Corrosion Fatigue Life Research Articles

The fatigue crack propagation in nanocrystalline materials in the hydrogen environment

In this article, the effect of the external corrosion environment on dislocation emission is introduced, and the microscopic mechanism of fatigue crack propagation (FCP) in a hydrogen environment is studied. Meanwhile, based on the discrete distributed dislocation method, the corrosion FCP model of nanocrystal materials is established. In the framework of our model, the FCP is mainly determined by the irreversibility of the crack tip dislocation. The research results indicate that the aggregation of hydrogen atoms at the crack tip (CT) promotes the dislocations emission and increases the FCP rate. Meanwhile, considering the application of materials in different hydrogen circumstances, the effects of changes in the distance between hydrogen atoms and the crack tip and the radius of hydrogen atoms on crack propagation rate are studied. The results show that the accumulation of hydrogen atoms at the crack tip promotes the fatigue crack growth rate in nanocrystalline materials. Compared with the air environment, the maximum increase in crack propagation rate is about 45% under the action of hydrogen environment. Meanwhile, increasing the grain size and dislocation emission angle helps to increase the crack propagation rate. The research in this paper provides a theoretical basis for evaluating the corrosion fatigue life of metal materials.

LBE corrosion fatigue life prediction of T91 steel and 316 SS using machine learning method assisted by symbol regression

This study employs machine learning models assisted by symbol regression to achieve satisfactory corrosion fatigue life prediction for T91 steel and 316L stainless steel (SS) used in 4th generation advanced nuclear power plants. Symbol regression features improve the performance of all considered machine learning models. The artificial neural network (ANN) model shows the most significant improvement of 22 % decrease in RMSE regarding to the model without symbol regression features. Additionally, the well-trained ANN model is transferred to predict 316L SS with a 50 % reduction in training samples, highlighting its potential for more efficient model training and deployment.

Improved corrosion fatigue performance of 316L stainless steel by surface porosification

The corrosion fatigue of 316L stainless steel with different surface morphologies was examined by cyclic deformation tests in a NaCl solution. Three different surface treatments were applied to the steel, i.e., mechanical polishing, electropolishing and anodization. The surface roughness depended on the treatments; the highest roughness was obtained for the anodized specimen owing to the formation of dimple structure. The formation of the dimple structure significantly increased the corrosion fatigue life compared to the other treatments. The improved corrosion fatigue performance was discussed in terms of the formation of slip steps on the steel surface.

Combining electric discharge surface alloying and high-frequency mechanic impact post-processing for increased corrosion fatigue life of as-welded transverse non-load-carrying attachments of the S355 steel

The combined effects of severe plastic deformation induced by high-frequency mechanical impact (HFMI) treatment and the electric discharge surface alloying (EDSA) with chromium on the corrosion fatigue life of low-carbon S355 steel transverse non-load-carrying specimens are studied in this paper. First, for various alternations of the combined HFMI + EDSA process, the surface alloyed layer integrity and depths were analyzed using scanning electron microscopy (SEM) accompanied with energy dispersive spectroscopy (EDS) and hardness measurements. The alloying and hardening depths were respectively observed to be 10–30 μm and 0.15–0.75 mm and the surface hardness increased up to 3.6–3.9 GPa. Polarization tests demonstrated higher corrosion resistance of the EDSA-processed samples in 3%NaCl. The near-surface layers of the HFMI + EDSA(Cr) + HFMI processed sample characterized by X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) contain the dislocation-cell structure formation and partially dissolved cementite. The fatigue tests in 3%NaCl confirmed that the HFMI + EDSA(Cr) + HFMI post-weld process increased corrosion fatigue life (1.77 × 106 cycles) of the S355 steel welded joint at the stress level of 260 MPa by 2 and 12 times in comparison with the HFMI-treated (0.9 × 106) and as-welded (0.14 × 106) samples, respectively.

Failure analysis of automotive helical spring

As it is known, the suspension helical or coil spring contributes to the vehicle's driving comfort and protects the vehicle parts by softening the impacts depending on the road topography and keeping the suspension system stable without shaking. In this study, the cause of coil spring fracture in a B-segment vehicle was investigated systematically. Within the scope of the investigation, microscopy studies (optical and scanning electron), hardness, and metallographic studies were carried out, and finite element analysis was used to determine the stress distribution in the spring. The failure analysis showed that the fracture was fatigue induced, and the crack initiation was interestingly not on the inner surface of the spring where the stress was maximum but in the corrosion between the upper surface and the outer surface of the wire and in a region that makes an angle of approximately 20 degrees to the vertical. Considering the properties of the steel (AISI 9254) used in the spring, such as microstructure, hardness, and the stress values obtained from the finite element analysis (FEA), it is concluded that there was no problem in terms of design, materials, heat treatment, and processing history of the spring. However, FEA results simulating corrosion-induced pitting show that the pitting has a significant stress concentration, confirming the crack initiation assessment. In this context, it was understood that the final painting process applied to the part surface was insufficient to protect the spring against deteriorating effects such as rainwater / salty snow water from the road surface. It was concluded that improving the paint quality and/or installing a polymeric part to protect the spring against the effects of the road would be beneficial in solving the problem. Finally, in order to achieve high-performance springs, the use of steels with a combination of high strength and high fracture toughness (e.g. micro-alloyed) and/or the application of a precision shot peening process such as an ultrasonic method to the surface after heat treatment will contribute significantly to the corrosion fatigue life of the spring.

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.

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.

Remaining fatigue life assessment of corroded mooring chains using crack growth modelling

Failures caused by the combined actions of fatigue, corrosion and wear are important safety concerns for mooring chains used on floating structures in the oil and gas industry. Prediction of remaining corrosion fatigue life based on surface condition could therefore be a useful tool for the continued safe operation of corroded chains. This paper investigates the use of crack growth modelling for estimating the remaining corrosion fatigue life of mooring chains that exhibit significant pitting corrosion damage. A crack growth modelling approach is used to produce remaining fatigue life estimates for a selection of severely pitted mooring chains. Using fatigue crack growth rate test results for grade R4 high strength mooring chain steel, empirical crack growth laws are presented for free corrosion and cathodic protection conditions at load ratio R = 0.1. Two different methods for establishing equivalent cracks from surface scans of corrosion damage are presented. The mooring chains are proof loaded as part of their manufacturing process. Residual stresses introduced during this process have therefore been determined by finite element analysis and accounted for in the fatigue crack growth predictions. One of the equivalent crack models, accounting for the single dominant corrosion pit, provided quite accurate fatigue life predictions when compared with full scale test results.

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.

Fatigue life prediction of stud shear connectors under corrosion-fatigue coupling effect

Based on the three-stage fatigue crack growth model, a corrosion fatigue life prediction method considering the coupling effect of corrosion and fatigue is proposed in this paper. In this case, stress factor amplitude was claimed considering the coupling effect of corrosion and fatigue. Three push-out tests in corrosion conditions were conducted to study the failure mode of studs. The crack propagation of studs, obtained through the push-out tests, was simulated in FRANC 3D to establish a library of adequate stress factor amplitude. According to the corrosion degree of the specimens, the corrosion dissolution rate formula was formed, and the corrosion fatigue life of the specimen was predicted. Results show that the error between the predicted and experimental values is approximately 25%.

Effect of micro-galvanic corrosion on corrosion fatigue cracking of the weld joint of high strength bridge steel

The local electrochemical and corrosion fatigue cracking behavior of the weld joint of Q690qE high-strength bridge steel was investigated in simulated marine environment. It reveals the weld joint was vulnerable to corrosion fatigue failure in polluted marine atmosphere with the corrosion fatigue life considerably lower than that of parent metal. The micro-galvanic corrosion effect between CGHAZ and WM played a dominant role in the corrosion fatigue failure of the weld joint, leading to the final fracture mostly at CGHAZ. The micro-galvanic corrosion was caused by Volta potential variation among various subzones, which was evidenced by local electrochemical techniques.

The Effect of Atmospheric Chloride Ions on the Corrosion Fatigue of Metal Wire Clips in Power Grids

Corrosion fatigue is an important factor that limits the life of grid materials including wire clips. In order to study the effect of corrosion fatigue and to select suitable grid steels, this paper focuses on the corrosion fatigue properties of Q235 carbon steel, Q235 galvanized steel, and 316L stainless steel in the corrosive environments of air, 2wt% NaCl, 5wt% NaCl, and 8wt% NaCl. Through the fatigue test in the corrosive environment, and the surface morphology scanning and microstructure observation of the fracture, the following conclusions are drawn: the three materials are more susceptible to corrosion fatigue in the Cl− environment, and the higher the Cl− concentration, the greater the likelihood of fracture caused by corrosion fatigue for these three materials. By analyzing the surface roughness, dimples, and cracks in the microstructure, it is found that 316L stainless steel is highly sensitive to Cl− corrosion under cyclic stress, and Q235 galvanized steel is more resistant to Cl−. By plotting the stress fatigue life curve of Q235 galvanized steel, it is found that the corrosion fatigue life decreases as the Cl− concentration increases. For wire clips in areas with severe Cl− pollution, Q235 galvanized steel should be selected to achieve the best anti-corrosion fatigue effect; at the same time, the original parts should be repaired or replaced in a timely manner based on the predicted corrosion fatigue life.

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.

Corrosion fatigue damage mechanism and life evaluation of Inconel Alloy 690TT steam generator tube in high temperature pressurized water

Corrosion fatigue behavior of the actual Alloy 690TT steam generator (SG) tubes in high temperature water were systematically studied by using the designed boat-shaped specimen. Results demonstrated that the environmental fatigue correction coefficient of the SG tube in high temperature water was lower than that of round bar specimen in ANL model, which may be related to the internal surface oxide film rupture-persistent slip bands (PSBs) deformation zone preferential dissolution caused by the shape effect of SG tube. Moreover, the corrosion fatigue life of the actual SG tube was evaluated by the method of model correction.

Evaluation of Flexible Central Buckles on Short Suspenders’ Corrosion Fatigue Degradation on a Suspension Bridge under Traffic Load

Suspenders are the crucial load-bearing components of long-span suspension bridges, and are sensitive to the repetitive vibrations caused by traffic load. The degradation of suspender steel wire is a typical corrosion fatigue process. Although the high-strength steel wire is protected by a coating and protection system, the suspender is still a fragile component that needs to be replaced many times in the service life of the bridge. Flexible central buckles, which may improve the wind resistance of bridges, are used as a vibration control measure in suspension bridges and also have an influence on the corrosion fatigue life of suspenders under traffic load. This study established a corrosion fatigue degradation model of high-strength steel wire based on the Forman crack development model and explored the influence of flexible central buckles on the corrosion fatigue life of suspenders under traffic flow. The fatigue life of short suspenders without buckles and those with different numbers of buckles was analyzed. The results indicate that the bending stress of short suspenders is remarkably greater than that of long suspenders, whereas the corrosion fatigue life of steel wires is lower due to the large bending stress. Bending stress is the crucial factor affecting the corrosion fatigue life of steel wires. Without flexible central buckles, short suspenders may have fatigue lives lower than the design value. The utilization of flexible central buckles can reduce the peak value and equivalent stress of bending stress, and the improved stress state of the short suspender considerably extends the corrosion fatigue life of steel wires under traffic flow. However, when the number of central buckles exceeds two, the increase in number does not improve the service life of steel wire.

Corrosion mechanism and fatigue behavior of aluminum alloy with high silicon content

The corrosion and corrosion-assisted fatigue life degradation behaviors of Al–8Si alloy is investigated. The test results show that galvanic cells are formed in the inter-dendrites due to high Si concentration, leading to pitting corrosion. The Al2Cu phase and the Si-rich phase precipitate at the grain boundaries in the inter-dendrites, among which the Al2Cu phase is the most critical factor leading to intergranular corrosion. Subsequently, intergranular corrosion gradually develops into intragranular corrosion attributed to the higher dislocation energy in fine-grained Al grains. Additionally, it is found by comparing the corrosion potential and corrosion rate that high Si concentration would cause the decrease in corrosion resistance. Finally, the fatigue test results show that the corrosion could reduce fatigue life of Al–8Si alloy by 79.77% on average. Therefore, the corrosion-induced fatigue life degradation is very worth to be considered in structures.

Fatigue and corrosion fatigue behaviors of biodegradable Zn-Li and Zn-Cu-Li under physiological conditions

• The fatigue behaviors of biodegradable Zn alloys were investigated. • The corrosion fatigue behaviors of biodegradable Zn alloys were investigated. • The fatigue fracture mode of biodegradable Zn alloys was analyzed. Zinc (Zn) alloys are emerging as a new class of biodegradable metallic materials due to their good biocompatibility, suitable biodegradability, and nontoxicity. However, the dynamic loading in the human body, along with the corrosive physiological environment, brings great challenges to the application of biodegradable Zn alloys. At present, there are few reports on the fatigue and corrosion fatigue properties of Zn alloys in simulated body fluid (SBF). In the present work, extruded Zn-0.8Li and Zn-2Cu-0.8Li alloys were selected in order to systematically evaluate their fatigue and corrosion fatigue behaviors both in air at ambient temperature and in SBF at 37 °C. Results revealed that the fatigue limits of the extruded Zn-0.8Li and Zn-2Cu-0.8Li alloys were about 135 and 180 MPa, respectively, in air at ambient temperature. However, the fatigue limits of the two alloys decreased to 65 and 80 MPa, respectively, in SBF at 37 °C and showed a linear relationship between the corrosion fatigue life and the stress amplitude. The sources of fatigue cracks in air were internal microstructural defects or weak mechanical properties of the material, while the initiation of corrosion pits on the surface was the main reason for the source of the formation of fatigue cracks in SBF. The fracture mode of the extruded Zn-0.8Li and Zn-2Cu-0.8Li alloys was quasi-cleavage fracturing. Compared to static immersion testing, cyclic loading significantly increased the corrosion rates of the two experimental alloys in a corrosion fatigue environment.

An Experimental Analysis of the High-Cycle Fatigue Fracture of H13 Hot Forging Tool Steels.

In this study, the axial fatigue behaviour of hot forging tool steels at room temperature was investigated. Fatigue tests were performed on two steels within the same H13 specification. The fatigue tests were carried out in the high-cycle fatigue domain under normal conditions. These tests were also performed on specimens in contact with a corrosive medium, applying stress values that led to the high-cycle fatigue domain under normal conditions for the sake of comparison. Both materials showed similar fatigue strengths when they were tested under normal conditions. In contrast, corrosion fatigue lives were much lower than in normal tests and differed significantly between the two steels. Crack initiation was triggered by microstructural and surface defects in the normal tests, whereas the formation of corrosion pits caused crack initiation in the corrosion fatigue tests. Moreover, a fracture surface analysis revealed dissimilar crack propagation areas between both steels, which suggested that both steels had different fracture toughness. These results were in line with the differences observed between the carbide and grain sizes of both of the material microstructures.

In situ corrosion fatigue life of 2198-T8 Al–Li alloy based on tests and DIC technique

Abstract The advanced aluminum–lithium alloy is used in aircrafts fuselage. Based on the combination of fatigue test and digital image correlation technique, the influence of pre-corrosion and in situ corrosion damage on the fatigue performance of 2198-T8 aluminum–lithium alloy was investigated. The integrated evolution process of fatigue crack and strain distribution fields of two types of the damaged sheets were captured and evaluated by the digital image correlation technique. The results reveal a declining tendency of in situ corrosion fatigue life with the rise of solution temperature, as well as the decrease of flow rate. But, at increasing the NaCl concentration, the fatigue life tends to decrease first and then increase. The observed fatigue behavior and related phenomena are directly associated with fracture morphology such as micro-cracks and corrosion pits. The analysis indicates a competition mechanism between fatigue and corrosion, the fatigue damage dominates the failure process under lower NaCl concentration on the contrary to the higher one that the corrosion damage is the dominant factor. Considering the effect of flow rate on the surface adhesion, the crack tends to initiate at the position of low flow rate. The simulation on the flow field presents an attractive similarity with experimental results.

A Review on Surface Integrity of Ball Burnishing Process

Surface quality of product plays a vital role to take competitive advantages in present market condition. Surface finish is an important service characteristic of a product, such as corrosion resistance, wears resistance and fatigue life. Burnishing is one of the cost-effective surface finishing processes which is utilized in the aerospace, biomedical and automotive industries to increase the component's reliability and performance. Burnishing produces a very smooth surface finish by pressing a ball or roller against the machined workpiece. In addition, due to the surface plastic deformation caused by the movement of the hardened ball or roller, the mechanical and physical properties such as residual stresses, surface finish, hardness, roundness, diameter reduction, wearing, etc. could also be improved. These positive improvements are dependent on burnishing process parameters such as speed, feed rate, burnishing force, ball diameter, strategy and a number of revolutions, etc. Diverse studies have been focused on the theoretical, numerical and experimental stages of this process in order to analyze and predict the influence of process parameters. The most important purpose of this work is to present the reviewed state of the art of various studies of the burnishing process, providing a general overview of the developing research of the process. The studied materials and the main parameters are discussed, stating the value ranges preferred by different researchers. In addition, other important parameters are discussed such as: kind of tool, geometry of the working piece, design of experiments, kind of lubricant and effect of the process on the surface integrity of the workpiece.