81.

FIG. 10. Distribution of bended fibers in the samples. (Color figure

available online.)

FIG. 11. Distribution of misaligned fibers in the samples. (Color figure

available online.)

FIG. 12. Distribution of pulled out fibers in the samples. (Color figure

available online.)

FIG. 13. Distribution of delamination in the samples. (Color figure

available online.)

FIG. 14. Distribution of cracks in the samples. (Color figure available

online.)

USE OF INFRARED THERMOGRAPHY TO STUDY KENAF-PU DEFECTS 1161

Dow

nloa

ded

by [

Zah

ra D

asht

izad

eh]

at 0

9:25

30

July

201

2

2. Krishnapillai, M.; Jones, R.; Marshall, I.H.; Bannister, M.; Rajic, N.

NDTE using pulse thermography: Numerical modelingof

composite subsurface defects. Composite Structures. 2006, 75 (1–4),

241–249.

3. Choi, Manyong; Kang, Kisoo; Park, Jeonghak; Kim, Wontae; Kim,

Koungsuk. Quantitative determination of a subsurface defect of

reference specimen by lock-in infrared thermography. NDT & E Inter-

national. 2008, 41 (2) ,119–124.

4. Meola, Carosena; Maio, Rosa Di; Roberti, Nicola; Carlomagno, Gio-

vanni Maria. Application of infrared thermography and geophysical

methods for defect detection in architectural structures. Engineering

Failure Analysis. 2005, 12 (6), 875–892.

1162 Z. DASHTIZADEH ET AL.

Dow

nloa

ded

by [

Zah

ra D

asht

izad

eh]

at 0

9:25

30

July

201

2