纳米铝合金的断裂与塑性变形

Fracture and Plastic Deformation of Nanometer Crystalline Aluminium Alloy

在结构非均匀的多晶材料中,局域化塑性变形不仅在微观层次而且也在介观层次上具有波动特征,并以塑性波形态进行扩展,这一现象与材料亚韧性断裂之间有相互关系。纳米晶、亚微米微晶2009铝合金试样在经受拉伸应力实验时,试样上各点的应变量在三维方向上均呈波动性变化,且随着外加载荷的增加而波动的幅度增加。塑性变形的波动的传播是在加载过程中,试样内的剪切稳定性丧失后,由于晶粒群转动,在试样上沿最大剪应力方向形成了吕得尔斯条带而逐步形成的。主剪切带形成了一个塑性变形的波峰,接下去侧生条带和次生带形成波峰和波低谷区,周而复始,形成了塑性变形的波动的传播。应力应变峰值的形成与材料缺陷所造成应力集中有关。试样于应力集中点起始迅速开裂。宏观断裂强度仅体现了材质缺陷弥散程度的统计平均数。

The wave propagation feature of local area plastic deformation was observed not only at microscopic level,but also at mesoscopic level for the non-uniform poly-crystal metals.This phenomenon was related with the second tenacity and stiffness in material.When the specimen of nanometre crystalline sub-micro crystalline 2009 aluminium alloy was under tension,deformations of different local areas in the specimen were non-uniform and different from the macro-deformation of specimen in the tension test.Strains of material were characterized by wave propagations,plastic strains propagation in three dimensions,and the amplitude of the wave were directly in proportion to the load that acted on the specimen.During the loading process,the wave propagation of plastic deformation was caused by crystalline grains turning directions to take shape after the shear stability in the specimen was lost.Along the orientation of maximum shearing stress a Lüders band was formed at the initial stage of plastic deformation and spread forward with the wave propagation gradually.A crest factor was formed by the main shear band,and then the wave low district formed the side band and second tenacity.The formation of peak value stress was related to the concentration of stress caused by material flaw.The specimen fractured rapidly at the stress concentrated point.The fracture intensity of the sample at macroscopic level merely displayed the statistical mean value of material quality flaw dissemination degree.