Scatter of measured K_(IC) related to the scatters of local parameters X_f, σ_f and ε_(pc)

摘要

42 values of K_(IC) measured at -100°C are related to the measured values of local fracture stress σ_f and the fracture distance X_f by the formula: K_(IC)= β~(-(N+1)/2)(X_f)~(1/2)[(σ_f)~((1+N)/2N)/(σ_y)~((1-N)/2N)]. The scatters of K_(IC) caused by σ_f or X_f are assessed separately at constant values of X_f or σ_f. It is found that at a constant X_f the scatter of K_(IC) induced by the scatter of σ_f accounts for only 20% of the total scatter, while at a nearly constant σ_f the scatter of K_(IC) caused by the scatter of X_f can reach almost 100% of the total scatter of K_(IC). It means that the effect of the scatter of X_f on the scatter of K_(IC) is much larger than that of σ_f. This idea is opposite to the assumption widely accepted in local approach that the distribution of various sizes of the carbide particles which present various values of σ_f is the main event in the statistical calculation. Instead, the random distribution of (X_f) of weakest particles with the lowest values of σ_f should be considered as the determining factor in statistical assessment for the cleavage fracture.