Stress Corrosion Fracture Research Articles

Corrosion fatigue crack propagation behaviour in different micro-regions of steel/aluminum laser-MIG hybrid fusion-brazed joints

Evaluating corrosion fatigue crack propagation (CFCP) behaviour in different micro-regions of steel/aluminium welded joints is crucial for ensuring the safety and reliability of these joints in service environments. However, the CFCP behaviour of steel/aluminum welded joints has rarely been studied. This study explores the CFCP behaviour of steel/aluminium laser-metal inert gas hybrid fusion-brazed joints in different micro-regions under a simulated corrosive environment (3.5 wt% NaCl solution) at room temperature. A self-made 5 KN electronic servo testing machine was used to apply a sinusoidal wave load (stress ratio R = 0.1, frequency = 0.5 Hz) to single-edge notched tensile specimens. The notches were located at the weld, heat-affected zone (HAZ) and steel/aluminium interface (abbreviated as interface). The fatigue crack propagation rate (da/dN) of different micro-regions in steel/aluminium welded joints followed the order of interface > weld > HAZ under corrosive environment and air conditions. Compared with air, the corrosive environment triggered a markedly higher da/dN, irrespective of notch location at the weld, HAZ or interface. This accelerated da/dN resulted from the combined effects of anodic dissolution, chloride ions and galvanic corrosion. The electron backscatter diffraction results indicated that compared with the weld and HAZ specimens, the HAZ specimen exhibited lower da/dN, attributed to its small grains, higher proportion of high-angle grain boundaries and increased geometrically necessary dislocation density. Fatigue striations were clearly observed on the weld and HAZ fracture surfaces, while a brittle fracture pattern was observed on the corrosion fatigue fracture surface for the interface.

Synergistic Effect of Cr and Fe Elements on Stress Corrosion Fracture Toughness of Titanium Alloy

Synergistic Effect of Cr and Fe Elements on Stress Corrosion Fracture Toughness of Titanium Alloy

Low-Cycle Corrosion Fatigue Deformation Mechanism for an α+β Ti-6Al-4V-0.55Fe Alloy

Titanium alloys with high strength and good corrosion resistance have become one of the critical bearing structural materials in marine engineering. But in service, corrosion fatigue would occur under the synergetic action of cyclic external load and corrosion environment, threatening the safety of components. In this study, compared with low-cycle fatigue in laboratory air, the low-cycle corrosion fatigue deformation mechanism and fracture characteristic of the Ti-6Al-4V-0.55Fe alloy were investigated in 3.5% NaCl corrosion solution under selected stress amplitudes. The results showed that under low stress amplitude, corrosion fatigue was determined by fatigue damage and corrosion damage, causing a reduction in fatigue life. The local stress concentration caused by corrosion pits and dislocations pile-up accelerated the initiation of fatigue cracks, and other corrosion behavior including crevice corrosion promoted fatigue crack propagation; the corrosion solution increased the surface damage. While under high stress amplitude, due to the short contact time between the sample and solution and higher applied stress, the fatigue life is determined by fatigue damage caused by multiple slips.

Analysis of corrosion fatigue coupling effect of high-strength steel wire based on multi-stage competition assisting theory

To accurately elucidate the failure mechanism of high-strength steel wire under the coupling influence of corrosion fatigue, this study conducts experimental and theoretical research. First, the characteristics of coupled corrosion and fatigue were investigated through experimental research, laying the foundation for the development of a new theory. Subsequently, a novel theory, the Multi-Stage Competitive Assisting Theory (MSCAT), accounting for the coupling effects of corrosion fatigue, was proposed, and the specific details of this theory and parameter selection were explained. Finally, this theory was implemented in Abaqus to simulate the entire process of corrosion fatigue fracture in steel wire. The computational results were compared with experimental data, confirming the accuracy of the proposed theory.

Fracture failure analysis of the main shaft of a large sewage treatment equipment

In view of the main shaft fracture failure accident occurred in the service process of a sewage treatment equipment, this paper carried out the fracture macro analysis, chemical composition analysis, material mechanical properties testing, metallographic structure analysis, fracture micro morphology analysis of the failure of the main shaft. The analysis results show that there are cold cracks in the weld and toe of the main shaft of the equipment, and the cracks expand under the action of rotating and bending alternating loads. The main shaft speed of the equipment is 3r/min, the load change frequency is very small, and the corrosive medium has sufficient time to play a role in the crack tip, fatigue cracks further propagated, leading to corrosion fatigue fracture of the main shaft. So in order to prevent this kind of failure, it is suggested to improve the welding process regulations for the equipment of the main shaft and rationally select welding materials.

Corrosion Fatigue Assessment of Bridge Cables Based on Equivalent Initial Flaw Size Model

Bridge cables under traffic loads are more prone to failure during the service life due to the corrosion–fatigue coupling effect. In this study, a novel lifespan model based on the equivalent initial flaw size (EIFS) theory is established to analyze the various stages of the lifespan of steel wires. Additionally, a comprehensive corrosion-fatigue lifespan calculation method for parallel steel wire cable is established based on the series–parallel model. A case study of the Runyang Suspension Bridge is conducted to evaluate the evolution of corrosion-fatigue damage in bridge cables during the service life. The results indicate that under the action of corrosion-fatigue, steel wires are more prone to crack initiation, and their fracture toughness is further reduced. In cases where the corrosion level is relatively low, the steel wires of the bridge cables experience no corrosion-fatigue fracture. When the steel wires have initial defects and are subject to corrosion-fatigue conditions, their fracture lifespan is dependent on the severity of the corrosive medium. The reduction in the service life of the cables under the corrosion environment is much greater than that under heavy loads. This research may contribute to the understanding of corrosion-fatigue damage in bridge cables, involving assessment, maintenance, and replacement for bridge cables.

Effect of Coating on Stress Corrosion Performance of Bridge Cable Steel Wire

Hot galvanization on steel surfaces can isolate the steel from corrosive environments and alleviate the stress corrosion cracking caused by the anodic dissolution mechanism. However, the cathodic protection potential of the coating is excessively negative, which may aggravate the hydrogen embrittlement problem. The effect of a coating on the stress corrosion performance of bridge cable wire was studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), a thermal desorption analysis (TDA), an electrochemical workstation, and an FIP test. The results show that hot-dip ZnAl and ZnAlMg alloy coatings can significantly prolong the stress corrosion fracture time of steel wire substrates. From a macroscopic perspective, the stress corrosion cracking fracture is a brittle fracture caused by hydrogen embrittlement. Moreover, the coating type has little effect on the fracture morphology of bridge cable wire. In NH4SCN solution (50 °C, 20 wt.%), a corrosion product layer composed of ZnS and Al2O3 was formed on the surface of the coated steel wire. The electrochemical analysis showed that the corrosion resistance of the ZnAlMg coating was better than that of the ZnAl coating, which was the main reason for the improvement of the stress corrosion performance.

Specific Features of Corrosion-Fatigue Fracture of Steel and Hybrid Pump Rods

Specific Features of Corrosion-Fatigue Fracture of Steel and Hybrid Pump Rods

General principles and criteria of failure of solids on different scale-structural levels under static and alternating loading

Experimental and theoretical studies of the fracture regularities under monotonic and alternating loadings, including stress-corrosion fracture, revealed the main scale-structural levels of the brittle fracture (formation of a strip structure, nucleation of microcracks, microstructurally short non-propagating cracks and short propagating cracks, merging of short cracks with a macrocrack nucleation) and viscous fracture (an evolution of dislocation in slip bands, cellular structure formation, nucleation of a pit relief with micropores, merging of pores with a formation of meso-shear bands and initiation of a viscous crack, growing of a viscous crack under inelastic deformation) of crystal bodies. A transition from one level to another is determined by changes in the fracture mechanisms and occurs with varying degrees of probability. The necessity of considering the destruction as a hierarchical random step-by-step process on all scale-structural levels is substantiated. The fracture of plastic materials is considered as the sum of independent or dependent events, namely the initiation and growing of brittle cracks and evolution of pores through various mechanisms. Attaining of the limit states is determined by the statistics of the distribution of inhomogeneities throughout the entire body volume. The results of physical studies (using electron microscopy, X-ray structural analysis, etc.) provide determination of the geometry and density of defects, dislocations, pores, cracks at different levels. Macrocharacteristics of static, long-term and fatigue strength are determined using methods of mechanical tests. The regularities of the fracture evolution of engineering structures are determined using methods of non-destructive testing (ultrasonic analysis, acoustic emission analysis, magnetic flaw detection, etc.). A brief analytical review of the main known physical approaches — dislocation and energy structural theories, dislocation continuous theories, dilaton-frustron models, stochastic physical theories, and phenomenological approaches, including continuum damage theory and fracture mechanics — is presented. The analysis of gained data leads to the necessity of describing fracture in the framework of stochastic multilevel models. We consider the approach according to which the probability of reaching limit sates at each level under arbitrary multiaxial loading is determined by linear functionals of the loading process, kernels of the functionals being random functions of time. For simple proportional loading, the theory of brittle fatigue scale-structural failure is presented.

SIMULATION AND SELECTION OF A PROTECTION TYPES IN THE DESIGN STAGE OF SHIPS AND OFFSHORE STRUCTURES

The requirements of the rules and regulations of the Classification Societies are based on the assumption that during the construction and operation of ships the hull corrosion protection measures are implemented according to the standards and other regulatory documents currently in force. For the purposes of designing the ship hull structures, the load components for different corrosion protection types have been obtained in the paper. There have been collected the data on the relationship between the corrosion protection weight load and the ship displacement, which enables to select the lowest corrosion protection type by weight. Technical and economic parameters of corrosion protection of ship hull structures have been analyzed. To achieve the objective of the paper a cumulative simplified approach of economic feasibility of selecting the corrosion protection type for ship hull structures has been employed. It has been determined that a total cost of protection from stress-corrosion fractures decreases for the ships with a displacement of more than 6000 [t] in the case of usage of the impressed current cathodic protection instead of the sacrificial anode cathodic one. The results of the investigation can be used by shipbuilders at the ship design stage, which enables to make a correct selection of a corrosion protection type and decreases its total cost.

Mechanism of corrosion fatigue fracture of friction stir welding joints of 7075 aluminium alloy in 3.5% NaCl solution

Mechanism of corrosion fatigue fracture of friction stir welding joints of 7075 aluminium alloy in 3.5% NaCl solution

Peculiarities of stress corrosion fracture of sensitized and neutron irradiated chromium-nickel austenitic steel

The results of SEM studies of fracture surfaces for the 12Cr18Ni9 austenitic steel ruptured under a fixedtensile load in FeCl3 water solutionand in air are presented. The samples of austenized, sensitized at 650° and irradiated with neutrons (to 1020n/cm2) steel were examined. It was shown thatirradiation hardening and sensitizing annealing increased the susceptibility of steel to intergranular cracking in corrosive solution. Structural features of formation of the strain-induced α’-martensite and its reinforcing effect on fracture in various environments are discussed.

Investigation of stress corrosion cracking behavior of L360QS in different groove angles by electrochemical and SSRT method

The effect of two different groove angles on stress corrosion cracking (SCC) sensitivity of welded joints was investigated by electrochemical and SSRT methods, and the fracture surface of tensile specimens was observed by SEM. The electrochemical results show that the corrosion resistance of HAZ region increases with the increase of welding groove angle, while the corrosion resistance of weld region decreases with the increase of welding groove angle. The results of SSRT of the welded joint show that, under the condition of no applied potential, under different welding groove angles (8°/15°), The maximum tensile strength is 546.08 MPa/560.64 MPa, the maximum fracture life is 44.6 h/46.8 h, the maximum elongation after fracture is 9.40%/9.73%, and the maximum reduction of area is 63.53%/65.14%. With the negative increase of applied potential, the SCC sensitivity of welded joint also shows an obvious increasing trend. The fracture morphology of the SSRT tensile test shows that with the negative increase of applied potential, the fracture changes from dimple-like ductile fracture to typical brittle fracture, and obvious stress corrosion fracture occurs.

On the influence of thermo-mechanical process history on stress corrosion cracking of solution annealed type 304 stainless steel

The effect of thermo-mechanical process history on microstructure development and stress corrosion cracking behavior of solution annealed Type 304 stainless steel has been investigated. Metallographic screening and electron backscatter diffraction analysis has been carried out to characterize microstructure after thermo-mechanical processing treatments. The application of cold reductions between 5% and 20%, followed by solution annealing treatments, resulted in different microstructure characteristics. Mixed-mode trans-/intergranular stress corrosion fractures were observed, and heat treatment at 950 °C resulted in changes of failure mode to predominantly transgranular. Fractographic assessment of the different themo-mechanical process conditions revealed a relationship between Grain Size (ASTM GS), Grain Boundary Character Distribution (GBCD), and Time to Failure (t f ).

4D microstructural characterization of corrosion and corrosion-fatigue in a Ti–6Al–4V / AA 7075-T651 joint in saltwater environment

Dissimilar alloy couples are susceptible to environmentally assisted damage owing to the presence of crevices and potential difference between the constituent alloys. In this study, x-ray computed tomography has been employed to non-destructively study the corrosion behavior of a dissimilar alloy fastener-plate couple (AA7075-T651/Ti–6Al–4V) in a 3.5 wt% NaCl environment. Following this, the specimen was subjected to corrosion fatigue and post fracture failure analysis was performed. The precise locations of corrosion pitting damage in the specimen were studied with respect to corrosion time. Microstructural factors that contribute to crack initiation were identified using a correlative microscopy-based approach and are discussed.

Influence of Temperature and Carbon-Dioxide Pressure on the Corrosion and Stress-Corrosion Fracture of Pipe Steels in Model Stratal Water

Influence of Temperature and Carbon-Dioxide Pressure on the Corrosion and Stress-Corrosion Fracture of Pipe Steels in Model Stratal Water

Damage Behavior of 30CrMnSiA Steel under Coupling action of Marine Atmospheric Environment and Tensile-compressive Load

The coupling test of marine atmospheric environment and tensile-compressive load for 30CrMnSiA steel was carried out with the coupling test equipment of marine atmospheric environment and tension, compression and bending load. The damage behavior of 30CrMnSiA steel on the coupling action of marine atmospheric environment and tensile-compressive fatigue load was discussed. The metallographic results showed that the damage behavior characteristics of static test and coupling test were consistent. The decrease of tensile strength, proof strength plastic extension and percentage elongation after fracture of 30CrMnSiA steel were accelerated by the coupling action of marine atmospheric corrosion and tensile-compressive fatigue load. And the accelerated ratio of the coupling test was more than 10 times that of the static exposure test. The fracture morphology results showed that the fracture of the coupling test was corrosion fatigue fracture, and the cracks of 30CrMnSiA steel in the coupling test extended from the fatigue source to the core, forming directional corrosion fatigue damage.

A Short Review on Polymer, Metal and Ceramic Based Implant Materials

The present work focuses on the evaluation of polymer, metal and ceramic based biomaterials with particular emphasis on success rate of these materials till date along with the merits and demerits of these material system. Currently, the search for the materials with improved performance is on rise for biomedical (mainly total hip replacement, THR) applications owing to increase in the number of orthopedic patients worldwide. The clinicians utilized polymer and metal-based implants in ancient times to heal and treat the bone imperfections as well as fractures. The next generation materials required an update on properties, cell material interactions, repair and regeneration, that can only be acquired from recent knowledge related to materials. The commonly employed polymers (natural based polymers, proteins or polysaccharides; and synthetic polymers, poly (lactic acid), poly (glycolic acid), poly (ε-caprolactone), poly(3-hydroxybutyrate) (PHB)) and metals (SS, Mg-alloy, Ti-alloys, Co-alloy, silver, and nickel-titanium alloys) failed to fulfill the long-term durability and lacked in generating adequate bonding with the bones. It is intended that the facts and details abridged in this review article ought to be a beneficial tool in the development of progressively eminent implant materials like ceramic based materials against premature failure, cyclic stress generation, wear, corrosion fatigue, implant loosening and ultimate fracture.

Practical Experience with the Methodology of Prediction of Corrosion-Fatigue Failures of Steam Turbine Rotating Blades

Corrosion fatigue fractures initiating from corrosion pits are one of the most serious problem during service of rotating blades of the low-pressure parts of steam turbines. A methodology for fatigue failure prediction, originally based on the knowledge obtained by EPRI (Electric Power Research Institute), using corrosion pits parameters assessment and local stresses calculation was adapted to the conditions of ČEZ a.s. power stations. This contribution deals with the evaluation of the corrosion state of blades of three low pressure rotors after long service. Measurement was done in power stations equipped with turbines of power 200 MW and 110 MW respectively. Possibilities and uncertainties (influence of filling of pits with oxides, cyclic stress calculations, and the selection of the geometric factor Y) and their elimination are discussed.

Study on corrosion fatigue properties and fracture characteristics of 7075 aluminum alloy FSW joint

Taking 7075-T6 aluminum alloy friction stir welding joint as the research object, the microstructure, 3.5 wt % NaCl solution corrosion fatigue life and corrosion fatigue fracture characteristics were studied, and the corrosion fatigue performance and fracture process of 7075 aluminum alloy friction stir welding joint were analyzed. The results showed that: the S-N curve equation of corrosion fatigue of 7075-T6 aluminum alloy friction stir welded joint is lgN=5.845-0.014S, With the increasing of stress amplitude, the corrosion fatigue life decreased greatly. The corrosion fatigue crack originated in the thermal affected zone of the joint, gradually expanded and finally broke in the welded core zone of the joint. There were multiple crack sources in the corrosion fatigue fracture, and with the influence of stress concentration, the crack source originated in the corrosion pit. The high stress aggravated the corrosion damage of the corner part of the sample, led to more serious corrosion than that of the plane position. Obvious intergranular fracture and fatigue striation appeared in the crack growth zone. Under the combined action of corrosive medium and alternating load, the crack growth zone suffered the most serious corrosion, and the anodic dissolution occurred at the grain boundary, resulting in the morphology characteristics of “rock candy” and “ant nest”. Instantaneous fault zone was brittle fault,and there were a lot of cleavage steps and secondary cracks in this zone, the pore morphology appeared in the second phase particle distribution region.