Hans-Martin Thomas

FLUX LEAKAGE MEASUREMENTS FOR DEFECT CHARACTERIZATION USING A HIGH PRECISION 3‐AXIAL GMR MAGNETIC SENSOR

High‐precision magnetic field sensors are of increasing interest in non destructive testing (NDT). In particular GMR‐sensors (giant magneto resistance) are qualified because of their high sensitivity, high signal‐to‐noise ratio and high spatial resolution. With a GMR‐gradiometer and a 3D‐GMR‐magnetometer we performed magnetic flux leakage measurements of artificial cracks and cracks of a depth of ≤50 μm still could be dissolved with a sufficient high signal‐to‐noise ratio. A semi‐analytic magnetic dipole model that allows realistic GMR sensor characteristics to be incorporated is used for swiftly predicting magnetic stray fields. The reliable reconstruction based on measurements of artificial rectangular‐shaped defects is demonstrated.

Sensitivity of penetrant and magnetic particle testing

Abstract The sensitivity of penetrant and magnetic particle testing (PT and MT) depends, among other things, on the quality and performance of the “detection media” (for PT designated as “product family”). The determination of the sensitivity is carried out on “reference pieces” with natural or artificial gap-like flaws by determining the visibility of the indications as a measure of the performance. European standardisation specifies the requirements of detection media, in accordance with prEN ISO 3452-2 for PT and EN ISO 9934-2 for MT for type and batch as well as for process control testing. This paper describes the evaluation and qualification of performance during the type testing procedure. The proposed methods are validated by experimental investigations using an image processing system for the determination of the visibility. The reliability of the proposed methods is discussed with reference to the qualification of the detection media.

MAGNETIC RESPONSE FIELD OF SPHERICAL DEFECTS WITHIN CONDUCTIVE COMPONENTS

The determination of magnetic distortion fields caused by inclusions hidden in a conductive matrix using homogeneous current flow needs to be addressed in multiple tasks of electromagnetic non‐destructive testing and materials science. This includes a series of testing problems such as the detection of tantalum inclusions hidden in niobium plates, metal inclusion in a nonmetallic base material or porosity in aluminum laser welds. Unfortunately, straightforward tools for an estimation of the defect response fields above the sample using pertinent detection concepts are still missing. In this study the Finite Element Method (FEM) was used for modeling spherically shaped defects and an analytical expression developed for the strength of the response field including the conductivity of the defect and matrix, the sensor‐to‐inclusion separation and the defect size. Finally, the results also can be useful for Eddy Current Testing problems, by taking the skin effect into consideration.

A numerical study of the inclusion problem in electromagnetic testing

Abstract The determination of magnetic distortion fields caused by inclusions hidden in a conductive matrix using homogeneous current flow needs to be addressed in multiple tasks of electromagnetic non-destructive testing and materials science. This includes a series of testing problems such as the detection of tantalum inclusions hidden in niobium plates, metal inclusion in a nonmetallic base material or porosity in aluminum laser welds. Unfortunately, easy tools for an estimation of the defect response fields above the sample using pertinent detection concepts are still missing. In this study the Finite Element Method (FEM) was used for modeling spherically shaped defects, and an analytical expression was developed for the strength of the response field including the conductivity of the defect and matrix, the sensor-to-inclusion separation, and the defect size. Finally, the results were adapted to Eddy Current Testing problems, in which the skin effect was taken into consideration for an appropriate estimation of the signal strength.