基于数字图像相关的激光修复镍基合金疲劳损伤表征方法研究

Study on fatigue damage characterization method of laser repair nickel-based alloy based on digital image correlation

开展激光修复镍基合金的疲劳试验,对研究修复材料疲劳性能及分析其失效行为具有重要意义。疲劳过程中,试件产生局部损伤,会导致材料力学性能恶化。如何建立光学变形场与疲劳损伤参数的定量关系实现对疲劳损伤的有效表征,是实验力学领域备受关注的问题。从激光修复镍基合金疲劳失效行为研究的需求出发,本文建立了基于单相机三维数字图像相关的疲劳光力学测试系统,并设计了包含“修复基体-修复边界-修复区”的组合型拉伸疲劳试件,在建立的测试系统下可同时测量和表征试件三种区域的全场变形。利用所建立的测试系统,实现了激光修复材料在拉-拉疲劳过程中的全场变形在线测量,得到了不同疲劳周次下的试件基体、修复边界和修复区的位移场与应变场;根据测量得到的应变场提出了疲劳中以试件历经不同循环周次后的残余应变为损伤参量的表征方法,并获得了修复镍基合金试件疲劳过程中残余应变场的演化规律。试验结果表明,在疲劳过程中,试件残余应变场内存在应变集中现象,应变集中幅值随疲劳周次的提高而增加,试件残余应变集中区域内的应变集中值远高于非应变集中区域,因此根据该结果可有效地预测疲劳裂纹萌生的时机与位置。

Fatigue tests on nickel supper alloy repaired by laser is of great significance to study the fatigue behavior and conduct failure analysis for the repaired materials. During the fatigue process, local damage of material may lead to the reduction of mechanical properties of materials. In order to meet the needs of fatigue failure analysis of laser repairing materials, how to establish the relationship between the measured deformation field and damage parameter has drawn great attention in the field of experimental mechanics. Aiming at this issue, a fatigue testing system based on single camera 3D digital image correlation is established, and an integrated tensile specimen including nickel supper alloy, repaired material and interface is designed and manufactured to measure the full-field deformation of the three regions simultaneously. By using the developed measurement system, the in-situ full-field deformation of the specimen during a tension-tension fatigue process is measured. The displacement field and strain field at different fatigue cycles are characterized. A fatigue damage analysis method with the residual strain of specimens after different cycles as the damage parameter is proposed. The evolution rules of residual strain field during fatigue of laser repair nickel-based alloy are analyzed. From these results, we find that there is a strain concentration zone during the fatigue process, and the strain concentration amplitude increases with the number of cycles, which is far more than that in the non-strain concentration area. The proposed method can offer an effective prediction for fatigue time and location of crack initiation.