Fatigue Properties Of Materials Research Articles

IKonPro®: A software for the probabilistic prediction of rolling contact fatigue

This work develops a software for the probabilistic prediction of rolling contact fatigue in multiple-row ball bearings subject to any loads and rotations. iKonPro®, as it has been named, calculates the failure probability of the raceways and the bearing, taking as input the material fatigue properties, contact-load and -angle distributions for discrete load cases, and the subsurface stress responses to different ball loads. The software is based on the determination of ball kinematics and equilibrium, raceways stress states, and local and global failure probabilities. Here, iKonPro® is applied to a wind-turbine pitch bearing and the results demonstrate that it correctly captures the size effect.

Distinguishing evaluation of plastic deformation and fatigue damage using pulsed eddy current testing

The vessels and pipes of nuclear power structures are subjected to complex forces. The structures suffer sudden loads that lead to plastic deformation and cyclic loads that result in fatigue damage. In practice, two types of microscopic damage may occur simultaneously. The effect of plastic deformation on material fatigue properties remains unclear, and there is a lack of effective methods to distinguish plastic deformation and fatigue damage. To address these issues, the fatigue life curve of 304 stainless steel is experimentally measured, and the influence of fatigue life due to the presence of plastic deformation under a certain load is investigated. It's identified that preset plastic deformation below 15% will increase the fatigue life of the structure. Additionally, a pulsed eddy current signal processing and reconstruction method based on the empirical modal decomposition (EBD) method is proposed. Finally, the pulsed eddy current signal characteristics of plastic deformation and fatigue damage are analyzed, and a distinguishing evaluation method of fatigue damage with preset plastic deformation is established.

Bayesian model averaging for probabilistic S-N curves with probability distribution model form uncertainty

Reliability analysis of engineering components or structures heavily relies on accurately estimating the fatigue properties of materials. However, significant uncertainty exists regarding the distribution form and value in fatigue data, posing significant challenges in constructing a robust probability fatigue model. To address this challenge, we propose a Bayesian model averaging (BMA) method to incorporate model form uncertainty into the estimation of the probability density of fatigue life. The performance of BMA was verified through numerical experiments using both simulated and experimental data. The results highlight the robustness and reliability of BMA compared to individual models, as it effectively incorporates model form uncertainty. The proposed BMA model offers a general framework for developing probabilistic fatigue models with high robustness and accuracy in their predictions. This model contributes to advancing the field of reliability analysis by addressing the challenges posed by uncertainty and enhancing the understanding of fatigue properties for engineering components and structures.

Thermal-mechanical-equivalent fatigue load method for mechanically fastened Hybrid-material structures

It is difficult to verify the fatigue performance of mechanically fastened hybrid-material structures under the complex environment-load spectrum. A thermal–mechanical-equivalent fatigue load method was proposed, so that the structure has the same fatigue damage distribution under the equivalent load and the original thermal–mechanical load. By considering the influence of environmental temperature on the structural fatigue performance and the dispersion of material fatigue property, the calculation model for the fatigue damage distribution of fastened structure was established. The equivalent load could be determined according to the designed tolerance value of distribution difference. The effectiveness of method was verified by 7050-T7451 aluminum alloy/CFRP laminate plate three-bolt single-lapped hybrid fastened specimens.

A complete SRSS format for the response spectrum method of high-cycle fatigue life assessment considering modal truncation error correction

In this paper, a more accurate and efficient format of the fatigue response spectrum method is further proposed considering modal truncation error. Firstly, the quasi-static response of higher-order modes is taken into account to modify the modal truncation error. Then, an analytical description of the cross-correlation between the modal responses as well as quasi-static response is developed by two coefficients associated with the natural frequency and modal damping ratio. Finally, the expected damage rate is transformed into a summation of modal damage responses strictly, resulting in a dual improvement in accuracy and efficiency. In numerical examples, the correctness and efficiency are verified and the influences of load spectrum and material fatigue properties on the modal truncation error are further investigated.

Analytical model for measurement of stresses using two-hole drilling

Residual stresses have a significant effect on the strength, deformation, plasticity, and fatigue properties of materials. In general, tensile residual stresses are adverse to material performance and component life, while compressive residual stresses can improve material fatigue strength. In this study, an analytical model employing two-hole drilling (THD) is proposed for the measurement of interior stresses. Firstly, the analytical solution for the distortion of the reference hole induced by drilling an adjacent hole is derived using the complex variable method. Based on the analytical solution, the reverse procedure is established to determine the original stress state. Then, the comparative validations of the THD method with the deep hole drilling (DHD) method are performed in conjunction with the finite element (FE) simulations for the beam subjected to bending, the unloaded elastoplastic beam, and the shrink fitted assembly. Finally, parametric analysis is conducted and the results show that: the influence of drilling an adjacent hole on the reference hole rises with the increase of the hole diameters or the decrease of the hole spacing; the THD method is able to give good estimations for the stresses with linear, parabolic, and sinusoidal distributions, although the accuracy is reduced for the prediction of the longitudinal residual stress in the cold-formed section; the uncertainties in evaluated stresses ascend linearly with the increase of the measurement error in the diameter of the reference hole. Relative to the DHD method, the THD method has the merits of less damage and less equipment required and can provide an effective approach for the measurement of stresses inside materials.

Technique for Introducing Internal Defects with Arbitrary Sizes and Locations in Metals via Additive Manufacturing and Evaluation of Fatigue Properties

Mechanical component failure is usually caused by metal fatigue originating from small defects in metallic materials. Thus, it is important to precisely capture the fatigue properties of materials containing small defects. Fatigue tests of materials with artificial surface defects introduced by drilling have been conducted. Using the resulting data, an equation for predicting the material fatigue limit has been proposed on the basis of the √area parameter model, and its effectiveness has been confirmed for various materials. However, for additive manufactured (AM) materials that contain internal defects resulting in failure, controlling the size of the defect where the fracture originates is extremely difficult. Therefore, verification of the predictive ability of the √area parameter model for AM materials is impossible, in contrast with other materials that fail because of surface defects. In this context, developing a technique to intentionally introduce internal defects with arbitrary sizes at arbitrary locations can provide insights that help predict the fatigue limit of AM materials. This study aimed to establish a technology for quantitatively evaluating the effect of internal defects on the fatigue properties of AM materials by introducing internal defects with arbitrary sizes at arbitrary locations via AM. Specimens with different defect sizes and locations were prepared. Prior to the fatigue tests, the defect sizes and locations were measured non-destructively via X-ray computed tomography (CT). The fatigue tests were conducted in air at room temperature. All the specimens failed because of the intentionally introduced internal defects, and the fatigue lives became shorter with increasing defect sizes, except for the specimens with defects adjacent to the surface. In those cases, fatigue cracks easily reached the surface; therefore, the fatigue lives were speculated to be shorter than those of the specimens with the same defect sizes. Moreover, the defect sizes determined from the fracture surfaces by scanning electron microscopy were nearly consistent with those determined by X-ray CT.

Anisotropy Evaluation and Defect Detection on Laser Power Bed Fusion 316L Stainless Steel.

Because of rapid heating, cooling, and solidification during metal additive manufacturing (AM), the resulting products exhibit strong anisotropy and are at risk of quality problems from metallurgical defects. The defects and anisotropy affect the fatigue resistance and material properties, including mechanical, electrical, and magnetic properties, which limit the applications of the additively manufactured components in the field of engineering. In this study, the anisotropy of laser power bed fusion 316L stainless steel components was first measured by conventional destructive approaches using metallographic methods, X-ray diffraction (XRD), and electron backscatter diffraction (EBSD). Then, anisotropy was also evaluated by ultrasonic nondestructive characterization using the wave speed, attenuation, and diffuse backscatter results. The results from the destructive and nondestructive methods were compared. The wave speed fluctuated in a small range, while the attenuation and diffuse backscatter results were varied depending on the build direction. Furthermore, a laser power bed fusion 316L stainless steel sample with a series of artificial defects along the build direction was investigated via laser ultrasonic testing, which is more commonly used for AM defect detection. The corresponding ultrasonic imaging was improved with the synthetic aperture focusing technique (SAFT), which was found to be in good agreement with the results from the digital radiograph (DR). The outcomes of this study provide additional information for anisotropy evaluation and defect detection for improving the quality of additively manufactured products.

Thermal fatigue testing with repeatable temperature cycles on thermomechanical simulator

This paper presents two thermal fatigue tests developed to simulate the typical thermal fatigue behavior of hot-work tools and rolls. The tests are carried out on a Gleeble 1500D thermomechanical simulator with computer-controlled heating and cooling of the test specimens. In the first test, internal cooling of the specimens is performed, and in the second test, external cooling is performed. This allows constant test conditions and the collection of reliable experimental data on the thermal fatigue behavior. The internally cooled test rig is used for testing the thermal fatigue properties of bulk materials. Indefinite chill double-poured cast iron is used to present the basic capabilities of the test. At the material, the cracks take flattened graphite–cementite pathways. The external cooling test rig, on the other hand, is designed for comparative testing of four surfaces simultaneously. Thus, the capabilities of the second test are presented in the comparative testing of three different laser-welded functionally graded material surface layers and the basic H13 tool steel, simultaneously. The highest thermal fatigue resistance is shown by the weld with the lowest silicon (Si) content. Quantitative evaluation of thermal fatigue resistance as well as following of degradation processes in both tests is enabled.

Fatigue crack growth behaviour of wire arc additively manufactured steels

Combining welding technology with robotics, wire arc additive manufacturing (WAAM) is emerging as a viable method of construction. To facilitate its wider application, in particular with structural integrity in mind, an improved understanding of the fatigue properties of WAAM materials is needed. Hence, an experimental investigation into the fatigue crack growth (FCG) behaviour of WAAM plates made of normal- and high-strength steels has been conducted and is reported herein. Following material characterisation, FCG tests on 13 machined compact tension specimens were undertaken, extracted in different directions from WAAM plates built using a parallel deposition strategy. Fractography of the tested specimens was also performed to analyse the mechanisms of crack growth. The material testing demonstrated an approximately proportional relationship between the hardness and ultimate strength. From the FCG tests, Paris’ law constants were derived for the WAAM normal- and high-strength steel specimens, revealing consistently lower material constants m for the latter. Similar FCG behaviour to that of equivalent, conventionally-produced steels, with no significant anisotropy, was found. The observed response was shown to be generally well captured by the FCG laws given in BS 7910, with the recommended curve for unwelded steels providing a close match to the experimental data and the recommended curve for welded steels providing conservative predictions. Additional FCG data on WAAM steels printed using the parallel and oscillatory deposition strategies were collected and analysed. It was shown that the two deposition strategies led to similar crack growth rates for WAAM normal-strength steels, but distinct FCG behavioural trends for WAAM high-strength steels. Finally, the fractographic analysis showed that the WAAM specimens exhibited principally brittle behaviour during FCG but somewhat ductile behaviour before fracture.

A fatigue limit evaluation method based on plastic strain incremental energy dissipation theory

Metallic materials frequently undergo fatigue failure during long-term service. Therefore, the study of fatigue performance detection methods with high precision and wide application ranges is crucial to reduce fatigue failures and accidents of materials and structures. In this study, a plastic strain incremental energy dissipation theory (PSIEDT) is established, and a general expression for fatigue limit is derived with the starting point of the plastic strain increment. Taking 42CrMo4 steel as an example, and its temperature and deformation fields are obtained synchronously using infrared thermal imaging and digital image correlation. Its fatigue limit is evaluated using the energy dissipation theory based on the plastic strain increment. The results show that the relative error between the fatigue limit measurement accuracies of the developed method and the method proposed by Luong is 1.64 %. The relative error of the fatigue limit obtained for the local damage region is only 0.18 %, which has a high measurement accuracy. At the microscopic level, the onset of plastic strain corresponds to a change in the microstructure of the material from reversible deformation (viscoelastic) to permanent deformation (plasticity). Therefore, the strain measurements have higher sensitivity than the temperature measurements. Considering the limited heat release of many materials, the new method has a wide application range, can rapidly obtain material fatigue properties, and has good engineering application prospects.

Improved Fatigue Performance and Cost-Effectiveness of Natural Rubber Latex–Modified Cement-Stabilized Pavement Base at Raised Temperatures

The increased temperature at the early state of curing affects the fatigue properties of pavement base materials. The fatigue properties of stabilized pavement bases and subbases govern the performance and service life of pavement structures. This research study utilized natural rubber latex (NRL) to enhance the tensile fatigue properties of cement-stabilized base materials at various temperatures. The effects of influence factors such as cement content (3%, 5%, and 7%), NRL replacement ratio (0%, 10%, 15%, 20%, 25%, and 30%), and temperature (25°C, 40°C, and 60°C) on indirect tensile strength (ITS), indirect tensile resilient modulus (IT Mr), and indirect tensile fatigue life (ITFL) were studied in this research. NRL replacement was found to improve the UCS, ITS, IT Mr, and ITFL of cement (C)-stabilized soil up to the highest values at the optimum NRL replacement ratios, which were 20%, 15%, and 10% for cement contents of 3%, 5%, and 7%, respectively. The cement-NRL (C-NRL)-stabilized samples were found to have superior ITS, IT Mr, and ITFL values compared with C-stabilized samples for the same cement content but had the same rate of reduction in ITS due to the raised temperature. For the NRL replacement ratio on the dry side of optimum, the C-NRL-stabilized samples had lower rate of IT Mr reduction than the C-stabilized samples, although they had the same ITS due to the higher toughness. Therefore, the rate of ITFL reduction of C-NRL-stabilized samples was lower than that of the C-stabilized samples. It was proven in this research that the NRL replacement could reduce the thickness (superior IT Mr) of a cement-NRL-stabilized base course for a given traffic volume and service life, and therefore the construction (material and operation) cost by 17.26% benchmarked to a C-stabilized base course. Finally, the cost-effective design method for C-NRL-stabilized bases course was proposed, which will promote the use of NRL as an alternative green additive instead of synthetic polymer.

Fatigue Analysis for Automotive Wheel Bearing Flanges

The automotive wheel bearing is an integral component of automobiles that transfers rotation and supports the weight of the vehicle. The life of automotive wheel bearings can be categorized into the raceway and flange lives. The raceway life is based on the spalling that occurs in the raceway and can be determined analytically using the basic rating life calculation method for the rolling bearing.The flange life is based on failure involving the flange and can be numerically predicted through fatigue analysis. In particular, the fatigue analysis for predicting the flange life must consider rotation owing to the bearing characteristics, unlike the general fatigue analysis. In this study, we examined the fatigue analysis of the automotive wheel bearing flange while considering rotation. We performed sequential stress and fatigue analyses using commercial software. As the fatigue material properties are required for fatigue analysis, we obtained the properties by conducting a rotary bending fatigue test on the bearing materials. To verify the results of the analysis, we compared the analysis results with the test results. The validity of the proposed fatigue analysis was confirmed.

Effect of shot peening on electrophoretic deposition of bioactive glass coating on AISI 316L stainless steel

Bioactive glass coating of SiO2–CaO–P2O5 was synthesized and deposited on shot peened stainless steel AISI 316L substrates through electrophoretic deposition. Shot peening is known to enhance the fatigue properties of the substrate material; however, the present study aims to investigate how this prior shot peening can affect on the electrophoretic coating properties and performance. Shot peening was carried using two different sets of parameters as conventional shot peening (Almen intensity: 15A and coverage:100%), and severe shot peening (Almen intensity: 7C and coverage:1500%). The coated samples were studied regarding deposition thickness, microstructure, macrotexture and surface roughness, as well as wettability with contact angle tests. Corrosion behavior was also investigated using potentiodynamic polarization and electrochemical impedance spectroscopy in simulated body fluid solutions at 37 °C. The results confirmed that the coating thickness decreased from 55.3 μm for CNP to 27 μm and 9.5 μm for CCSP and CSSP respectively. Shot peening applied before electrophoretic deposition modulated the wettability and corrosion resistance of the coated samples through variation of roughness and the extent of grain refinement. As well as, the water contact angle of CSSP sample was equal to 15.64° which is much lower than CNP (55.3°). Also, the amount of coated samples’ corrosion rate changed by this order CCSP (1.91 × 10−2)>CNP (1.31 × 10−2)>CSSP (1.07 × 10−2). The high surface energy on shot peened samples caused the smaller BG grain size deposited on surfaces. The amount of BG grain size of each sample is as follow CNP 2.12 ± 1.6 μm, CCSP 1.34 ± 0.8 μm and CSSP 0.81 ± 0.3 μm.

Improved fatigue properties of cement-stabilized recycled materials – Lateritic soil using natural rubber latex for sustainable pavement applications

This research project investigates the role of a new recycled pavement material and natural rubber latex (NRL), in improving the resilient and fatigue performances of cement-stabilized recycled materials and lateritic soil (LS) blends under traffic loads. Two types of recycled materials, being steel slag (SS) and recycled concrete aggregate (RCA) and 5% cement content by weight were studied in this research. The dry rubber content in NRL to cement (r/c) ratios of 0%, 3%, 5%, 10%, and 15% were designed as the influence factor. The results indicated that mechanical strength properties namely unconfined compressive strength (UCS) and indirect tensile test (ITS), as well as fatigue properties namely indirect tensile resilient modulus (IT Mr) and indirect tensile fatigue (ITF) were enhanced with the NRL additive. Beyond the optimum r/c ratio, the excessive amount of NRL generated thick NRL films and retarded the cement hydration products, resulting in low strength and performance improvement. The r/c ratios of 3% and 5% were found to be the optimum r/c ratios for cement-NRL stabilized SS:LS and RCA:LS blends, respectively. The brittleness and permanent deformation of cement-stabilized SS/RCA:LS blends were significantly improved by the NRL additive. The superior mechanical and physical properties of SS and RCA were also attributed to the enhancement of fatigue characteristics of the cement-NRL stabilized blends. Finally, the mechanistic and fatigue models of cement- and cement-NRL stabilized soil with recycled material replacements were proposed, which are important for pavement designers and engineers when using a mechanistic-empirical pavement design approach.

Experimental Study on Mechanism, Aging and Fatigue Performance of Warm Mixing Speed Melting SBS Modified Asphalt Binders

In this study, two kinds of quick melting modifier SBS-T and SBS-W, as well as the traditional SBS modifier, were used in the optimization design of asphalt binders. The changes in material structure and fatigue properties of three polymer-modified asphalt after adding 3% Sasobit to warm mix agent were investigated. The feasibility of SBS-T and SBS-W in asphalt binder was discussed from the modification mechanism and fatigue properties. In order to reveal the modification mechanism, the interaction mechanism between the fast-melting SBS modifier and the base asphalt was characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The temperature sensitivity and viscoelastic properties of SBS-T and SBS-W modified binders were determined by frequency scanning (FS). The fatigue properties of SBS-T and SBS-W modified binders were tested by linear amplitude scanning (LAS). The results of FTIR showed that there was no chemical reaction between the SBS-T and SBS-W and the base asphalt. XRD results showed that SBS-W-modified asphalt has stronger fluidity. The results of FS and LAS showed that the asphalt binder with Sasobit has good stiffness and elastic recovery ability, and the same SBS-T and SBS-W have better temperature sensitivity and deformation resistance. In addition, the fatigue life of asphalt binder under the linear viscoelastic continuous damage theory is increased 3.9 times by SBS-W.

Historical review and future prospect for researches on very high cycle fatigue of metallic materials

AbstractSince the first paper on the fatigue of metallic materials by J. Albert in 1837, tremendous numbers of papers have been published in various journals by many researchers all over the world. Based on such a long history, several papers on the very high cycle fatigue (VHCF) in the life‐time longer than 107 cycles had appeared in some journals during the period of 1980's. One characteristic finding in these works is the fact that the metallic material can fail even at the stress level lower than the conventional fatigue limit. This fact means that the conventional fatigue design of mechanical structures cannot give the safety of the practical products in the very high cycle regime. Due to this fact, fatigue properties of structural materials in very long life regime has become an important subject; and a lot of studies have been carried out, and many important results have been accumulated until now. Typical aspects on VHCF property are summarized as follows: (1) the fatigue crack tends to occur around the interior inclusion, (2) fine granular area (FGA) is formed around such an inclusion, and (3) duplex S–N characteristics appear in the VHCF regime. In this paper, a brief historical review together with the future prospect on the very high cycle fatigue of metallic materials is attempted for the sake of reference to facilitate the research in this area.

Coupling effects of microstructure and defects on the fatigue properties of laser powder bed fusion Ti-6Al-4V

The coupling effects of microstructure and macro-scale defects are significant for the fatigue properties of metallic materials. However, this correlation is still vague for additively manufactured materials. Therefore, the fatigue properties and microstructure of laser powder bed fusion (LPBF) Ti-6Al-4V were studied in this work, it is found that there is an anomalous trade-off relationship between the hardness and the high-cycle fatigue properties. Surprisingly, the softest microstructure has better fatigue resistance, i.e., its tensile strength is reduced by over 23%, while its fatigue strength is increased by ∼28%, compared with the hardest stress-relieved state. Statistical analysis on the fatigue source morphologies indicates that the hard α′ microstructure is sensitive to lack of fusion (LOF)-type defects while the soft lamellar (α + β) microstructure is sensitive to pore-type defects, which may be related to the higher tolerance concerning sharp defects for the soft microstructure relative to the hard one. Through considering the transition of the fatigue cracking mechanism and the effect of the microstructure, a fatigue life prediction model has been developed based on the Murakami theory, which does not only give a sound explanation for the trade-off relationship but is also in good agreement with the fatigue data for different defect characteristics and microstructure states at different applied stress amplitudes.

Synthetic SN Curve of Steel Beams with Web Opening

Steel beams with web opening have become a popular structural element nowadays owing to their several structural and architectural benefits. This study numerically investigates a study of the behavior of steel beams with a web opening subjected to fatigue loading using the finite element software ANSYS. Simply supported I-section steel beams with a single web opening were studied under a fully reversed, uniformly distributed vertical load. Fatigue loading, material properties, and boundary conditions are discussed in detail. Finite element analysis was used to determine the effect of the web opening on the normal stress induced in the steel beam and consequently on fatigue stress life. Then, a parametric study was performed to investigate the effect of two geometric parameters (opening size alpha and opening location beta ). In addition, suitable fatigue categories were suggested to guarantee safety against fatigue failures. Further, an analytical method for predicting the synthetic SN curves for steel beams with web opening was introduced. The proposed method was validated using SN curves obtained from FE results and was proven safe and slightly conservative for steel beams with a single web opening of various sizes and locations, as well as spans.

Correlation model between surface defects and fatigue behavior of 2024 aluminum alloy

Surface defects and microstructure have a significant impact on the fatigue properties of materials. In this paper, surface roughness was considered as surface micro-defects, and the correlation between surface defects and fatigue properties of 2024 aluminum alloy was investigated by applying laser scanning microscopy and electron backscatter diffraction (EBSD) techniques, combined with monotonic tensile tests and fatigue tests. It was found that the Gumbel distribution could better describe the size distribution of surface defects. Meanwhile, the fatigue limit was predicted based on the extreme value statistics of surface defects and the modified Murakami model, and compared with the experimental fatigue limit. Then an extended Kitagawa-Takahashi diagram was developed to evaluate the defect tolerance. In addition, a fatigue life prediction model considering surface roughness as a surface defect and taking into account short crack extension was proposed and validated against experimental data.