INTERNAL STRUCTURE DAMAGE EVOLUTION IN COMPOSITE USING SYNCHROTRON RADIATION

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1 INTERNAL STRUCTURE DAMAGE EVOLUTION IN COMPOSITE USING SYNCHROTRON RADIATION Xaofang Hu Xaopng Wu * 1 (Unversty of Scence and Technology of Chna, Key Laboratory of Mechancal Behavor and Desgn of Materals, Chnese Academy of Scences, Hefe Anhu,230027,Chna) ABSTRACT In ths paper SR lght s used for the observaton of nternal structure and damage evoluton n composte materal by three knds of technques: (1) Scannng X-ray mcroscopy, (2) X-ray Absorbng Imagng, and (3) X-ray Computed Tomography. By Scannng X-ray Mcroscopy, a slcon thn plate wth thckness of 0.5mm was detected by soft X-ray. The resoluton of scannng mage was 2µm. Wth X-ray Absorbng Imagng technque, epoxy resn matrx composte renforced by sngle boron fber undergone tensle loadng was observed. Also, the damage evoluton for B-2223/ Ag HTS (hgh temperature superconductng) tapes at 77K under tensle loadng were nvestgated wth the same method. In order to obtanng the 3-D nternal structures, the X-ray Computed Tomography technque was used to nspectng the nternal topology of snterng ceramcs. 1. INTRODUCTION Synchrotron radaton (SR) source produces ntense, tunable, monochromatc, and hghly collmated beam, t s sutable to examnng the nnermost structures of opaque materals by measurng the X-ray energy transmtted through the materals. The X-ray transmsson attenuaton values are drectly related to materal s consttuents and are a functon of the atomc number. It s useful to feature detecton, densty measurements, consttuent dentfcaton, and dmensonal measurements [1-9]. Comparng wth conventonal optcal mcroscopy or SEM, SR technque does not requre polshed surfaces or seral sectons. It has the advantage for nondestructve observaton of nternal structures n materals. Combnng wth dfferent approaches and selectng proper X-ray energy, t can detect varous materals. 2. EXPERIMENTS AND DISCUSSION (1) Scannng X-ray Mcroscopy Ths experment was performed at mcroscopy beam lne of Hefe Natonal * 1 Correspondng author: Xaopng Wu, Department of Mechancs and Mechancal Engneerng, Unversty of Scence and Technology of Chna, Hefe Anhu, , Chna. Tel: ; Fax: ; E-mal: xpwu@ustc.edu.cn

2 Synchrotron Radaton Laboratory (NSRL). A thckness of 0.5mm slcon thn plate, whch was broken by laser mpact, was examned by means of scannng X-ray mcroscopy. The SR X-ray was converged as a small spot to mpnge on the specmen that was held on two-dmensonal precson movable stage. Frst of all SR source was separated nto monochromatc X-ray by nterferometer and the wavelength 32 Ǻ was selected. Then t was further focused to a mcro spot by mcro Fresnel zoneplate to scan the specmen pont by pont and the transmtted X-ray was detected by photon-counter to gve the dgtal mage. Wth ths wavelength the transparency of specmen s good and the contrast s hgh between slcon and vods on mage. The nternal damage of slcon plate was shown n Fg.1 and Fg.2. The receved photon numbers descrbed the cracks and vods wth dfferent heght and color. The hgh clff n Fg.1 or red strp n Fg.2 represented the crack about 10µm wdth. There were many vods n front of the man crack, and trended to lnk together to form the new crack. The mage resoluton was depended on the sze of focused spot. It was 2µm n ths experment. The scannng area was 50µm 50µm. Fg.1 3-D drawng for nternal damage of slcon plate Fg.2 2-D drawng shown damage wth color (2) X-ray Absorbng Imagng The X-ray absorbng magng technque used wde spectrum X-rays comng from SR source. The X-rays were drectly projected on to materal specmen. The transmsson rays were recorded by photo-resst PMMA or X-ray flm. In order to observe the structure damage evoluton, a specal tensle stage was desgned for the tenson of specmen. Tensle pull-off tests were performed on epoxy resn matrx renforced by boron fber at lthography beam lne of NSRL. A 0.3(W) 0.3(T) 20(L)-mm specmen was examned. The boron-fber was 130µm n dameter and covered wth carbon layer n 20µm thck. The experment was done n the vacuum chamber. The wavelength of X-rays was 5 Ǻ ~20 Ǻ. The PMMA photo-resst was used to record the mage. The flaw, damage accumulaton and cracks growth at nterface between fber core and cover were observed durng the fber suffered tenson, Fg.3. It could be seen that there were orgnal defects at

3 nterface 1 and 2 (Fg.3-a). Durng loadng, the defects developed nto a group of mcro cracks, and expanded towards the fber core. Furthermore, new mcro-cracks 3 were produced n the vcnty (Fg.3-b). Wth the ncrease of load, the mcro-cracks developed contnuously (Fg.3-c) a b c Fg.3 Damage evoluton at nterface between cover and fber core 9µm Another experment on the observaton of nternal structure damage evoluton n B-2223/Ag HTS (hgh temperature superconductng) tape at 77K under tensle loadng had been done at the X-ray tomography beam lne of Bejng Synchrotron Radaton Faclty (BSRF). The X-ray wavelength range of the beam lne s 0.3 Ǻ ~2.5Ǻ. The monoflament tape was chosen to perform the experment, and t was composed of oxde core B 2 Sr 2 Ca 2 Cu 3 O x wth Ag sheath. The specmen dmensons were about 3.3(W) 0.2(T) 26(L)-mm. At begnnng, the tape kept lnear elastcty. The crtcal current densty Jc was almost as Jco as constant (as shown n Fg.5). Wth the ncrease of load, the tape came nto plastc flow refer to the yeld pont (Fg.4-b, Fg.5 at pont σ 1 ). The mcrocracks ntated n core and ran cross the tape. Crtcal current densty J c decreased dramatcally after ths pont. The tape began to lose superconductng capablty. Increasng load sequentally, the mcrocracks became more and more untl the mcrocraks assembled to macro penetrable transverse one. Fnally the tape was fractured. 3.3 mm a b c d e Fg.4 Damage evoluton photographs of monoflament B-2223/Ag tape at 77K

4 1.0 σ II σ Jc/Jc(σ=0) σ I Mono-flament B-2223/Ag Stress (MPa) Stran (%) Fg. 5 J c /J c0 ~stran~stress curve of monoflament B-2223/Ag tape (3) X-ray Computed Tomography The SR-CT system had been developed to mage materal structures nondestructvely n three dmensons. Parallel X-rays pass through a specmen postoned on a rotaton stage, then are recorded by hgh resoluton X-ray flm (better than 2µm). The specmen s rotated by a small angle, and another two-dmensonal absorpton mage s obtaned. Ths process contnues untl of specmen rotaton has been recorded. Reconstructon software wth convoluton re-projecton arthmetc converts X-ray absorpton profle data nto two-dmensonal reconstructons of the lnear attenuaton coeffcents n the specmen nteror. These values are rendered nto three-dmensonal vew. The sntered porous ceramcs was nvestgated by SR-CT. Wth ths technque 3-D pore geometrcal topology, quanttatve obtaned. The experment was also performed at X-ray tomography beam lne of BSRF. An X-ray of wavelength 1.34 Ǻ was selected for projecton. The 10 photon flux at λ=1.34 Ǻ was 6 10 photons s -1 ma -1 mrad % BW -1. Specmen was a sntered ceramc cylnder wth dameter of 5mm. The snterng temperature was C. The composton of the ceramcs s shown n Table-1. Project mages were recorded at 2 0 ntervals, and 90 mages were obtaned for 3-D reconstructon. Fg.6 shows a sngle projecton slce at angle 0 0. The part of length 6mm was Area for calculatng pore pore rato and average densty were rato and average densty D=5mm Fg.6 Projecton slce at 0 0 l=4mm d=6mm Area for reconstr ucton t Correspondng to Fg.7

5 chosen for reconstructon, and 4mm for calculatng pore rato and average densty. The reconstructon topologes of cross secton for dfferent layer were gven n Fg.7. It was correspondng to the 2mm part n Fg.6. The nnermost pores, ther dstrbuton and changes along longtude were clearly shown. The resoluton of reconstructon mage was about 10µm. The elements and ther mass attenuaton coeffcents of the specmen were gven n table-2. Table-1 Composton lsts Compos ton() Mass rato(r) SO % Al 2 O % Na 2 O 14.7% CaO 8.4% Table-2 Elements and mass attenuaton coeffcents Elements() Mass rato(r ) Mass Attenuaton coeffcents(μ /ρ ) S 35.43% Al 0.56% Na 10.91% Ca 6.0% O 47.1% Fg.7 Secton topology of dfferent layer Calculaton for pore rato ε was based on formula (1) N ε = ( µ, j ) ) ( µ (, j ) µ N ( µ (, j ) ) ar 100 % (1) N( ) and μ(,j) represented sum of pxels and reconstructon lnear attenuaton coeffcent at pxel (, j) respectvely. Accordng to the reconstructon results, the calculated value of pore rato was 35.74% n volume. To obtan the average densty, the total average mass attenuaton coeffcent (µ/ρ) should

6 be calculated accordng to formula (2). µ µ = R ρ ρ (2) total ρ s densty and R s mass rato. The calculated result was as followng. µ ρ total = µ (, j) = g / cm ρ(, j), j Accordng to formula (3), the average densty of the specmen was calculated as ρ = 2.26g / cm 3 3 m ethod ρ = 2.04g / cm. Error was wthn the 9.7%. 2. It was agreement wth the value whch was measured by Archmedes (3) 3. CONCLUSIONS SR X-ray s a powerful tool to nspect materal nondestructvely. By the monochromatc synchrotron radaton, t s possble to unambguously measure the absolute values of the X-ray attenuaton coeffcent for the dfferent structures n the materals. Wth the development of hgh resoluton recordng transducer and SR technques, t would take an mportant role n the materals observaton. The avalablty of such expermental data should have a profound effect on the modelng of damage evoluton n compostes and other advanced materals. ACKNOWLEDGEMENTS Ths work was performed under the support of Natonal Nature Scence Foundaton of Chna under Contract No and BSRF Foundaton. The authors would lke to thank Dr. Jngle Yang, Dr. Xaonng Jng and Prof. Yulan Tan at BSRF for ther contrbuton for ths work. References: 1. Rchard H. Boss and Gary E. Georgeson, Composte structure development decson usng X-ray CT measurements, Materal Evaluaton (1995) T.Hrano and K.Usam, In stu x-ray CT under tensle loadng usng synchrotron radaton, J. Mater. Res., Vol. 10, No.2 (1995), J.H.Knney et al, Nondestructve nvestgaton of damage n compostes usng X-ray tomography (XTM), J.Mateer.Res.Vol.5 (1990), E. Mare, L. Babout, J.Y. Buffere, R. Fougeres, Recent results on 3D characterzaton of mcrostructure and damage of metal matrx compostes and a metallc foam usng X-ray tomography, Materals Scence and Engneerng, A (2001) Lame, D.Bellet, M.D Mchel, D.Bouvard, Bulk observaton of metal powder snterng by X-ray synchrotron mcrotomography, Acta Materala, 2004 (n press) 6. B. L. Illman et al, Synchrotron Applcatons In forestry and forest products, Synchrotron

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