An alternating current potential difference calibration study and fatigue crack growth in steel

Grabowski, Leon (1983). An alternating current potential difference calibration study and fatigue crack growth in steel. University of Birmingham. Ph.D.

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Alternating current potential difference calibration data has been generated for the 'growth' of reference flaws and fatigue cracks upto depths of 24.58 mm in EN3B steel. The response between alternating current potential difference and flaw/crack depth was found to satisfy a degree 2 polynomial relationship which could be approximated to degree 1 over small changes in flaw/crack depth. Traditional methods of rationalising the data failed, and so an empirical normalising technique was developed which normalised all calibration data irrespective of calibration regime. Fatigue studies of EN19 steel conducted at R = 0.1 in the a/w regime 0.09 to 0.39 revealed that thresholds were independent of crack length. Near threshold crack growth exhibited threshold hysteresis, which was attributed to oxide induced crack closure. Measurement of crack closure during threshold testing at R = 0.1 and 0.7 revealed that near threshold crack growth was closure dominated, and the R effect could be rationalised by adopting a ΔK\(_{eff}\) approach.
Fatigue threshold behaviour of EN3B steel of ferrite grain size 10 and 53 μm exhibited similar trends to EN19. At R = 0.1 thresholds were greater and exhibited a grain size effect. Tentative arguments describing this trend are forwarded based on crack closure arising from microstructural crack growth and fretting fatigue.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
Licence: All rights reserved
School or Department: Department of Metallurgy and Materials
Funders: Other
Other Funders: Science Research Council, GKN Group Technology Centre
Subjects: T Technology > TN Mining engineering. Metallurgy


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