Fatigue Crack Growth Research Articles

DEVELOPMENT OF HYDROGENATED SBR-BASED VULCANIZATE WITH SUPERIOR TIRE TREAD PERFORMANCE

ABSTRACT Currently, the tire industry is exploring eco-friendly tires with improved rolling resistance, traction, abrasion resistance, and fatigue properties. The present study investigates the potentiality of the hydrogenated styrene butadiene rubber (HSBR), a special and modified grade of styrene butadiene rubber (SBR) as a tyre tread material. The rheological, mechanical, dynamic mechanical, abrasion resistance, fatigue resistance, aging resistance and ozone resistance properties of the developed HSBR-based composites were critically evaluated and compared with those of conventional rubbers such as natural rubber (NR), emulsion styrene butadiene rubber (ESBR) and solution styrene butadiene rubber (SSBR) based composites. Interestingly, the HSBR-based vulcanizates exhibited superior modulus, tensile strength, abrasion resistance, fatigue crack growth resistance, resistance to thermo-oxidative aging, and ozone resistance as compared to the conventional SBR–based vulcanizates. The modulus at 300% elongation of the HSBR-based vulcanizate was approximately 74% and 11% higher than that of the ESBR- and SSBR-based composites, respectively, whereas the improvements in tensile strength were approximately 88% and 64% and the improvements in abrasion resistance were approximately 250% and 200% than that of the ESBR and SSBR vulcanizates, respectively. The tensile strength and fatigue resistance characteristics of the HSBR vulcanizate were also nearly similar to those of the NR vulcanizate. The findings demonstrate that HSBR can be a potential tire tread material with robust physico-mechanical properties and durability.

Hydrogen embrittlement effects on remaining life and fatigue crack growth rate in API 5L X52 steel pipelines under cyclic pressure loading

Transporting hydrogen gas through the existing natural gas pipeline network offers an efficient solution for energy storage and conveyance. Hydrogen generated from excess renewable electricity can be conveyed through the API 5L steel-made pipelines that already exist. In recent years, there has been a growing demand for the transportation of hydrogen through existing gas pipelines. Therefore, numerical and experimental tests are required to verify and ensure the mechanical integrity of the API 5L steel pipelines that will be used for pressurized hydrogen transportation. Internal pressure loading is likely to accelerate hydrogen diffusion through the internal pipe wall and consequently accentuate the hydrogen embrittlement of steel pipelines. Furthermore, pre-cracked pipelines are susceptible to quick failure mainly under a time-dependent cyclic pressure loading that drives fatigue crack propagation. Meanwhile, after several loading cycles, the initial cracks will propagate to a critical size. At this point, the remaining service life of the pipeline can be estimated, and inspection intervals can be determined. This paper focuses on the hydrogen embrittlement of API 5L steel-made pipeline under cyclic pressure loading. Pressurized hydrogen gas is transported through a network of pipelines where demands at consumption nodes vary periodically. The resulting pressure profile over time is considered a cyclic loading on the internal wall of a pre-cracked pipeline made of API 5L steel-grade material. Numerical modeling has allowed the prediction of fatigue crack evolution and estimation of the remaining service life of the pipeline. The developed methodology presented in this paper is based on the ASME B31.12 standard, which outlines the guidelines for hydrogen pipelines with reference to the ASME BPVC Section VIII, Division 3, Article KD-10.

Towards a Fracture Mechanics-Based Assessment for Fatigue Life Prediction of Ni–Ti Stents

The fatigue failure of Ni–Ti peripheral stents still represents an open issue of major concern due to the non-linear material behavior, the complex loads acting in vivo, and the manufacturing process. The fatigue assessment currently exploits total-life methodologies devoted to preventing crack nucleation. This work investigates a complementary fracture mechanics-based approach accounting for crack propagation from pre-existing manufacturing defects. Fatigue crack growth tests were performed on rolled Ni–Ti samples with a thickness and microstructure comparable to that of stents. A fracture mechanics-based assessment was implemented to predict the fatigue durability of surrogate samples tested at different mean and alternate strains. The fracture surfaces of the samples were inspected to determine a statistical distribution of defect size at the fracture origin. The cyclic J-integral was adopted as the crack driving force parameter, and it allowed to account for the complex response of the material, undergoing energy dissipations during phase transformation. Encouraging fatigue life predictions conforming to experimental data were obtained in the finite-life regime, whereas conservative estimates were computed below the fatigue threshold. This approach can be reverted to determine the maximum acceptable material defects for specific applications, providing a useful tool to manufacturing companies.

Parametric characterization of the Christopher–James–Patterson model for crack propagation in welded zone of A7N01 Aluminum alloys

AbstractAluminum alloy is a widely used material in railway vehicle structures. In order to accurately analyze the crack propagation mechanism of Aluminum alloy welding structures and predict their crack propagation life, this study focuses on the A7N01 Aluminum alloy and proposes a full‐field strain solution method based on the least‐squares method. For the first time, digital image correlation (DIC) experimental measurements are combined with the finite element analysis method to determine the shape and size of the plastic zone at the crack tip of the compact tension (CT) specimen. And it also calculates the crack propagation driving force parameters of the Christopher–James–Patterson (CJP) model using traditional crack propagation driving parameters. The research results revealed that the plastic zone at the crack tip captured by DIC experiments is in good agreement with the finite element simulation results. Additionally, the crack growth rate curve of the A7N01 Aluminum alloy, fitted based on the CJP model, is insensitive to the stress ratio. The results offer an effective approach to utilizing the da/dN‐∆KCJP curve in analyzing A7N01 Aluminum alloy and welded structural failures, broadening the scope of engineering applications for the CJP model.

Effect of hydrogenation on fatigue crack growth resistance of diffusion bonded TC4 titanium alloy laminates

A method was proposed to improve the fatigue crack growth (FCG) resistance of TC4 (Ti6Al4V) titanium alloy laminate by hydrogenation/low-temperature diffusion bonding/dehydrogenation (H-DB-DH) combined process. Effects of hydrogen contents and different dehydrogenation temperatures on FCG behaviors and tensile properties as well as microstructures were investigated. Residual hydrogen contents beneath fatigue fracture surfaces were measured to determine the safe dehydrogenation temperature. The hydrogen content of 0.3 wt% and dehydrogenation temperature of 780 °C are optimal to produce TC4 laminate with a 9.87 % improvement of FCG life compared with the diffusion bonded one without hydrogenation. FCG rate decrease results from the comprehensive effect of recrystallization volume fraction increase, grain refinement, mean geometrically necessary dislocations (GNDs) density decrease and texture intensity weakness as well as texture diversity improvement. This paper provides theoretical support for fatigue property improvement of titanium alloy by hydrogen diffusion bonding process.

A Model to Account for the Effects of Load Ratio and Hydrogen Pressure on the Fatigue Crack Growth Behavior of Pressure Vessel Steels.

A phenomenological model for estimating the effects of load ratio R and hydrogen pressure PH2 on the hydrogen-assisted fatigue crack growth rate (HA-FCGR) behavior in the transient and steady-state regimes of pressure vessel steels is described. The "transient regime" is identified with crack growth within a severely embrittled zone of intense plasticity at the crack tip. The "steady-state" behavior is associated with the crack growing into a region of comparatively lower hydrogen concentration located further away from the crack tip. The model treats the effects of R and PH2 as being functionally separable. In the transient regime, the effects of the hydrogen pressure on the HA-FCGR behavior were negligible but were significant in the steady-state regime. The hydrogen concentration in the steady-state region is modeled as being dependent on the kinetics of lattice diffusion, which is sensitive to pressure. Experimental HA-FCGR data from the literature were used to validate the model. The new model was shown to be valid over a wide range of conditions that ranged between -1≤R≤0.8 and 0.02≤PH2≤103 MPa for pressure vessel steels.

Investigating the influence of stress ratio variation on the crack growth rate in friction stir welded dissimilar aluminum alloys

This research focuses on the friction stir welding (FSW) of dissimilar aluminum alloys AA2024 and AA7075 and investigates the effect of different stress ratios on crack growth within dissimilar welded joints. The FSW process was performed at 760 rpm rotational speed and a feed rate of 50 mm/min. Subsequent crack growth tests were conducted on Compact Tension (CT) specimens extracted from the dissimilar FSW joint, applying varying stress ratios (R: −0.5, 0.0, 0.1, 0.5, 0.8) at a maximum load (Pmax) of 5 kN and a frequency of 6 Hz.The study meticulously analyzed and compared the tensile properties of weld joints and base metals. The hardness profile was plotted across the various weld zones. Experimental data were utilized to construct fundamental curves such as the a-N curve, crack growth rate curve, and stress–strain curve, enabling the determination of Paris constants. Notably, the research unveiled a clear relationship between stress ratio and fatigue life, indicating a decrease in fatigue life as the stress ratio increased. Specifically, the highest fatigue life of 45,000 cycles was observed at R=−0.5, while the lowest of 26,000 cycles was noted at R=0.8. Furthermore, electron microscopy was employed to scrutinize the fracture surface, providing valuable insights into its behavior.

Effect of Low Temperature on the Fatigue Crack Propagation Behavior of Underwater Manned Vehicle Rudder Materials in Arctic Environments.

During polar navigation, adverse environmental conditions like cold temperatures, fatigue, and corrosion can affect surface and underwater manned vehicles (UMVs). Understanding the fatigue fracture growth behavior of polar ship steel is crucial for ensuring safety. This study investigates the mechanical properties and fatigue fracture propagation of steel used in underwater vehicle rudders under various low-temperature conditions through experimental research. It compares and analyzes the static mechanical characteristics, fatigue crack growth rate, and fracture morphology of underwater manned vehicle rudder steels at different low temperatures. Findings show enhancements in yield strength, tensile strength, elastic modulus, and fatigue crack propagation life of steel 925A, steel 20#, and their welded parts under low-temperature conditions. The tensile strength of 925A steel, 20# steel, and their welded parts increases by 6.87%, 14.61%, and 12.55%, respectively, as the temperature decreases from 20 to -60 °C. The yield strength also increases by 14.17%, 29.09%, and 15.76%, respectively. Fatigue crack propagation rate experiments were conducted under different constant low-temperature conditions. This study offers direction for future modeling and experimental testing.

Study on the creep crack growth testing of metals based on direct and indirect methods

Research on creep crack growth in defective materials or structures at high temperatures is essential for structural security evaluations. As the creep displacement rates of the specimens are estimated using the stress intensity factor KI and plastic J-integral JP, the traditional ASTM method is essentially an indirect method and some limitations have been discovered in previous studies. Based on the quasi-static load–displacement and creep displacement rate models for specimens with mode-I crack, an indirect method for creep crack growth testing is proposed according to the derived formula of elastic and plastic displacement rate and a direct method that obtains the creep crack growth rate of materials using only the crack length a. Furthermore, an iterative method for obtaining the real-time crack length through displacement–time curves was discussed by combining the indirect and direct methods. The proposed methods were verified using the results of finite element analysis (FEA) and experimental results for various materials. These results show that the direct method for creep crack growth testing is simpler and more effective than the indirect method, and the results predicted by the new methods are consistent with those obtained using traditional and literature-based methods.

Numerical simulation of laser shot peening and fatigue performance test of AA2524 thin plate

In this study, laser shot peening (LSP) is applied to 2524 aluminum alloy (AA2524). The effects of LSP parameters (the range and the position of LSPed area and LSP times) on the residual stress distribution of the specimen are analyzed using ABAQUS software. The fatigue crack growth (FCG) experiment is conducted, and the FCG of both unpeened and LSPed specimens is simulated using the extended finite element method (XFEM). Then the Paris equation is used to predict specimens’ fatigue life. The results suggest that the compressive residual stress (CRS) gain effect increases as the width perpendicular to the crack tip increases in rectangular LSPed areas of the same size. Furthermore, when comparing specimens of LSPed area situated 0 and 3 mm from the fracture tip, it is observed that the specimen of LSPed area located 5 mm away exhibits the slowest rate of crack propagation.

Hydrogen Embrittlement Detection Technology Using Nondestructive Testing for Realizing a Hydrogen Society.

Crack detection in high-pressure hydrogen gas components, such as pipes, is crucial for ensuring the safety and reliability of hydrogen infrastructure. This study conducts the nondestructive testing of crack propagation in steel piping under cyclic compressive loads in the presence of hydrogen in the material. The specimens were hydrogen-precharged through immersion in a 20 mass% ammonium thiocyanate solution at 40 °C for 72 h. The crack growth rate in hydrogen-precharged specimens was approximately 10 times faster than that in uncharged specimens, with cracks propagating from the inner to outer surfaces of the pipe. The fracture surface morphology differed significantly, with flat surfaces in hydrogen-precharged materials and convex or concave surfaces in uncharged materials. Eddy current and hammering tests revealed differences in the presence of large cracks between the two materials. By contrast, hammering tests revealed differences in the presence of a half size crack between the two materials. These findings highlight the effect of hydrogen precharging on crack propagation in steel piping and underscore the importance of early detection methods.

Effect of multi-pass overlapping friction stir processing on fatigue behavior of Al-Cu alloy

More than half of mechanical breakdowns stem from fatigue failure, often occurring suddenly and without warning. Friction stir processing (FSP) enhances the material's toughness and resilience to fatigue by refining its grain structure. This study investigates how multi-pass overlapping technique impacts the fatigue crack growth rate of FSPed Al-Cu alloy. Microstructural analysis revealed that the stir region exhibited uniformly dispersed and fragmented precipitates and finely recrystallized ultrafine grains. The hardness and strength were reduced, and ductility was enhanced after FSP due to high thermal cycling. Fatigue testing demonstrated a significant increase in fatigue life and reduced fatigue crack growth rate attributable to the combined effects of precipitation and grain refinement during cooling-assisted FSP. SEM examination of fatigue fracture surfaces revealed dimples indicative of ductile failure in the rapid crack propagation zone, while the steady-state propagation region displayed striation markings and secondary fractures.

Ultrasonic vibration assisted directed energy deposition of titanium alloy: Microstructure control, strengthening mechanisms and fatigue crack behavior

Large-scale titanium alloy structural components fabricated using direct energy deposition (DED) technology have broad application prospects. However, the columnar grain structures and inhomogeneous microstructure due to the inherent characteristics of additive manufacturing seriously affects the mechanical properties of components. In this study, high-intensity ultrasound vibration was introduced into the wire-arc DED deposition of TC4-DT titanium alloy. The results showed that ultrasonic vibration assistance (UVA) significantly improves the grain structure (refine prior-β grain size and weaken α texture) of the as-deposited component, without introducing additional porosity. Compared to conventional wire-arc DED deposited components, the yield strength and tensile strength of UVA alloys increased by 22.23 % and 15.06 %, respectively. Furthermore, the difference in α grain structure caused by UVA results in different fatigue crack growth behaviors. The disorder orientation of the α laths enhanced the fatigue crack initiation resistance of the wire-arc DED component with UVA. This study shows the excellent mechanical properties of UVA DED fabricated TC4-DT alloy, paving the way for the design, fabrication, and application of large structural components of titanium alloys.

Study on the dynamic fracture mechanical properties of ultra high-performance concrete under the influence of steel fiber content

Ultra-high performance concrete (UHPC) is characterized by its ultra-high strength and durability, making it suitable for use in large-span bridges, super high-rise buildings, and other special structures. These types of structures often have high requirements for crack control, making the exploration of UHPC's fracture mechanics properties of significant importance. Therefore, this paper sets up four steel fiber contents (0 %, 0.6 %, 1.2 % and 1.8 %) and four strain rates (10−5/s, 10−4/s, 10−3/s and 10−2/s), totaling 16 working conditions. The hydraulic servo system combined with digital image correlation (DIC) technology was used to conduct fracture mechanics tests on UHPC three-point bending beams. The test results show that the unstable fracture load of UHPC increases with the increase of strain rate and steel fiber content, and increasing the steel fiber content can enhance the strain rate effect of UHPC to a certain extent. Additionally, combined with the J-criterion model, this study proposed a dynamic criterion for the unstable fracture load of UHPC considering the influence of steel fiber content. The initial fracture toughness, unstable fracture toughness, and fracture energy of UHPC are significantly more affected by steel fiber content than by strain rate. Through DIC technology, the analysis of UHPC crack propagation shows that UHPC without steel fibers experiences rapid crack expansion in the Pre-90 % to Peak stage, with less influence from the strain rate. However, UHPC with steel fibers exhibits a more uniform crack growth rate, with the crack emergence phase gradually lagging as the strain rate increases. For UHPC without steel fibers, the crack opening displacement (COD) at the unstable fracture load point surges suddenly, while the COD development in UHPC with steel fibers is slower. At lower strain rates, an increase in steel fiber content leads to an earlier sudden increase phase in UHPC's COD; at higher strain rates, the influence of steel fiber content on the sudden increase phase of UHPC's COD is more scattered. The research results of this paper provide a theoretical basis for the calculation and analysis of the dynamic response of UHPC structures under seismic loads.

Phase-field modeling of crack growth under coupled creep-fatigue

Crack growth under coupled creep-fatigue strongly influences service life of metallic components operating at high temperatures. However, there lack numerical models that enable direct simulations of crack growth and plasticity development under coupled creep-fatigue. In this study, a unified phase-field model is developed for simulating crack growth under fatigue, creep, and coupled creep-fatigue. This model is able to reproduce the Paris laws for both brittle and ductile materials in pure fatigue mode, which shows that the degradation rate due to cyclic stress in ductile materials is generally larger than that in brittle materials. Fatigue simulations with different yield strengths demonstrate that plasticity facilitates crack growth in typical ductile materials. High-throughput simulations are performed under coupled creep-fatigue conditions, with varying hold-stress levels and hold-time. By analyzing crack growth rate under different hold-time, a creep-fatigue interaction term is obtained. Simulation results demonstrate that the creep-fatigue interaction is caused by smaller stress gradient and enhanced degradation rate ahead of the crack tips under coupled creep-fatigue, compared to the situation of pure fatigue. This work reveals the origin of different Paris-law exponents in brittle and ductile materials and demonstrates how the interplay between creep and fatigue affects crack growth.

Uncertainty quantification in residual stress affected fatigue crack growth life

In recent years a number of studies have been performed in which the impact of residual stress on structural performance, especially fatigue performance, has been evaluated both experimentally and analytically. These efforts are leading to an emerging paradigm in which residual stresses are represented explicitly in structural design, analysis, manufacturing and sustainment calculations. In order for this new approach to be become minimally viable, it is necessary to be able to quantify both the residual stresses in the structural component in question, and the impact that those residual stresses have on component strength and life. However, to achieve general acceptance, especially for critical applications in which the presence of the residual stress directly impacts whether or not the component will meet its design requirements, deterministic quantification alone may not be sufficient. Thus, it may be necessary to quantify the uncertainties in both the residual stresses and the resulting fatigue lives.

Study of creep and creep crack growth fatigue of aging ASTM A297/A297M-19 HP steel modified with niobium

Study of creep and creep crack growth fatigue of aging ASTM A297/A297M-19 HP steel modified with niobium

Digital twin Bayesian entropy framework for corrosion fatigue life prediction and calibration of bridge suspender

This paper proposes an intelligent digital twin framework for corrosion fatigue life prediction and calibration of suspender wires integrated with mechanism-driven, sensor-driven, and information fusion. A general probabilistic information fusion strategy is constructed to handle entropy-based external constraints and classical Bayesian updating. Statistical moment, range bound, and point data are considered to investigate the effect of various types and sequences of information. A small-time domain fatigue crack growth model is proposed to overcome the limitations of traditional cycle-based methods, which can capture the large and small cycles of random fatigue stress. The virtual sensor-based stress time-history response is obtained under different traffic flow densities through digital twin finite element model of a suspension bridge. The results show that with and without considering interval bound leads to different fatigue life prediction results, especially for statistical moment data fusion, and the maximum difference is approximately 54%. The average prediction life of suspender wires is gradually close to the actual service life as crack observations increase. The standard deviations of the corrosion fatigue life decrease by 88%, when simultaneously integrating moment, interval, and point data.

Investigation on the fatigue crack growth behavior of welded joints in EH690 high-strength marine steel

EH690 high-strength steel (HSS) is extensively utilized in marine engineering due to its exceptional strength. The fatigue crack growth (FCG) behaviors of EH690 HSS welded joints in different zones (base metal (BM), heat-affected zone (HAZ), and weld metal (WM)) were investigated by conducting FCG tests with various stress ratios (R). The results demonstrate that the WM and HAZ materials exhibit enhanced resistance to FCG compared to the BM material. The higher stress ratios result in increased fatigue crack growth rates (FCGRs). The welded residual stress (WRS) distribution in the welded joints was predicted considering solid-state phase transformation (SSPT). Subsequently, a comprehensive analysis of the WRS influence on FCG behavior shows that the residual compressive stress enhances the material’s resistance to FCG. Additionally, the effect of R on the FCG behavior of the material was investigated by employing the Walker model, and the applicability of the Walker model was discussed as well. Finally, the FCG mechanisms of the different zones in the welded joint were investigated from a microscopic perspective, further exploring the influence of R on the FCG behavior.

Probabilistic hydrogen-assisted fatigue crack growth under random pressure fluctuations in pipeline steels

The increasing demand for energy and the global threat of climate change have driven the search for alternative energy sources, with hydrogen emerging as a prominent substitute for fossil fuels. The fatigue behavior of pipeline steels under gaseous hydrogen is a critical problem that is impeding the industry's adoption of hydrogen into the current natural gas infrastructure. A brief review of existing hydrogen-assisted fatigue crack growth (HA-FCG) studies, which reveal several key gaps, is given first. Existing HA-FCG models predominantly address constant amplitude loading, while the realistic driving force is random loading in gas pipelines. Also, the current uncertainty quantification studies for HA-FCG focus on material randomness and overlook the large uncertainties associated with random pressure fluctuations. To address these issues, this study proposes a HA-FCG model that utilizes a time-based subcycle approach, allowing for direct application to random spectrum loads without the need for cycle counting. A model parameter as a function of hydrogen operating conditions is introduced to capture the different regimes in HA-FCG, and the model predictions are compared with ASME B31.12 code. Following this, statistical analysis of random pressure fluctuation data collected from natural gas pipelines at multiple locations is performed. The realistic industry pressure data shows distinct statistical features, and it is observed that the high-fidelity data (high sampling frequency) is beneficial for accurate fatigue life predictions. Uncertainty quantification and load reconstruction are performed by the Karhunen–Loève expansion with a post-clipping procedure, leading to a probabilistic HA-FCG analysis. The paper concludes with key findings and suggests directions for future research.