Issue 14

M. N. James e ences of pla astic full-field

t alii, Frattura e sticity that h fringe data.

d Integrità Strut ave, up to no

turale, 14 (2010 w, largely be

) 5-16; DOI: 10 en ignored a

.3221/IGF-ESIS.

14.01

shi fitt

elding. It do ing error whe

es, however, n compared

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nd gives a lo

wer

I N

TERGRANU

LAR FATIGU

E

dep dis stru thr Th sam I

plasticity-ind eels with a b n movemen atom conte dislocations is non-planar d asymmetri s to move a on on the sa

ntergranula alloys, e.g. consequen endent on t locations, wh cture of a ½ ee 1 / 6 [1 1 1] is leads to sl e as that req

r faceting du certain α-iron ce of crystal emperature, ich are less [111] screw fractional dis ip asymmetry uired to mov

ring fatigue s and ultra-l structure a strain rate an mobile than dislocation in locations whi whereby th e it in the op

is a second ow carbon st nd dislocatio d interstitial non-screw a bcc alloy ch also sprea e shear stres posite directi

uced phenom ody-centred c t [16]. Slip nt and are g and which m , lying in thr cally on three dislocation i me plane.

enon that o ubic (bcc) cr mechanism overned by ake cross-sl ee {1 1 1} p {1 1 2} plan n one directi

ccurs infrequ ystal structur s in bcc all the behaviou ip more diff lanes (Fig. 2) es in the twi on on a slip

ently in spe e, and is a di oys are stro r of long sc icult. The c . It spreads nning sense plane is not

cific rect ngly rew ore into [18]. the

Figur period

e 2 : Core of a ically repeating The arrows ar crew disloca planes. Int w interstitial s rise to shap long grain b tended crack s subjected t xample of th ed in the au alance severa are likely to bility and dee gen, typically however, l ined above. Mn in solid lower interst steels, desp ng crack init

½[111] screw the three (11 e the relative ( tions hence d erstitial atom atom conten e changes of oundaries w paths plasti o fully revers is phenomen tomotive ind l conflicting be subject t p-drawing c 10-200 wt p ow interstitia IG cracking solution. Su itial C, B or N ite plastic def iation and lo

dislocation pa 1) layers (distin screw) displac epends on st s present in t (e.g. C, B, N bcc grains u hich favours c deformatio ed loading in on occurs in ustry for for requirements o reversed cy apability are a pm (0.001 w l content ( may also be sceptibility t [16]. ormation bei ng life fatig

rallel to the pl guished by di ements of neig ress-assisted the cores of ) would the ndergoing fu the nucleatio n may be str high cycle fa interstitial-fr ming thin ga , i.e. deep-dr clic loading ssisted by ve t % to 0.02 w < 40 ppm) promoted w o brittle frac ng strongly l ue, the fatigu

ane of the figu fferent colour hbouring atom thermally ac screw disloc refore prom lly reversed n of intergr ongly localis tigue where l ee (IF) steels uge sheet b awing capabi in service. T ry low amou t %). At th promotes IG ith high stre ture has bee ocalised at gr e performan

re. The atomic ed atoms) alon s along the disl tivated gener ations appare ote slip asym cyclic deform anular fatigu ed within gra evels of plas which const ody panels. lity, fatigue r he conflict in nts of interst e small plast cracking ngth IF stee n shown to ain boundari ce is little d

block is form g the dislocati ocation line [17] ation of kink ntly make th metry in bcc ation. Stres e cracks. Du in boundarie tic strain rang itute one of t In performa esistance, ten requiremen itial elements ic strains typ through the l grades con be higher in es, which lea ifferent to o

ed by on line. .

1 0} sier slip ons ent y in ups ese and use on, ycle etry sed e of ting able

Th and [19 asy can gro sus An of allo ligh inc bor fati me lev inc In par

e motion of s {1 1 2} slip ] and ultra-lo mmetry give then form a wth along ex ceptible alloy interesting e bcc steels us ys have to b t weight and reased forma on and nitro gue loading, chanism outl els of P and reased P and the case of IF ticularly duri

pairs on {1 is process ea alloys. This s concentrati ring subsequ s, particularl e are low. he major gro nce terms, th sile strength ts arises beca such as carb ical of high c slip asymm taining increa the presenc ds to IG face ther compar

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