Understanding Fatigue Crack Growth Behavior at Low Frequencies for a Mn–Ni–Cr Steel in 3.5 % NaCl Solution Under Controlled Cathodic Potential
28 Feb 2015-Materials Performance and Characterization (ASTM International)-Vol. 4, Iss: 2, pp 157-167
TL;DR: In this paper, a frequency shedding method is used to estimate fatigue crack growth rate over a range of frequencies between 0.01 and 5.1 Hz at a constant stress intensity factor range of 15MPa √m.
Abstract: Fatigue crack growth behavior at low loading frequencies for a Mn–Ni–Cr steel immersed in 3.5 % NaCl solution, with and without cathodic polarization, is investigated and presented in this paper. Frequency shedding method is used to estimate fatigue crack growth rate over a range of frequencies between 0.01 and 5 Hz at a constant stress intensity factor range of 15 MPa √m. The effectiveness of cathodic potential of −900 mV SCE in containing corrosion contribution to crack growth is estimated by comparing with published data on fatigue crack growth rate in lab air and 3.5 % NaCl solution without cathodic polarization. It is noted that there are three regions of crack growth rate as a function of applied frequencies when the data is plotted in log–log scale: linear crack growth rate, plateau crack growth rate, and high crack growth rate. The crack growth rate of steel in 3.5 % NaCl solution at 15 MPa √m is scanned for different cathodic potentials between −760 mV SCE and 1150 mV SCE at 0.01 and 0.1 Hz. The potentials at which the crack growth rates are the maximum and the minimum are found to be −760 and −950 mV, respectively. The optimum cathodic protection potential for the minimum corrosion fatigue crack growth rate ranges between −900 and −950 mV. This optimum potential for the minimum corrosion crack growth rate is more negative than the cathodic potential required for restraining the corrosion effects on fatigue strength of steel to normal ambient air behavior.
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01 Jan 2019
TL;DR: The developments to estimate the fatigue properties of materials using small volume of sample material—similar to scooped samples are presented and the optimum electrode potential for a fatigue crack growth study has been identified.
Abstract: Accurate and reliable life prediction is one of the challenges faced by engineers working in safety-critical domains such as power plants, transportation, and offshore structures. This paper presents the developments to estimate the fatigue properties of materials using small volume of sample material—similar to scooped samples. Cyclic ball indentation and cyclic small punch testing methods have been developed over a period of nearly two decades and have been demonstrated to predict the fatigue properties of in-service materials. Some salient results are discussed in this paper. In the case of offshore structures, the synergistic effect of mechanical loading at a low frequency combined with the corrosive environment accelerates the damage. Life prediction for such structures requires data on corrosion-fatigue crack growth at low frequencies. This is a time-consuming effort and hence there is a need to estimate the properties through novel test methods. Frequency shedding method is proposed to estimate the fatigue crack growth rate behavior in corrosive environments. Further, designers and operators of offshore equipment resort to avoidance of free corrosion through the use of electrode potentials. However, the choice of electrode potential is dependent on the stress state. Through a systematic study, the optimum electrode potential for a fatigue crack growth study has been identified and the same is discussed here. It is hoped that the results of this study and the directions shown to carry out the data generation under more realistic conditions would help the life prediction and life extension community at large.
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TL;DR: In this article, a mathematical model was developed to describe the mass transport and electrochemical conditions in a corrosion fatigue crack in steel in 3.5% NaCl and in sea water for both freely corroding and anodic polarization conditions.
56 citations
TL;DR: The results of recent experiments on measuring corrosion fatigue crack propagation rates in structural steel immersed in seawater with and without cathodic polarisation are reported in this article, where measurements of electrochemical potentials near the growing crack tip are used to learn more about the mechanisms and rate-determining processes influencing the rate of crack growth.
50 citations
TL;DR: In this paper, the authors measured fatigue crack growth rates over wide ranges of stress intensities (from threshold to nearly critical stress intensity) on HY130 steel in 3.5% sodium chloride aqueous solution at several cyclic frequencies, stress ratios, and potentials.
Abstract: Fatigue crack growth rates over wide ranges of stress intensities (from threshold to nearly critical stress intensity) were measured on HY130 steel in 3.5% sodium chloride aqueous solution at several cyclic frequencies, stress ratios, and potentials. The growth rates are compared with reference data measured in laboratory air. The growth rate curves for both environments can be approximated by two linear sections converging at low stress intensity ranges to the same threshold, which depends only on the stress ratio. The upper parts of the lines with lower slopes converge again to the point where maximum stress intensity approaches its terminal value. As a result, the maximum environmental acceleration of crack growth appears at intermediate stress intensities, and it increases with decreasing frequency and potential. Data indicate a relatively low susceptibility of HY130 steel to corrosion fatigue. With increasing stress ratio R the fatigue crack growth threshold is shifted to lower stress intensity ranges by the same amount in both air and salt water environments. The effect of R on growth rate can be introduced into a power law expression.
49 citations
01 Nov 1972-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, fatigue tests were carried out on 4140 steel heat treated to various hardness levels and environmental effects were reported in dry and moist air, aerated and deaerated 3 pet NaCl solution, and under conditions of cathodic protection and of passivity.
Abstract: Fatigue tests were carried out on 4140 steel heat treated to various hardness levels. Environmental effects are reported in dry and moist air, aerated and deaerated 3 pet NaCl solution, and under conditions of cathodic protection and of passivity. Critical corrosion rates were measured below which the environment does not affect fatigue life. The results are interpreted in terms of environmentally-induced plastic deformation.
44 citations
TL;DR: In this paper, a new model based on synergistic interactions between the environment and deformation during loading was proposed to predict the effects of cycle frequency on crack growth rates of a cathodically protected, high-strength low-alloy steel weld metal.
27 citations