纳米晶体铝在单轴拉伸下的位错堆积对微裂纹扩展的影响

The Effect of Dislocation Stacking on Microcrack Growth of Metallic Crystals under Uniaxial Tension

针对纳米晶体材料,研究了单轴拉伸载荷作用下纳米晶体铝中的裂纹与裂纹尖端发射的位错所形成的滑移面之间的相互作用.通过分布位错法,将裂纹和滑移面等效为均匀分布的连续位错,获得了裂纹面上应力场.并引入裂纹尖端的无位错区,研究了裂纹尖端无位错区对微裂纹的萌生和主裂扩展之间的影响.结果表明,不考虑裂纹尖端无位错区时,裂纹长度较短,会先在晶界处形成微裂纹,主裂纹与微裂纹汇合形成偏折裂纹,主裂纹较长时,主裂纹会直接穿晶扩展.滑移面与裂纹尖端夹角较大时,会增加裂纹尖端发射的位错个数,从而抑制主裂纹的扩展.裂纹长度的增加会导致尖端发射位错数目的减少,裂纹尖端发射的位错会增加材料的断裂韧性.考虑裂纹尖端无位错区时,无位错区先于晶界处出现微裂纹,通过主裂纹与微裂纹之间位错的相互发射,导致裂纹与尖端处微裂纹汇合,有效加速了主裂纹的扩展.

For nanocrystalline materials,under uniaxial tensile load,the interaction between crack and slip surface formed by the dislocation emitted from the crack tip in nanocrystalline aluminum is studied.By means of the distributed dislocation method,the crack and slip surface are equivalent to a continuous dislocation with uniform distribution.The stress field on the crack surface is obtained,the dislocation-free zone at the crack tip is considered,and the effect of dislocation-free zone at the crack tip on the initiation and propagation of microcracks is studied.The results are as follows.When the dislocation-free zone at the crack tip is not considered and the crack length is short,microcracks first form at the grain boundary,and the main crack and microcracks then merge to form deflection cracks.When the main crack is long,it propagates directly through the grain.When the angle between the slip surface and the crack tip is large,the number of dislocations emitted from the crack tip increases and the propagation of the main crack is restrained.With the increase of crack length,the number of dislocations emitted from the crack tip decreases,and the dislocations emitted from the crack tip enhance the fracture toughness of the material.When the dislocation-free zone at the crack tip is considered,microcracks appear prior to grain boundaries in the dislocation-free zone.The mutual emissions of dislocations between the main crack and the microcracks lead to the confluence of the crack and the microcracks at the tip,effectively accelerating the propagation of the main crack.