#### Location

La Jolla, CA

#### Start Date

1-1-1991 12:00 AM

#### Description

The alternating current field measurement (acfm) technique of crack detection and measurement in metals is described elsewhere in these proceedings by Lugg [1] and by Dover [2]. In common with many eddy-current crack inspection probes, acfm probes are usually operated at a frequency f such that the electromagnetic skin-depth (1) δ=(μ,μ0σπf)−1/2 is much smaller than the depth of a significant crack. In this formula μr is the relative magnetic permeability of the test piece and σ its electric conductivity. Such thin-skin fields near a surface-breaking fatigue crack, with a uniform incident field, have been calculated by using a modified surface impedance boundary condition which includes a line source of magnetic flux to model the effect of the crack [3], [4].

#### Book Title

Review of Progress in Quantitative Nondestructive Evaluation

#### Volume

10B

#### Chapter

Chapter 7: Characterization of Materials

#### Section

Properties

#### Pages

1663-1677

#### DOI

10.1007/978-1-4615-3742-7_77

#### Copyright Owner

Springer-Verlag US

#### Copyright Date

January 1991

#### Language

en

#### File Format

application/pdf

Measurement of Material Constants for the Surface Impedance Boundary Condition

La Jolla, CA

The alternating current field measurement (acfm) technique of crack detection and measurement in metals is described elsewhere in these proceedings by Lugg [1] and by Dover [2]. In common with many eddy-current crack inspection probes, acfm probes are usually operated at a frequency f such that the electromagnetic skin-depth (1) δ=(μ,μ0σπf)−1/2 is much smaller than the depth of a significant crack. In this formula μr is the relative magnetic permeability of the test piece and σ its electric conductivity. Such thin-skin fields near a surface-breaking fatigue crack, with a uniform incident field, have been calculated by using a modified surface impedance boundary condition which includes a line source of magnetic flux to model the effect of the crack [3], [4].