Corrosion Fatigue Crack Growth Rate Research Articles

Corrosion fatigue crack growth behavior of 316NG heat affected zone in simulated pressurized water reactor environment

The corrosion fatigue crack growth (FCG) behavior of the 316NG heat affected zone (HAZ) exposed to simulated pressurized water reactor (PWR) environment has been investigated. The results show that significant residual strains and lattice misorientations exist in the HAZ near the welding root. Z-phase precipitates are present in both the HAZ and annealed 316NG base metal. The FCG rate of the HAZ is much higher than that of the base metal. In PWR water, the corrosion FCG rate of the HAZ is strongly dependent on the cyclic loading frequency, but the effect of dissolved oxygen is negligible.

Effect of loading frequency on corrosion fatigue crack growth rate of 7N01 aluminum alloy

The fatigue damage of engineering structures is mostly caused by cyclic stress and external environmental factors. Therefore, the study of corrosion fatigue crack propagation is of great significance to the safety and durability of structures. The effects of different loading frequencies (10Hz, 1Hz and 0.1Hz) on fatigue crack growth rate of 7N01 aluminum alloy in humid air were studied by using load control method. The results show that the corrosion fatigue crack growth rate is basically the same at 10Hz and 1Hz, When the loading frequency decreases to 0.1Hz, the corrosion fatigue crack growth rate is slightly higher than 10Hz and 1Hz.

Waveform and frequency effects on corrosion-fatigue crack growth behaviour in modern marine steels

The primary focus of this work is to investigate the sensitivity of cyclic waveform, frequency (f), load level and microstructure on the corrosion-fatigue crack growth rate (CFCGR) in modern normalised-rolled (NR) and thermomechanical control process (TMCP) ferrite-pearlite steels in the Paris Region of the da/dN vs. ΔK log-log plot. Constant amplitude sinewave (si) and trapezoid waveform (generally referred to here as hold-time (h-t)) were used under frequencies of 0.2 Hz, 0.3 Hz and 0.5 Hz and stress ratio of 0.1. Comparison is also made between the crack path in the S355 TMCP steel under si and h-t in seawater (SW). The role of microstructure in retarding or accelerating fatigue crack growth in SW is also discussed. Experimental results showed that the CFCGR corresponding to the si is higher than that of the h-t for all the load levels and frequencies examined. It was observed that reduction in the f and fatigue load level increased the CFCGR for the h-t but had little effect on the si. Generally, f in the range 0.2–0.5 Hz had little effect; and for a given f an increase in load led to a reduction in the CFCGR, in the Paris Region (PR) for both si and h-t in SW. Under both si and h-t, the CFCGR in the TMCP steels (e.g. S355G8 + M, S355G10 + M) is lower than that of the normalised steels (e.g. S355J2 + N). Metallurgical analyses on the fractured surface of corrosion-fatigue specimens show that the main active crack tip blunting process is the primary factor controlling the CFCGR of steel at high stress intensity factor range (SIFR) and low f in SW. The results obtained from this study have been discussed in terms of the potential impact on the structural design and integrity of offshore wind turbine foundations.

The Effects of Loading Frequency, Sensitization, and Crack Length on Corrosion Fatigue of AA5456-H116

The effects of fatigue loading frequency (f), sensitization, and crack length on corrosion fatigue crack growth rates (da/dN) were investigated for AA5456-H116 under full immersion in 3.5 wt% NaCl. Results from fracture mechanics-based experiments conducted at a constant stress-intensity range (ΔK) and load ratio (R) suggest that highly sensitized AA5456-H116 microstructures (ASTM G67 nitric acid mass loss tests [NAMLT] value of 24 mg/cm2 and higher) exhibit increased da/dN over microstructures in the as-received condition (NAMLT 5 mg/cm2) and the onset of an inverse f-dependence. For a single, high level of sensitization (70 mg/cm2), da/dN increased 3.5× as f decreased from 10 Hz to 0.03 Hz. At a singular low loading f of 0.03 Hz, high sensitization levels (65 mg/cm2) accelerated da/dN fivefold over da/dN in the as-received condition. The da/dN of microstructures below a critical NAMLT value of 24 mg/cm2 were f-independent. Specifically, in microstructures with a low sensitization level (ASTM G67 NAMLT value less than 24 mg/cm2), there was no increase in da/dN as f decreased from 1 Hz to 0.03 Hz. At any singular f, sensitization up to 24 mg/cm2 did not accelerate da/dN over the rate in an as-received microstructure. Additional testing established that the inverse f-dependence of da/dN observed in highly sensitized microstructures cannot be attributed to crack length effects. Two hypotheses are discussed that may explain the observed inverse relationship between f and da/dN in microstructures at or above the critical NAMLT value of 24 mg/cm2.

Corrosion fatigue crack growth behavior of alloy 52 M in high-temperature water

The corrosion fatigue (CF) crack growth behavior of Alloy 52 M in high temperature water was investigated in various water chemistries with dissolved oxygen (DO), dissolved hydrogen (DH) or Ar. The experimental results indicated that at higher load ratio (R), the CF crack growth rates (CGRs) in oxygenated water was slightly higher than Ar deaerated water, while under lower R, the relationship was reversed. Micro-characterization of the crack paths and fracture surfaces revealed that severe crack branching and localized inter-dendritic cracking occurred in oxygenated water, while relatively straight transgranular cracking developed in hydrogen and Ar deaerated water. Minor environmental enhancement of CGRs for Alloy 52 M weld metal was detected in oxygenated water but no environmental enhancement of CGRs was detected in hydrogen or Ar deaerated water.

The foundations of fracture impedance spectroscopy

The foundations of Fracture Impedance Spectroscopy (FIS) as a theoretical framework for analyzing and predicting fatigue and corrosion fatigue crack growth rate in real structures under complex loading waveforms from laboratory data obtained under simple, “pristine” loading conditions is presented. FIS is based upon an analogy between current flow (crack growth rate) in an electrical circuit in response to an applied, time-dependent voltage (time-dependent stress intensity factor). In this paper, the framework of the theory and its application for two different aerospace alloys are presented.

Prediction of corrosion fatigue crack growth rate in alloys. Part II: effect of electrochemical potential, NaCl concentration, and temperature on crack propagation in AA2024-T351

We report here on the prediction of corrosion fatigue crack growth rate (CFCGR) for Aluminum Alloy 2024-T351 in aqueous environments under cyclical sinusoidal loading. Using the General Corrosion Fatigue Model (GCFM) described in Part I, the CFCGR was calculated as a function of environmental variables, including the electrochemical potential, NaCl concentration, loading frequency, stress intensity factor range, and temperature, in addition to the contribution from mechanical fatigue. Based on the influence of the environment, the changes in the potential drop down the crack enclave and the corrosion current density in a 1:1 electrolyte were also calculated from which the CFCGR was estimated. Corrosion fatigue crack growth in this alloy is readily understood in terms of the competition between environmental factors as described by the differential aeration hypothesis and the hydromechanics (advection) of the system resulting from the cyclical opening and closing of the crack.

The effect of sensitization and fatigue loading frequency on corrosion fatigue of AA5083-H131

Corrosion fatigue crack growth rates (da/dN) of AA5083-H131 when loaded in 3.5 wt% NaCl increase as the level of sensitization increases and exhibit a strong inverse fatigue loading frequency dependence when heavily sensitized. High Mg 5xxx series Al alloys are known to exhibit decreased resistance to intergranular corrosion and intergranular stress corrosion cracking due to the formation of the active Al3Mg2-β phase on grain boundaries when exposed to slightly elevated temperatures for prolonged periods of time, a phenomenon known as sensitization. High resolution fracture mechanics based experiments conducted at constant ΔK and R-ratio under full immersion in 3.5 wt% NaCl show that da/dN in a heavily sensitized microstructure increases by an order of magnitude for each order of magnitude decrease in fatigue loading frequency, while da/dN for the as-received and unsensitized microstructure has little to no frequency dependence. Futhermore, for higher frequency loading at 1 Hz, da/dN for the highly sensitized microstructures is one order of magnitude higher than the as-received microstructure; while for the low frequency loading at 0.01 Hz, da/dN for the highly sensitized microstructure is three orders of magnitude higher than the as-received microstructure. The findings of this study suggest that typical higher frequency laboratory testing studies at 10 Hz may severely underestimate fatigue life under service relevant loading conditions.

Effects of laser shock peening on corrosion fatigue behavior of 2Cr13 stainless steel

Effects of laser shock peening (LSP) with different coverage layers on corrosion fatigue (CF) resistance of 2Cr13 stainless steel were investigated by residual stress measuring, corrosion fatigue testing and fatigue fracture morphology observing. The results show that LSP can induce high compressive residual stress on the surface of 2Cr13 stainless steel, and the value of surface compressive residual stress increases with the increase of LSP coverage layer. The CF life of LSP specimens is much larger than that of as-machined specimens, and it increases with the increase of LSP coverage layers; the CF crack growth rate of LSP specimens decrease compared with that of as-machined specimens, and it decreases with the increase of LSP coverage layers. After the analysis, we can conclude that the fatigue fracture surface of as-machined specimens is flat and contains few secondary cracks. However, for LSP specimens, due to high surface compressive residual stress induced by LSP, the growth of corrosion fatigue crack is effectively restrained, resulting in a river pattern morphology.

Environmentally assisted cracking of forged 316LN stainless steel and its weld in high temperature water

The corrosion fatigue (CF) and stress corrosion cracking (SCC) crack growth rates (CGRs) of type 316LN SS and its welds that are used for pressurized water reactor primary water components were evaluated. Effects on CGRs of loading condition, water chemistry and metallurgical microstructure were studied. Experimental results indicated that stress intensity factor K, loading ratio, and frequency control the CGRs of materials along with corrosion potential, chloride, and pH also significantly influencing the cracking behavior. Similar CGRs under various conditions were observed in the base metal and its weld, with low SCC susceptibility in hydrogenated water, but high SCC susceptibility in oxygenated water. The weld metal showed lower SCC CGRs than base metal in oxygenated high purity water but shifted to higher values after adding ppb levels of chloride because of the presence of δ-ferrite in the weld.

Effects of laser shock peening with different coverage layers on fatigue behaviour and fractural morphology of Fe-Cr alloy in NaCl solution

Effects of massive laser shock peening (LSP) treatment as a function of coverage layer on surface residual stress, microstructure, and corrosion fatigue (CF) resistance of Fe-Cr alloy were studied by X-ray diffraction technique, scanning electron microscope observations, and corrosion fatigue crack growth (CFCG) testing. Special attention was paid to the details of compressive residual stress and fracture morphology, and the influence mechanism of coverage layer on CF behaviour was also determined. Results indicated that LSP generated deeper compressive residual stress and effectively decreased the CFCG rate, and increased coverage layers further improved the corrosion fatigue life of notched specimens.

Response relationship between loading condition and corrosion fatigue behavior of nickel-aluminum bronze alloy and its crack tip damage mechanism

Corrosion fatigue is one of the major forms for nickel‑aluminum bronze alloy used in marine propeller. It is greatly important to understand the corrosion fatigue behavior of nickel‑aluminum bronze alloy in seawater for the purpose of improving the service life of marine equipment. In this study, corrosion fatigue crack growth rate of nickel‑aluminum bronze alloy in 3.5% NaCl solution was tested under various stress intensity factors, stress ratios and loading frequencies to reveal its corrosion fatigue mechanism. The results show that corrosion environment significantly accelerates the crack growth and decreases the corrosion fatigue threshold, which is attributed to the corrosion reactions between the metals of crack tip and corrosive medium. Among the various factors, loading frequency has more predominant influence on the corrosion fatigue crack growth rate of nickel‑aluminum bronze alloy, which can be rationally explained by the hydrogen embrittlement mechanism. Additionally, in the process of corrosion fatigue crack growth, the acidification and the dealumination would occur at the crack tip, resulting in the corrosion dissolution of κ phases and the deterioration in mechanical properties of crack tip.

Prediction of corrosion fatigue crack growth rate in alloys. Part I: General corrosion fatigue model for aero-space aluminum alloys

In this work, a General Corrosion Fatigue Model (GCFM) was developed for predicting corrosion fatigue crack growth rate (CFCGR) in metals under cyclical loading. The GCFM is based on an equation for the potential drop from the external surface to the crack tip of metals as derived from the principle of differential aeration. Development of the GCFM involves consideration of cyclic loading on the CFCGR and of advection between the in-crack and external environment. We demonstrate the influence of corrosion environment and cyclic loading on the crack growth rate in Al-Li alloys in a 1:1 electrolyte (0.6 M NaCl).

Quantifying the Deleterious Effect of Sea Water on the Fatigue Life of Welded Steel Joints Using a Fracture-Mechanics Approach

Numerous studies have been conducted to investigate the deleterious effect of sea water on the fatigue life of welded joints for offshore structures subjected to wave loading (0.15 Hz to 0.5 Hz). In contrast, little research has been conducted to quantify this effect on the fatigue life of marine structures subjected to lower cycle frequencies. In the present study, a fracture-mechanics based approach in conjunction with the finite-element method has been used to model fatigue tests carried out on tee-butt welded joints in aqueous 3.5 wt.% NaCl (an analogue for sea water) under freely corroding conditions and various cycle frequencies (from 1 Hz to < 0.001 Hz) subjected to a constant stress range. This type of analysis can now be carried out because a more comprehensive corrosion-fatigue crack-growth-rate dataset for these low cycle frequencies has recently been published. Fatigue cracking in tee-butt welded joints was successfully modelled, and the results of this modelling, which are consistent with corrosion-fatigue crack-growth rates, indicate that the fatigue life of these tee-butt welded joints can be reduced by up to about 6.7 times in a salt-water environment for very low cycle frequencies (< 0.001 Hz) compared with the fatigue life in air.

Impact of solution conductivity and crack size on the mechanism of environmentally assisted crack growth in steam turbines

AbstractAn overview is presented of recent experimental measurements of environmentally assisted crack growth rates for steam turbine blades in simulated condensate solutions. The most notable observation is the complex dependence of stress corrosion and corrosion fatigue crack growth rates on crack size and solution conductivity in the low conductivity solutions associated with turbine condensates. Recent modelling of crack electrochemistry for this system has enabled rationalisation of most of these observations. An intriguing implication of the merging of experimental data and modelling is that the mechanism of cracking could also be dependent on crack size and solution conductivity.

Corrosion Fatigue Crack Propagation Rate Characteristics for Weldable Ship and Offshore Steels with Regard to the Influence of Loading Frequency and Saltwater Temperature

Abstract After Vosikovsky (1975), the corrosion fatigue crack growth rate (CFCGR) characteristics have been divided into three regions. The region-III rates are very close to mechanical fatigue crack growth rates. CFCGR formulae, including the long-crack length effect (in region I only), the loading frequency effect (in region II only), and the saltwater temperature effect, have been proposed. It has been assumed that CFCGR is proportional to f-k, where f is the loading frequency and k is a constant. The averaged k-value for all steels of yield stress (YS) below 500 MPa, usually with ferrite-pearlite microstructures, is higher than that for YS &gt; 500 MPa, usually with quenched and tempered microstructures. The temperature effect does not appear in region I below room temperature. In the remaining cases, that is, in region I for elevated temperatures and in region II for both low and elevated temperatures, the CFCGR increases with increasing temperature. Under a potential of -0.8 V, a long-crack-length effect, qualitatively similar to analogous effect for free corrosion conditions, appears.

Corrosion Fatigue Crack Growth Behavior of Alloy 690 in High-Temperature Pressurized Water

Corrosion fatigue crack growth behavior of Alloy 690 was investigated in air and high-temperature pressurized water environments. The stress intensity factor amplitude threshold (ΔKth) was obtained, and the effects of stress intensity factor (ΔK), cyclic frequency (f), loading ratio (R), and material orientation on the corrosion fatigue crack growth rates were studied. The observed environmental acceleration on corrosion fatigue crack growth was quantitatively analyzed, and an empirical formula and the Ford-Andresen model were utilized to describe and explain the corrosion fatigue behavior of Alloy 690.

The characteristics of load frequency of corrosion fatigue crack growth rate for Ti–6Al–4V alloys

The characteristics of load frequency of corrosion fatigue crack growth rate for Ti–6Al–4V alloys

Technical Note:Frequency Dependence of Fatigue Crack Growth Rate of Alloy 690TT in High-Temperature Boron-Lithium Water

Alloy 690TT is a widely used material for steam generator tubes in pressurized water reactors, where it is susceptible to corrosion fatigue. In this study, the effect of loading frequency on the corrosion fatigue behavior of Alloy 690TT in boron-lithium water was investigated under small-scale yielding conditions. Along with stress ratio, the loading frequency had a significant influence on the crack path and fatigue crack growth rate. Both the corrosion fatigue crack growth rate and the environment enhancement factor were quantitatively correlated with the loading frequency in the form of exponential functions.

Effect of cyclic frequency on fracture mode transitions during corrosion fatigue cracking of an Al-Zn-Mg-Cu alloy

Abstract There are complex issues remaining to be resolved before environment-assisted cracking models can be included in structural mechanics programs that are currently used to analyze mechanical fatigue crack growth. Considered here is the effect of cyclic frequency on fracture mode transitions that occur during corrosion fatigue of high-strength Al-Zn-Mg-Cu alloys. These alloys are used in civilian and military aircraft applications where they are exposed to detrimental aqueous saline environments. A previously developed “critical hydrogen at a critical distance” crack growth model is used to rationalize the observed transitions in crack-path fracture-modes, from intergranular (IG), to brittle transgranular (BTG), to ductile transgranular (DTG), as the alternating stress intensity factor and cyclic frequency increase beyond critical values. Corrosion fatigue crack growth rate data obtained on Al-Zn-Mg-Cu alloy 7017-T651 base metal and heat-affected “white zone” metal tested in aqueous NaCl solutions over a frequency range of 0.01–70 Hz are analyzed. For the white zone metal, dependence of the critical crack velocity on the critical frequency, at which the IG-BTG transition occurs, undergoes an abrupt reversal as the critical frequency increases above about 0.1 Hz. Mechanisms potentially responsible for this change in frequency dependency are discussed in the context of the critical hydrogen model. The transition from low to intermediate frequency behavior is speculated to be due to a change in the critical distance from microstructural control, for frequencies at or below 0.1 Hz, to control by the critical hydrogen criterion at higher frequencies. The low frequency behavior is discussed relative to the transition from static load stress corrosion cracking to low frequency corrosion fatigue, which occurs as cyclic frequency increases above zero.