Theme Days of the HRO Design Forum 20.-21.8. 2014 Lappeenranta University of Technology, Lappeenranta Vetokuormitetun päittäisliitoksen väsymislujuus hitsatussa tilassa Nykykäytännön arviointia ja vaihtoehtoisia tarkastelutapoja Fatigue strength of tensile loaded steel butt-welded joints in as-welded condition Evaluation of current practice and alternative considerations Timo Nykänen and Timo Björk Lappeenranta University of Technology, Laboratory of Steel Structures, P.O. Box 20, FIN-53851 Lappeenranta, Finland timo.nykanen@lut.fi, timo.bjork@lut.fi Friday, February 27, 2015 Design Forum of optimized welded structures (HRO)
The aim of the present study is to validate the fatigue strength of tensile loaded butt-welded joints by re-analysing fatigue data collected from the literature, to study the qualities (accuracy) of fatigue strength predictions, and to try to explain, at least partly, the apparent inconsistencies implicit in the results presented in the literature [5-19, ]. Tutkimuksen tarkoituksena siis: Vetokuormitetun päittäisliitoksen väsymislujuuden määrittäminen hitsatussa tilassa kirjallisuudesta kerätyn datan avulla ja sen vertaaminen nykykäytännön mukaiseen arvoon. Tutkia väsymislujuusennusteiden hyvyyttä (tarkkuutta) Yrittää ainakin osaksi selittää kirjallisuudessa esiintyviä ilmeisiä (näennäisiä) ristiriitaisuuksia väsymiskoetuloksissa ja niiden tulkinnoissa. Liittyen lähinnä jäännösjännityksen ja R-suhteen vaikutukseen Esimerkiksi as-welded (R = 0 0.1) vs. Ohtan menetelmä 3
Collected experimental fatigue data Ref Steel S y R m t R n n run-out K m Process Wang [11] Q235B 267 435 8 0.1 17-1.1 * 30 * - 16Mn 390 591 8 0.1 5-1.1 * 30 * - SS800 700 835 8 0.05 18-1.1 * 30 * - Remes [21] S275 285 438 12 0 11-1.19-1.28 29, 18 SAW ** 12 0 5-1.36-1.59 14 Hybrid LF ** Remes [22] S275 285 438 12 0 8-0.98-1.06 29, 18 SAW ** 12 0 10-1.02-1.06 18, 48 Hybrid MF ** 12 0 7-1.17-1.36 17, 59 Hybrid LF ** Radziminski [23] HY-80 621 724 25.4 0 14-1.1 * 30 * GMAW HY-100 760 867 25.4 0 13-1.1 * 30 * SMAW HY-130 965 1034 25.4 0 13-1.1 * 30 * Nykänen [18] Optim 1100 QC 1100 1250 6 0.05-0.57 17 4 0.90-1.19 21, 16 GMAW ** 6 24 9 0.95-1.12 22, 32 GMAW-P ** Ohta [6,24,25,26] SP410 284 441 20-1 0.58 31 11 1.01 30 * SAW SPV490 579 628 20-1 0.84 36 13 1.01 30 * SUS304 HP 275 618 20-1 0.56 31 12 1.00 30 * NRIM [27] SM50B 388 543 9 0 76 11 1.06 36 SMAW 356 530 20 0 47 7 1.07 41 351 520 40 0 32 1 1.04 43 NRIM [28] SM58Q 581 634 9 0 27 11 1.04 32.5 SMAW 586 632 20 0 30 9 1.02 32.2 NRIM [29] HT80 (A517) 799 825 9 0 31 11 1.01 23.8 SMAW 806 840 20 0 39 9 1.02 31.0 NRIM [30] HT80 (A517) ~727 ~834 20 0 31 14 1.01-1.04 24-34 SMAW ~733 ~826 20 0 29 15 1.00-1.02 15-28 GMAW 667 814 20 0 17 8 1.01-1.07 18-24 SAW NRIM [31] SM50B ~488 ~565 20 0 41 21 1.01-1.04 25-35 SMAW ~465 549 20 0 29 15 1.01-1.03 15-52 GMAW ~436 ~521 20 0 29 15 1.01-1.03 18-38 SAW Maddox [32] Mild steel 224 414 12.7 0 12-1.1 * 30 * SMAW Harris [33] ASTM A7 ~230 ~396 19 0 13-1.1 * 30 * SMAW AvestaPolarit [34] Duplex g2205 607 835 3 0.1 13-1.1 * 48 GMAW ** (EN 1.4462) 3 0.1 19-1.1 * 20 GTAW n 775 196 For R = 0 0.1 and N = 10 4 210 6 n = 532 * Unknown K m and chosen as recommended in [2] Hybrid LF CO 2 -laser combined MAG welding, laser travels first. Hybrid MF CO 2 -laser combined MAG welding, MAG travels first. K f = 1.58 3.18, K f mean = 2.184 K m mean = 1.053, mean = 30.4 o ** one-side welding (Units: MPa, mm, deg.) 4
Nominal stress system Ok? Collected fatigue data in the nominal stress system (Fig. 1) 5
Notch stress system Concentration factors Misalignments [2]: 3l e Km 1Km, 1Kme, 1, where Km, 1 and Kme, 13 2 t t The measure 2l is the distance between clamps, [rad] is the angular misalignment and e is the axial misalignment. Weld, Anthes et al. [35]: K K t m t b 0.2131 0.2491 0.3556 sin( 6.1937) t 2 3 t 1 0.138 1 0.169 1.503sin 1.968sin 0.713sin 0.2070 t 2 3 t 1 0.156 1 0.1811.207 sin 1.737sin 0.689 sin deg. Effective notch stress method, ENS [2]: K K f m, b t m, b 1 mm The combined stress concentration, K f,was finally calculated as follows: K K K 1 K f f m m f b 0.29190.3491sin( 3.2830) 6
Notch stress system!!! FAT225, kun m = 3 Liian suuri? Collected fatigue data in the notch stress system (Fig. 3) 7
Statistical methods Standard fitting procedure Standardimenetelmä In the case of linear regression, the fitted mean SN-curve is of the form log N log C mlog logcchar logcmean k1stdv f where m is the slope of the curve in log-log and with the fatigue data considering log N f (the response) as a function of log (the independent variable). A design curve at 95% survival probability level is normally calculated from the mean value logc mean on the basis of two sided tolerance limits of the 75% confidence level of the logc mean : logcchar logcmean k1 Stdv, where Stdv is the standard deviation of log C [2, 36]. Minimization of the sum of squared perpendicular distances from a line (MSSPD ) Vaihtoehtoinen menetelmä, joka pitäisi antaa parempi sovitus The comparison of the perpendicular offsets approach with the traditional approach reveals that the perpendicular 2 offsets approach provides a better fit. [37] The minimization of the square of the perpendicular distances R leads to the following equations for the fitting parameters: Minimoidaan pisteiden kohtisuorien yabx log N logcmlog etäisyyksien neliön summa sovitesuorasta 2 2 2 R R R y abx / 1b minimum, when 0 and 0 i i a b n 2 2 i1 2 2 2 2 2 2 [ i i ( i i) 4 ( i i) ]/2 i i where u log ( log ) / n and v log N ( log N ) / n logc mean f m v u v u uv uv n i i j i fi f j1 j1 (log N mlog ) / n log C (log N mlog ) / nk Stdv f i char f i i * Deming, W. E. (1943) Statistical adjustment of data. Wiley, NY (Dover Publications edition, 1985). ISBN 0-486-64685-8. http://en.wikipedia.org/wiki/deming_regression n j i 1 y Vertical offsets x Perpendicular offsets Deming * regression (orthogonal). The red lines show the error in both x and y. This is different from the traditional least squares method which measures error parallel to the y axis. The case shown, with deviations measured perpendicularly, arises when x and y have equal variances. 8
Results of fitting procedures All broken specimen data included, R test = -1 0.84 (n = 775): Nominal stress method m FAT mean [MPa] FAT char [MPa] r 2 Stdv of log(c) corresp. log (N) Stdv of log(c) corresp. log () Standard procedure 3 141 89 0.947 0.3419 0.1140 3.18 145 95 0.939 0.3407 0.1071 MSSPD 4.51 170 119 0.942 0.4020 0.0892 Vastaa IIW:n suosituksia Notch stress method m FAT mean [MPa] FAT char [MPa] r 2 Stdv of log(c) corresp. log (N) Stdv of log(c) corresp. log () Standard procedure 3 304 198 0.970 0.3236 0.1079 3.16 313 208 0.970 0.3225 0.1021 MSSPD 4.28 361 255 0.985 0.3720 0.0869 FAT mean vastaa IIW:n suosituksia FAT char : FAT198 < IIW FAT225 Data range for broken specimen: N = 10 4. 210 6 and R test = 0 0.1 (n = 532) *) Nominal stress method m FAT mean [MPa] FAT char [MPa] r 2 Stdv of log(c) corresp. log (N) Stdv of log(c) corresp. log () Standard procedure 3 141 95 0.926 0.2908 0.0969 2.3 119 73 0.967 0.2775 0.1207 MSSPD 4.28 167 117 0.911 0.3700 0.0866 Hajonta pieneni!!! Notch stress method m FAT mean [MPa] FAT char [MPa] r 2 Stdv of log(c) corresp. log (N) Stdv of log(c) corresp. log () Standard procedure 3 299 211 0.986 0.2592 0.0864 2.52 269 179 0.990 0.2526 0.1001 MSSPD 4.08 347 254 0.991 0.3160 0.0774 *) Reduced data set, only broken specimen results in the life range 10 4 2 10 6 were included, as recommended in [38]. 9
Comparison of results Reduced data set Nominal stress method SN - curve : m N C?! Sovittamalla suora test vs. pred pistejoukkoon, saadaan oheiset tulokset?! Vastaavuus sitä parempi mitä lähempänä suoraa pisteet sijaitsevat 10
Comparison of results All broken specimen data included Nominal stress method SN - curve : m N C?!?! 11
Comparison of results Reduced data set Notch stress method SN - curve : m N C k?!?!! 12
Comparison of results All broken specimen data included Notch stress method SN - curve : m N C k?!?!! 13
SN-curves nominal - standard Ok,? konservatiivinen? 14
SN-curves nominal - MSSPD Ok,??? R = 0.6 0.84 15
SN-curves notch - standard? Ok,? Jos FAT198? 16
SN-curves notch - MSSPD Ok,? Lähtökohtaisesti on edellä oletettu, että lokaali R suuri vetojäännösjännityksistä johtuen, jolloin kuormituksen R-suhteella ei pitäisi olla vaikutusta selvä vaikutus on kuitenkin nähtävissä Päätelmiä:?? R = 0.6 0.84 Standardisovitus, m = 3 Nominal: FAT90 ok Notch: FAT198 < IIW FAT225 Pakottamalla m = 3 saadaan ulkoisen kuormituksen korkea R-suhde otetuksi huomioon!? Pitkällä kestoiällä ennusteet konservatiivisia MSSPD Nominal & Notch Sovitus näyttää paremmalta, Korkea R-suhde ongelmana Ilmeisesti syynä: Vähän R > 0.5 ja max = S y kokeiden tuloksia Kommentti: Usein pienillä koesauvoilla jäännösjännitykset Kuitenkin alhaisia tai jopa puristuksella, jolloin R-vaikutus johtuisi pääasiassa kuormituksen R:stä!? 17
R-effect simplified consideration Asumption: Residual stress res 0 Smith, Watson, and Topper (SWT) [4] If the plastic strains are small : 2 2 ref 1Rref maxa ref, if Rref =0 2E 1 R 1R 1R R R 0 2E1Rref The mean stress correction factor is also : f 1R => Pelkästään kuormituksen R-suhteeseen perustuva tarkastelu SWT R-vaikutus Oletetaan: Ei jäännösjännityksiä Plastiset venymät pieniä => R R local Fitted stress range vs. N f Nominal stress method: = test [(1-R ref )/(1-R test )] 1/2 Notch stress method: = k fmax test [(1-R ref )/(1-R test )] 1/2 All broken specimen data included, R test = -1 0.84 (n = 775): Nominal stress method R test = -1 0.84 m FAT mean [MPa] FAT char [MPa] r 2 Stdv of log(c) corresp. log (N) Stdv of log(c) corresp. log () Standard procedure 3 143 90 0.947 0.3457 0.1152 3.27 150 99 0.935 0.3432 0.1050 MSSPD 4.67 175 124 0.947 0.4060 0.0869 Notch stress method R test = -1 0.84 m FAT mean [MPa] FAT char [MPa] r 2 Stdv of log(c) corresp. log (N) Stdv of log(c) corresp. log () Standard procedure 3 309 201 0.984 0.3228 0.1076 3.28 324 220 0.985 0.3196 0.0974 MSSPD 4.43 371 266 0.994 0.3680 0.0831 Vastaa IIW:n suosituksia R = 0 tulos?!!! FAT mean vastaa IIW:n suosituksia FAT201 < IIW FAT225 R = 0 tulos?!!! 18
Comparison of results Nominal stress method SN - curve : m m N 1 R C, R 0 2 ref 19
Comparison of results Notch stress method SN - curve : m m N k 1 R C, R 0 2 ref 20
Reference SN-curves notch stress method R ref = 0 Lovijännitykset muunnettu SWT:lla vastaamaan R = 0 ja sovitettu referenssikäyrät (master-käyrät) 21
SN-curves notch stress method R-effects, standard fitting, m = 3 SN-käyrät vastaten R = -1, 0 ja 0.5 m = 3 Kommentti: R > 0 muuttuu konservatiiviseksi Sitä konservatiivisempi mitä suurempi R Pitkällä kestoiällä konservatiivinen 22
SN-curves notch stress method R-effects, standard fitting, m = 3, comparison with IIW!? SN-käyrät vastaten R = -1, 0 ja 0.5 m = 3 Vertailu IIW -suosituksiin Kommentti: IIW high RS vastaa suunnilleen tapausta R = 0?!? 23
SN-curves notch stress method Standard fitting, m = 3, no SWT Kommentti: Käyrä edellä vastaten R = 0 käytännössä sama kuin ilman SWT:a 24
SN-curves notch stress method R-effects, MSSPD, m = 4.43 SN-käyrät vastaten R = -1, 0 ja 0.5 m = 4.43 R = 0.6 0.84 Kommentti: R > 0 hieman konservatiivinen Sitä konservatiivisempi mitä suurempi R Ennuste kuitenkin selvästi parempi kuin jos m = 3 Pitkällä kestoiällä konservatiivinen 25
SN-curves notch stress method R-effects, MSSPD, comparisons Kommentti: Jotainhan tästäkin näkee, kun jaksaa tutkiskella! 26
SN-curves notch stress method MSSPD, m = 4.28, no SWT Kommentti: Käyrä edellä vastaten R = 0 hieman ylempänä kuin ilman SWT:a 27
SN-curves nominal stress method R-effects, MSSPD, comparisons Nominal Vertailu ainoastaan Ohtan tuloksiin Huom! Vastaavuus on vielä parempi, jos referenssikäyrä määritetään pelkästään Ohtan tulosten perusteella! For R > 0 the correction factors are the conservative the higher R-ratio. Comparison of the MSSPD-fitted SN-curves, which include the applied stress ratio effect, with the results of Ohta et al. [6, 24-26] using the nominal stress system. 28
SN-curves notch stress method R-effects, MSSPD, comparisons Notch Vertailu Ohtan ja Kranz & Sonsino tuloksiin Selvää yhtenevyyttä ennustekäyrien ja Kranz & Sonsino käyrien kanssa Kranz & Sonsino: Comparison of the MSSPD-fitted SN-curves, which include the applied stress ratio effect, with the results of Ohta et al. [6, 24-26] and Kranz and Sonsino [16] using the notch stress system. 29
SN-curves notch stress method R-effects, comparison with experimental results R = 200, 268, 368 Hobbacher, A. (2013) The notch stress method for fatigue assessment of welded joints. Presentation in Theme Days of the HRO Design Forum 21.-22.8. 2013, Holiday Club Tampere Spa, Tampere, Finland. MSSPD, all data included, SWT m 4.43, FAT = 266 R1 R0.0 R0.4 R0.5 R0 char 1R R 266 1 ( 1) 376 266 1 (0.0) 266 266 1 (0.4) 206 266 1 (0.) 5 18 8 MSSPD, reduced data, no S WT m 4.08 R 0.5?? Standard, all data included, SWT m 3 1R R R1 R0.0 R0.4 R0.5 R0 201 1 ( 1) 284.3 201 1 (0.0) 201 201 1 (0.4) 155.7 201 1 ( 0.5) 142.0 Standard, reduced data, no SWT m 3 254 0.5?? 211? MSSPD, all data included, no SWT m 4.28 R 0.5?? R 255 0.5?? 198 Standard, all data included, no SWT m 3 R Kommentti: MSSPS + SWT näyttää toimivan, kun m = 4.43 Standard + SWT ei näytä toimivan, kun m = 3 Yleinen kommentti SWT:sta: Kun res = 0, SWT näyttäisi toimivan MSSPS kanssa, tosin muuttuu konservatiiviseksi, kun R > 0 sitä enemmän mitä suurempi R johtuu plastisista venymistä 30
R-effect more comprehensive consideration Lokaaliin R-suhteeseen perustuva tarkastelu We may try to take the plasticity effect (and thus the local stress ratio) into the account by introducing a plasticity correction factor fpl, Rs,, where s = res /R m. The corrected mean stress correction factor is then f(, R, s) f (, R, s) f ( R) 1R pl SWT This is quite complicated relation that depends on the applied stress range, applied stress ratio, R, residual stress level and material. Simplifying asumptions: Ramberg-Osgood relationship with the typical material parameter estimates for steels based on ultimate strength are used (n = 0.15, H = 1.65R m ) [1] An ideal kinematic hardening behavior was assumed for simplicity Neuber s rule for plasticity local Määritetään R local paikallisen venymän menetelmällä [1] In order to demonstrate the method, the plasticity correction factor is calculated only for local stress ranges = 225 and 304 MPa, corresponding ultimate strengths of R m = 400, 600, 800 and 1000 MPa. The coefficients for the fitted plasticity correction factor equation and the corresponding correlation coefficients r, are presented in Table below, when R = -1 0.5 and s = 0 1. 1 2 2 2 b crdr es fs gsr hsr fpl, R, s a/1 e R m a b c d e f g h r 2 225 400 1.5858-0.3612 0.6797 0.4605-0.9962 0.4290 1.2068-1.1642 0.9955 600 1.9235-0.08534 0.4024 0.4046-1.6713 0.7816 1.6870-1.2019 0.9939 800 2.2393 0.1681 0.2729 0.3145-2.1934 1.0640 1.8314-1.1550 0.9944 1000 2.5287 0.3657 0.2274 0.2685-2.5769 1.2723 1.8480-0.8860 0.9951 304 400 1.4410-0.4287 0.8228 0.3681-0.6461 0.2539 0.7911-0.7583 0.9975 600 1.6891-0.2863 0.5695 0.4636-1.1980 0.5278 1.3990-1.2199 0.9949 800 1.9484-0.06311 0.3758 0.3883-1.6910 0.7839 1.6880-1.1298 0.9944 1000 2.1932 0.1364 0.2733 0.3139-2.0880 0.9946 1.7940-0.9720 0.9947 1 n max max max E K nom 1 K f maxmax res E 1R 1 n 1 2 2E 2K K 2 f nom E min max min R local max 31 2
Comparisons s = res /R m Keskijännityksen korjauskerroin f, R, s 1Rlocal res = 0 R0 m 2 m N (1 R ) C local C m 1 Rlocal, joten N FAT FAT 1R local res >> 0 Kommentti: Kun vetojäännösjännitys suuri, on kuorman R-suhteen vaikutus vähäinen Ääritapauksissa lähes sama korjauskerroin kuin IIW-suosituksissa " Predicted mean stress correction factors (R m = 600 MPa) and comparisons with scaled (to correspond R ref = 0) fatigue enhancement factor f(r) by IIW [2] and Kranz & Sonsino [16]. R ref = 0 32
Effects on SN-curves (relative) Mielivaltaisesti valitulla referenssikäyrällä (vastaten R = 0, s = 0), ktso alla. $ R suuri res >> 0 # Notch stress method SN - curve : R ref 0 m k N f, R, s C or m 2 m N 1R C k local m R suuri res = 0 # # R = 0 res >> 0 Kommentti: # Erot suhteellisen pieniä Lujemmilla teräksillä puristusjäännösjännitys (suhteellinen) parantaa väsymislujuutta varsinkin suuremmilla kuormanvaihtojen lukumäärällä Predicted effects of R-ratio and residual stress level on SN-curves The slope for base SN-curve was arbitrary chosen (to give m = 3, when R = 0.5, s = 0.5 and R m = 1000 MPa) 33
Effects on SN-curves (relative) Mielivaltaisesti valitulla referenssikäyrällä (vastaten R = 0, s = 0), ktso alla. & $! Kommentti: Lujemmilla teräksillä puristusjäännösjännitys (suhteellinen) parantaa väsymislujuutta varsinkin suuremmilla kuormanvaihtojen lukumäärällä Etu kuitenkin menetetään, jos R suuri % #! Kommentti: Ennustettu R local vaikutus Lujempi teräs korkeampi keskijännitys Predicted effects of R-ratio and residual stress level on SN-curves The slope for base SN-curve was arbitrary chosen (to give m = 3, when R = 0.5, s = 0.5 and R m = 1000 MPa) 34
Preliminary comparisons Muodostetaan master-käyrä (base line) alla olevin oletuksin ja verrataan koetuloksiin Siis olettaen, että pienissä koesauvoissa res 0 The curves are assumed to be based on R = 0, s = 0 and R m = 600 MPa data!! Data points: R m = 396 1250 MPa!!! Mean base line estimate : Mean base line estimate : (Based on IIW mean curve) N 304 210 3 3 6 f 15.43 10 f,0,0 N f 3.7 (Based on MSSPD mean curve) N 361 210 4.28 4.28 6 f 19.955 10 f, 0, 0 N f 5.4 Muodostetaan siten, että kumpikin käyrä antaa likipitäen saman tuloksen, kun R = 0, s = 0 ja R m = 600 MPa Käytännössä joudutaan tekemään käyränsovitus pistejoukkoon, joka ei ole tarkalleen suoralla (ero pieni) muunnoksesta johtuen s = 0 s = 0 Kommentti: Tämä tapaus näyttäisi vastaavan paremmin koetuloksia 35
Preliminary comparisons Sama kuin edellä vertailu ainoastaan Kranz & Sonsino ja Ohta et al. tuloksiin Ensin perustuen IIW:n käyrään The curves are assumed to be based on R = 0, s = 0 and R m = 600 MPa data!! Data points: R m = 440 630 MPa!!! Most ~630 MPa! s = 0 Base line estimate : (Based on IIW mean curve) N 304 210 3 3 6 f 3.7 15.43 10 f,0,0 N f Effect of R + res s 0.0 0.0 0.65 0.65 R 0.0 0.5 0.5 0.0 FAT mean 303 251 230 244 As a comparison, also the scaled (to correspond R ref = 0) factors of Kranz and Sonsino [16] are presented for fully penetrated welds (A) and for fully and nonfully penetrated welds, and with non-fully penetrated welds with circular and long holes (A, B, C, D). 36
Preliminary comparisons Sama kuin edellä vertailu ainoastaan Kranz & Sonsino ja Ohta et al. tuloksiin Sitten perustuen MSSPD sovituksella saatuun käyrään The curves are assumed to be based on R = 0, s = 0 and R m = 600 MPa data!! Data points: R m = 440 630!!! s = 0 Base line estimate : (Based on MSSPD mean curve) N 361 210 4.28 4.28 6 f 5.4 19.955 10 f,0,0 N f Effect of R + res s 0.0 0.0 0.65 0.65 R 0.0 0.5 0.5 0.0 FAT mean 356 302 280 298 Kommentti: Ennusteen mukaan väsymislujuus pienenee edelleen, jos korkea R-suhde ja suuret vetojäännösjännitykset! Kommentti: Tämä tapaus näyttäisi vastaavan paremmin koetuloksia kuin edellinen Kun R > 0 ennuste parempi kuin lineaarisessa tapauksessa Kun R = -1 ennuste huonompi kuin lineaarisessa tapauksessa As a comparison, also the scaled (to correspond R ref = 0) factors of Kranz and Sonsino [16] are presented for fully penetrated welds (A) and for fully and nonfully penetrated welds, and with non-fully penetrated welds with circular and long holes (A, B, C, D). 37
Example Real base line for Optim 1100 QC based on as-welded data An attempt was also made to predict the fatigue strength of UP treated joints (red) based on the base line of the as-welded state (blue). MAG welding. R m = 1055 MPa, which is used in the following analysis. The measured mean residual stress gives s = -0.1062 in as-welded condition. For the UP treated joints, the residual stress varied from 132 to 315 MPa. The mean value of 240 gives s = -0.2275, when the ultimate strength was assumed to remain the same as in as-welded condition. MSSPD Rough estimate: Assuming that the ENS works for UP treated joints as well! Mean weld notch (toe) radius, mm As-welded After UP Surface 0.39 Surface 0.81 Root 0.5 Root 0.99 Kommentti: Tässä jäännösjännitykset mitattu pinnalta ei yhteismitallinen ENS-jännityksen kanssa NB: UP, R = 0.38 Crack initiation site: Surface, unsuccessful UP treatment, specimen failed from reinforcement side of groove! Base line for ultra-high strength steel based on as-welded state test results and MSSPD-fitting procedure, and comparison of predictions with test results [18]. 38
Example Real base line for Optim 1100 QC based on as-welded data An attempt was also made to predict the fatigue strength of UP treated joints (red) based on the base line of the as-welded state (blue). MAG welding. R m = 1055 MPa, which is used in the following analysis. The measured mean residual stress gives s = -0.1062 in as-welded condition. For the UP treated joints, the residual stress varied from 132 to 315 MPa. The mean value of 240 gives s = -0.2275, when the ultimate strength was assumed to remain the same as in as-welded condition. Standard Rough estimate: Assuming that the ENS works for UP treated joints as well!! After prediction model NB: UP, R = 0.38 Crack initiation site: Surface, unsuccessful UP treatment, specimen failed from reinforcement side of groove! Base line for ultra-high strength steel based on as-welded state test results and standard fitting procedure with free slope, and comparison of predictions with test results [18]. 39
Päätelmiä Nimellisen jännityksen menetelmän mukaiset FAT char = 89 ja FAT mean = 141 (vastaten K m mean 1.05 ja mean 30 o ), jotka saatiin standardisovituksella käyttäen kiinteää kaltevuutta m = 3, vastaavat hyvin normien arvoja Tehollisen lovijännityksen menetelmän mukaisiksi vastaaviksi arvoiksi saatiin FAT char = 198 ja FAT mean = 304. Karakteristinen arvo on selvästi pienempi kuin IIW:n ilmoittama 225 MSSPD sovitus antaa paremman korrelaation sekä väsymislujuuden, että kestoiän suhteen Kun jäännösjännitykset on pieniä, lineaariseen materiaalikäyttäytymiseen perustuva SWT-parametri näyttäisi toimivan. Korkeilla R-suhteilla se osoittautui sitä konservatiivisemmaksi mitä korkeampi R-suhde on Lokaalisen R-suhteen käyttö näyttäisi ottavan keskijännityksen paremmin huomioon Alustavien SWT-parametriin perustuvien arviointien mukaan korkealla R-suhteella ja pienillä koesauvoilla saatuihin tuloksiin perustuva väsymislujuus ei välttämättä takaa todellisten hitsattujen rakenteiden väsymislujuutta Parempaan ennusteeseen voitaisiin päästä, jos esitetyn menetelmän mukaista masterkäyrää muodostettaessa voitaisiin ottaa kunkin koesauvan jäännösjännitys/lujuus, lujuus,, huomioon. Hieman yleisempi masterkäyrä olisi voitu muodostaa ottamalla lujuus huomioon ja olettamalla res = 0. Laskennassa käytettävän jäännösjännityksen suuruus pitäisi ilmeisestikin määrittää samoin perustein kuin tehollisen lovijännityksen suuruus. Sopiva laskenta-arvo voisi olla 0.4 mm syvyyteen ulottuvan jäännösjännitysjakauman keskiarvo Multiaxiality factor s 2.5 * 0.4 mm, 0 mm 40 0 2.50.4 mm 1 mm f
Conclusions The following conclusions are drawn based on re-analysis of a large amount of fatigue data: The derived results in the nominal stress system FAT char = 89 and FAT mean = 141 (corresponding to K m mean 1.05 and q mean 30 o ) with standard fitting procedure and fixed m = 3 are in a good agreement with codes. The corresponding fitting using the notch stress system gives FAT char = 198 and FAT mean = 304. The characteristic value is clearly lower than the recommended design fatigue class 225. Use of FAT198 might harmonize the nominal and notch stress fatigue assessment methods. The perpendicular offsets approach gives more reasonable correlation between the predicted and experimental values for both the fatigue life and the fatigue strength than the standard procedure, at least from the designer s viewpoint. For joints with negligible residual stresses, the SWT-parameter based on linear material behavior appears to give good results, except for high applied R-ratios where it seems to be a little conservative. Use of the local stress ratio instead of the applied stress ratio takes the mean stress effect better into consideration and seems to explain some of the apparent inconsistencies that seem to exist between different investigations. Preliminary calculations with the SWT-approach, based on the comparisons made and assuming that the approach is applicable and effective in this context, indicate that high applied R-ratio in small size specimen tests might not inherently guarantee safe fatigue strength for welded joints that are loaded with high applied R- ratio and contain high tensile residual stresses as found in real welded structures. The R local based method seems to be quite promising. In order to test and verify the method more properly we should be able to determine the base line first. 41
Thank you Acknowledgements The authors wish to thank Rautaruukki Corporation, FIMECC Ltd. and the Finnish Funding Agency for Innovation (TEKES) for the founding this BSA-project, which enabled to complete this research work. Project, which is a part of the Breakthrough Steels and Applications (BSA) programme..
Source material [1] Radaj, D., Sonsino, C. M. and Fricke, W. (2006) Fatigue assessment of welded joints by local approaches. 2 nd Ed. Cambridge: Woodhead Publishing. [2] Hobbacher, A. (2007) Recommendations for fatigue design of welded joints and components. International Institute of Welding, Paris, IIW Document XIII-1823-07/XV-1254-07. [3] Eurocode No. 3: Design of steel structures. Part 1.1: General rules and rules for buildings. ENV 1993-1-1: 1992, Brussels. [4] Dowling, N. E. (2007) Mechanical Behavior of Materials, Engineering Methods for Deformation, Fracture, and Fatigue, 3 th Ed. Pearson Prentice Hall, USA. [5] Ohta, A., Suzuki, N. and Maeda, Y. (1997) Unique fatigue threshold and growth properties of welded joints in a tensile residual stress field. Int. J. Fatigue 19, 303-310. [6] Ohta, A., Suzuki, N. and Maeda, Y. (2002) Shift of S-N Curves with Stress Ratio. IIW-Document XIII-1922-02. International Institute of Welding. Weld World 2003; 47(1/2). [7] Ohta, A., Maeda, Y. and Suzuki, N. (1993) Effect of yield strength on the basic fatigue strength of welded joints. Fatigue Fract. Engng Mater. Struct. 16(5), 473-479. [8] Gurney, T. R. (1979) Fatigue of welded structures, 2 nd Ed. Cambridge University Press. [9] ESDU 75016 (1975) Fatigue strength of transverse fillet and cruciform but welds in steels. [10] Kudryavtsev, Y. and Kleiman, J. (2010) Measurement of residual stresses in welded elements and structures by ultrasonic method. International Institute of Welding, Paris, IIW Document XIII-2339-10. [11] Wang, T., Wang, D., Huo, L. and Zhang, Y. (2009) Discussion on fatigue design of welded joints enhanced by ultrasonic peening treatment (UPT). Int. J. Fatigue 31, 644 650. [12] Casavola, C., Masellis, D. and Pappalettere, C. (2004) Residual Stresses and Fatigue Strength of Butt Welded Components. Conference: 2004 SEM X International Congress & Exposition on Experimental & Applied Mechanics. [13] Sonsino, C. M., Fricke, W., de Bruyne, F., Hoppe, A., Ahmadi, A. and Zhang G. (2012) Notch stress concepts for the fatigue assessment of welded joints Background and applications. Int. J. Fatigue 34, 2-16. [14] Pedersen, M. M., Mouritsen, O.Ø., Hansen, M. R., Andersen, J. G. and Wenderby, J. (2010) Re-analysis of fatigue data for welded joints using the notch stress approach. Int. J. Fatigue 32, 1620-1626. [15] Sonsino C.M., Bruder T. and Baumgartner, J. (2009) SN-curves for welded thin joints suggested slopes and FAT-values for applying the notch stress concept with various reference radii. International Institute of Welding, Paris, IIW Document IIW- XIII-2280-09. [16] Kranz, B. and Sonsino C.M. (2009) Verification of the notch stress concept for the reference radii of r ref = 1.00 and 0.05 mm. International Institute of Welding, Paris, IIW Document IIW-XIII-2274-09/XV-1312-09. [17] Lieurande, H. P., Huther, I. and Lefebvre, F. (2007) Effect of weld quality and postweld improvement techniques on the fatigue resistance of extra high strength steels. International Institute of Welding, Paris, IIW Document XIII-2184-07. 43
[18] Nykänen, T., Björk, T. and Laitinen, R. (2013) Fatigue strength prediction of ultra-high-strength steel butt welded joints. Fatigue Fract. Eng. Mater. Struct. 36, 469 482. doi: 10.1111/ffe.12015. [19] Pedersen, M. M., Mouritsen, O.Ø., Hansen, M. R., Andersen, J. G. and Wenderby, J. (2009). Comparison of Post Weld Treatment of High Strength Steel Welded Joints in Medium Cycle Fatigue. International Institute of Welding, Paris, IIW Document XIII-2272-09. [20] Sonsino, C. M. (2009) Effect of residual stresses on the fatigue behaviour of welded joints depending on loading conditions and weld geometry. Int. J. Fatigue 31, 88-101. [21] Remes, H. (2013) Strain-based approach to fatigue crack initiation and propagation in welded steel joints with arbitrary notch shape. ). Int. J. Fatigue 52, 114 123. [22] Remes, H. (2008) Strain-based approach to fatigue strength assessment of laser-welded joints. Doctoral thesis, Helsinki University of Technology, Espoo, Finland. [23] Radziminski, J. B., Lawrence, F. V., Wells, T. W., Mah, R. and Munse, W. H. (1970) Low cycle fatigue of butt weldments of HY-100(T) and HY-130(T) steel. University of Illinois,Urbana, Illinois. [24] NRIM (1983) Data sheets on fatigue properties for butt-welded joints of SB42 carbon steel plate for boilers and other pressure vessels - Effect of stress ratio. http://smds.nims.go.jp/opentest/en/content/fatiguelist.html/28/11/2013. [25] NRIM (1984) Data sheets on fatigue properties for butt-welded joints of SPV50 steel plate for pressure vessels - Effect of stress ratio. http://smds.nims.go.jp/opentest/en/content/fatiguelist.html/28/11/2013. [26] NRIM (1986) Data sheets on fatigue properties for butt-welded joints of SUS304-HP(18Cr-8Ni) hot rolled stainless steel plate - Effect of stress ratio. http://smds.nims.go.jp/opentest/en/content/fatiguelist.html/28/11/2013. [27] NRIM (1978) Data sheets on fatigue properties for butt-welded joints of SM50B high tensile structural steel plates. http://smds.nims.go.jp/opentest/en/content/fatiguelist.html/28/11/2013. [28] NRIM (1979) Data sheets on fatigue properties for butt-welded joints of SM58Q rolled steel for welded structure Effect of specimen size. http://smds.nims.go.jp/opentest/en/content/fatiguelist.html/28/11/2013. [29] NRIM (1979) Data sheets on fatigue properties for butt-welded joints of high steel (Class 800 MPa) for welded structure Effect of specimen size. http://smds.nims.go.jp/opentest/en/content/fatiguelist.html/28/11/2013. [30] NRIM (1980) Data sheets on fatigue properties for butt-welded joints of high steel (Class 800 MPa) for welded structure Effect of welding procedure. http://smds.nims.go.jp/opentest/en/content/fatiguelist.html/28/11/2013. [31] NRIM (1981) Data sheets on fatigue properties for butt-welded joints of SM50B rolled steel for welded structure Effect of welding procedure. [32] Maddox, S. J. (1991) Fatigue strength of welded structures, 2nd Ed. Woodhead Publishing. [33] Harris, L. A. and Nordmark, G. E. (1954) The fatigue and static properties of butt welds in structural steels. University of Illinois, Urbana, Illinois. [34] Liljas, M. and Ericsson, C. (2002) Fatigue behaviour of stainless steel welds. AvestaPolarit AB, R&D, SE-774 80 Avesta, Sweden. 44
[35] Anthes, R. J., Köttgen, V. B. and Seeger, T. (1993) Kerbformzahlen von Stumpfstößen und Doppel-T-Stößen. Schweißen und Schneiden 45, Heft 12. [36] Lieurande, H. P., Huther, I. and Lefebvre, F. (2007) Effect of weld quality and postweld improvement techniques on the fatigue resistance of extra high strength steels. International Institute of Welding, Paris, IIW Document XIII-2184-07. [37] Weisstein, E. W. Least Squares Fitting--Perpendicular Offsets. From MathWorld -- A Wolfram Web Resource. http://mathworld.wolfram.com/leastsquaresfittingperpendicularoffsets.html/13/3/2014 [38] Schneider, C. R. A. and S J Maddox, S. J. (2003) Best practice guide on statistical analysis of fatigue data. International Institute of Welding, Paris, IIW Document IIW-XIII-WG1-114-03. [39] Karakas, Ö. (2013) Consideration of mean-stress effects on fatigue life of welded magnesium joints by the application of the Smith Watson Topper and reference radius concepts. Int. J. Fatigue 49, 1 17. [40] Olivier, R., Köttgen, V. B. and Seeger, T (1989) Schweißverbindung I Schwingfestigkeitsnachweise für Schweißverbindungen auf der Grundlage örtlicher Beanspruchungen (Welded Joints I - Fatigue strength assessment method for welded joints based on local stresses). FKM-Forschungsheft 143, Frankfurt/M, FKM, 1989. [41] Olivier, R., Köttgen, V. B. and Seeger, T (1994) Schweißverbindung II Untersuchung zur Einbindung eines neuartigen Zeit- und Dauerfestigkeitsnachweises von Schweißverbindungen auf Stahl in Regelwerke (Welded Joints II investigation of inclusion into codes of a novel fatigue strength assessment method for welded joints in steel). FKM-Forschungsheft 180, Frankfurt/M, FKM, 1994. [42] Hobbacher, A. (2013) The notch stress method for fatigue assessment of welded joints. Presentation in Theme Days of the HRO Design Forum 21.-22.8. 2013. Holiday Club Tampere Spa, Tampere, Finland. [43] Stoschka, M., Leitner, M. and Barsoum, Z. (2013) An alternative HFMI master S/N-curve approach. International Institute of Welding, Paris, IIW Document XIII-WG2-134-13. [44] Leitner, M., Stoschka, M. and Eichlseder, W. (2014) Fatigue enhancement of thin-walled, high- strength steel joints by highfrequency mechanical impact treatment. Welding in the World 58(1), 29-39. 45
Hitsausmenetelmän vaikutus 46
Lujuuden vaikutus 47