LOP XAC DINH SU PHAN UNG DU THEO CHI^U SAU BANG PHUONG PHAP

NGHISN cCru-TRAO D 6 I

XAC DINH SU PHAN

B 6

UNG

S U A T

DU THEO CHI^U SAU BANG PHUONG PHAP C A T LOP

DETERMINATION OF IN-DEPTH RESIDUAL STRESS DISTRIBUTION BY LAYER REMOVAL METHOD

Tran Minh Tiln, Le Chi Cmmg Truong Dai hoc Su phjm Ky thuat TP. H6 Chi Minh T6M TAT

IJ'ng sudt du tren bi mdi vgt lieu tinh thi cd Ihi gay ra bien dgng hope phd huy vgt ligu;

do do, vigc xde dinh img sudt du cd vai trd quan trgng trong qud trinh xu ly vd cdi thign dieu kign ldm vigc cua chi tiit mdy. Nghien cieu ndy se gi&i thigu phuang phdp cdt l&p de xdc djnh sv ptidn bd img sudt cbt qua chiiu ddy cita mdu thu. Phuang phdp thich hpp dilng decdt l&p md khong sinh them img suat du m&i tren bi mat mau thie Id ddnh bdng dign hda. Sau khi cat l&p, Ong sudt dit Iren bi mgt mdu dupc do bdng nhiiu xg X-quang. Vigc xdc dinh sit phdn bd irng sudt du theo ehieu sdu duge thuc hign Iren mau Ihep €45. Ket qud cho thdy, ung sudt du phdn bd khdng dong nhdt theo chieu sdu cua mdu thie.

Tir kh6a: f/ng sudt du, phucmg phdp cdt l&p, nhieu xg X-quang, ddnh bdng dign hda.

ABSTRACT

Residual stress in the surface layer of crystalline materials may cause deformation or damage of materials, determination of residual stress plays an important role in treatment and improvement process of the working conditions of machine components. This paper will present the technique using layer removal method lo determine the residual stress distribution through the thickness ofihe specimen. The appropriate method uses for removing layer that does not introduce Ihe new residual stress in the surface layer ofihe specimen is the eleetropolishing technique. Ttie residual stress in the surface ofihe specimen is measured by X-ray diffraction for removing layer. Determination of the in-depth residual stress distribution was carried out on steel €45 specimen. The result shows that the residual stress distribution is the inhomogeneous in the direction of the thickness.

Keywords: Residual stress. Layer removal method. X-ray diffraction, Eleetropolishing.

1. GIOI THIfU nhi?t, hojc gia cong co. ITng suit du la nguyen nhan gay ra phd hiiy chi tilt vJ c6 inh hudng Ung suat du U Uang thai ung suit ton tnre tilp din dp bin moi cua chi till, tai phan Ion ben trong vat li^u khi khong c6 tac

dung cua ngojii luc. lfng suit du co thi phit Nhilu phuong phap da dugc phit triln sinh trong hau hit qua trinh san xuit nhu xii ly dl xic dinh umg suit du, chiing dugc chia lam

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hai lo^i. Phuang phap phi huy (destructive techniques DT), bao gom: Phuang phap khoan lo, phuang phip vong loi, phuong phip cit lop va phuong phip cSt tilt dien. Phuong phip khong phi huy (nondestructive techniques NDT), bao gom: Phuang phap nhilu xa X-quang (XRD), nhilu xa Neutron, phuang phip sieu am va phuong phip dien tit [2-3].

U'ng suit du phan bl ben trong vat lieu c6 anh huang den tinh chat va cuong do mon ciia chi tiet may, do do, viec xic dinh ling suit du theo chieu sau dong vai tro quan trpng trong v i ^ cii thi$n dilu ki?n lam viec cua chi tilt.

Tiong trudng hpp nay, phuang phip cit lap dupc kit hpp vcri nhilu xa X-quang dl xic dinh chinh xic su phan bl iing suit du theo chilu s^u ciia v$t li^u.

phip cit lap bing cong nghe dinh bong dien hoa la mot trong nhung phuang phip thich hop nhit, vi phuang phip niy dung de lay di timg lop vit lieu tu miu thii ma khong sinh them bit Cli mpt thanh phin ung suit du moi tai be mat mau va CO the dat dirpc dp bong cao [6,10,12].

Nghien ciiu niy da irng dung phuang phip cit lop bing danh bong di^n hoa va ket hpp do ling stmt du bing nhieu xa X-quang de xic dinh su phan bo ling suit du theo chieu sau ciia vat lieu.

2. XAC BINH iTNG SUAT DlT B A N G PHU'ONG P H A P N H I E U XA X-QUANG v A C A T L d P

2.1. Dinh bing difn h6a Phuong phip nhilu xa X-quang li

phuang phip khong phi huy ciu tnic vjt li$u, cho ket qui chinh xic vl ting suit du vi kha ning tu d$ng h6a de dang, do d6 dupc ling dyng tren nhieu loai vit li?u khic nhau. Tuy nhien, phuang phip nay c6n gip han chl trong truong hpp xic djnh trang thii iing suit du phin bl theo chilu day cua vit li$u, vi khi ning xuyen thiu cua tia X trong ky thuit vjt lifu li tuong dli nhd (khoing vii micrd).

Vi$c xic djnh va do lu6ng iing suit du theo chilu siu ddi hoi phii cit timg lop bl m§t tii mau thii, vi viy phuong phip cit lop la phuong phap thuong dupc iing dung. Phucmg phip cat ldp la phuang phip don gian, dl ding xic djnh ling suit du theo chilu siu tii bl mit raau bing cich liy di timg ldp vit li$u mong.

Vdi phucmg phip cit lop bing cic phucmg phip CO khi, hojc phucmg phip gia cong bing tia lira di?n (electro-discharge machining - EDM) dupc sir dung de cit timg ldp vit lieu cua miu thit se sinh them img suit du mdi do nhiet dp cao ttong qui trinh gia cong, tit dd lam thay dli ttirdng iing suit ban dau ciia bl rait [9]. Phuang

Dinh bdng di?n hda la m0t trong nhGng phuong phip ciia dinh bdng kim loai va hpp kim, theo dd, lop vat li?u dupc liy di tir be mit bing cich ndi mau thu vdi anot trong bl di^n phin (hinh 1). Dinh bdng dien hda cd thi dupc irng dung tt-en hiu het cic chi tilt cd hinh d?ing va kich thudc khic nhau [5].

^ ^ ^

Hinh 1. Sa do ddnh bdng dipn hda:

t) Dung dfch danh bong;

2) Caidi. 3) Anoi. 4) Nguon

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Quy Dinh dinh bdng dien hoa gdm 3 budc:

- Chuin bi: Loai bd diu, ma, oxit hoac cic tap chit khic bira tren bl mit miu mi chiing cd the lim giim chit lupng hoic gay ra su khong ddng nhat cho dinh bdng dien hda.

- Dinh bdng di?n hda: Thuc hien dinh bdng bl mit hoic tien hanh liy di mpt ldp vat lifu de thu dupc dp diy mong mudn.

- Xu ly sau dinh bdng: Muc dich cua xu ly sau khi danh bdng li de xu ly cic hda chat cdn sdt l^i tten be mit va lam khd bl mit nham phye vy cho quy trinh do iing suit du.

Sau khi cit Idp, ting suit du tten bl mit miu ctia tiing ldp dupc do bing nhilu x? X-quang.

2.2. Xic djnh iing suit bing nhilu x; X quang

tfinh 2. Hg tga dg diing de xde dtnh img sudt

Xit h0 tpa d0 dung dl do img suit (hmh 2), trong dd S, la h$ tpa dp xic djnh bl mjt miu vdi S|, Sj nim tten bl mit mau. L, li h? tpa dp do, vudng gdc vdi cic mit phing nguyen tli (hkl). Lj nim tt^n rajt phing mau t?o vdi S rapt gdc <p. Ph4p do ling suit du dupc thifc hi?n dya tten nhieu xji X-quang thong qua djnh luit Bragg [1]:

Trong dd: J, li budc sdng tia X, e 14 gdc Bragg, dyj li khoang cich tinh thi ciia mit phing nhilu x;! (hkl). Khi xuat bifn iing suit du ti^n Idp bl mit thi khoing cich d^^ giila cic mit nguyen tii sS thay ddi so vdri khoang cich ban dau d^. Bing vifc tinh toin vj tri dinh ctia dudng nhieu x^ thi biln d ^ g cua mau thii dupc xic dinh thong qua khoing cich d^^. Tit biln dang, ta cd thi xic dinh dupc uong suit du dl ding thdng qua moi quan hf iing suit biln d^g theo phuong trinh sau:

E +(722 sin

1 + v

+ <7 E l + v

(cr,, cos^ <p + <T^^^\n2(p (2)

-(<T„-KT;j+0-j,)

•((T,3 cos^ + <T23 sin ^)sin2^

Trong dd: E la modun dan hoi, v li hf so Poisson. Ddi vdi ttudng hpp mau thii dupc xft d ttang thii iing suit phing, phupng ttinh (2) ttd thinh:

_^»r-^o

l + v . 2 V ,

(3)

Vdi a^ li ling suit thinh phin theo hudng S^. Phuang trinh (3) cd thi dupc vilt Iji:

l + v

(4)

A = 2(/.„ sin 6 ₍₁₎ Diy li phuang ttinh thi hifn raoi ( hf d-sin> cd hf so gdc ra li:

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0 £. r (5)

Tti phuong trinh (5), ta cd the suy ra ling suit du dupc xic djnh tii hf sd gdc m bing phuang trinh:

E

dA\ + v ⁽⁶⁾

Trong dd: dj li khoing cich mit nguyen hi d n ^ g thai chua cd irng suit. Vi li vit lifu ding hudng nen dg dupc tinh nhu dilm khdng phy thupc ung suit ttong phuong trinh tuyln tinhd-sinV nhu sau:

sm i/t

l + v ⁽⁷⁾

23. Xic djnh phin bo ihig suit theo phuvng phip tuyln bing phirong phip cit Idp

Theo Iy thuyet din hdi, irng suit du theo phuang phip tuyln z qua timg ldp cit li mdt him phin bd ciia cic gii trj iing suit dupc do [7,8]. Trong trudng hpp mau thir cd be mit phing, him phan bd nay dupc bieu dien bing mli lien hf sau:

o'(^i) = <'-(^i)

JzM^.eJ^d. (8)

Trong do: a(Zj) \k umg suSt th\rc, a^(z,) Ik umg suat duQC do sau khi dt ldp, H la chieu diy ban d§u cua mau thu, z, la chilu day cdn lai sau khi cM Idp.

Khi ldp umg su^t cua v^t lieu dur^ lay di, p h ^ img suat cdn lai trong mau va tren bd m$t tiq> xuc sd bj thay d&i. Do dd, phep do ung

suit du tren bd mSt sau khi cat ldp c4n dugc hieu chinh [4,11]. Gia tri hi?u chinh C(2,) dupc xae dinh nhu sau:

C(Z,) = (7(Z,)-(T,(Z,)

= 2'l^±-6z,'l^dz (9)

Phuong trinh (9) cung the hi?n sv chdnh l?ch giOa ung suit du th^c va ung suit du dugc do t^i dp sau z,.

3. TIEN TRINH THV'C NGHlfM 3.1. Miu thir

Tien trinh thyc nghiem dugrc th\rc hi^n tren 9 mSu thdp C45 (ki hi?u tu MO ddn M8) cd kich thudc 10 mm x 20 nmi x 20 mm (chieu dai X chidu rpng x chieu dky). Tat ca cac mau tren deu dupc cit ra tCr m$t miu thdp cd kich thudc ban diu n o mm x 20 mm x 20 mm, sau khi tdi trong nudc tur SSO^C, dupc mai vk danh bdng bd mat bing giiy nhim ddn P2000. B ^ g 1, trinh bay thanh phan hda hpc cua mau thu.

Bdng 1. Thdnhphdn hda hpc cua thep C45 (%):

c

0.45 -0.5

SI

O.40

Mn

DJO-0,80

P

«).AS

s

<O.AS

Cr

<0.40

Mo

<0.I0

Ni

<0.40

3.2. Thyc Dghifm cit Idp

Trong bai bao njly, danh bdng di$n hda

\k phucmg phap cat ldp dupc umg dyng dd liy di ldp vat li?u tu bd mat miu. Dung dich dimg dd thyc nghi?m ddnh bdng di?n hda dupc pha tr^n theo ti le nhu sau: H^SO^ 15% (d = 1,84), H3PO, 63 % (d = 1,7), CrOj 10% vk Hp 12%.

Tidn trinh th\rc nghidm dupc th\rc hi^n vdi cAc thdng sd thich hpp sau khi diing thur nghi?m de kiem tra, trong dd, nhi?t dp tdi uu cua dung djch la 62°C (hinh 3).

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si

Hmh 3. Md td thuc nghiem cdt l&p Bang 2, trinh bay chieu day mdi ldp liy di tu mau MI ddn mau M8 cua th\rc nghiem cat ldp va chiing dupc do bang thudc micrometer.

MIU MO khdng tidn hanh cit ldp diing de do ung suat du bd m$t ling vdi chieu day ban dau.

Bdng 2. Chieu ddy l&p cdt (pm)

Ml 4 M5 28

M2 8 M6 36

M3 13 M7 45

M4 21 M8 55

3.3. Do irng suat dir bing nhieu xa X-quang Sau khi thuc nghifm cit ldp, tiln hanh do img suit du tren cic bl mit cua miu bing nhieu x? X-quang. Phep do dupc dure hifn tren hf may nhieu x? X'Pert Pro - Panalytical, trong dd ngudn phat tia X nhilu x? li CuKa vdi pho nhilu X? cd gdc nhilu xa 26 tir 80° din 85°. Tiln hinh do nhieu xa vdi cac gdc v = 0°; 18,4° vi 26,6° cho mdi phep do.

Nhieu x? X-quang irng dyng phuang phip sinV de phin tich ung suit du tren timg miu. Gia sii vit lieu li ddng nhit vi iing suit du chi phu thupc vio dp siu tinh tit bl mit cua miu. Quy trinh u miu d nhiet dp 500°C, dl loai bd texture nen mau dupc xem nhu vit lifu ding hudng. Vit lifu thep C45 cd hing sd modun

dan hdi va hf sd Possion tuong ling la 205 GI^

vi 0,29 dupc sii dyng dl tinh iing suit du. Di^

kifn do ung suit du bing nhilu x? X-quang troi tit ci cic miu dupc trinh biy trong bing 3.

Bdng 3. Dieu kign do img sudt du bdng nhiiu xg X-quang

Bucxa Budc sdng A.

Mat phing nhieu x?

BQIQC Di^n kp dng phdng Cudng dd dng phdng Thdi gian preset Budc quet

CuKa 1.541 A'

(211) Ni 45 kV 40 mA 30s 0.1"

Hinh 4, la ket qua be mit miu sau ddnii bdng. Thuc nghifm cit ldp cho thiy bl m«

mau thu dupc cd dp bdng cao t^o thuin lpi cho qua trinh do iing suit du dupc de ding vi chinh xic bing nhifu xg X-quang.

Hinh 4. Mdu sau khi cdt l&p

4. KET QUA VA KHAO SAT

Hinh 5, bieu diln cic dudng nhilu » dupc do tai cic gdc \|( = 0°; 18,4° vi 26,6' vi dupc npi suy bing him Gauss dl xic djnh vj Hi dinh cua dudng nhieu xg.

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Diffracuop ogle 26. dap Hinh 5 Du&ng nhieu xa cua MO Hinh 6, the hi?n mdi quan h? giira khoang each mat tinh the d va sin^y, dupc gpi la dd thi sin^y. ung suit dupc xae dinh tu dp L ddc ciia dudng thing tuyen tinh d-sin^ theo Fphuong trinh (6). LTng suat du ciia mau MO la

-1.941 MPa. Ung suat du cua cdc mau cdn lgi dupc trinh bay trong bang 4.

Hinh 6. Dd thf d-sin^i//

Gia tri hieu chinh cua cac ung suat du dupc do tinh bing phuang trinh (9). Dua tren ket qua tinh dupc, ta tim dupc mdi quan h^ giifa chieu day Idp cit Az va gia tri hi?u chinh C(z) (hinh 7).

Thickness of removal layers, \aa Htnh 7. Mdi quan hp giua Az vd C(z)

Kdt qua cho thSy, chieu day ldp cat va gia tri hi?u chinh ti Id thuan vdi nhau, dieu do chung td ring, khi chidu day ldp cit cang tang thi chenh lech gifta gia tri ung suit du dupc hi^u chinh so vdi gia trj ung suat du dupc do cang ldn. Bang 4, trinh b^y ket qua gia tn ung suat du dupc do ojz) va ung suat du dupc hi^u chinh a(z) ung vdi chieu day ldp cat Az.

Bdng 4. Gid trj dng sudt du dugc do vd ung sudt du dugc hipu chinh

Miu MO Ml M2 M3 M4 M5 M6 M7 M8

Az(|ini)

-

4 8 13 21 28 36 45 55

"Jit

(MPa) -1,941 -611 -489 109 490 88 197 -211 -136

(MPa) -1,941 -609 -486 114 498 99 211 -193 -115 Hinh 8, bieu diln su thay ddi cua ling suit du dupc do vi ung suit du dupc hifu chinh theo chilu siu z. Kit qui cho thiy, irng suit du cd su phin bd khdng dong nhit theo chilu "

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NGHieNCCrU-TRAOOOl

sau ciia miu thir. Dieu do cd nghia la s\r phan bd ling suit du tir bd mat vao ben trong mau thu cd ca su hi?n di?n cua iing suat du keo va ling suit du nen. Gik tri ung suit du nen ldn nhit la -1.941 MPa tai bd m^t va gia tri ung suit du keo ldn nhit la 498 MPa. Kdt qua ciing cho thiy, iing suat du nen va keo dupc sinh ra trong mau thu khi miu dupc xii Iy vdi quy trinh nhiet Iuyen bing phuong phap tdi va mai tren giay nham.

9 0 0 .

- 9 0 0 -

- 1 0 0 0 -

-IBOO-

-^

• y • i 30

1 - • - Mcmaim) 1 t Conectedl

4 0 ^ ^ . is...,-* ao

TliickDcu of rafno.ml ta]wn.|m Hinh 8. Sit phdn bd ung sudt du

S.KtTLUi^N

Cic kit luin sau dupc riit ra:

- Su phin bd ling suit du theo chilu siu tren miu thep di dupc xic dinh thdng qua qui ttinh thuc nghifm ung dyng phuong phip cit ldp biiig cdng nghf dinh bdng difn hda vi do iing suit du bing nhieu xj X-quang.

- Quy trinh tdi miti ttong nudc tir 850°C, dupc mii va dinh bdng bing giiy nhim sinh ra iing suit du nfn va kfo phin bd tit bl mit vao ben ttong miu thir.

- Ket qua phan bd iing suit du trong khoing chilu diy 55pin cho thiy, iing suit du cd su phin bd khdng ddng nhit theo chilu siu ciia mau thu.

Kit qui nay md ra hudng phit triln tilp theo trong nghien ciiu su inh hudng cua cic

thdng sd dinh bdng difn hda ciia thuc nghifm cit Idp den chit lupng dinh bdng va chieu diy cit ldp.*

Ngiy nh|n bai: 10/7/2016 Ngay phin bifn: 14/8/2016 Tii Ufu tham khio:

[ t ] . B.D. CuUity (2001), Elements of X-ray Diffi'aaion.

3K1 ed.. Prentice Hall, Inc., pp. 93-95.

[2]. J. Lu (1996), Handbook of Measurement of Residual Stresses, The Fairmont Press, Inc., pp. 1-4.

[3]. F.A. Kandil, J.D. Lori, A.T. Fry and P.V. Grail (2001), A Review of Residual Stress Measurvmem Methods - A Guide to Technique Selection, National Physical Laboratory, UK, pp. 16-19.

[4]. G. Totten, M. Howes, T. Inoue (2002), Handbook of Residual Stress and Deformation of Steel, ASM International, pp. IDS-IOS.

[5]. Nguyin Khuong (2009), Mg dien, TJp U, NXB.

Khoa hgc v i Ky thuit. H i N^i, pp. 150-166.

[6]. B.Ekmek9i, N. Ekmek(i, A.E. Tekkaya, A. Enten (2004), Residual stress measurement with layer removal method, CMES-04 Proceedings of the First Cappadocia International Mechanical Engineering Symposium.

[7]. M. Mahmoodia, M. Sedighi, D.A. Tanner (2012), Investigation of through thickness residual stress distribution in equal channel angular rolled Al 5083 alloy by layer removal technique and X-ray dip-aciion.

Materials and Design, Vol. 40, pp. 516-520.

[8]. M.G. Moore, W.R Evans (1958), Mathemaliatl Correction for Stress in Removed Layers in X.Ray Diffraction Residual Stress Analysis, SAE Transactions, Vol. 66, pp. 340-345.

[9]. M.E. Fitzptrick, A.T. Fry, R Holdway, F.A. Kandil, J. Shackleton and L. Suominen (2005), Determination of Residual Stresses by X-ray Diffi-action-Issue 2, Hatiooai Physical Laboratory, UK, pp. 35-36.

[10]. R. Alkaisee, R.L. Peng (2014), Influence of Layer Removal Methods in Residual Snvss Prvfiting of a Shot Peened Steel using X-ray Diffi-action, Advanced Materials Research, Vol. 996, pp. 175 - 180.

[11]. V. Savaria, R Bridier, R Bocher (2012), Computational quantification and correction of the errors induced hy layer removal for subsurface residual sftess measurements. International Joumal of Mechanical Sciences, Vol. 64, pp. 184-195.

[12]. RS. P r e v ^ (1986), X-ray diffraction residual shvss techniques, Metals Handbook. 10. Metals Park:

American Society for Metals, pp. 380-392.

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