| ABSTRACT: | EXPERIMENTAL STUDY OF LIMITATIONS ASSOCIATED WITH THE DETECTION AND
SIZING OF FATIGUE CRACKING IN MEDIUM TO LOW INTEGRITY WELDS.
T Armit 1, and S Arnold 2
1Lavender International NDT Ltd., UK.; 2 Health and Safety Executive, UK.
Accurate prediction of equipment subject to intense cyclic loading is essential for public safety.
Unfortunately this prediction is not always as anticipated subsequently leading to failures that can cause
serious injury or even fatalities. Bearing this in mind a series of experiments were instigated to investigate
the limitations associated with detection and sizing of fatigue cracks.
This paper discusses findings from the experimental work which was conducted on welds typical of those
encountered in structural steelwork including those used in amusement park rides. Welded plates used for
these experiments were all subjected to crack propagation in a cyclic stress machine generating accelerated
fatigue. This mechanism was chosen to replicate accurately the crack morphology found in naturally
occurring fatigue. Nondestructive techniques applied for crack detection include radiography, manual
ultrasonics, time of flight diffraction, ultrasonic phased arrays and eddy current testing. Techniques used to
assess the through wall extent of the cracks were as previously mentioned with the exclusion of radiography.
Material thicknesses used for this work ranged from 6mm through to 25mm including many transitional
joints some of which include backing bars. Results obtained from each technique are compared for detection
capability and precision of sizing and conclusions are drawn as their appropriate limitations.
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