Non-destructive inspection method

• US 20050122099A1
• Filed: 09/24/2002
• Published: 06/09/2005
• Est. Priority Date: 09/25/2001
• Status: Active Grant

• Current Assignee: Nippon Kouatsu Electric (HK) Co. Ltd., Daihatsu Motor Company Limited (Toyota Motor Corporation)
• Original Assignee: Magnegraph Co., Ltd., Daihatsu Motor Company Limited (Toyota Motor Corporation)
• Inventors: Kimura, Takashi, Imamoto, Kazunobu
• Granted Patent: US 7,109,702 B2
• Time in Patent Office: Days
• US Class Current: 324/239
• CPC Class Codes: G01N 27/82 for investigating the presence of flaws
• CPC Class Codes: G01N 27/9046 by analysing electrical signals

Abstract

A non-destructive inspection includes: magnetizing a target by a first magnetostatic field (S2); shutting off the magnetostatic field (S3); measuring, at measurement points, the transient change of a differential magnetic flux density of a first residual magnetic field of the target (S4); obtaining a first time constant by the main time constant of the transient change at each measurement point (S5); magnetizing the target by a second magnetostatic field (S2); shutting off the second field (S3); measuring, at the measurement points, the transient change of a differential magnetic flux density of a second residual magnetic field of the target (S4); obtaining a second time constant by the main time constant of the transient change for each measurement point (S5); and obtaining information about the internal structure of the target by the distribution differences between the first and the second time constants at the measurement points (S7).

Claims

1. A non-destructive inspection method including:

a step of magnetizing an inspection target by applying a first magnetostatic field to the target;

a step of shutting off the first magnetostatic field and measuring transient change in a differential magnetic flux density of a first residual magnetic field passing through the magnetized target, the measuring being performed at a plurality of measurement positions;

a step of obtaining a first time constant provided by a main time constant of the transient change for each of the measurement positions;

a step of magnetizing the target by applying a second magnetostatic field to the target;

a step of shutting off the second magnetostatic field and measuring transient change in a differential magnetic flux density of a second residual magnetic field passing through the magnetized target, the measuring being performed at each of the measurement positions;

a step of obtaining a second time constant provided by a main time constant of the transient change for each of the measurement positions; and

an information obtaining step of obtaining information about an internal structure of the target based on a difference between distribution of the first time constant and distribution of the second time constant at the measurement positions.

2. The method according to claim 1, wherein the measurement positions are in a row facing the target.

3. The method according to claim 1, wherein the information about the internal structure in the information obtaining step is obtained based on a ratio function which is derived from a distribution function of the first time constant with the measurement position as a variable and a distribution function of the second time constant with the measurement position as a variable.

4. The method according to claim 1, wherein the information about the internal structure in the information obtaining step is obtained based on a difference function which is derived from a distribution function of the first time constant with the measurement position as a variable and a distribution function of the second time constant with the measurement position as a variable.

5. The method according to claim 1, wherein the target is a spot weld section in a jointed plate member made by spot welding two sheet metals.

6. The method according to claim 5, wherein the information obtained in the information obtaining step includes information about a shape of nugget section included in the spot weld section.

7. A non-destructive inspection method comprising:

a scanning step including a cycle of magnetizing a target by applying a magnetostatic field to the target, shutting off the magnetostatic field to measure transient change in a differential magnetic flux density of a residual magnetic field which passes through the magnetized target at a plurality of measurement positions, and obtaining a main time constant of the transient change for each of the measurement positions, the cycle being repeatedly performed for each of a plurality of magnetostatic fields of different magnetic flux densities;

an analyzing step of analyzing a change that the main time constant undergoes at each measurement position as the plurality of magnetostatic fields are changed in the scanning step; and

an information obtaining step of obtaining information about an internal structure of the target based on an analysis result obtained by the analyzing step.

8. The method according to claim 7, wherein in the analyzing step, at each of the measurement positions, a magnetic flux density of a critical magnetostatic field is determined, for which field the change of the main time constant during the scanning step with respect to changes in the magnetostatic field achieves a maximum value, and wherein in the information obtaining step, information about the internal structure of the target is obtained based on a distribution function of the critical magnetostatic field with the measurement positions as a variable.

9. The method according to claim 7, wherein the measurement positions are in a row facing the target.

10. The method according to claim 7, wherein the target is a spot weld section in a jointed plate member made by spot welding two sheet metals.

11. The method according to claim 10, wherein the information about the internal structure obtained in the information obtaining step comprises information about a shape of a nugget section included in the spot weld section.