Fatigue crack propagation through weld heat affected zones |
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Authors: | K R Dowse C E Richards |
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Affiliation: | (1) Scientific Services Department, Portishead, Central Electricity Generating Board, South Western Region, Bristol, Somerset;(2) Materials Division, Central Electricity Research Laboratories, USA |
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Abstract: | Fatigue tests were performed on specimens containing weld heat affected zones at two orientations to the stress axis. Two
heat affected zones were studied, one in Ducol W30 (a low alloy steel) and the other in mild steel. Under conditions of constant
alternating and maximum stress intensity a fatigue crack only propagated at a uniform rate when it was remote from the heat
affected zone. A heat affected zone which was harder than either the parent plate or weld metal was found to reduce crack
propagation rates by a factor of up to 2 by restricting the plastic zone size around the crack tip. The changes in crack propagation
rate could not be related uniquely to the conditions of the material immediately adjacent to the crack tip. Furthermore, the
shape of the plastic zone was found to influence the direction of the propagation of a fatigue crack which always deviated
toward regions of lower flow stress. A crack was never found to follow the interface between the weld metal and the parent
metal heat affected zone because the flow stresses were not the same on either side of the interface. There was no difference
in crack propagation mechanism between the parent plate and its heat affected zone for the stress conditions imposed.
Formerly with Central Electricity Research Laboratories, Materials Division, Leatherhead, Surrey, England |
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