Non-destructive evaluation

Non-destructive evaluation (NDE) is an interdisciplinary field dealing with the quantitative characterization of materials and structures by non-invasive means. Possible applications can be found in flaw detection, monitoring material degradation and on-line quality control. To probe microstructural features and/or characterize subsurface features of the material, several physical phenomena can be employed giving rise to a broad variety of methods based on for instance ultrasonic, radiographic, optic and also electromagnetic phenomena.


In this context, the evaluation of the magnetic hysteretic properties of ferromagnetic materials such as construction steel, shows large potential for NDE: the magnetic hysteretic behaviour as such is strongly influenced by microstructural defects and residual strains and moreover magnetic measurements are straightforward, cheap and don’t require surface preparation of the material.

Applications

Evaluation of low cycle fatigue damage accumulation by the online monitoring of magneto-elastic properties

Magnetic domains reorganize under the influence of the applied cyclic mechanical stress at constant applied magnetic field: this interaction between magnetic and mechanical behaviour is called magneto-elastic coupling and is shown schematically in Fig. 1.

 

 

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Figure 1: Magneto-elastic coupling: schematic overview.

 

The variation, induced by for instance metal fatigue material degradation, of the hysteretic relation between the magnetisation and the applied cyclic stress can be monitored online during the cyclic loading itself. To investigate the evaluation of material degradation of construction steel caused by low cycle fatigue in detail, the experimental set-up shown in Fig. 2 is employed.

 

 

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Figure 2: Picture of the experimental setup consisting of two parts: a magnetic system to apply a magnetic field and to measure the magnetization, and a mechanical apparatus to apply the cyclic uniaxial loading and to measure the stress and strain of the sample under test.

 

During the stress-controlled cyclic mechanical loading test, a constant magnetic field is continuously applied to the sample, and for each stress cycle the stress-induced change in magnetisation M(s) is measured (Fig. 3). When analysing the changes of the relation M(s) during the fatigue test, three stages in the fatigue lifetime can be distinguished (Fig. 4) . The transition to the final fatigue stage, occurring at approximately 90 to 95% of the fatigue lifetime, can be used to estimate the remaining fatigue life of steel components.

 

 

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Figure 3: Variation in magnetisation M as a function of cyclic mechanical stress s, for several stress cycles during the fatigue lifetime (in %, relative to the number of cycles to failure).

 

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Figure 4: Peak-to-peak Variation magnetization M as a function of the fatigue lifetime, for two fatigue tests.
 

 

Relevant publications

L. Vandenbossche, L. Dupré, J. Melkebeek (2005), Monitoring the fatigue state of steel by evaluating the quasi-static and dynamic magnetic behaviour, Journal of Applied Physics, vol. 97 (10), Art. No. 10R307.

L. Vandenbossche, L. Dupré, J. Melkebeek (2006), Evaluating material degradation by the inspection of minor loop magnetic behavior using the moving Preisach formalism, Journal of Applied Physics, vol. 99 (8). Art. No. 08D907.

L. Vandenbossche, M. J. Konstantinovic, A. Almazouzi and L. Dupré (2007), Magnetic evaluation of the hardening and softening of thermally aged iron-copper alloys, Journal of Physics D: Applied Physics, vol. 40, pp. 4114-4119

L. Vandenbossche, M. J. Konstantinovic, L. Dupré (2008), Magnetic hysteresis characterization of the irradiation-induced embrittlement of Fe, Fe-Cu model alloys, and reactor pressure vessel steel, Journal of Magnetism and Magnetic Materials, vol.320 (20), pp. e562-e566.

L. Vandenbossche, L. Dupré (2009), Fatigue damage assessment by the continuous examination of the magnetomechanical and mechanical behavior, Journal of Applied Physics, vol. 105 (7), Art. No. 07E707.

  

External links

EELAB is a member of the Universal Network for Magnetic Non-destructive Evaluation
http://www.ndesrc.eng.iwate-u.ac.jp/UniversalNetwork/

General site about Non-destructive Testing (NDT) with Conference Proceedings, Journal Articles, News, Products and Services
http://www.ndt.net/

Contact

For more information: lode.vandenbossche@ugent.be, luc.dupre@ugent.be