表面扩散控制下币型微裂纹的演化

SHAPE EVOLUTION OF PENNY-SHAPED MICROCRACKSCONTROLLED BY SURFACE DIFFUSION

根据表面扩散控制下物质迁移规律,建立轴对称有限单元法,分析了币型微裂纹的外形演化过程．在表面扩散控制下,形态比为β的币型裂纹演化的物理图像是:当β＜βⅠ＝18.0,币型裂纹直接球化; 当β≤β＜βⅡ＝34.6,演化为一环状裂腔;当βⅡ≤β＜βⅢ＝148.9时,演化为一环状裂腔和球形空洞;当βⅢ≤β＜βⅣ=240.0,演化为两环状裂腔．和分离出环状裂腔过程相比,球化过程是快过程;在逐层分离出环状裂腔过程中,后一级的分离相应前一级的分离是快过程．

Based on the theory of surface diffusion, an axi-symmetric finite element methodis developed to simulate shape evolutions of penny-shaped microcracks. The results show thatthe final shape is determined by the microcrack aspect ratio β(β = D0/h0, where h0 is thecenter thickness, D0 the diameter of the microcrack), and four critical aspect ratios are obtained,denoted by βⅠ, βⅡ, βⅢ and βIV. When β < βI = 18.0, the microcrack will directly evolveinto a spheroid. Otherwise, it is separated into one or several rings without or with a spheroiddependent upon its aspect ratio: when βI ≤ β < βⅡ = 34.6, the microcrack evolves into aring, when βⅡ ≤β < βⅢ = 148.9, a ring with a spheroid at the center of the ring; whenβⅢ≤β < βIV = 240.0, two rings, and so on. The spheroidization is a fast process compared tothe process of ring separation. During the processes of separating into multi-rings, the subsequentseparation is a faster process than the former, and the area of ring section decreases.