May 29-June 3, 2016
Load history has been known to affect fracture and stress corrosion behavior. The degree to which it affects depends on the severity of the load history. It is known that shop peening can retard the SCC lives markedly in steels. Similarly, prestraining can reduce the KIscc and plateau velocity in high strength steels.
These types of experiments are difficult to quantify their effects on the SCC behavior. One can analyze the prestarining effects in a better way by analyzing the effects of single overloads followed by constant applied load to study the behavior. Such experiments can be done by observing the ‘incubation time’ for a crack to initiate in a fatigue precracked sample, at various constant applied loads in a chemical environment. Such experiments have been conducted on 7075 aluminum alloy and a 4130 steel. It is observed that results are similar in behavior. The data indicates the overall behavior can be analysed by suggesting that the total stress at the crack tip is related to the contributions from chemistry of the environment and an additional factor from “internal stress” Hence we can describe the overall data in terms of:
KIscc = Kapplied + Kinternal stress + Kenvironment
Such trends in the behavior, has been observed in prestrained steel alloys prior to environmental exposure. The general behavior suggests that the internal stress affects the threshold KIscc more than the plateau velocity. The general SCC behavior is affected by both chemistry and internal stress under external static or cyclic loads.
K. Sadanand and Asuri K. Vasudevan, "Mechanical & chemical driving force affecting crack nucleation" in "International Workshop on the Environmental Damage in Structural Materials Under Static Load/Cyclic Loads at Ambient Temperatures", A.K. Vasudevan, Office of Naval Research (retired), USA Ronald Latanision, Exponent, Inc., USA Henry Holroyd, Luxfer, Inc. (retired) Neville Moody, Sandia National Laboratories, USA Eds, ECI Symposium Series, (2016). http://dc.engconfintl.org/edsm/15