Lifetime Enhancement of Propulsion Shafts Against Corrosion Fatigue by Laser Peening
Author: Lloyd A. Hackel, Jon E. Rankin | Curtiss-Wright Surface Technologies
Source: The Shot Peener magazine, Vol 33, Issue 2, Spring 2019
Doc ID: 2019023
Year of Publication: 2019
Abstract:
This paper reports substantially enhanced
fatigue and corrosion-fatigue lifetimes of propulsion shaft
materials, 23284A steel and 23284A steel with In625 weld
overlay cladding, as a result of shot or laser peening. Glass
reinforced plastic (GRP) coatings and Inconel claddings are
used to protect shafts against general corrosion and corrosion
pitting. However salt water leakage penetrating under a
GRP can actually enhance pitting leading to crack initiation
and growth. Fatigue coupons, untreated and with shot or
laser peening were tested, including with simultaneous salt
water immersion. Controlled corrosion of the surfaces was
simulated with electric discharge machining (EDM) of deep
pits enabling evaluation of fatigue and corrosion-fatigue
lifetimes.
Results specifically show high energy laser peening
(HELP) to be a superior solution, improving corrosionfatigue
resistance of shaft and cladding metal, reducing the
potential for corrosion pits to initiate fatigue cracks and
dramatically slowing crack growth rates. At a heavy loading
of 110% of yield stress and with 0.020 inch deep pits, laser
peening increased fatigue life of the steel by 1370% and by
350% in the corrosion-fatigue testing.
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