Uniaxial Tensile Behavior and Specimen Size Effect of Commercially Pure Aluminum Subjected to Low-cycle Fatigue Pre-deformation

摘要

In order to explore the influences of fatigue pre-deformation on mechanical properties of structural materials and the corresponding specimen thickness effect, commercially pure aluminum (CP Al) was chosen as the experimental material. The results re veal that the uniaxial tensile yield strength ovs obviously increases for CP Al with 2.0mm thickness as the fatigue life fraction D (= N/N_f, the ratio of pre-cycle N to fatigue life N_f) is in the range from 2% to 75%, and the uniform strain σ_(YS) can be improved at the D ranging from 2% and 50%, meanwhile, higher ultimate tensile strength σ_(UTS) is remained. After CP Al sheets with the thickness spanning from 0.2 to 2.0 mm were pre-fatigued at a constant D of 5%, their e values evidently increase at the same thickness from 0.3 to 2.0 mm, and a higher σ_(UTS) is maintained. Meanwhile, the critical thickness t_c (below which the decrease in σ_(UTS) suddenly becomes notable) reduces from 0.5 mm of the un-fatigued state to 0.3 mm of the pre-fatigued state. The fatigue pre-deformation increases the uniform deformation degree in grain interiors, and promotes the formation of more ill-developed cells in sub-grains and wall-cells and the development of the sub-grains in thinner sheets, so that the pre-fatigued Al sheets with different thicknesses exhibit ductile failure and a higher σ_(UTS) is obtained.