1Cr18Ni9Ti不锈钢的非比例循环强化性能

对1Cr18Ni9Ti不锈钢进行了各种比例和非比例循环本构实验，其中包括圆路径、正方形、正菱形、蝶形、三角形和两种十字形应变路径。表明其具有明显的非比例循环附加强化。在相同的等效应变幅值上，材料的附加强化与路径密切相关。对于圆路径，其附加强化度最大可达60％。通过对不同应变历史的实验研究表明，先前小的非比例度的加载历史对后继大的非比例度路径的强化没有影响；而先前大非比例度的加载路径对后继小非比例度路径的循环强化有较大影响。

NON-PROPORTIONAL CYCLIC HARDENING BEHMIORS OF 1Cr18Ni9Ti STAINLESS STEEL

Various proportional and non-prpoprtional conditutive mperfornis were conducted on 1Cr18Ni9Ti stainless steel thin-walled tubular specimens. The specimen used in test has an outer diameter of 25 an and an inner diameter of 21 mm. The experiments were run on MTS809 Tension-Torsional Fatigue Testing Machine. The tensile and shear strains were measured by a tension-torsional extensometer with 25 mm gauge length, and they are gathered by a PC comparer. The experiments include circular, square? rhombic, butterfly, triangular, and two kinds of cru- ciform paths. A step by step increased strain range test for single SPecimen was used in measuring cyclic stable stress-strain curves. The experimental results show the additional hardening in metal under non-proportional loading. The maximum additional hardening for circular path is abort 60%. The additional hardening closely relates to strain path under the same Mises equivalent strain ranges. The sequence is that the cyclic hardening of circular path > square path = rhombic path > triangular path > butterfly path > cruciform 1 path > cruciform 2 path > proportional path. Because the different cyclic hardenings for two kinds of cruciform paths, it is not suitable to define a nonproportionality by path geometry. In order to study the effects of the compleX loading history on cyclic hardening, two loading histories composed of different strain paths hot the same strain range were designed. History A is torsional cyclic + uniaxial cyclic + torsional cyclic +cur- ciform 1 cyclic + circular cyclic + torsional cyclic loading. History B is uniaxial cyclic + torsional cyclic + uniaxial cyclic + cruciform 1 cyclic loading. Comparing the results of two experiments, the stress range is almost the same for two kinds of cruciform paths at 60% accumulated plastic strain, though the loading history is different. It shows that previous small non-proportionality loading histories do not affect the hardening of the subsequence larger non-proportionality path. When material is under torsional cyclic loading after undergoing nonproportioual cyclic loading, the cyclic soften always appearss but the previous stable stress can not be recovered. It shows that material has memory effect for previous stress response of strain history, but the microstructure of metal has been changed after nonproportional cyclic loading, thus the stress can not be com- pletely recovered. It shows that previous large non-proportionality loading histories do affect the hardening of the subsequence small non-proportionality path.