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1、1,金属材料形变与强化机制的分子动力学研究,http:/ ( 韧脆转变 ) 形变孪晶 相变和新晶粒形核 原子-连续模型的尺寸行为,NiAl,Fe,界面微结构 (MD) 蠕变和筏化机制 (MD+FE+) 形状和尺寸以及体积分数的影响; 纳米尺寸效应行为(MD+FE+CM+MMM),http:/ 形变孪晶 相变和新晶粒形核,铁中裂尖形变机制的分子动力学模拟,http:/ et al., PNAS,MD,http:/ 0.1KIC/800步 0.1KIC/4000步,KI=1.6KIC,Brittle fracture in bcc-iron,(a) 010 , KI=1.11KIC (b) 110
2、 , KI=1.27KIC (c) 110 , KI=1.49KIC (d) 010 , KI=1.9KIC,Anisotropy for cleavage fracture,Stacking fault (SF),Twinning,http:/ 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,p360-366,Brittle to ductile t
3、ransition,KI=2.2KIC,5K,100K,200K,300K,http:/ 形核及生长机制,对裂纹扩展 影响,A:100 ; B:110 ; C:111 ,http:/ N-body potential,Get initial cracks according to continuum mechanics,Relax the crack by MD,Observe the structure evolution of the crack tip,different loads,different types of crack,bcc-Iron,fixed-displacement
4、 boundary condition,4000 steps,510-15s,37nm-37nm,Plane strain condition,Length of crack: 3.7nm,procedure,http:/ linear elastic continuum theory,Displacement field u,Initial crack,http:/ Sih, H. Liebowitz (ed.), in Fracture: An Advanced Treatise (vol.2), Academic, New York, 1968, p67.,Crack tip field
5、 for plane strain condition,http:/ evolution of the crack tip for different types of cracks,A:100 crack B:110 crack C:111 crack,KI = 1.9 KIC,the stress-induced phase transformation or recrystallisation can only occurs at KI 1.8 KIC,http:/ 110 crack,C: 111 crack,partial dislocations emission on succe
6、ssive planes,bcc-hcp,http:/ 110 crack,C: 111 crack,90 steps,110 steps,140 steps,40 steps,80 steps,140 steps,http:/ transformation,a: 2.8665 to 2.733 ,b: 4.0525 to 4.7336 ,http:/ 100 crack,new grain nucleated with a different orientation from the original bcc crystal (90),boundary between the twin st
7、rip and the new grain is a symmetrical tilt boundary with the rotation angle of 70.5,http:/ grain nucleation,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,and,20 steps,60 steps,140 steps,ht
8、tp:/ of shear stress,A: 100 crack B: 110 crack,A,B,C,C: 111 crack,symmetric,unsymmetric,http:/ 裂尖相变过程中新相为hcp结构。由于hcp结构能量高于bcc结构能量 (0.11eV/atom) ,相变过程只能在外载很高时才能发生。,界面结构 相变机制 裂纹沿裂尖新晶粒晶界扩展,Y-F Guo, Y-S Wang, D-L Zhao. Acta Materialia (in press),http:/ transformation in NiAl,B2,110 crack plane is the on
9、ly cleavage plane in B2 NiAl (MD, experiments),http:/ crack,100 crack,B2-L10,http:/ crack,100 crack,http:/ 尺寸相关行为,裂尖应力奇异性,http:/ UX随距离r变化曲线,垂直于裂纹表面方向:dy , dx 随距离r变化曲线,http:/ = 1.6KIC;LY为原子区在Y方向长度,http:/ = 1.9KIC (a)LY=140;(b)LY=280;(c)LY=360,Y-F Guo, Y-C Gao. Computational Materials Science, 2006, 3
10、6:432-439.,http:/ 的范围之内, 原子弛豫后的裂尖离散区半径约为100 如果原子区直径大于300,可以运用固定位移边界条件有效模拟bcc-Fe中裂纹的低温脆性解理扩展行为 连续模型在小于300 (30nm)的范围内不再适用,原子尺度应力,模型 本征,http:/ 运用应力边界条件 运用固定位移边界条件时采用移动边界技术,http:/ (b)弛豫4000步后的裂尖组态,初始载荷1.2KIC,每弛豫500步根据裂尖移动的距离更新边界,载荷达到1.4KIC后可以观察到裂纹稳态扩展,KI = 1.4KIC,http:/ (基体相) + 硬 ( 沉淀相/ ) 无晶界(相界;共格性好) 纳
11、米尺寸效应行为,结构特点,http:/ (70或更高) 、尺寸 (0.3-0.5m ) 、 形状 (立方) ,及本身的固溶强化程度等,筏化现象,/,在高温施加应力条件下,特别是1100K以上,沉淀相会发生定向粗化形成筏状,这种筏化行为直接影响了镍基高温合金的蠕变疲劳寿命,并且断裂面通常沿筏化方向发生 (外应力的幅值和方向、晶格错配度、 弹性常数差),http:/ (MD); 蠕变和筏化机制 (MD+FE+) 形状和尺寸以及体积分数的影响; 纳米尺寸效应行为(MD+FE+CM+MMM),Size? Temperature? Stress?,http:/ Wu,Y-F Guo, Y-S Wang. Transactions of Nonferrous Metals Society of China (accepted),the critical external tensile stress of about 180Mpa is required for bowing a creep dislocation in the horizontal matrix channel at 950,tensile stress of 300Mpa,http:/ FOR YOUR ATTENTION!,http:/
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