Jim Fulton

Study of the new eddy current non-destructive testing sensor on ferromagnetic materials

A new eddy current non-destructive testing (NDT) sensor developed at NASA Langley Research Center can accurately detect fatigue cracks and measure material and non-conducting coating thicknesses. This paper presents experimental and finite element modeling data on the characteristics of the sensor on ferromagnetic materials. Fatigue crack detection and lift-off characteristics in steel and aluminum are compared and discussed. >

Magneto-Optic Image Classification Using Neural Networks

The aging aircraft program sponsored by the FAA is keen on improving existing technologies and developing new techniques for the detection of cracks and corrosion in aircraft structures. This program is a part of the overall scheme of addressing the global aging infrastructure problem. The authors have been involved in the aging aircraft program through the NASA Langley Research Center (LaRC).

AC magnetic field frequency dependence of magnetoacoustic emission

It has previously been proved that there is a strong correlation between the low-frequency AC applied magnetic field amplitude dependence of the asymmetry of the magnetoacoustic emission (MAE) burst and the strength of the domain-wall-defect interaction in iron-base ferromagnets. The AC magnetic field frequency dependence of the asymmetry is investigated in the range of 1 to 200 Hz. When represented by the third moment of the rectified acoustic emission pulses, the asymmetry becomes a bell-shaped function of frequency with its center located around 25 Hz. The experiment is performed with low-carbon, high-yield stress steel specimens of three different levels of domain-wall-defect interaction strength. The results show that the increase in the interaction strength causes a vertical down shift of the asymmetry in the entire frequency range investigated.<<ETX>>

Multi-mode excitation and data reduction for fatigue crack characterization in conducting plates

Advances in the technique of fatigue crack characterization by resonant modal analysis are achieved through a new excitation mechanism and data reduction of multiple resonance modes. A non-contacting electromagnetic device is used to apply a time-varying Lorentz force to thin conducting sheets. The frequency and direction of the Lorentz force are such that resonance modes are generated in the test sample. By comparing the change in frequency between distinct resonant modes of a sample, detecting and sizing of fatigue cracks are achieved and frequency shifts caused by boundary condition changes can be discriminated against. Finite element modeling is performed to verify experimental results.<<ETX>>

Application of Self Nulling Eddy Current Probe Technique to the Detection of Fatigue Crack Initiation and Control of Test Procedures

A major part of fracture mechanics is concerned with studying the initiation and propagation of fatigue cracks. This typically requires constant monitoring of crack growth during fatigue cycles and the knowledge of the precise location of the crack tip at any given time. One technique currently available for measuring fatigue crack length is the Potential Drop method [1]. The method, however, may be inaccurate if the direction of crack growth deviates considerably from what was assumed initially or the curvature of the crack becomes significant. Another popular approach is to optically view the crack using a high magnification microscope, but this entails a person constantly monitoring it. The present proposed technique uses an automated scheme, in order to eliminate the need for a person to constantly monitor the experiment. Another technique under development elsewhere is to digitize an optical image of the test specimen surface and then apply a pattern recognition algorithm to locate the crack tip.