A Study on the Degradation of Mechanical Properties for the Carbon Composite at a High Temperature and High Humidity of Environment

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1 IOSR Journal of Mechancal and Cvl Engneerng (IOSR-JMCE) e-issn: ,p-ISSN: 3-334X, Volume 3, Issue 5 Ver. VII (Sep. - Oct. 6), PP A Study on the Degradaton of Mechancal Propertes for the Carbon Composte at a Hgh Temperature and Hgh Humdty of Envronment Sun Ho Go, Sung Woo Hong, Hong Gun Km 3, Lee Ku Kwac 4 (Department of Mechancal Engneerng, Jeonju Unversty, South Korea) (Module System R&D Group, Insttute of Automotve Convergence Technology, South Korea) 3 (Insttute of Carbon Technology, Jeonju Unversty, South Korea) 4 (Department of Manufacturng and Desgn Engneerng, Jeonju Unversty, South Korea) Abstract: Carbon Fber Renforced Plastc(CFRP) materals of the arcraft can absorb water, whch could decrease the adheson strength of these materals and cause ther volumes to change wth varaton n nternal stress. Therefore, t s necessary to study the changes of the characterstcs n the extreme envronments n order to dentfy the envronmental mpact of CFRP. In ths study, we evaluated the propertes of CFRP by the tensle test and bendng test as specfed n ASTM standard. After the fabrcaton of the CFRP specmen drectly by usng a water bath to set the envronmental temperature and humdty, specmens were soaked n dstlled water at 75, for one week, two weeks and three weeks respectvely. Mechancal Characterstcs of CFRP were observed through Tensle test and Bendng test. Keywords: hgh temperature, strength reducton, temperature chamber, tensle strength I. Introducton Carbon fber can be used n the form of composte materal such as carbon fber renforced hgh molecular polymer composte materal, carbon fber renforced metallc composte materal, carbon fber renforced ceramc composte materal, and carbon fber renforced carbon composte materal thanks to ts excellent mechancal characterstcs and lghtness, drvng out competng materals that have been used so far and expandng ts applcaton cases to chemcal ndustry, sport goods, automotve ndustry, bo engneerng as well as to aerospace area such as applcaton for space shuttle[,]. The carbon fber renforced plastc, one of the many carbon-based composte materals that uses carbon fber as ts stffenng agent and thermo-hardenng resn as base materal, demonstrates an excellent mechancal property for statc load but cannot be expected to demonstrate such excellent mechancal property n a hgh temperature and humd envronment. The very mechancal property that makes the composte materal such an excellent substance s known to be changng the molecular arrangement and chemcal property of the base materal when faced wth some envronment factors such as temperature and humdty, especally when nfltrated wth mosture, thereby deteroratng the nterfacal and mechancal property of the consstng materals. Furthermore, the mosture absorbed by the base materal s known to be changng the nner stress condton by expandng absorbed mosture as well as deteroratng the bond stffness by separatng the chemcal bond between fber and base materal. Ths study, therefore, s amed at analyzng accurate tendency of such mechancal transformaton by makng a specmen usng carbon fber 3K prepreg among varous carbon fber renforced plastcs and mmersng t n a dstlled water heated up to 75 before performng a tenson test and 3-pont bendng test[3,4]. II. Theoretcal Background. Lamnatng theory Majorty of the theores on lamnaton consder that each lamnated ply s stuck tghtly wth other ply and each ply s composed of unform materal wth well-known physologcal property. And the physologcal property of each ply s Isotropc, Orthotropc, or Transversely Isotropc whle each ply s n the state of plane stress. In the case of the lamnated plate used n ths study, ts stress components can be appled as shown n equaton () from the perspectve of materal mechancs. n N t a = ply ζ L () a [ θ ] = [ θ ] Where t stands for the thckness of each ply, L lamnate. And the extensonal stffness of the composte lamnated plate should satsfy equaton () below[5]. DOI:.979/ Page

2 A Study on the Degradaton of Mechancal Propertes for the Carbon Composte at a Hgh n [ θ ] [ θ ] αβ = t ply Qαβ () = A. Moldng process of carbon fber pre-preg The carbon fber prepreg s an aelotropc substance that demonstrates hgh stffness, specfc rgdty and excellent fatgue resstance but low shock resstance. There are dverse methods for moldng carbon fber prepreg ncludng Press Moldng Method, Vacuum Bag Moldng Method and Autoclave Moldng Method. The autoclave moldng method appled to ths study s used for manufacturng aerospace composte materals that do not requre massve producton volume but hgh stffness, hgh strength and hgh qualty property. They can be produced n unform thckness wth hgh temperature and vacuum pressure whle the addtonal autoclave pressure helps mprove the qualty of surface profle. And ts hgh bondng strength between layers mproves fber volumetrc rate and eases elmnaton of bubbles between materals[6]..3 Correlaton of the composte materal and the temperature, humdty Mosture would nfltrate nto the base materal owng to dsperson acton when t contacts composte materal or nfltrate nto the nterface owng to the capllary phenomenon. Such nfltraton acton s beng accelerated f ts surface s damaged and cracks from an exposure to elements and such nfltraton prompts plastczng acton n whch hydrogen-bond between molecules s broken owng to the mosture nfltraton, whch agan lowers glass transton temperature thereby nflctng sgnfcant mpact n decreasng ts stffness. The glass transton temperature drops by % per % absorpton rate. In general, composte materals thcker than certan level are known to take up to years before the mosture penetrates down to the core of the lamnaton snce ts nfltraton speed s very slow n the room temperature. However, t s absolutely necessary to dentfy what deterorates the bondng property va the plastczaton acton whch breaks down Van Del Waals bondng between hgh molecular polymer chans. In ths paper, the author ntends to hghlght the need for such study by conductng the mechancal experment[7]. III. Test Methods 3. Manufacturng of specmen In ths study, two specmens for.5t tensle strength test and bendng test were made through lamnaton of carbon fber prepreg whch s used as lghtweght materal, before ther respectve mechancal strength was assessed by performng tensle strength and 3-pont bendng test, respectvely, on four dfferent specmens that were prepared by mmersng them n a hot water for zero week, week, weeks, and 3 weeks. The carbon fber 3K prepreg used n the test was a fabrctype WSN-3K made by SK Chemcal wth ts ngredents and mechancal property shown n Table and Table, respectvely. Frst, a roughly.5t (carbon fber 3K, prepreg 5Ply) specmen was produced by usng the Ply lamnaton method wth ts meltng temperature kept for 9m at 85, curng temperature for 9m at 5 and ts vacuum pressure at - bar and autoclave pressure at 4bar. The curng cycle appled for ths specmen s shown n Fg. [8]. Table Physcal propertes of carbon fber 3K pre-preg Physcal Propertes - Prepreg Type : Woven Fabrc - Fber Areal Weght : 4 g / m - Weave Style : Plan - Resn Content : 4% - Thckness :.77mm - Total Weght : 336 g / m Table Mechancal propertes of carbon fber 3K pre-preg - Tensle Strength : Mechancal Propertes 45 kgf / mm 3 - Tensle Modulus : 4 kgf / mm - Fber Densty : - Resn Densty :.77g / cm.g / cm DOI:.979/ Page

3 A Study on the Degradaton of Mechancal Propertes for the Carbon Composte at a Hgh Fgure. Curng cycle of carbon fber 3K prepreg The specmen for tensle strength test was made n accordance wth ASTM D-583 wth ts mmetc dagram and test specmen processng as shown n Fgure performed, whereas the specmen for 3-pont bendng test was made n accordance wth ASTM D-79 wth ts mmetc dagram and test specmen processng performed as shown n Fg.3[8-]. (a) Sketch of tensle test specmen (b) Tensle test specmen Fgure. Tensle specmen of carbon fber 3K prepreg (a) Sketch of 3-pont bendng test specmen (b) 3-pont bendng test specmen Fgure. 3 3-Pont bendng specmen of carbon fber 3K prepreg 3. Hgh temperature and humdty condtons In an attempt to meet test condtons by usng the prepared specmens, a thermal chamber was used to create a hgh temperature and most envronment. A total of four specmens, one that s gven wth no condton and three remanng specmen kept n a hot water for zero week, week, weeks and 3 weeks wthn bar nsde the thermal chamber (ambent temperature: 75, relatve humdty: %) were created whle ther relablty aganst envronmental condtons were sustaned by checkng temperature once per day usng an nfrared temperature sensor. The nsde and outsde condton of the thermal chamber wth regard to ths test are shown n Fg. 4 and Fg. 5. Fgure. 4 Insde vew of temperature chamber Fgure. 5 Set the envronment of temperature and humdty 3.3 Tensle testng The tensle strength test was performed to calculate the relatonshp between stress and elongaton percentage by recordng the strength and deformaton requred to break a standard specmen wth specfed sze and shape by pullng t to one drecton at contnuous speed. And the 8 unversal materal property tester by MTS n the Unted States was used for the man specmen. The head speed was set at mm/mn n accordance DOI:.979/ Page

4 A Study on the Degradaton of Mechancal Propertes for the Carbon Composte at a Hgh wth ASTM D-583 whle ts tensle strength was analyzed by usng equaton (3) and tensle stran rate by usng equaton (4). where : ζ = tensle stress at th data pont, MPa P = load at th pont, N A = average cross-sectonal area where : ε = tensle stran at th data pont, N δ = extensometer dsplacement at th data pont, mm L = extensometer gage length, mm g ζ = P / A (3) ε = δ / L (4) g Fgure. 6 Experment system for tensle test pont bendng testng The 3-pont bendng test s performed to determne softness or strength of a specfc materal by measurng deformaton resstance and breakng strength when a bendng moment was exerted to the materal. The 8 unversal materal tester by MTS n the Unted States was used for the test whle the span dstance and head speed were set up n accordance wth the ASTM D-79 specfcatons and ts bendng strength and bendng deformaton rate analyzed usng equaton (5) and equaton (6), respectvely. The tensle strength test was performed by comparng ts respectve strength measurements accordng to the dfferent perod of beng exposed to hgh temperature and most condton whle measurements of fve dfferent specmens were averaged to ensure the relablty of the test. ζ = 3PL / bd (5) where : ζ =stress n the outer fbers at mdpont, MPa P =lad at a gven pont on the load-deflecton curve, N L =support span, mm b =wdth of beam tested, mm d =depth of beam tested, mm where : ε =stran n the outer surface, mm/mm D =maxmum defecton of the center of the beam, mm L =support span, mm, d= depth, mm ε = 6Dd / L (6) DOI:.979/ Page

5 Tensle Strength Tensle Strength Tensle Strength Tensle Strength A Study on the Degradaton of Mechancal Propertes for the Carbon Composte at a Hgh Fgure. 7 Experment system for bendng test IV. Results And Dscusson 4. Tensle testng It was measured as 69MPa for normal specmen, 634MPa for the specmen kept for one week n a hot water, 69MPa for the specmen kept for two weeks, and 578MPa for the specmen kept for three weeks, or equvalent of strength reducton measurng 56MPa, 8MPa and Mpa, respectvely, as compared to the normal specmen. and the respectve S-S Curve for dfferent type s shown n Fg. 8 through Fg. whle related data shown n Table 3 and tendency n the strength deteroraton n Fg.. As such, deteroraton n the tensle strength and stffness of the specmens that were made of carbon composte materal when they were exposed to a hot and humd envronment was confrmed. In partcular, the tensle strength of the specmen whch was exposed for one week dropped rapdly and decreased over tme but no lnear pattern was observed n the specmen. Ths s beleved to be stemmng from the fact that carbon fber and resn, both aelotropc materals, dd not demonstrate constant pattern n ther most mmerson rate dependng on the extent of nternal processng # # stran (mm/mm) Fgure. 8 Results obtaned from tensle test(normal) stran (mm/mm) Fgure. 9 Results obtaned from tensle test(week) # # stran (mm/mm) Fgure. Results obtaned from tensle test (weeks) stran (mm/mm) Fgure. Results obtaned from tensle test (3weeks) DOI:.979/ Page

6 A Study on the Degradaton of Mechancal Propertes for the Carbon Composte at a Hgh Table 3 Data of tensle test(normal 3weeks) Specmen No Average Normal week weeks weeks Tensle Strength Normal week weeks 3weeks Specmen Type Fgure. Results obtaned from tensle test(normal - 3weeks) 4. Bendng testng The bendng test was performed by comparng ther strength dependng on the perod beng exposed to hot and humd condton whle measurements of fve dfferent specmens were averaged to ensure the relablty of the test. It was measured as 9MPa for normal specmen, 86MPa for the specmen kept for one week n a hot water, 6MPa for the specmen kept for two weeks, and 48MPa for the specmen kept for three weeks, or equvalent of strength reducton measurng 5MPa, 3MPa and 43Mpa, respectvely, as compared to the normal specmen. and the respectve S-S Curve for dfferent type s shown n Fg. 3 through Fg. 6 whle related data shown n Table 4 and tendency n the strength deteroraton n Fg. 7. As such, deteroraton n the tensle strength and stffness of the specmens that were made of carbon composte materal when they were exposed to a hot and humd envronment was confrmed. In partcular, the stffness of the specmen whch was exposed for one week dropped least unlke n the case of ts tensle strength but no lnear pattern was observed n the specmen. Ths s beleved to be stemmng from the fact that the hydrogen bondng strength between molecules decreases owng to most nfltraton but ts nfltraton speed s very slow thereby maxmzng the nfluence of temperature. Therefore, t s beleved to be dffcult to dentfy any clear trends n delamnaton between ply or n cracks n the base materal gven the characterstcs of the aelotropc substance. # 3 5 Stress Stress 5 # Stran(mm/mm) Fgure. 3 Results obtaned from bendng test(normal) DOI:.979/ Stran(mm/mm) Fgure. 4 Results obtaned from bendng test(normal) 8 Page

7 A Study on the Degradaton of Mechancal Propertes for the Carbon Composte at a Hgh 3 # 5 # 5 Stress Stress Stran(mm/mm) Stran(mm/mm) Fgure. 5 Results obtaned from bendng test(normal) Fgure. 6 Results obtaned from bendng test(normal) Table 4 Data of bendng test(normal 3weeks) Specmen No Average Normal week weeks weeks Bendng Strength Normal week weeks 3weeks Specmen Type Fg. 7 Results obtaned from bendng test (normal - 3weeks) V. Concluson In ths paper, the tensle strength and bendng strength tests were conducted on four dfferent types of specmens before comparng the results wth the related test condtons n an attempt to verfy the correlaton between the deteroraton of mechancal strength of carbon fber composte materal and hot and humd condton. When the test condtons were sustaned at 75 for ambent temperature and % for relatve humdty by usng a thermal chamber, the strength has deterorated contnuously for three weeks, thereby confrmng that a hot and humd condton exerts sgnfcant nfluence on the delamnaton between ply and crack development n the base materal. but no lnear result was observed wth regard to the strength deteroraton. Such result s beleved to be stemmng from the fact that nfltraton nto the nterface s beng realzed wth an rregular pattern due to the capllary reacton whch was prompted by the ar bubbles nsde carbon fber and resn whch are both aelotropc substances. It s beleved based on a prelmnary research that the result s not so much nfluenced by most nfltraton as by hot temperature. DOI:.979/ Page

8 A Study on the Degradaton of Mechancal Propertes for the Carbon Composte at a Hgh Acknowledgements Ths research was supported by basc scence research program through the Natonal Research Foundaton of Korea(NRF) funded by the mnstry of educaton, scence and technology (No.3RAA658) and fnancally supported by the Natonal Foundaton of Korea(NRF) funded by the Korea Government(MISP) (No.4RAAA54594) and (No.4RAAA53533) References [] H. J. Shn, The Strength Evaluaton and Nondestructve Testng of Carbon Fber Compostes, Jeonju Unversty, Republc of Korea, MA, 3. [] J. H. Km, The Tensle Characterstc of Carbon and Slca Renforced Compostes Under Elevated Temperature, Journal of the Korean Socety for Composte Materals, 6(3), 3, [3] P. Cappa, K. McConnel and L. Zachary, A Temperature Calbraton of a Temperature/Stran Transducer based on Two Stran Gauges, Internatonal Journal of the Stran, 9(4), 993, [4] J. O. Lee, J. S. Lee and K. S. Cho, The Analyss of Falure Mechansm durng Tensle of CFRP, Journal of the Korean Socety for Composte Materals, 5(), 99, -3. [5] S. K. Lee, S. K. Oh and K. W. Nam, A Study on the Fracture Behavor of CFRP n Tensle and Fracture Toughness Tests by Acoustc Emsson, Journal of The Korea Socety for Nondestructve Testng, 5(), 995, [6] M. G. Km, S. K. Kang and C. G. Km, Tensle Propertes of CFRP Compostes wth Dfferent Resn Composton under Cryogenc Temperature, Journal of The Korean Socety for Composte Materals, (4), 7, -8. [7] Lee, S. E., Lee, W. J., Km, C. G., A Study on Tensle Propertes of Mult-Walled Carbon Nanotube/Epoxy Compostes, Journal of the Korean Socety for Composte Materals, 7(5), 4, -7. [8] Standard Test Method for Tensle Propertes of Renforced Thermosettng Plastcs usng Straght-Slded Specmens, ASTM D 583-,. [9] Standard Test Method for Tensle Propertes of Polymer Matrx Composte Materals, D339/D339M-4, 4 [] T. H. Km, Analyss of Correlaton accordng to the Orentaton of Carbon Fber Composte Mechancal and Thermal Propertes, Jeonju Unversty, Republc of Korea, MA, 6. DOI:.979/ Page