基于应变相对变化量的机体疲劳裂纹识别方法

Fatigue crack identification method based on relative change of strain in engine block

针对发动机机体疲劳试验中微裂纹诊断困难的现象,提出一种基于应变相对变化量的裂纹识别方法.建立机体的仿真模型,对可能出现裂纹的部位进行假象裂纹设制,并计算出现裂纹前后的应变值,得出结构出现裂纹前后应变的相对变化量,通过对应变相对变化量差分,求得差分曲线的有效零值点及有效极值点,由有效极值点与有效零值点确定位置指标,最终对裂纹部位进行定位.仿真计算结果表明:该方法对裂纹诊断具有敏感性,对裂纹的识别精度高,能够对给定应变测点连线上何处出现裂纹进行识别,定位最大误差为2.25%.

Crack identification is very difficultin the fatigue testof engine block, and a method for crack identification was put forward based on the differential of relative strain variation. Corresponding simula- tion model of block was established to simulate block fatigue test according to the block structure, loading mode and material, and three cracks were pre-produced on the simulation model, where cracks were possible to occur, meanwhile the corresponding strain were calculated from both undamaged and damaged block. The relative change of the strain and the differential curve can be obtained easily, so valid zero and extreme points of differential curve were easily found. According to zero and extreme points, the crack position can be indentified accurately, and the maximum error was only 2.25%. The simulation results indicates that the method is sensitive to crack and have a great significance to damage identification for block fatigue test.