MD Abraham et al PNAS 4 Brittle fracture

MD Abraham et al. , PNAS 4

Brittle fracture in bcc-iron Stacking fault (SF) Anisotropy for cleavage fracture KI=1. 6 KIC (a) {010} <101>, KI=1. 11 KIC Twinning (b) {110} <101>, KI=1. 27 KIC (c) {110} <001>, KI=1. 49 KIC (d) {010} <001>, KI=1. 9 KIC 0. 1 KIC/300步 0. 1 KIC/800步 5 0. 1 KIC/4000步

Brittle to ductile transition 5 K 100 K KI=2. 2 KIC 200 K 300 K *Guo Y-F, Wang C-Y, Zhao D-L. Mater Sci Eng A, 2003, 349(1 -2): 29 *Y-F Guo, C-Y Wang, Y-S Wang. Phil. Mag. Lett, 2004, 84(12): 763 断裂理论基础, 范天佑著, 科学出版社, 2003, p 360 -366 6

procedure Get initial cracks according to continuum mechanics different loads different types of crack Plane strain condition Relax the crack by MD Observe the structure evolution of the crack tip bcc-Iron 37 nm-37 nm F-S N-body potential fixed-displacement boundary condition 4000 steps 5× 10 -15 s Length of crack: 3. 7 nm 8

Initial crack Anisotropic linear elastic continuum theory Displacement field u 9

Crack tip field for plane strain condition G. C. Sih, H. Liebowitz (ed. ), in Fracture: An Advanced Treatise (vol. 2), Academic, New York, 1968, p 67. 10

Structure evolution of the crack tip for different types of cracks A: {100} <110> crack B: {110} <110> crack C: {111} <110> crack KI = 1. 9 KIC the stress-induced phase transformation or recrystallisation can only occurs at KI 〉1. 8 KIC p 11

bcc-hcp B: {110} <110> crack partial dislocations emission on successive planes C: {111} <110> crack 12

90 steps 110 steps 140 steps B: {110} <110> crack 40 steps 80 steps C: {111} <110> crack 140 steps 13

Phase transformation a: 2. 8665 Å to 2. 733 Å b: 4. 0525 Å to 4. 7336 Å bcc hcp 14

p new grain nucleated with a different orientation from the original bcc crystal (90 ) A: {100} <110> crack p boundary between the twin strip and the new grain is a <110> symmetrical tilt boundary with the rotation angle of 70. 5� 15

New grain nucleation and 20 steps 60 steps 140 steps p new grain grows with the growth of two twin regions, and the lengths of the new grain in and directions are always equal to the thickness of the twin region 16

Distribution of shear stress A: {100} <110> crack B B: {110} <110> crack A C symmetric C: {111} <110> crack unsymmetric 17

Phase transformation in Ni. Al B 2 {110} crack plane is the only cleavage plane in B 2 Ni. Al (MD, experiments) 19

B 2 -L 10 {110} <001> crack {100} <001> crack 20

{110} <110> crack {100} <110> crack 21

原子区尺寸对裂尖结构演化的影响 LY=29Å LY=57Å LY=140Å KI=1. 2 KIC KI=1. 1 KIC KI=1. 6 KIC KI=1. 9 KIC KI=1. 6 KIC KI=1. 9 K 27 IC

原子区尺寸对裂尖结构演化的影响 KI = 1. 9 KIC (a)LY=140Å；(b)LY=280Å；(c)LY=360Å Y-F Guo, Y-C Gao. Computational Materials Science, 2006, 36: 432 -439. 28

tensile stress of 300 Mpa the critical external tensile stress of about 180 Mpa is required for bowing a creep dislocation in the horizontal matrix channel at 950℃ W-P Wu，Y-F Guo, Y-S Wang. Transactions of Nonferrous Metals Society of China (accepted) 35