## 4 Experimental Results
\(\Delta\mathrm{x}_{2,\mathrm{x}}\) is defined as the distance between \(\mathrm{x}_{\mathrm{L}}\{\Delta\mathrm{V}_{2,\mathrm{x}};0\}\), the left peak position, and \(\mathrm{x}_{\mathrm{R}}\{\Delta\mathrm{V}_{2,\mathrm{x}};0\}\), the right peak position close to the x position of the peak, \(\mathrm{x}_{\mathrm{C}}\{\Delta\mathrm{V}_{2,\mathrm{x}};\mathrm{peak}\}\). The relationship between \(\Delta\mathrm{x}_{2,\mathrm{x}}\) and the crack angle is discussed in Figure 20, along with another angle estimation function, \(\Delta\mathrm{V}_{2,\mathrm{x}}\). \[\Delta\mathrm{x}_{2,\mathrm{x}}=|\mathrm{x}_{\mathrm{C}}\{\Delta\mathrm{V}_{2,\mathrm{x}};\mathrm{peak}\}-\mathrm{x}_{\mathrm{L}}\{\Delta\mathrm{V}_{2, \mathrm{x}};0\}|-|\mathrm{x}_{\mathrm{C}}\{\Delta\mathrm{V}_{2,\mathrm{x}}; \mathrm{peak}\}-\mathrm{x}_{\mathrm{R}}\{\Delta\mathrm{V}_{2,\mathrm{x}};0\}| \tag{51}\]  
Figure 17: MFD distribution in the X direction on a line passing through the center of the specimen (y = 5.1 mm): **(a)** raw data; with **(b)** background data subtracted; and **(c)** average value subtracted. \[\Delta\overset{\rightarrow}{\mathrm{V}}_{1}(\mathrm{x},\mathrm{y})=\overset{ \rightarrow}{\mathrm{V}}_{\mathrm{raw}}(\mathrm{x},\mathrm{y})-\overset{ \rightarrow}{\mathrm{V}}_{\mathrm{back}}(\mathrm{x},\mathrm{y}) \tag{46}\]0 MFD distribution in the Y direction on a line passing through the center of the specimen (y = 5.1 mm): **(a)** raw data; with **(b)** background data subtracted and **(c)** average value subtracted. Comparing \(\mathrm{V_{raw,y}(x,5.1)}\) in Figure 18a and \(\Delta\mathrm{V_{1,y}(x,5.1)}\) in Figure 18b, the background signal of approximately \(-0.5\) V (at approximately \(-0.1\) G) is applied uniformly. An MFD with different signs to the left and right around the crack occurred, and the overall absolute value increased as the crack direction to depth increased. This can be explained by the trend of the y-component of \(\overset{\rightarrow}{B}_{\mathrm{RDM}}(x,z)\) in \[\Delta\overset{\rightarrow}{\mathrm{V}}_{1}(\mathrm{x},\mathrm{y})=\overset{ \rightarrow}{\mathrm{V}}_{\mathrm{raw}}(\mathrm{x},\mathrm{y})-\overset{ \rightarrow}{\mathrm{V}}_{\mathrm{back}}(\mathrm{x},\mathrm{y}) \tag{46}\]1  
Comparing \(\mathrm{V_{raw,Z}(x,5.1)}\) in Figure 19a and \(\Delta\mathrm{V_{1,Z}(x,5.1)}\) in Figure 19b, a background signal of about \(0.05\) V (corresponding to about \(0.01\) G) is applied uniformly. MFDs with different signs are observed on the left and right sides of the cracks. At this time, the left and right signs are opposite to those shown in \[\Delta\overset{\rightarrow}{\mathrm{V}}_{1}(\mathrm{x},\mathrm{y})=\overset{ \rightarrow}{\mathrm{V}}_{\mathrm{raw}}(\mathrm{x},\mathrm{y})-\overset{ \rightarrow}{\mathrm{V}}_{\mathrm{back}}(\mathrm{x},\mathrm{y}) \tag{46}\]2 This is consistent with the theoretical consideration of RDM shown in \[\Delta\overset{\rightarrow}{\mathrm{V}}_{1}(\mathrm{x},\mathrm{y})=\overset{ \rightarrow}{\mathrm{V}}_{\mathrm{raw}}(\mathrm{x},\mathrm{y})-\overset{ \rightarrow}{\mathrm{V}}_{\mathrm{back}}(\mathrm{x},\mathrm{y}) \tag{46}\]3 The overall absolute values of \(\Delta\mathrm{V_{1,Z}(x,5.1)}\) increased as the overall inclination angle increased. This can be explained by the tendency of the z-component of \(\overset{\rightarrow}{B}_{\mathrm{RDM}}(x,z)\), as shown in \[\Delta\overset{\rightarrow}{\mathrm{V}}_{1}(\mathrm{x},\mathrm{y})=\overset{ \rightarrow}{\mathrm{V}}_{\mathrm{raw}}(\mathrm{x},\mathrm{y})-\overset{ \rightarrow}{\mathrm{V}}_{\mathrm{back}}(\mathrm{x},\mathrm{y}) \tag{46}\]4 From the above results, the domain model for evaluating fatigue cracks is validated as a model in which the RDM where the y-component occurs and the VDM where the x- and z-components overlap. In addition, a model in which magnetic domains are not deformed when cracks occur is appropriate because the change in the MFD increases based on the depth direction of fatigue cracks at the same depth. When stress is generated, it can be expressed as Equation (52).