锆-4合金低周疲劳断口裂纹扩展能量及分形特征研究

Study on Patulous Energy and Fractal Properties of Crack for Zircaloy-4

摘要:

对锆-4合金低周疲劳裂纹扩展过程进行了探索性的研究。通过分析锆-4合金低周疲劳断口在裂纹扩展方向上能量及分形维数变化趋势，发现锆-4合金动态裂纹扩展中扩展期由3个阶段组成，每一阶段的能量和分形维数都不同。A-B段的能量最小，归一化值为0-0．0156，A-B段的分形维数居中，在工工方向均值为2．2796，标准差为0．0277，在LH方向均值为2．4516，标准差为0．0592。D-E段能量远大于A-B段，归一化值为0．8754～0．9652，但分形维数最小，LL方向均值为2．2214，标准差为0．0131，LH方向均值为2．3477，标准差为0．0550。F-H（或G-H）段能量最大，归一化值达到1，同时分形维数也达到最大，LL方向均值为2．3414，标准差为0．0704，LH方向均值为2．5398，标准差为0．0263。虽后，根据二次电子成像原理以及锆-4合金低周疲劳断口的形貌特征对此现象进行了初步分析。

Abstract:

In this paper,the low-cycle fatigue fracture crack growth is investigated gropingly for Zr-4 alloy(Zircaloy-4).By analyzing the trend of patulous energy and fractal dimension in the crack growth direction,three stages(A-B,D-E,and F-H) of different energies and fractal dimensions are discovered in the growth period of dynamic crack.The normalized energies are 0~0.0156,0.8754~0.9652,and 1 for the A-B,D-E,and F-H stages,respectively.But for the fractal dimension,it is in the middle for the A-B stage,its mean value and standard deviation in LL and LH directions are 2.2796,0.0277 and 2.4516,0.0592,respectively;and it is minimal for the D-E stage,its mean value and standard deviation in LL and LH directions are 2.2214,0.0131 and 2.3477,0.0550,respectively;it is maximal for the F-H stage with the mean value and standard deviation in LL and LH directions of 2.3414,0.0704 and 2.5398,0.0263,respectively.Finally,the phenomena were studied on the morphology of low-cycle fatigue fracture by SEM for Zircaloy-4.