锆-4合金低周疲劳断口的小波分形特征研究

Study on Wavelet Fractal Properties for Alloy Zr-4

断口表面的分形维数是断裂表面粗糙度的一种度量,它和材料的韧性相关。应用小波分解技术,用“双毯法”提取了锆-4合金低周疲劳断口在低频、水平高频、垂直高频、对角高频方向上的分形维数。结果表明锆-4合金低周疲劳断口具有分形特征;分形维数与疲劳寿命有关,疲劳寿命越高,分形维数越大;随着分解级数的增加,不同寿命的断口分维值之间差距加大,小波分解的级数越多,越能获得有效的特征量;同一断口,放大倍数不同,分形维数差异较大。低倍下(≤4000XD),随分解级数增加,对角方向上高频信号变化更复杂,分维值上升较快;高倍下(≥8000XD),断口的复杂性降低。

Fractal dimension of fractured surfaces is used in measuring surface roughness of fractured surfaces, which is relevant to the material toughness. This paper, based on wavelet decomposition technology, extracts fractal dimension of the alloy Zr-4 low-cycle fatigue fracture （Zircaloy-4） in the low frequency, horizontal high frequency, vertical high frequency and the diagonal high frequency directions by means of covering blankets. It is showed that Zircaloy-4 has fractal properties and the fractal dimension has good relations to fracture fatigue life. The higher the fatigue life is, the larger the fractal dimension is. With increase of decomposition series, if fatigue life is dissimilar, the difference of fractal dimension is enlarged. The more the wavelet decomposition series are, the more the effective characteristic can be received. Moreover, difference of fractal dimension is much large for dissimilar magnified multiple in the same fracture. With increasing of decomposition series, we can see that in the low multiple （≤4000XD） there is the more complex transformation for the high frequency signal of the diagonal and the more rapid rise of fractal dimension. On the contrary, fractal complexity is reduced in the high multiple （≥ 8000XD）.