PSI - Issue 13

Atsuhisa Kitade et al. / Procedia Structural Integrity 13 (2018) 1845–1854 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

1850

6

n



n  =

i j

j

1 ,

(2)

=

KAM

The results are shown in Fig.9. In each map, the trigger point part is indicated by a black arrow. The IQ map shows the sharpness of the orientation, and the portion where the direction cannot be read clearly is displayed in black. The MA, which is the brittle fracture trigger point, cannot clearly read the orientation because of its high carbon concentration and high dislocation density Therefore, the position of MA of the fracture trigger point could be identified accurately. The GROD map represents a bearing difference from a certain reference orientation within one crystal grain. As a result, the amount of local plastic strain can be measured. High GROD parts with markedly different orientations within crystal grains are displayed in red. Looking at Fig.9(c), it is possible to observe a red portion where plastic strain accumulates in the left part of MA. Within large crystal grains, the effect of pile-up of dislocation is large, indicating that the strain is greatly accumulated near MA. On the other hand, the KAM map shows the bearing difference from the neighboring part, and according to this, the left part of the MA is not displayed in red. In other words, it is suggested that the strain does not accumulate abruptly near MA, but gradually accumulates from the corner of the crystal grain.

(a)GROD (b)KAM Fig.8 Definition of Grain Reference Orientation Deviation (GROD) and Kernel Average Misorientation (KAM)

(a) Inverse pole figure map

(b) Image Quality map

(c) GROD map

(d) KAM map

Fig.9 Orientation maps in various methods by EBSD data around trigger point