A study of fatigue crack tip characteristics using discrete dislocation dynamics
A study of fatigue crack tip characteristics using discrete dislocation dynamics
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DOI：
10.1016/j.ijplas.2013.08.016
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发表时间：
2014-03
影响因子：
9.8
通讯作者：
Minsheng Huang;J. Tong;Zhenhua Li
中科院分区：
文献类型：
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作者：
Minsheng Huang;J. Tong;Zhenhua Li
用离散位错动力学(DDD)模拟了循环加载条件下跨环裂纹的尖端变形，同时考虑了位错攀移和位错晶界穿透。建立了一个具有代表性的单元来模拟材料的本构行为，并根据实验数据对DDD模型参数进行了拟合。对多晶镍基高温合金穿晶裂纹的近尖端本构行为进行了数值模拟。再现了循环蠕变或应变棘轮现象，与连续介质力学中的粘塑性和晶体塑性模型得到的结果相似。棘轮效应与位错堆积、位错攀移和位错-GB穿透有关，其中位错攀移似乎是高温情况下的主要机制。棘轮行为似乎有一个独特的离散特征，即在滑移带内发生的棘轮行为比在其他地方发生的更明显。在裂纹尖端周围的颗粒中激活了多个滑移系统，而在远离裂纹尖端的颗粒中激活了单一的活动滑移系统。目前的DDD结果表明，裂纹尖端前方的近尖端棘轮应变似乎是一种物理现象，这可能对建立基于物理的裂纹扩展模型具有特别重要的意义。
The near-tip deformation of a transgrannular crack under cyclic loading conditions has been modelled using discrete dislocation dynamics (DDD) with both dislocation climb and dislocation-grain boundary (GB) penetration considered. A representative cell was built to model the constitutive behaviour of the material, from which the DDD model parameters were fitted against the experimental data. The near-tip constitutive behaviour was simulated for a transgranular crack in a polycrystalline nickel-based superalloy. A phenomenon of cyclic creep or strain ratchetting was reproduced, similar to that obtained using viscoplastic and crystal-plastic models in continuum mechanics. Ratchetting has been found to be associated with dislocation accumulation, dislocation climb and dislocation-GB penetration, among which dislocation climb seems to be the dominant mechanism for the cases considered at elevated temperature. Ratchetting behaviour seems to have a distinctive discrete characteristic in that more pronounced ratchetting occurred within slip bands than elsewhere. Multiple slip systems were activated in grains surrounding the crack tip, as opposed to single active slip system in grains away from the crack tip. The present DDD results show that, the near-tip ratchetting strain ahead of the crack tip seems to be a physical phenomenon, which may be of particular significance for developing a physical-based model of crack growth.