Abstract
This paper reports on a study of the effects of dynamic and static loading on eddy current (EC) crack signals in aerospace materials. In situ EC measurements were performed on a series of fatigue crack samples grown in Al 6061 bars under dynamic loading. The EC signals detected at a fixed location on the fatigue cracks were found to vary periodically with cyclic loading. Under dynamic tension, the amplitude of the vertical component of the crack signal, which is perpendicular to the lift off direction, increases with the load amplitude and the effect is stronger for longer cracks. Such changes in EC signals are attributable to crack morphology changes (i.e. crack opening) under tension. In contrast, the amplitude of crack signal remains relatively unchanged under compression, possibly due to the insulation effect of the oxidation layer on the crack face. The loading effects on crack signals in the Al samples were confirmed by obtaining c‐scan images of the fatigue cracks under static loads. C‐scans conducted on a series of Ti 64 fatigue crack samples under static loads revealed significantly stronger stress‐induced changes of crack signal for Ti 64 than for the Al samples. The results are interpreted in terms of load‐induced crack morphology changes, taking into account of likely differences between the Al and Ti alloy samples.
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