A dissertation submitted to the Faculty of Engineering, University of
the Witwatersrand, Johannesburg, in fulfilment of the requirements for
the degree of Master of Science in Engineering.
Johannesburg 1988 / Fatigue crack closure characteristics were studied in a 70i7 aluminium
alloy in the as received (AR) and heat treated (HT) conditions with
the view of establishing the general closure trends and how well the
modified closure parameter AKeff (- K^ax ' K0_) was capable of
characterising fatigue crack growth. The results of this work
indicated that a significant amount of strain intensification occurred
below K0p which implied that AKe££ generally underestimated the
stress intensity range experienced at the crack tip during cyclic
loading.
The major objective of this dissertation was to determin' whether a
relationship exists between the distance over which closure develops
from zero to a steady state jlcsure value, and the distance over which
short crack growth behaviour occurs.
Two techniques were used to eliminate closure for a fatigue crack in a
compact temion specimen. Closure development was then measured as a
function crack length and a steady state closure value was
approached tier about 0.19 mm in the AR material and 0.?8 mm in the
HT material irrespective of AK. This distance compared well with that
distance over which short cracks exhibited "anomalous" behaviour.
This implies that anomalous short ctack behaviour is dependent on the
distance over which closure develops in this alloy, although
microstructural influences may play a rola.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/16793 |
| Date | 27 January 2015 |
| Creators | Garz, Reiner Ernst |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf, application/pdf, application/pdf, application/pdf |
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