High Temperature Fatigue Life Research Articles

High-temperature low-cycle fatigue characteristics of the 12Cr10Co3MoWVNbNB turbine rotor steel

Low-cycle fatigue (LCF) experiments of the 12Cr10Co3MoWVNbNB steel at 598 °C and a strain amplitude ranging from 0.27 % to 0.55 % were executed to reveal the fatigue characteristics, fatigue fracture mechanism, and further to predict the high-temperature fatigue life of the new-style turbine rotor steel. The results indicate that the steel exhibits a high-temperature fatigue softening characteristic. During the high-temperature LCF, the cracks are generated at surface or subsurface defects of the specimens, and the fatigue striations and dimples are apparent on the fracture surfaces of the crack propagation zone and the final fracture zone, respectively. The Smith-Watson-Topper (SWT) and Manson-Coffin models are suitable to predict the high temperature fatigue life of the steel at high/low strain amplitudes, respectively. In terms of finite element analysis of the turbine set rotor, it is determined that the steady state strain of the rotor steel is approximately 0.2 %. And thus, the fatigue life of the steel rotor is estimated as 172,500 cycles at the strain amplitude, based on the Eq. (6) in this work. After 100,000 cycles at the strain amplitude, the yield and tensile strengths of the steel specimens are only reduced by 1 % and 3 %, respectively, indicating a long residual life, which is consistent with the above predicting result.

High Temperature Fatigue of Additively Manufactured Inconel 718: A Short Review

Abstract With the increasing interest in adopting additively manufactured (AM) IN718 for high-temperature applications, driven by the design and manufacturing flexibility offered by AM technologies, understanding its fatigue performance is crucial before full-scale adoption. This paper reviews the recent literature on the high-temperature fatigue behavior of AM IN718. The review focuses on two primary stages of fatigue damage: fatigue crack initiation and fatigue crack growth. Notably, most existing studies have concentrated on fatigue crack initiation, and thus, this review emphasizes this aspect. In the fatigue crack initiation stage, discrepancies in low cycle fatigue (LCF) and high cycle fatigue (HCF) life performances are observed in the literature. Some studies have shown that the average room temperature (RT) fatigue life of AM IN718 is superior or comparable to that at high temperatures in the LCF regime. Conversely, in the HCF regime, high-temperature fatigue life is sometimes found to be superior to that at room temperature. However, other studies indicate no clear trend regarding the effect of temperature on HCF life. Although various mechanisms have been proposed to either improve or degrade fatigue performance across the LCF, HCF, and very high cycle fatigue (VHCF) regimes, the underlying reasons for the distinct behaviors in these regimes remain unclear. Competing mechanisms, such as surface oxide formation and thermally driven dislocations glide, can potentially enhance or reduce fatigue life. However, the interaction and control of these mechanisms over the fatigue strength of AM IN718 are not yet fully understood. Systematic studies are required to elucidate their roles in high-temperature fatigue. Microstructural investigations have suggested that controlling the formation and precipitation of deleterious secondary phases is crucial for tailoring the high-temperature fatigue strength of AM IN718. Therefore, it is imperative to design heat treatment protocols informed by a comprehensive understanding of phase formation kinetics to improve the high-temperature fatigue performance of AM IN718 compared to their traditionally manufactured (TM) counterparts. This is particularly important for IN718 parts manufactured using directed energy deposition technology, which currently lacks standardized heat treatment procedures. The review also identifies open research areas and provides recommendations for future work to address these gaps.

Fatigue life and experimental study of high-temperature bellows based on the improved Manson-Coffin equation

Based on the high-temperature fatigue failure mechanism, this study proposes the use of the maximum shear strain range of crystal slip systems as the fatigue damage parameter and improves the Manson-Coffin equation accordingly. An Inconel-625 bellows model is constructed using the ANSYS Workbench platform for thermo-mechanical coupled analysis (temperature of 650 °C, displacement load of 7 mm, internal pressure of 0.3 MPa). Stress tests, including circumferential and axial stress, are conducted on the bellows to verify the accuracy of the finite element model. The six strain components in the model are extracted, and the improved Manson-Coffin equation is applied to calculate the fatigue life of the high-temperature bellows, resulting in a value of 12,318 cycles. Additionally, high-temperature fatigue life tests are performed on the Inconel-625 bellows under the conditions of 650 °C, 7 mm displacement load, and 0.3 MPa internal pressure, yielding a measured fatigue life of 9163 cycles. By comparing the experimental results of this study with those from relevant literature and plotting error band charts, it is demonstrated that the results obtained using the improved Manson-Coffin equation fall within a two-fold error band, validating the applicability of the improved Manson-Coffin equation for calculating the high-temperature fatigue life of bellows with different temperatures and models.

Enhancement of high-temperature fatigue properties of 310S stainless steel welded joints by strengthened grinding process inducing gradient structure

This study employed the strengthened grinding process (SGP) for surface enhancement treatment of 310S stainless steel weld joints. The surface characteristics and high-temperature fatigue performance were investigated. Initially, the effects of different SGP durations on the surface morphology, microhardness, and residual stress of the weld joints were studied. Subsequently, the high-temperature fatigue life of samples processed through SGP was examined, and the potential mechanisms underlying the impact of SGP on the high-temperature fatigue behaviour of 310S stainless steel weld joints were discussed. The maximum hardness of SGP-6M samples was 337 HV, while the average hardness of UP samples was 163 HV, and the maximum hardness of SGP-6M samples increased by 90.18 % compared to UP samples. The surface residual stress changed from a residual tensile stress of 205.24 MPa to a residual compressive stress of −864.76 MPa. At 25 °C, 500 °C, 600 °C, and 700 °C, the fatigue life increased by 36.9 %, 31.7 %, 25.9 %, and 18.6 %, respectively. This research demonstrates that SGP is an effective method for increasing the high-temperature fatigue life of turbine blades.

High-temperature fatigue life improvement of small-deep holes by using a novel cold expansion process in a nickel-based superalloy

Cold expansion of holes is a typical strengthening technology widely used in aviation parts and can effectively improve the fatigue life of hole structures. In this paper, a novel hole strengthening technology called the multi-annular convex hull rotating cold expansion process (MCR-CEP) for small-deep holes (diameter 1.72 mm, depth 10 mm) is proposed. After application of MCR-CEP at different expansion degrees (δ= 20–50 μm), the hole walls exhibit a lower surface roughness (Ra from 0.152 μm to 0.296 μm), higher microhardness (HV from 465 to 510), an obvious plastic deformation layer (depth of 15–35 μm) and a compressive residual stress layer. Under the optimal expansion degree (δ= 40 μm), the average fatigue life of the MCR-CEP specimens increased by 1.06–3.18 times at different thermal loads (300–700 °C) and mechanical loads (700–1000 MPa). The results of scanning electron microscopy (SEM) examination of fatigue fractures show that the possibility of crack initiation can be effectively reduced by the existence of a low surface roughness and plastic deformation layer in the top layer of the hole wall when the tested temperature is lower than 600 °C. The higher the mechanical loads are, the closer the crack initiating source is to the surface of the hole wall.

Development and performance of data-driven models for the prediction of the high-temperature fatigue life of alloy 617

Regularised linear regression (RLR) and recurrent neural network (RNN) data-driven models for the prediction of the high-temperature (850 °C, 950 °C) fatigue life of Alloy 617 are developed, trained, and tested using available experimental datasets. The predictions of these data-driven models are compared with the semi-empirical Coffin-Manson and Goswami models. It is shown that the data-driven models can match, or in some cases even outperform, the semi-empirical models while providing the advantage that they are temperature independent. However, it is also shown that these data-driven models cannot extrapolate accurately beyond the experimental data used for their development and training.

Fatigue life prediction of 3D braided carbon/carbon composites with braided angle variation at elevated temperature

The braiding angle of 3D braided carbon/carbon composites (C/CCs) will change during high temperature fatigue loading, which will affect the fatigue properties of 3D braided C/CCs. In order to realize this dynamic simulation in the high temperature fatigue life prediction of 3D braided C/CCs and further improve the prediction accuracy of high temperature fatigue life of 3D braided C/CCs, a high temperature fatigue life prediction model of 3D braided C/CCs considering the change of braiding angle with fatigue cycle number was established. The establishment of the prediction model mainly includes: a meso-scale representative volume elements (RVEs) of 3D braided C/CCs considering yarn direction and fiber bundle cross-section shape is established at the meso-scale; the high temperature residual stiffness and residual strength models of fiber bundles considering high temperature and stress level are established. Based on the experimental data characteristics of high temperature fatigue residual stiffness of 3D braided C/CCs, a mathematical model of cycle number/braided angles (CN/BAs) is established. The fatigue life prediction model was used to predict the 3D braided C/CCs at 700°C and stress levels of 87% and 85%. The results showed that the prediction error of single flower node was less than 5%. The fatigue life prediction error is less than two times the tolerance.

Influence of stirring process during slurry formation on the casting defects and high-temperature fatigue of rheocast AlSi7Mg alloys

The effects of the stirring phase during slurry formation on the defect’s content and the influence on the high-temperature fatigue behaviour of a rheocast AlSi7Mg alloy were investigated. Single or double-stir step was used during RheoMetal processing. Metallographic and image analysis techniques were performed to quantitatively examine the defect’s changes occurring with different stirring methods. Samples were cross-sectioned along the gauge length, and the pores content was measured. Uniaxial fatigue tests were performed at high temperature (150 °C) with the staircase method, applying a stress ratio of R = −1. Fracture surfaces were examined using a scanning electron microscope to determine the fatigue crack initiation sites, type and size of the defects. Shrinkage porosity has more probability of acting as a crack initiator than gas porosity or oxides. The double-stir step effectively reduces the size of pores compared to the conventional technique; it reduces porosity to less than half if compared to the single-stir process. Shrinkage pores distribution show a higher population of smaller pores for the double-stir process. According to the Dixon-Mood formula, the mean fatigue strengths are comparable. The capability of the double-stir to reduce porosity is evident, even having no significant effect on the high-temperature fatigue life.

Effect of Strain Range and Hold Time on High Temperature Fatigue Life of G17CrMoV5-10 Cast Alloy Steel

Abstract In this work, cast steel G17CrMoV5-10 was investigated. The material subject to investigation as part of this study is commonly used to manufacture steam turbine casings. Modern steam turbines operate under elevated temperature and complex oscillated loads. Thus, the focus of this study was to investigate material under behavior during low cycle fatigue (LCF) test performance at 500°C with and without hold time in tension. During all types of test, cyclic softening of cast steel was noticed. Increasing of total strain rate and applying hold time significantly reduce fatigue life. During hold time, due to temperature and tension the material creep what is confirmed by increasing inelastic stain accommodation.

Effect of microstructures restoration on high temperature fatigue behavior of DZ125 superalloy

Combination of hot isostatic pressing (HIP) and rejuvenation heat treatment (RHT) technology was used to restore creep-damaged DZ125 directional solidified superalloy, and the influence of microstructure restoration on high temperature fatigue behavior of the samples was explored. The results show that the HIP+RHT process could effectively heal internal cavities and recover the degraded γ′ phase in creep-damaged DZ125 superalloy to cubic particles similar as in as-received sample. After restoration treatment, the stress concentration areas inside the sample eradicated with the healing of the internal cavities, and the fatigue source areas were limited only to near surface than initiating from inside as in the as-received and creep-damaged samples. As a result, the restored sample had higher crack initiation life and lower crack propagation rate compared to as-received and creep damaged samples. The TEM microstructure characterization near fatigue fracture showed that the restoration of the degraded γ′ phase eliminated tangled dislocation in creep damaged sample and produced evenly distributed dislocations in the γ channel with short curved line-like morphology, like the as-received sample, which effectively hindered the dislocations movement during subsequent deformation, and strengthen the fatigue resistant of alloy. Therefore, it can be concluded that the HIP-RHT process, through the combined effect of internal cavities healing and the restoration of the degraded microstructures, renders higher high temperature fatigue life than creep-damaged and even higher than as-received DZ125 superalloy.

Effect of diesel and microwave on the properties of crumb rubber and its modified binders

Some novel methods are introduced to improve thermal storage stability and pavement performance of crumb rubber modified binder. In this paper, the objective was to investigate the effects of compound activation on the molecular structure and physical properties of crumb rubber, as well as rheological properties and thermal storage stability of crumb rubber modified binders. Two activation methods, with and without diesel pre-swelling, and six microwave radiation intensities were designed in this study. Fourier transform infrared spectroscopy (FTIR) test, swelling equilibrium test and dynamic mechanical thermal analyzer (DMA) test were performed to evaluate the characteristic functional groups and physical properties of crumb rubbers before and after activation. Additionally, rheological properties test at various service temperatures and thermal storage stability test were carried out on the crumb rubber modified binders. The results show that certain microwave radiation intensity would break the C-S and C=S bonds and reduces the cross-linking density of crumb rubber. Activation mode was the main factor affecting high temperature stability, fatigue life and low temperature relaxation property rather than microwave radiation intensity compared with control one. In addition, thermal storage stabilities of activated crumb rubber modified binders were better than control one. The more radiation intensity, the improvement effect of thermal storage stability is. Synthesizes each kind of property, diesel pre-swelling and microwave radiation intensity of 1.2 kJ/g was a preferable combination in this study.

Effect of thermal exposure on microstructure and high-temperature fatigue life of Al-Si piston alloys

A very effective approach is proposed here to increase the high-temperature fatigue life of an Al-Si piston alloy. Compared with traditional T6 heat treatment, the high-temperature fatigue life can be improved by three times of magnitude with thermal exposure treatment, which reduces the negative effects of gradually decreasing high-temperature fatigue life due to over-aging of piston durability. Specimens heat-treated by various processes have been tested in a rotating bending test machine under conditions of 50 MPa, 350 °C, and 80 Hz to observe the effects of thermal exposure on microstructure and high-temperature fatigue life. The thermal exposure treatment provides an effective method to optimize Si and the thermally stable phases of δ-Al3CuNi and γ-Al7Cu4Ni. It is one of the most important methods for improving the high- temperature fatigue life of an Al-Si piston alloy.

Influence of laser peening on the high-temperature fatigue life and fracture of Inconel 718 nickel-based alloy

High-temperature fatigue test was performed to study the effects of laser peening (LP) on the fatigue behavior of Inconel 718 nickel-based alloy at high temperature. Compressive residual stress (CRS) induced by LP was investigated at both room and high temperature. Microstructural evolution was also studied before and after LP process. The macro- and micro-fracture morphologies in fatigue crack initiation (FCI) region, fatigue crack growth (FCG) region and finial rupture (FR) region of LPed samples with different laser power densities at different temperatures were systematically analyzed. The results showed that LP process can enhance the fatigue life of IN718 nickel-based alloy at both room and high temperature. Excessively high temperature (e.g. 800 °C) may result in a sudden decrease in the fatigue life of LPed samples due to the weakening of grain boundaries and oxidation damage. The losing of coherent strengthen between γ″ phase and matrix was another reason for the rapid reducing of fatigue life. Compared to the untreated samples, the crack source transferred from the surface to deeper layer indicated that LP can retard the crack initiation on the metal surface, which is conducive to enhance the final fatigue life. Some direct evidence, such as the decreased distance between the parallel fatigue striations, the tortuous crack growth path in the LPed specimen confirmed the retarding effects of LP on the FCG. The mechanism of microcracking and the dynamic plastic behavior of LPed specimens during high-temperature fatigue test of IN718 nickel-based alloy were also discussed.

High-temperature fatigue life prediction method for rubber bushing of new-energy vehicles based on modified fatigue damage theory

Rubber bushing are important components in suspension of new-energy vehicles. It is of great practical engineering significance to conduct in-depth study of high temperature fatigue characteristics. On the high temperature fatigue test bench, the same batch of dumbbell rubber test pieces with the same material as rubber bushing and the same vulcanization process were subjected to fatigue test at different temperatures, then the arithmetic mean value of the fatigue life of each rubber test piece was taken as the fatigue life at given temperature. It was found that the fatigue life of the rubber test piece at each temperature can be well fitted when the peak of engineering strain is taken as the damage parameter. Moreover, on the basis of the fatigue damage theory, the Arrhenius high temperature aging factor was introduced to correct the fatigue damage formula considering the influence of temperature on fatigue life. The finite element analysis was used to determine the peak of engineering strain of the dangerous point of the rubber bushing at 70 °C, and the modified fatigue damage formula was employed. The prediction value of the rubber bushing fatigue life was calculated and compared with the bench test result. It is shown that the predicted fatigue life dispersion coefficient is less than 2, indicating the effectiveness of the proposed high temperature fatigue life prediction method. The research in this paper can provide reference for the durability design and fatigue life prediction of rubber parts in new-energy vehicles.

Interfacial and mechanical performance of grouted open-graded asphalt concrete with latex modified cement mortar

Latex modifier can improve the homogeneity of cement mortar. In this paper, interfacial and mechanical performance of grouted open-graded asphalt concrete (GOAC) with latex modified cement mortar (LCM) are investigated. The fluidity, flexural strength and compressive strength of LCM with three different Latex contents were measured for selecting the optimum Latex content of cement mortar. Meanwhile, pull-out test and shear test were adopted to test the strength of LCM-Matrix asphalt concrete (MAC) interface and Cement-MAC interface. Moreover, rutting test, three point bending test, freeze-thaw splitting test, soaked Marshall stability test, fatigue test were adopted to compare the mechanical performance of GOAC with that of dense asphalt mixture. The results show that Latex modifier has a positive effect on the strength of cement mortar, but has a negative effect on its fluidity. Furthermore, 1.2% was the optimum Latex modifier content for LCM. Meanwhile, the average adhesive strength and shear strength of LCM-Asphalt mortar (AM) system is higher than that of Cement-AM system, increased by 34.3% and 20.6% respectively. It indicates that the LCM-MAC interface is stranger than Cement-MAC interface. Moreover, GOAC has better high temperature stability, moisture susceptibility and fatigue life than dense asphalt mixture. However, the brittle cracking resistance of GOAC is inferior to that of dense asphalt mixture.

Effect of heat treatment on the high temperature fatigue life of single crystalline nickel base superalloy additively manufactured by means of selective electron beam melting

The high temperature low cycle fatigue behavior of specimens manufactured from a single crystalline nickel base superalloy processed by selective electron beam melting (SEBM) has been investigated with respect to the effect of different heat treatments. The fatigue lifetime of heat treated material was significantly higher than that of as-built material. Applying hot isostatic pressing (HIP) with an integrated heat treatment resulted in even longer fatigue life. Lifetime limiting crack initiation occurred at interfaces of melting layers, at micro-porosity generated during solidification or, in HIP treated samples, at precipitates which formed at the location of collapsed pores.

무인기용 레큐퍼레이터 소재의 용접부에 대한 고온 피로수명 예측

무인기용 레큐퍼레이터 소재의 용접부에 대한 고온 피로수명 예측

질화 열처리로 인한 잔류응력이 엔진 밸브용 Cr-Ni 합금강의 고온 피로수명에 미치는 영향 평가

질화 열처리로 인한 잔류응력이 엔진 밸브용 Cr-Ni 합금강의 고온 피로수명에 미치는 영향 평가

The effect of platinum-aluminide coating features on high-temperature fatigue life of nickel-based superalloy Rene®80

Low cycle fatigue is the most important failure mode in Aviation/Industrial engine rotary turbine parts. In this paper, the influence of Pt-aluminide coating parameters on high temperature low cycle fatigue behavior of superalloy Rene?80 which is used to manufacture turbine blades, has been investigated. For this purpose, initial platinum layers of different thicknesses (2?m and 8?m) were coated on fatigue specimens. Then the aluminizing process was performed with two conditions of low temperature-high activity and high temperature-low activity. The results of microstructure investigations performed by scanning electron microscope and X-ray diffraction phase analysis indicated a three-layer structure for the coating (bi-phase (Ni,Pt)Al+PtAl2, single-phase (Ni,Pt)Al and interdiffusion zone) with different chemical compositions at both thicknesses of the platinum layer and using both aluminizing methods. Also, the results of low cycle fatigue tests at 871?C, R=0 and strain rate of 2?10 -3 s-1 showed a decline in fatigue properties in coated specimens as compared to uncoated sample, at total strains of 0.4, 0.8, and 1.2%. This reduction was lower in the low temperature-high activity with platinum layer thickness of 2?m, while it was more significant in the high temperature-low activity with the platinum layer thickness of 8?m. The fractography studies on coated and uncoated specimens indicated a mixed mode of ductile and brittle fracture.

Assessment of specific contribution of residual stress generated near surface anomalies in the high temperature fatigue life of a René 65 superalloy

AbstractThis study evaluates the influence of residual stresses induced by the fabrication of surface anomalies on the fatigue crack growth in a nickel based superalloy. To separate the notch effect of the geometry from the residual stress field induced by fabrication of the surface flaws, two V‐type anomalies are considered: scratches and dents with equivalent morphology and size. A specially designed heat treatment has been used to reduce the magnitude of residual stresses around these anomalies in order to highlight their effects on the different stages of the crack propagation, under low cycle fatigue conditions at 400 °C. The crack initiation life is short for both anomalies but in the presence of compressive residual stresses, a decrease of the fatigue crack growth rate has been observed during the first stages of the crack propagation. Furthermore, the results showed that without residual stresses, scratches and dents exhibit the same behaviour. Thus, the residual stress field below surface anomalies is the main parameter controlling the fatigue life from surface anomalies.