疲劳损伤钢件修复的最佳时机

Optimization of repairing effect for fatigue damaged steel specimens

为了研究影响疲劳损伤中间退火修复效果的诸因素 ,找出最佳修复时机的变化规律 ,在恒应变± 0 .5 %和± 0 .8%控制下 ,对 40Cr调质钢进行疲劳循环加载 ,求得存活率为 90 %时的寿命Nf。将试样疲劳加载到少于Nf 的不同周次后 ,再进行中间退火修复。发现中间退火可以延长损伤件的疲劳寿命。本次试验条件下能使疲劳寿命提高到原始试样的二倍。修复效果与损伤周次和承受的循环应变大小有关。用高灵敏度电阻仪和TEM对疲劳损伤过程与修复后材料的微观结构进行测试和观察。发现中间退火不能使损伤的材料恢复到原始材料状态。疲劳加载对材料的微观变化有两个相反的影响 ,疲劳损伤导致形成微观裂纹 ,但疲劳加载在材料中累积的应变能在中间退火过程中 ,作为附加驱动力 ,促使材料更加均匀、稳定 ,从而减少了形成微裂纹的条件。当循环应变增加 ,获得最佳修复效果的损伤周次减少。

In order to study influencing factors for repairing effect and to found out an optimization of repairing.The quenched and tempered 45Cr steel was used. The fatigue test was conducted in constant cyclic strain ±0.5% and ±0.8% control and the number of lifetime N f was counted with 90% survival probability. Intermediate annealing treatment was used to heal the specimens after different fraction of N f. It was found that intermediate annealing can prolong life of damaged materials. The total life of annealed specimens could arrive at as high as twice than that of virgin specimens in the case of present experimental condition. The repairing effect is closely related to the damaging cycles, as well as to the cyclic strain(or stress)amplitude. By the high sensitive electric resistance instrument and TEM. It was found the damage and the intermediate annealing both incur the microstructure changes, but the intermediate annealing can not recover the material to the virgin situation. During the annealing process, the strain energy can be as the additional driving force to let the materials be more homogeneous,stable and reduce the probability of microcrack initiation.The optimal cycles for better repairing effect was reduced as the cyclic strain increases.