TA1箔力学性能和断裂行为的尺寸效应

Size effect of mechanical properties and fracture behavior of TA1 foil

对不同晶粒尺寸的100μm厚TA1箔进行单轴拉伸试验,研究其力学性能和断裂行为的尺寸效应,并构建基于尺寸效应的微尺度本构方程。结果表明,随着晶粒尺寸增大,钛箔的拉伸应力及强度呈现增大的趋势,伸长率先缓慢下降至25%,随后快速降低。拉伸过程中颈缩阶段和平缓阶段不断缩短,除晶粒尺寸为56.88μm的试样外,其余试样断口夹角处于50°~60°,为典型的剪切型断裂。晶粒尺寸超过21.08μm后,断口表面的撕裂棱和韧窝数量不断减少,断裂模式由塑性断裂转变为准解理断裂,晶粒尺寸大于36.14μm后,钛箔基体从HCP-Ti结构转变为FCC-Ti结构,位错密度降低,断口表面出现明显的解理断裂特征,断裂模式完全转变为解理断裂。基于表面层模型构建考虑尺寸效应的本构模型,可精确预测微尺度钛箔拉伸过程中的力学特性。

Uniaxial tensile experiments were carried out on TA1 foils with thickness of 100μm and different grain sizes to study the size effects of mechanical properties and fracture behavior,and the micro-scale constitutive equation based on the size effects was constructed.The results show that the tensile stress and strength of titanium foil increase with the increase of grain size,and the elongation decreases slowly to 25%at first,and then decreases rapidly.During tensile process,the necking stage and the gentle stage shorten continuously.Except for the sample with grain size of 56.88μm,the fracture angle of the other samples is 50°-60°,which is typical shear fracture.When the grain size exceeds 21.08μm,the number of tear edges and dimple on the fracture surface decreases continuously,and the fracture mode changes from plastic fracture to quasi-cleavage fracture.When the grain size exceeds 36.14μm,the titanium foil matrix changes from HCP-Ti structure to FCC-Ti structure,and the dislocation density decreases,and obvious cleavage fracture characteristics appear on the fracture surface.The fracture mode completely changes to cleavage fracture.Based on the surface layer model,the constitutive model considering the size effect can accurately predict the mechanical properties of micro-scale titanium foil during tensile process.