Corrosion Fatigue Crack Growth Research Articles

The effect of variable humidity on corrosion fatigue of AA7085-T7451 with surface salt deposits

Corrosion fatigue (CF) crack growth is quantified as a function of relative humidity (RH) using AA7085-T7451 samples with NaCl deposited to understand the effect of deliquesced surface electrolyte droplets on CF performance when humidity varies. Fracture mechanics testing holding mechanical driving forces for cracking constant and incrementally increasing humidity show that crack growth rate (da/dN) more than doubles once RH moves above 78–80% RH. When decreasing RH, some amount of drying below the efflorescence RH (ERH) and/or a sufficient time is needed to pass in order for da/dN to return to that expected for a dry crack tip. All in all, this study establishes time of crack tip wetness as an important parameter for predicting fatigue lifetimes in atmospheric conditions, a parameter that cannot be solely predicted by RH, as accelerated cracking can continue for a limited amount of time even when RH is brought below the ERH.

Corrosion fatigue crack growth model for aluminum alloys in jet fuel

AbstractAluminum alloys are primary structural materials in aircraft fuel systems, where jet fuel can influence the fatigue crack growth (FCG) behavior of materials. This paper presents a model for calculating the FCG rate of aluminum alloys in jet fuel environment. The model is based on elastoplastic fracture mechanics and revises the interaction terms in the linear superposition model by accounting for the corrosive environment and the crack closure effect. The derivation process of the model is discussed in detail. To validate the efficacy of the model, FCG tests were conducted on three types of aviation aluminum alloys, namely, 2524‐T3, 7050‐T7451, and 7075‐T62 in the jet fuel. The experimental results were compared with FCG rates in the laboratory air environment. Findings indicate that the proposed model effectively captures the primary trends observed in the experimental data. In addition, the failure surfaces of the specimens were observed using a super‐depth‐of‐field optical microscopy system.

Prediction of corrosion fatigue crack growth rate in aluminum alloys based on incremental learning strategy

The 2xxx series aerospace aluminum alloys, vital for aircraft structures due to their excellent mechanical strength and corrosion resistance, face challenges with corrosion fatigue failure, impacting material integrity and aircraft safety. Accurately predicting the corrosion fatigue crack growth rate is crucial for these materials’ reliability in aerospace applications, ensuring safety and operational efficiency. Various unique incremental learning strategies like structural optimization, regularization, and replay were used to enhance the predictive model’s adaptability to continually updated data without the need to retrain the entire model, thus overcoming “catastrophic forgetting.” Based on these strategies, a series of XGBoost models for the prediction of corrosion fatigue crack growth rate in aerospace aluminum alloys have been developed. The results demonstrate that the replay strategy excels in maintaining the accuracy of historical data, while structural optimization and regularization strategies stand out in adapting to new data and effectively preventing overfitting. Combining these three strategies, the models maintain good accuracy and a low forgetting rate across all steps, with an accuracy rate exceeding 0.95 and a forgetting rate below 0.05 in all incremental steps, showcasing excellent knowledge retention capabilities. The models achieve a balanced performance in learning new tasks and retaining old knowledge.

Review on Environmentally Assisted Static and Fatigue Cracking of Al-Mg-Si-(Cu) Alloys

This paper reviews the relevant literature and covers the main aspects of the environmentally assisted cracking of Al-Mg-Si-(Cu) alloys. Apart from a brief overview of the major microstructural and mechanical properties, it presents research results on the corrosion sensitivity and stress corrosion susceptibility of Al-Mg-Si alloys. Possible mechanisms of stress corrosion cracking and corrosion fatigue in aluminum alloys, such as anodic dissolution and/or interaction with hydrogen, are considered. A number of factors, including atmospheric or solution conditions, applied stress, and material properties, can affect these mechanisms, leading to environmentally assisted cracking. Specific attention is given to Al-Mg-Si alloys with copper, which may increase the sensitivity to intergranular corrosion. The susceptibility to both intergranular corrosion and stress corrosion cracking of Cu-containing Al-Mg-Si alloys is mostly associated with a very thin layer (segregation) of Cu on the grain boundaries. However, the effect of Cu on the corrosion fatigue and fatigue crack growth rate of Al-Mg-Si alloys has received limited attention in the literature. At the current state of the research, it has not yet been holistically assessed, although a few studies have shown that a certain content of copper can improve the resistance of aluminum alloys to the environment with regard to corrosion fatigue. Furthermore, considerations of the synergistic actions of various factors remain essential for further studying environmentally assisted cracking phenomena in aluminum alloys.

Thermal corrosion fatigue crack growth behavior and life prediction of 304SS pipeline structures in high temperature pressurized water

The influence of transient water temperature changes on the fatigue crack growth behavior of 304SS pipeline structures was studied based on high-throughput testing method through the modification of dual loop circulating water equipment. Results demonstrated that the fatigue crack growth rate gradually decreased with the decrease of cooling rate, and the crack growth rate was exponentially related to the cooling rate. Both the base material and weld of the stepped pipe showed a transgranular cracking mode, and propagated continuously by slip-oxidation mechanism. Compared with the fine equiaxed grain of the base material, the grain in the weld was coarse and the residual strain was large, and the crack growth rate of the weld was obviously higher. Then, the thermal fatigue crack growth rate model for stepped pipes was established by combining finite element thermo-mechanical coupling simulation and three-dimensional crack propagation analysis software, and the model was modified based on the experimental results.

Application of Machine Learning (ML)-based multi-classifications to identify corrosion fatigue cracking phenomena in Naval steel weldments

Corrosion fatigue (CF) crack detection in welded ship hull structures is quite crucial as well as challenging for ensuring their structural integrity. This is conventionally done by offline ship hull survey and inspection methods, which have large time and cost implications. Data-driven approaches of ship hull crack detection are promising in this regard. Corrosion fatigue crack growth rate (CFCGR) behaviour of shipbuilding steel was studied for its base metal (BM), fatigue-prone heat affected zones (HAZs) of Submerged Arc Welding (SAW), and shielded metal arc welding (SMAW) joints of Naval-grade steel. The results indicated the highest CFCGR for BM, intermediate for SAW, and smallest for SMAW welds. This was attributed to 44% lath martensite observed in the SMAW HAZ microstructure as compared to 33% in SAW HAZ. A novel ML-based method has been proposed for CF crack location identification by a multi-classification approach using CFCGR data for structural health monitoring (SHM) applications. Prediction of crack location (either BM, SMAW HAZ, or SAW HAZ) was investigated using K-nearest neighbour (KNN), linear support vector machine classifier (LSVC), Naïve Bayes (NB), decision tree (DT), random forest (RF), and artificial neural network (ANN) models. DT and RF models were found to perform very well even without scaling and hyper-parameter tuning operations and exhibited 98–99% classification accuracy. Scaling and tuning operations resulted in significant improvements in accuracy of KNN models from 43% to 84% (minmax scaling) and 98% (standard scaling). Significant improvement in the accuracy from 37% to 98% ANN model was achieved by standard scaling. The proposed method shall be useful in data-driven real-time crack location identification in ship hull structures.

Corrosion Fatigue Behavior of 6000 HP Fracture Pump of the Valve Body Under Different Plunger Stroke Times and Acid Fracture Fluid Environment

Abstract As a key equipment for oil and gas extraction, the fracture pump is prone to failure due to fatigue crack in the crossbore of valve body. First, under acid fracture fluid and different loading frequencies, the fatigue crack growth rate of 17-4PH stainless steel was obtained by test, and the test data were used the modified Paris law. Then it is applied to numerical simulations to research the fatigue crack growth behavior of the valve body. The results show that the higher the loading frequency in the fracture fluid, the lower the fatigue crack growth rate, which is consistent with the test results. The influence of the working pressure on the stress intensity factor of the crack front is greater than that of the plunger stroke times. The model accurately predicts the fatigue crack orientation and corrosion fatigue crack growth life of the valve body.

Effect of cathodic protection on the corrosion fatigue crack growth behavior and fatigue life of XS-grade shipbuilding steel

Shipbuilding steels are subjected to corrosion fatigue damage phenomena due to conjoint effects of cyclic loading by sea waves and corrosive seawater environment, which often leads to premature failure of ship hull structures. In practice, the impressed current cathodic protection (ICCP) technique is applied to mitigate ship hull corrosion by electrochemically making it cathodic. It is implemented by impressing a direct current to minimize the electrode potential to a predefined protection potential. It is significant to study the effect of ICCP on the corrosion fatigue crack growth rate (CFCGR) behavior and fatigue life assessment of ship hull structures. In this study, CFCGR behavior of high-strength XS-grade shipbuilding steel was investigated in unprotected freely corroding (FC) and protected ICCP (at – 800 mV) conditions using compact-tension specimens at 0.1 Hz frequency in artificial seawater (3.5 wt.% NaCl solution). After crack-closure corrections, it was found that the ICCP-protected specimen (∆KTH = 18 MPa √m) exhibited higher sub-critical or threshold corrosion fatigue crack propagation resistance as compared to the FC specimen (∆KTH = 14 MPa √m). Fractography of the FC specimen revealed the debonding of non-metallic inclusions and formation of micro-pits/secondary cracks as dominant damage mechanisms. ICCP-protected specimen exhibited a signature pattern of parallel secondary cracks and a proportional increase in their density with increasing stress intensity levels during primary crack growth. This fracture morphology indicated the primary-crack branching and further arrest, leading to retarded crack growth rates under ICCP-protection. Fatigue life analysis also confirmed this finding, where the beneficial ICCP-protection effect resulted in at least two times enhancement in fatigue lives from the unprotected FC condition.

The effect of long-term operation on fatigue and corrosion fatigue crack growth in structural steels

Operational degradation of steels under a combined action of mechanical loading and aggressive hydrogenating environments is a crucial problem for structural integrity. Among the mechanical properties, the characteristics of brittle fracture resistance, namely, impact strength and fracture toughness, as well as the plasticity characteristics, are highly sensitive to the operational degradation of structural steels. However, in the case of exposing of structures beside environmental influences to cyclic mechanical loading scenarios, their reliability depends on the degradation degree due to fatigue and corrosion fatigue. Tendency of in-service changes in the fatigue characteristics (fatigue crack growth rate and fatigue strength) can be unambiguous. In-service lifetime of structure due to the non-monotonic character of operational degradation of certain mechanical characteristics is divided into two stages: deformation strengthening (stage I) and in-bulk dissipated damaging (stage II). The operational degradation of steels is accelerated under influence of corrosive hydrogenating environments as a result of intensification of dissipated damaging. The effect of environments on acceleration of fatigue crack growth rate is mainly revealed in the mid-region of stress intensities, more significantly for in-service degraded metal, indicating its susceptibility to stress corrosion fatigue.

Experimental investigation on corrosion fatigue crack initiation and growth of heat-treated U75V rail steel

Understanding the corrosion fatigue mechanism of rail materials is of great importance to guide the assessment of the structural integrity of modern railway components. To this purpose, the corrosion fatigue crack (CFC) initiation and growth behaviors of heat-treated U75V rail steel are investigated under 3.5 wt% NaCl solution in terms of high-cycle fatigue, fatigue crack growth (FCG) rate, together with surface morphology and microstructure. Experimental results reveal that the U75V rail steel is susceptible to corrosion fatigue failure. Examinations on fractured samples clearly show that the electric potential difference between ferrite and cementite triggers the preferential anodic dissolution of ferrite, leading to corrosion fatigue crack initiation. The crack initiation is not only solely determined by the size of the corrosion pit, but also strongly influenced by its local shape. In comparison with the fatigue crack growth in air, the corrosion FCG tends to grow in a relatively straight path, because of hydrogen embrittlement. Additionally, the CFC behaviors indicate a tendency to transverse through soft-oriented grains and deflect upon encountering hard-oriented grains.

Fatigue crack growth of EH36 steel in air and corrosive marine environments

EH36 steel used in offshore platforms is susceptible to corrosion fatigue in marine environment. The corrosion fatigue performance in EH36 steel is influenced by various factors, such as maximum applied load, loading frequency and stress ratio. To investigate such effects, fatigue crack growth (FCG) tests on compact tensile (CT) specimens of EH36 steel were carried out in three different environments, including air, immersed seawater and wet-dry cyclic environment, by considering different maximum loads, loading frequencies and stress ratios. From the experimental tests, the relation of crack development and loading cycles and the relation of fatigue crack growth rate (FCGR) and stress intensity factor (SIF) range were obtained. Constants (C and m) in Paris law were obtained through fitting technique based on experimental data. Due to corrosion of marine environment, the fatigue life of EH36 steel decreases while the FCGR increases. The corrosion fatigue crack growth (CFCG) experimental results were compared with the predictions from Paris-law recommended in BS7910. A new CFCG calculation model consisting of environmental acceleration factors was proposed and evaluated for accuracy, and such model can be used for predicting the remaining fatigue life of EH36 steel in marine corrosive environment under the specified conditions. The fracture morphology of the specimens in different environments was observed by scanning electron microscope (SEM) to analyze the fracture mechanism. The fracture morphology of the CT specimens in two corrosive environments is almost same and appears as cleavage fracture.

A peridynamic model for corrosion-fatigue failure behaviour

Corrosion-fatigue is the main factor affecting the service life of aero-engine parts in marine or coastal environments. A numerical simulation method for modelling corrosion-fatigue failure based on peridynamic (PD) theory is presented. We established a coupling relationship between the mechanical and chemical fields according to the influences of displacement on damage, stress on corrosion behaviour, and corrosion behaviour on fatigue behaviour. Subsequently, we verified the model using the corrosion-fatigue crack growth prediction for S355 steel. The prediction and test results show the influence of corrosion behaviour on the fatigue crack growth rate. In addition, we verified the model through the corrosion-fatigue life prediction of a Ti-6Al-4V alloy sample with a corrosion pit. Compared with the test results, the prediction accuracy was limited to a scatter band of factor 2. These results indicate the validity of the proposed model in simulating the corrosion-fatigue behaviour.

Effect of different loading conditions on corrosion fatigue crack growth rate of a nickel-based alloy in supercritical water

Advanced ultra-supercritical (A-USC) technology improves the initial steam temperature to 650 °C and more. In such an extremely corrosive medium environment, metallic materials are susceptible to corrosion fatigue. In the present study, the aim is to evaluate the effect of maximum stress intensity factor (Kmax), stress ratio (R), waveform, frequency, and holding time (th) on the corrosion fatigue cracking behavior of C-HRA-2 (a candidate nickel-based alloy for A-USC units) in supercritical water (650 °C/25 MPa). The results show that with the increase of Kmax, the corrosion fatigue crack growth rate (CFCGR) increases and satisfies the exponential relationship. The decrease in R and frequency both cause the rise of CFCGR, which satisfies the logarithmic linear relationship. Sinusoidal and triangular wave loading have no significant effect on the CFCGR. Trapezoidal wave with th has a larger CFCGR while with the rise in th, the CFCGR increases. The crack propagation path is straight, perpendicular to the loading direction, and secondary cracks are also observed. Transgranular and intergranular mixed fractures occurred during continuous loading. The proportion of intergranular fracture increases significantly as holding time is applied. The corrosion fatigue crack growth of C-HRA-2 in supercritical water can be explained by dynamic embrittlement mechanism.

Life prediction of corrosion-fatigue based on a new crack growth rate model with damage and the extended finite element method

A fatigue crack growth rate model introducing corrosion damage is proposed in this paper, where the fracture parameter is modified by the damage variable and the exponential influence factor. The corrosion damage mechanism is coupled to the crack growth rate model, which quantifies the influence of the environment and reflects the interaction between corrosion and fatigue. To accurately predict the corrosion-fatigue crack growth life by the extended finite element method (XFEM), a simple crack surface updating method is developed. This method does not depend on the complex level set marching algorithm which often brings serious computational convergence problem, so it has good robustness and high efficiency. Moreover, the stress intensity factors at arbitrary crack tip can be calculated by combining the interaction integral method and the piecewise interpolation method, so it is suitable for the double crack-tip problem. The corrosion-fatigue crack growth life is calculated based on the cycle-by-cycle method and the corresponding algorithm is developed. The corrosion-fatigue crack growth life can be accurately predicted by calculating the corrosion damage and crack propagation length under each load cycle. In this paper, sufficient examples are given to verify the accuracy of the proposed method in simulating crack propagation path and predicting corrosion-fatigue life. Finally, this method is well applied to a practical engineering structure.

Corrosion fatigue crack growth in stainless steels: A peridynamic study

Fatigue crack growth (FCG) behaviors are accelerated by corrosive environments, resulting in higher corrosion FCG (CFCG) rates and more rapid structural failure. Current local-theory-based numerical methods do not effectively capture the CFCG behaviors of metallic materials. Recently, peridynamic (PD) models, which are nonlocal-theory-based, have demonstrated good descriptive ability for discontinuous problems, making it promising to simulate CFCG via PD methods. In this paper, a peridynamics-based CFCG simulation framework is proposed and applied for the CFCG simulation of the stainless steel, Type-634. This framework provides explanations of corrosion-induced faster crack growth from the view of degradations of material properties. And the simulated results agree well with the experimental testing results, demonstrating the effectiveness of the proposed model. Moreover, the effects of corrosion-related degradation function parameters and loading frequencies on CFCG results are explored, and the results demonstrate the generalizability of the simulation method. With further development and embedding more accurate physical models, this simulation framework will effectively assist real CFCG tests.

Study on crack propagation life of corrosion fatigue in orthotropic steel deck in steel bridges

The study of the corrosion fatigue life of steel bridges is of much significance. The remaining life of corrosion fatigue crack propagation is found to be lesser than fatigue crack propagation. The finite element model is established, the key points are meshed in small size, and the fatigue crack damage of local components is analyzed.The crack propagation life evaluation method of corrosion fatigue in orthotropic steel deck structure bridges is obtained based on the multi-scale finite element method. Stress intensity and corrosion are the main factors that affect the crack propagation life of corrosion fatigue. The stress intensity factor was analyzed by diaphragm spacings, diaphragm thickness, and roof thickness,It is understood that the thickness of the diaphragm has a great influence on the stress strength factor. Temperature, humidity and morphological characteristics of corrosion pits affect the rate of corrosion when exploring the influence of corrosion factors.The analysis of corrosion fatigue crack growth process shows that corrosion has a great influence on the remaining life of fatigue crack propagation.

Microstructure-dependent corrosion fatigue crack growth behavior of Ti-6Al-4V alloy in simulated body fluid

The fatigue crack growth rate (FCGR) of Ti-6Al-4V alloys in simulated body fluid (SBF) was first determined by direct current potential drop (DCPD) method. The results show that the acceleration effect of SBF corrosion environment on FCGR of lamellar structure is far greater than that of equiaxed and bimodal structures, especially in Paris region, which is mainly due to the high corrosion sensitivity of the lamellar α/β phase boundary to SBF under fatigue loading.

Corrosion fatigue crack growth behavior of a structurally gradient steel for high-speed railway axles

Considering the complex service environments that high speed railway axles are subjected to, the fatigue crack growth (FCG) behavior of a structurally gradient axle steel with different pre-crack depths both in air and a corrosive medium was investigated at a frequency of 5 Hz. The results indicated that in the high ΔK region, the FCG rate was dramatically accelerated by corrosion but the gap narrows as ΔK decreased. The accelerated corrosion FCG rate was a comprehensive result of the acceleration effect of the anodic dissolution, hydrogen-enhanced localized plasticity and the retardation effect of corrosion-induced crack-tip blunting. Despite the fact that the corrosion resistance gradually decreased as the pre-crack depth increased, the FCG rate in the corrosive medium gradually decreased. This was because fatigue loading played a more important role than corrosion in accelerating the corrosion FCG rate.

Corrosion fatigue crack growth in A7N01S−T5 aluminum alloy MIG welded joints

This paper studies the corrosion fatigue crack growth (CFCG) in 3.5 wt% NaCl solution of the local zones of A7N01S−T5 aluminum alloy metal inert gas (MIG) welded joints cut from high−speed train underframes after service lives of 1.8 million km. The results show that the base metal (BM) region exhibits the highest rate of CFCG compared to both the heat−affected zone (HAZ) and the weld metal (WM) zone. Crack features suggest that the corrosion fatigue failure mode of the BM is hydrogen−assisted propagation and that the failure mode for both the HAZ and WM is anodic dissolution. We calculate that the multi−site adsorption and substitution of Cl− on the surface of the passivation film can make the oxygen and aluminum atoms detach from the surface of the passivation film, causing its destruction and allowing the cracks to expand further. Hydrogen is more likely to accumulate and diffuse along the grain boundaries, reducing their strength and causing them to become the most likely orientation for crack propagation. This study provides the new insight into the specific CFCG mechanisms of each zone in aluminum alloy welded joints.

The influence of laser shock peening on corrosion-fatigue behaviour of wire arc additively manufactured components

The need for increased manufacturing efficiency of large engineering structures has led to development of wire arc additive manufacturing (WAAM), which is also known as direct energy deposition (DED) method. One of the main barriers for rapid adoption of the WAAM technology in wider range of industrial applications is the lack of sufficient performance data on the WAAM components for various materials and operational conditions. The present study addresses this essential need by exploring the effects of laser shock peening surface treatment on corrosion-fatigue crack growth (CFCG) life enhancement of WAAM components made of ER70S-6 and ER100S-1 steel wires. The experimental results obtained from this study were compared with the CFCG trends from nominally identical specimens without surface treatment and prove the efficiency of the examined surface treatment method for corrosion-fatigue life enhancement and crack growth retardation of WAAM built steel components, regardless of the material type and specimen orientation. Furthermore, the residual stresses in the WAAM built specimens with and without surface treatment were measured to validate the influence of beneficial residual stresses, arising from surface treatment, on subsequent CFCG behaviour of the material. The residual stress profiles show the beneficial compressive stress fields in the surface treated areas which result in CFCG life enhancement. The results from this study make significant contribution to knowledge by evaluating the suitability of WAAM built steel components for application in offshore environments.