Accelerated Crack Propagation Research Articles

Study on Multi-Crack Damage Evolution and Fatigue Life of Corroded Steel Wires Inside In-Service Bridge Suspenders

The parallel steel wires used in arch bridge suspenders experience random corrosion damage on their surfaces during service. Corrosion damage, including micro-cracks, pitting, and a combination of both, leads to significant stress concentration under axial loading, which affects the performance of the steel wires. The change in the stress field caused by surface damage alters the stress intensity factor at the crack tip, and the presence of adjacent crack tips significantly amplifies the stress intensity factor, thereby accelerating crack propagation. The development of small surface damages in the steel wires is difficult to control and observe through experiments. By utilizing finite element methods for simulation, it is possible to intuitively analyze the crack propagation process, the trend of stress changes at the crack tip, and the interaction between damages. Numerical simulation results based on Paris’ law indicate that corrosion pits have a certain impact on the stress intensity factor at the crack tip. The propagation process of coplanar double cracks is highly sensitive to the initial crack size and the distance between adjacent crack tips. When the crack spacing is less than the crack depth, the stress intensity factor at the adjacent crack tips exhibits significant amplification. Based on this phenomenon, the coplanar double-crack system can be simplified to a complete single crack for analysis. By comparing the fatigue life of the double-crack system with that of the equivalent single crack, the effectiveness of the simplification rule has been validated.

Small fatigue crack behavior of CP-Ti in thin-walled cruciform specimens under biaxial loading

This study investigates the small fatigue crack propagation behavior of commercially pure titanium (CP-Ti) using thin-walled cruciform specimens under in-plane biaxial loading, considering the effects of biaxial ratio and phase angle. Increasing phase angle results in more secondary cracks merging with main cracks perpendicular to the rolling direction (RD) and transverse direction (TD), a phenomenon attributed to the rise in shear stress that accelerates main crack growth. Higher loading biaxiality or a lower phase angle leads to decreased crack propagation rates and increased biaxial fatigue life. Electron backscatter diffraction (EBSD) analysis reveals that when the maximum normal stress aligns with the RD, prismatic slip primarily governs crack propagation, thereby accelerating crack propagation rates. Conversely, alignment with the TD reduces prismatic slip activity and crack propagation rates. Under equi-biaxial loading, prismatic slip activity decreases further, and crack propagation is dominated by multiple slip and twinning, consequently resulting in the slowest propagation rates. Additionally, a higher proportion of prismatic slip under high phase angle also accelerates crack propagation. Finally, incorporating Findley equivalent stress into the Chapetti model, which considers the crack length-dependent threshold effect, a highly accurate biaxial small fatigue crack propagation rate model is proposed.

Machine learning-aided risk-based inspection strategy for hydrogen technologies

Although technically challenging, effective, safe, and economical transport is crucial for enabling a widespread rollout of hydrogen technologies. A promising option to transport large amounts of hydrogen lies in employing retrofitted natural gas pipelines. Nevertheless, H2-rich environments tend to degrade pipeline steels, reducing their load-bearing capability and accelerating crack propagation. Regular inspection and maintenance activities can preserve the pipelines’ integrity and guarantee safe operations. The risk-based inspection (RBI) approach is based on estimating the risk for each component item. It focuses most inspection activities on high-risk components to reduce costs while maximizing the plant’s safety and availability. However, the RBI standards do not consider hydrogen-induced degradations and cannot be adopted for industrial equipment operating in H2 environments. This study proposes a novel ad-hoc methodology for the risk-based inspection planning of hydrogen handling equipment. A machine-learning model to predict the fatigue crack growth in gaseous hydrogen environments is developed and integrated with the conventional RBI approach. The proposed methodology is validated on three pipelines transporting hydrogen and natural gas in different concentrations. The results show how similar operating conditions can determine different degradation rates depending on the environment and highlight how hydrogen-enhanced fatigue can reduce the pipelines’ lifetime.

A new understanding of hydrogen-assisted cracking of coarse-grained heat-affected zone in X65 pipeline steel through {110} lath bainite boundary texture

The susceptibility of subzones of the coarse-grained heat-affected zone (CGHAZ) in X65 pipeline steel to hydrogen embrittlement was studied through an in situ crack-tip opening displacement test in an H2S-containing environment. The intercritically reheated CGHAZ (IC-CGHAZ) exhibited the highest embrittlement factor of 89.4%, compared to 64.0% for the sub-critically reheated CGHAZ (SC-CGHAZ). Hydrogen transportation by dislocations to massive-slender martensite/austenite (M/A) constituents initiated cracks in IC-CGHAZ. Deterioration of lath bainite (LB) boundaries, with separation of M/A-ferrite interface, accelerated crack propagation across prior austenite grains and promoted hydrogen-assisted degradation of fracture toughness. Reheated CGHAZ at a peak temperature of 620 °C led to an increased intensity of the {110} LB boundary texture by up to 52% in SC-CGHAZ. This enhanced texture facilitated dislocation slipping along {110} LB boundary planes, thereby promoting deformation compatibility and preventing the deterioration of LB boundaries in the presence of hydrogen.

High-Performance 2319 Aluminum Alloy via CMT-WAAM: Microstructure, Porosity, and Mechanical Properties

The process of cold metal transfer (CMT) wire arc additive manufacturing (WAAM) for 2319 aluminum alloy was studied. The research investigated the coarse and fine equiaxed grain bands and porosity of the 2319 alloy after solution aging treatment, with a focus on the mechanical properties and deformation behavior of the aluminum alloy at different positions and orientations. Pores and coarse second phases mainly appeared at grain boundaries but were also observed within coarse equiaxed grains. The yield strength of the top horizontal samples reached 325.5 MPa, one of the highest yield strengths reported for 2319 aluminum alloy in the literature. The coarse brittle second phases at grain boundaries were the main crack sources during the failure process of the samples. In the fine equiaxed grain layer, cracks propagated along the grain boundaries connected to the second phases, and the presence of pores accelerated crack propagation; in the coarse equiaxed grain layer, cracks directly penetrated through the grains.

Predicting subsurface inclusion initiated butterfly-wing cracking under rolling contact fatigue

Wind turbine (WT) gearbox bearings experience premature failures. Damage characterisation of failed bearings has shown that subsurface micro cracks and butterfly-wing cracks are associated with non-metallic inclusions in the bearing raceways. The existing studies are unable to predict crack propagation under rolling contact fatigue considering shakedown and ratchetting when the material around an inclusion experiences sufficiently high levels of stresses. In this study, a finite element (FE) damage model based on the Continuum Damage Mechanics (CDM) is developed, integrated with the modelling of plastic deformation and kinematic hardening when the material around inclusion is subjected to alternating tension and compression. Two damage types of manganese-sulphide inclusions are investigated, showing significant effects of inclusion boundary separation and internal cracking on the subsurface RCF crack evolution. The modelling results also show that higher surface traction, overloads and varied loading sequences, commonly experienced by WTs in operation, have significant effects on the increase of the subsurface butterfly-wing crack lengths, because of early crack initiation and accelerated crack propagation. The developed CDM FE model has shown its effectiveness in predicting the damage evolution to gain new insights of complex interactions of a number of critical factors that can lead to the premature failure of bearings.

Coupled effects of UV radiation and freeze–thaw cycles on the fracture behavior of asphalt concrete

The Qinghai-Tibet Plateau in China is characterized by extreme climate conditions, including intense ultraviolet (UV) radiation, frequent freeze–thaw cycles (FTCs), and significant temperature fluctuations. These conditions contribute to severe cracking in asphalt pavements. This study aims to investigate the impact of coupled damage from UV radiation and FTCs on the fracture behavior of asphalt concrete. To simulate the coupled environmental damage (CED) experienced by asphalt pavement in the field, an alternating two-factor laboratory procedure was developed. This procedure reflects the climatic conditions of the Qinghai-Tibet Plateau. The semi-circular bending test, combined with digital image correlation technology, was employed to evaluate the effects of temperature and CED cycles on fracture-related parameters of asphalt concrete. These parameters include the load–displacement curve, fracture toughness, and fracture energy. Fracture behavioral characteristics such as horizontal strain, crack length, crack propagation path, and crack mouth opening displacement were also analyzed. The results indicate that coupled damage from UV radiation and FTCs significantly weakened the fracture resistance of asphalt concrete. Compared with other fracture-related indicators, the most significant reduction observed was the fracture energy of 68.1%. The two environmental factors exhibited a mutually reinforcing effect on the fracture properties of asphalt concrete, with low temperatures further intensifying their influence. CED cycles delayed the initiation of cracks in asphalt concrete but accelerated crack propagation. This led to a reduction in time to failure by up to 57.6% and a maximum reduction in horizontal strain of 24%. Additionally, the cracking propagation path of asphalt concrete became more linear with increased crack mouth opening displacement. Future research should focus on the evolution of damage accumulation in asphalt concrete under CED cycles, with the goal of establishing predictive models for long-term service life.

Revelling pore microstructure impacts on the compressive strength of porous proppant based on finite and discrete element method

Ceramic spheres, typically with a particle diameter of less than 0.8 mm, are frequently utilized as a critical proppant material in hydraulic fracturing for petroleum and natural gas extraction. Porous ceramic spheres with artificial inherent pores are an important type of lightweight proppant, enabling their transport to distant fracture extremities and enhancing fracture conductivity. However, the focus frequently gravitates towards the low-density advantage, often overlooking the pore geometry impacts on compressive strength by traditional strength evaluation. This paper numerically bypasses such limitations by using a combined finite and discrete element method (FDEM) considering experimental results. The mesh size of the model undergoes validation, followed by the calibration of cohesive element parameters via the single particle compression test. The stimulation elucidates that proppants with a smaller pore size (40 µm) manifest crack propagation evolution at a more rapid pace in comparison to their larger-pore counterparts, though the influence of pore diameter on overall strength is subtle. The inception of pores not only alters the trajectory of crack progression but also, with an increase in porosity, leads to a discernible decline in proppant compressive strength. Intriguingly, upon crossing a porosity threshold of 10 %, the decrement in strength becomes more gradual. A denser congregation of pores accelerates crack propagation, undermining proppant robustness, suggesting that under analogous conditions, hollow proppants might not match the strength of their porous counterparts. This exploration elucidates the underlying mechanisms of proppant failure from a microstructural perspective, furnishing pivotal insights that may guide future refinements in the architectural design of porous proppant.

Effect of Mn alloying on the hydrogen‐assisted cracking behavior in multiphase/duplex stainless steel

There remains debate on whether Mn is beneficial or detrimental to hydrogen embrittlement in stainless steel. In this work, a series of stainless steels were designed to study the change of hydrogen embrittlement sensitivity, crack propagation, and hydrogen trapping behaviors upon Mn addition. The results suggest that adding 4 wt.% Mn increased hydrogen embrittlement susceptibility, whereas adding 8 wt.% Mn decreased hydrogen embrittlement sensitivity. Forming banded α'-martensite through austenitic grain is the main reason for the increased hydrogen embrittlement sensitivity when adding 4 wt.% Mn, by adsorbing hydrogen, promoting crack initiation, and accelerating crack propagation.

Numerical Analysis of Crack Propagation in an Aluminum Alloy under Random Load Spectra

This study develops a rapid algorithm coupled with the finite element method to predict the fatigue crack propagation process and select the enhancement factor for the equivalent random load spectrum of accelerated fatigue tests. The proposed algorithm is validated by several fatigue tests of an aluminum alloy under the accelerated random load spectra. In the validation process, two kinds of panels with different geometries and sizes are used to calculate the stress intensity factor, critical crack length, and crack propagation life. The simulated and experimental findings indicate that when the aluminum alloy is in a low plasticity state, the crack propagation life exhibits a linear relationship with the acceleration factor. When the aluminum alloy is in a high plasticity state, this study proposes an empirical formula to calculate the equivalent stress intensity factor and crack propagation life. The normalized empirical formula is independent of the geometry and size of different samples, although the fracture processes are different in the two kinds of panels used in our study. Overall, the numerical method proposed in this paper can be applied to predict the fatigue crack propagation life for the random spectrum of large samples based on the results of the simulated accelerated crack propagation process and the accelerated fatigue tests of small samples to reduce the cost and time of the testing.

Origin of surface oxidation induced the nucleation and propagation of microcracks in TNM alloy

This study investigated the impact of surface degradation caused by oxygen (O) and nitrogen (N) elements in the environmental atmosphere on the service failure of nearly lamellar TNM alloy. The results show that oxidation-induced phase transformations at the surface and subsurface regions strongly affect the alloy's tensile properties at high temperatures. The precipitation of Al2O3, which disrupts the integrity of the Ti2AlN layer, has a weaker deformation resistance capacity compared to the Z-phase. Under stress conditions, numerous dislocations concentrate at the Al2O3 phase, causing Al2O3 particles to easily detach and initiating crack nucleation at the Z-phase/Al2O3 interface. This is the origin of oxidation failure. Cracks nucleate at the Al2O3 detachment region, propagate, and connect with surface microcracks induced by the rough and loose outer oxide layer structure. This leads to the rapid propagation of cracks into the subsurface. The consumption of β-stabilizing elements at the surface, along with the internal diffusion of O and N elements into the subsurface region, results in the formation of the hard brittle Z-phase at the subsurface lamellar structure and a transition from β0 to α2 at the lamellar colony boundaries. The precipitation of α2 and Z-phase also accelerates crack propagation. In summary, the failure mode shifts from toughness fracture to brittle fracture.

Delamination mechanism in CF/EPOXY with open hole under mode II loading at different distances

This research addresses limitations in current aviation composite assembly techniques, often constrained by certification challenges. To enhance bonded composite components, open holes are frequently introduced, leading to increased vulnerability to delamination, a prominent failure mode in composite laminates. This study focuses on observing the impact of open holes on the mode II behavior of composites under various distances and hole diameter conditions. Results illustrate distinct load–displacement curves influenced by hole size, with shorter distances accelerating crack propagation, evidenced by reduced elastic regions and lower load values. Analyzing specimen appearances and crack patterns highlights stress concentration at the hole, influencing initiation and propagation. In the absence of a hole, cracks exhibit a zig-zag pattern near the loading point, while with a hole, they concentrate around it. Elastic region length varies with the pre-crack-to-hole distance, indicating accelerated crack propagation in shorter distances. This study underscores the direct influence of hole size on load values, emphasizing its pivotal role in determining composite mechanical properties. This research provides valuable insights into hole characteristics’ interplay with delamination behavior in carbon fiber-reinforced composites, essential for optimizing aerospace component design and structural integrity.

Fracture Behaviour of Aluminium Alloys under Coastal Environmental Conditions: A Review

Aluminium alloys have been integral to numerous engineering applications due to their favourable strength, weight, and corrosion resistance combination. However, the performance of these alloys in coastal environments is a critical concern, as the interplay between fracture toughness and fatigue crack growth rate under such conditions remains relatively unexplored. This comprehensive review addresses this research gap by analysing the intricate relationship between fatigue crack propagation, fracture toughness, and challenging coastal environmental conditions. In view of the increasing utilisation of aluminium alloys in coastal infrastructure and maritime industries, understanding their behaviour under the joint influences of cyclic loading and corrosive coastal atmospheres is imperative. The primary objective of this review is to synthesise the existing knowledge on the subject, identify research gaps, and propose directions for future investigations. The methodology involves an in-depth examination of peer-reviewed literature and experimental studies. The mechanisms driving fatigue crack initiation and propagation in aluminium alloys exposed to saltwater, humidity, and temperature variations are elucidated. Additionally, this review critically evaluates the impact of coastal conditions on fracture toughness, shedding light on the vulnerability of aluminium alloys to sudden fractures in such environments. The variability of fatigue crack growth rates and fracture toughness values across different aluminium alloy compositions and environmental exposures was discussed. Corrosion–fatigue interactions emerge as a key contributor to accelerated crack propagation, underscoring the need for comprehensive mitigation strategies. This review paper highlights the pressing need to understand the behaviour of aluminium alloys under coastal conditions comprehensively. By revealing the existing research gaps and presenting an integrated overview of the intricate mechanisms at play, this study aims to guide further research and engineering efforts towards enhancing the durability and safety of aluminium alloy components in coastal environments.

Molecular dynamics simulation of effects of loading parameters on fatigue crack growth behavior in titanium single crystal

AbstractThe fatigue crack growth behavior in single‐crystal titanium with a prismatic crack was simulated using molecular dynamics (MD) considering the effects of applied temperature, strain ratio, and strain rate. The results indicate that the material exhibits transient cyclic hardening behavior and dominant cyclic softening behavior. The peak tensile stress decreases with increasing temperature or decreasing strain rate. The deformation mechanism for crack growth involves prismatic dislocation emission and the formation of vacancy defects at different loading conditions. Deformation twinning occurs at the highest temperature, and a secondary crack emerges at the highest strain rate. The Mises stress concentration at the twin boundary and the coalescence between the initial and secondary cracks may accelerate crack propagation. The ΔJ shows good linear relationships with fatigue crack growth rate (FCGR), indicating that ΔJ possesses the potential to assess fatigue crack growth behavior at the atomic scale for ductile metallic materials.

Failure analysis of the end surface of the burner nozzle made of UMCo50 material in long-term high temperature oxygen-enriched sulfur-chlorine environment

As the core device of coal water slurry gasification technology, the failure of the burner nozzle will bring serious technical and safety problems. The purpose of this paper is to determine the mechanism of burner failure based on the characteristics of corrosion products and cracks. The results showed that the Cr2O3 oxide film on the surface of UMCo50 was damaged under the effect of mechanical erosion, high temperature and stress, and the corrosive elements S and Cl in the combustion chamber made it further cracked and peeled off. Therefore, the matrix was corroded and cracks occurred. During the crack propagation process, more M23C6 carbides were precipitated at the grain boundary, it caused Cr-depleted at the grain boundary, which reduced the corrosion resistance of the matrix near the grain boundary. The exfoliation of carbides distributed along the grain boundary also accelerated crack propagation. Through XPS and XRD analysis, it was found that the main corrosion products on the crack surface of the failed parts were: Cr2O3, CoCr2O4, CoO, Fe2O3, FeS. According to the causes of failure analysis, the corresponding improvement measures are put forward.

Effect of dendritic structure and secondary phases on the fatigue behavior of ERNiCrMo-3 weld metal

The effect of dendritic structure and secondary phases on the fatigue crack propagation mechanism of ERNiCrMo-3 weld metal was investigated. Element segregation in the weld metal induced severe lattice distortion in the interdendritic region, creating substantial variations in mechanical properties between the dendrite core and interdendritic region. This disparity resulted in an unstable crack propagation rate. The limited plastic deformation capacity of the interdendritic region caused a contraction in the local plastic deformation zone at the crack tip, increasing stress concentration and accelerating crack propagation. The fatigue crack in the interdendritic regions exhibited a rate of approximately 2.6 μm/cycle, surpassing the 1.5 μm/cycle observed in the dendrite cores. Meanwhile, element segregation promoted the precipitation of numerous Laves phases in the interdendritic regions. With increasing stress, micro-voids formed by broken Laves phases served as rapid channels for crack propagation. Post-weld heat treatment weakened the non-uniformity of the microstructure. The fatigue crack propagated at a rate of about 1.2 μm/cycle. Furthermore, the dissolution of Laves phases and the precipitation of γ″ enhanced the fatigue performance of the weld metal. Under equivalent stress levels, the fatigue life of post-weld heat-treated weld metal increased by approximately 1.2 times compared to that of as-welded metal.

Effect of retained austenite on impact-abrasion wear performance of high-strength wear-resistant steel prepared by dynamic partitioning process

The ductility and toughness of the high-strength wear-resistant steels can be improved by introducing retained austenite. However, the influence of retained austenite on the impact-abrasion wear resistance remains uncertain. This study investigates the effect of retained austenite on the impact wear performance of martensitic wear-resistant steel by introducing 5.2–9.2 vol% retained austenite through the dynamic partitioning (DP) process. The results display that the microstructures of the various DP-treated steels primarily consist of lath martensite and film-like retained austenite distributed between martensite laths. The three-dimensional atom probe (3DAP) analysis demonstrates that the retained austenite exhibits a significantly higher carbon concentration than the martensite, with carbon enrichment increasing gradually from the edge to the core of the retained austenite. In short-term impact wear tests (10 min), the weight loss of DP-treated steels is inversely proportional to the volume fraction of retained austenite. Conversely, in the long-term impact wear tests (20–90 min), it is positively proportional to the volume fraction of retained austenite. Initially, the strain-induced martensite transformed from retained austenite can absorb more impact energy, passivate the crack, and inhibit crack propagation, which is the dominant factor contributing to improved wear resistance. However, as impact wear progresses, the detrimental effects arising from the high hardness and poor plastic deformation ability of the strain-induced martensite become dominant, accelerating crack propagation during long-term impact wear tests. This study may provide insights into the microstructure design of the martensitic wear-resistant steels under impact wear conditions, specifically regarding the role of retained austenite.

A Systematic Review of Medium‐Mn Steels with an Assessment of Fatigue Behavior

Deformation‐induced mechanisms, namely, transformation‐induced plasticity (TRIP) and twinning‐induced plasticity (TWIP), are primarily responsible for improved tensile properties in medium‐Mn steels. Additionally, lower density and processing costs make these steels useful in various industries, particularly the automotive industry, which mandates a good understanding of underlying processing–microstructure–property correlations. Therefore, the present study reviews different thermomechanical processes and corresponding microstructural evolutions, followed by mechanical properties. In addition, an assessment of the fatigue behavior of medium‐Mn steels based on duplex or multiphase microstructure and associated mechanisms has been presented. In high‐cycle fatigue (HCF) loading, strain‐induced martensite formation through TRIP at the crack tip is a barrier to dislocation motion. It deviates the crack propagation path to adjacent phases, which results in higher fatigue life. On the other hand, relatively high martensite boundaries initiate microcracks and accelerate crack propagation, resulting in lower life in low‐cycle fatigue (LCF). However, the TWIP mechanism prevents cyclic softening and promotes cyclic saturation, extending fatigue life. The compositions of medium‐Mn steel for enhanced fatigue resistance have been proposed. To that end, it is hypothesized that the TRIP + TWIP mechanisms lead to exceptional LCF performance. Further, microalloyed medium‐Mn steels are expected to exhibit improved LCF and HCF behavior.

The time dependence of proton irradiation effect on the intergranular oxidation of 316 L stainless steel in high-temperature hydrogenated water

The time dependence of proton irradiation effect on the intergranular oxidation of 316 L stainless steel in simulated PWR primary water was clarified for the first time by ruling out the interference from grain boundary structure dependence. Interestingly, proton irradiation has an acceleration effect on the intergranular oxidation of 316 L stainless steel after shorter-term oxidation (less than 500 h) but a mitigation effect at later stage (more than 500 h). It was found that Cr depletion at the pristine grain boundary due to radiation-induced segregation (RIS) plays a dominant role at the early stage of oxidation, resulting in a deeper intergranular oxidation than in the non-irradiated region. Nevertheless, the Cr content at the intergranular oxide tip in the irradiated region builds up faster than in the non-irradiated region with time due to the enhanced solute (especially Cr) diffusivity in the irradiated region. The positive effect of enhanced Cr diffusivity on resistance to intergranular oxidation gradually dominates after longer-term immersion and eventually leads to a shallower intergranular oxide penetration in the irradiated region. The faster intergranular oxidation in irradiated region due to RIS at the early stage partly explains the accelerated crack propagation of irradiated material as the oxidation condition at the crack tip is similar to that at the early stage.

Pipeline reliability assessment and predictive maintenance considering multi-crack dependent degradation

Cracks due to corrosion are one of the main reasons for natural-gas pipeline leaks. Making the reliability assessment, prediction, and maintenance decision of pipelines based on measurable crack data is a central issue at present. The failure of pipelines is usually a result of the cumulative impact of multiple cracks. The interaction between adjacent cracks accelerates crack propagation, and greatly affects the degradation mechanism of pipelines. In this study, the reliability prediction and maintenance decisions were studied by considering the dependent degradation between multiple cracks in pipelines. Firstly, the initiation and propagation of pipeline cracks were modeled using a non-homogeneous Poisson process and a Gamma process, respectively. The interaction between cracks was defined to be a function of the random crack distance, which could be reflected by the change of shape parameters in the Gamma process. Secondly, the pipeline’s failure was defined as the competitive failure of the number of cracks, the maximum crack depth, and the total crack depth. The reliability prediction model of a pipeline under this failure mode was determined. A non-periodic combined maintenance policy considering both the pipeline condition and its predictive reliability was then proposed, and an optimal predictive maintenance decision model was constructed to minimize the long-term average cost rate. Finally, the effectiveness of the proposed model and policy was verified by a numerical experiment and a crack dataset of a transnational pipeline.