金属断裂表面的分形(Fractal)与断裂韧性

本文借助于图象分析技术使用Slit island方法研究了两种高强度钢不同热处理制度和不同试验温度条件下平面应变断裂表面的分形维数.结果表明,断裂表面是一种分形结构,断裂韧性K_(IC)值的对数随分形维数D_F增加成单调下降的直线关系.这种关系反映了不同热处理制度所引起的材料微观结构变化和不同试验温度所引起的断裂机制变化,D_F可以做为金属断裂韧性的一种度量。最后,用临界裂纹扩展力与不规则断裂表面真实面积之间的关系对结果进行了理论分析.

FRACTAL DIMENSION OF FRACTURED SURFACE AND FRACTURE TOUGHNESS IN METALS

The slit island method is employed to measure fractal dimensions D_F of fracturedsurfaces under plane strain conditions with the help of an image analysis technique for twohigh strength steels under different heat treatment conditions and at different test temperatures.It is shown that the fractured surfaces are of fractals. The values of D_F decrease smoothlywith an increase of the logarithm values of fracture toughness K_(IC), i. e. the fractal dimensionsD_F are approximately a linear function of the logarithm values of fracture toughness K_(IC). Thisrelationship might reflect the changes in the microstructure that occured during different heattreatments and the changes in the fracture mechanism that occured at different test temperatures.The fractal dimension D_F could be regarded as a measure of fracture toughness in metels. Fi-nally, the experimental results are explained in terms of the relation between critical crack exten-sion force and the true total area of the irregular fracture surfaces.