High Temperature Fatigue Research Articles

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.

Microstructure evolution characterization of Ni-based GH4720Li superalloy during strain-controlled fatigue at 550 °C

High-temperature fatigue property of Ni-based GH4720Li superalloy at 550 °C has been investigated at maximum strain from 0.8% to 1.1%. Microstructural characterization and oxidation behavior of superalloy during high-temperature fatigue have been analyzed by transmission electron microscopy and scanning transmission electron microscopy. The results show that a stable response following a slight cyclic hardening during initial cycles was revealed at the maximum strain from 0.8% to 1.0%. The stable response decreased with an increase in maximum strain. Continuous cyclic hardening was observed at the maximum strain of 1.1%. There is difference in dislocation substructures between primary γ′ precipitates and γ grains. Dislocation cell and mechanical twin were formed in the interior of primary γ′ precipitates and γ grains. The primary γ′ precipitate interface would migrate toward the interior of primary γ′ precipitates along twin boundaries, leading to instability of primary γ′ precipitates. The secondary γ′ depleted zone was distinctly generated near the surface due to the decomposition of secondary γ′ precipitates. The crack initiation and propagation during high-temperature fatigue were found inside the secondary γ′ depleted zone. The primary γ′ precipitates could effectively hinder the crack propagation. Al-rich oxide films (Al2O3) were initially produced at crack tips, because the rate of diffusion of Al was relatively higher than that of other elements at crack tips.

Investigation on High Temperature Rheological Behaviors and Fatigue Performance of Trans-Polyoctenamer-Activated Crumb Rubber Modified Asphalt Binder

Asphalt binders have been modified with Crumb rubber (CR) as an effort to fulfil the demand for the development of eco-friendly and sustainable pavements. The objective of this study was to investigate the high temperature rheological behaviors and fatigue performance of crumb rubber modified asphalt (CRMA) binder activated using trans-polyoctenamer (TOR). Long-term and short-term aging tests were performed on samples by thin film oven test (TFOT) and pressure aging vessel (PAV). Rotational viscosity (RV), softening point, and dynamic shear rheometer (DSR) tests were conducted to characterize the rheological and physical performance. A linear amplitude sweep (LAS) test was employed to evaluate the fatigue performance. The results show that TOR-activated CRMA is more capable of hardening the matrix bitumen and improving its high-temperature viscoelastic properties after TFOT. The high temperature viscoelasticity is significantly better than styrene-butadiene-styrene block (SBS) modified asphalt (SBSMA) and CRMA. TOR-activated CRMA exhibits strong rutting resistance, but it is more likely to generate fatigue cracks under the violent advancement of complex modulus. Therefore, TOR active agent has a negative impact on the fatigue performance of CRMA. SBSMA exhibited superior fatigue resistance. The viscosity temperature index (VTS) of TOR-activated CRMA and CRMA was basically identical; the TOR did not significantly improve the temperature sensitivity of CRMA.

Correlation analysis between aging behavior and rheological indices of asphalt binder

The aging of the asphalt binder seriously affects the performance of the asphalt pavement, so it is expected to obtain indices that can not only evaluate the aging resistance of the asphalt binder but also indicate the performance of the asphalt mixture. In this study, the changing of the rheological indices before and after asphalt aging were observed. The sensitivities to aging characterized by different rheological indices were also compared with each other. Moreover, the relationships among rheological indices were discussed. The results show that the aging has a significant impact on the rheological properties of asphalt. The addition of modifier obviously reduced the low-temperature relaxation modulus of asphalt and increased the absolute value of relaxation rate, thereby improving the low-temperature performance of asphalt road. The sensitivity analysis results of rheological indices to aging behavior show that rheological indice [R3.2kPa] obtained by multiple stress creep recovery test was most sensitive to short-term aging, while rheological indice [R]3.2kPa obtained by repeated creep recovery test was most sensitive to long-term aging, which helps to provide technical support for the quantitative characterization of the aging behavior of asphalt binder. Correlation analysis of rheological indices show that the indice mr(60 s) in frequency sweep test at low temperatures show a linear correlation with the indices Jnr3.2kPa in MSCR test and Nf in linear amplitude sweep test, indicating that the low-temperature relaxation rate of asphalt is closely related to its high temperature performance and fatigue performance.

Short Circuit Capability Characterization and Analysis of p-GaN Gate High-Electron-Mobility Transistors Under Single and Repetitive Tests

Short circuit (SC) capability of 650-V Schottky-type p-GaN gate high-electron-mobility transistors (HEMTs) under single and repetitive tests is characterized in this article. The investigated devices exhibit strong capability under a single SC test, but weak capability under repetitive SC tests with a bus voltage of 400 V and a gate drive voltage of 6 V. The failure mechanism under repetitive SC tests is revealed through electrothermal simulation and microscale failure spot analysis. Thermal fatigue cracks are formed due to the high temperature spike and local temperature fluctuations in the narrow GaN channel and buffer layers, leading to weak repetitive SC capability. The unique heat confinement effect in the GaN layer plays an important role in the formation of high temperature spike and fatigue cracks. The withstand time in a single SC test is several hundred microseconds due to fast drain current drop that results from high temperature and, to a lesser degree, the dynamic threshold voltage shift during the SC transient. The device failure in a single-event SC test is related to heat diffusion to a wider region. Some guidelines are proposed for handling and improving the repetitive SC capability.

Improvement of High Temperature Fatigue Properties of TiAl Alloys Fabricated by Electron Beam Melting Through Hot Isostatic Pressing Process

Improvement of High Temperature Fatigue Properties of TiAl Alloys Fabricated by Electron Beam Melting Through Hot Isostatic Pressing Process

Electron-microscopic analyses on high-temperature fatigue crack growth mechanism in a Ni-based single crystal superalloy

The microscopic mechanism of high temperature (900 °C) fatigue crack growth in a single crystal Ni-based superalloy is investigated. Particular attention is focused to its relation to the cyclic misorientation markings (CMMs), formerly termed EBSD (electron backscattered diffraction) striation, left along the crack wake. Observation of a cross-sectioned crack tip is conducted by various electron microscopy i.e. SEM, EBSD, high-voltage TEM and STEM-EDS. A {100} fatigue crack subjected to a relatively high ΔK (40 MPam1/2) shows CMMs with an interval corresponding to crack growth rate (2–4 μm/cycle), consisting of heavily dislocated γ (Ni) phase and less dislocated γ’ (Ni3Al) phase. It is also revealed that local oxidation along the γ/γ’ interface at the crack tip existed at the current temperature/ΔK level. On the bases of these findings, a rational yet qualitative crack growth model that incorporated both brittle/ductile processes is proposed.

High Temperature Cyclic Plastic Response of New-Generation ODS Alloy

The very recently developed coarse-grained new-generation oxide dispersion strengthened (ODS) alloys containing 5 vol.% homogeneously distributed yttrium nano-precipitates seems to be a promising oxidation-resistant structural material for applications at temperatures above 1000 °C. The primary aim of the present paper is the introduction of the new-generation oxide dispersion strengthened (ODS) alloy and the first testing of its high temperature fatigue properties at 800 °C, concurrently demonstrating a novel and very efficient methodology by using an incremental fatigue step test. The successful application of the methodology motivates the authors to test the fatigue properties of new generation ODS alloys at 1000–1200 °C in the near future.

Experimental and computational characterization of the effect of manufacturing-induced defects on high temperature, low-cycle fatigue for MarBN

Manufacturing-induced defects are a key source of crack initiation and component failure under high temperature cyclic loading. In this work, 3D X-ray micro-computed tomography and microstructural analysis of manufacturing-induced defects is presented for forged and cast MarBN martensitic-ferritic steel, along with high temperature, low cycle fatigue testing, for assessment of the comparative effects of two manufacturing processes. Forging is found to significantly reduce the volume fraction and complexity of manufacturing defects, compared to the cast material, resulting in approximately double the fatigue life. A voxel-based finite element methodology for experimentally-identified cast and forged manufacturing defects is presented, in conjunction with a multiaxial, critical-plane damage model, within a unified viscoplastic user-material subroutine. The effect of the complex morphologies of the manufacturing defects on high temperature fatigue crack initiation is thus quantified, highlighting the relative effects of the two different manufacturing processes.

Evaluation of phosphorus slag (PS) content and particle size on the performance modification effect of asphalt

To evaluate the modification effect of phosphorus slag powder (PSP) on the rheological performance of asphalt, five types of PSP with different particle sizes and different content were prepared and added into the AH-70 base asphalt. The dynamic shear rheometer (DSR) test was used to evaluate the influence of PSP content and particle size on the rheological properties of asphalt. Rolling thin film oven test (RTFOT) and pressure aging vessel (PAV) were used to simulate the asphalt aging after modification of PSP. The influence of aging conditions on the phosphorus slag modified asphalt (PSMA) was evaluated, and the impact of PSP on the function group of asphalt was analyzed by Fourier Transform Infrared spectroscopy (FTIR). The results indicated that the interaction between PSP and asphalt was mainly physical blending with some degree of chemical reactions. PSP was more sensitive to aged asphalt but less sensitive to original asphalt because it could react with some carbonyl groups. With the increase of PSP content, the shear complex modulus of PSMA increased first and then decreased, and the phase angle decreased first and then increased after RTFOT aging. With the increase of the specific surface area of PSP, the complex shear modulus of PSMA increased and the phase angle decreased. The result found that with the increase of the specific surface area, the high temperature rutting resistance and fatigue performance of asphalt was improved. This study provided important theoretical and practical guidance for the application of PSMA.

High temperature fatigue of heat treated secondary AlSi7Cu3Mg alloys

The high-temperature fatigue behaviour of a heat treated AlSi7Cu3Mg alloy is reported. Fatigue testing has been performed at room and higher temperatures (473 and 573 K) on specimens previously solubilised at 758 K for 24 h and further aged at 453 K for 8 h. Microstructural and fractographic investigations have been used to quantitatively examine the evolution of strengthening precipitates and the different fracture mechanisms. The results show how the fatigue behaviour is comparable in the temperature range between 293 and 473 K. Then, the fatigue strength decreases by increasing the testing temperature from 473 to 573 K. The uniform distribution of fine strengthening precipitates in the α-Al matrix is affected by higher test temperature, which promotes coarsening phenomena of the precipitates. The failure mode changes from brittle to ductile at 573 K.

High temperature fatigue of carbon/polyimide 8-harness satin woven composites. Part I: Digital Image Correlation and Micro-Computed Tomography damage characterization

This paper focuses on the experimental high temperature fatigue of Carbon/polyimide 8-harness satin woven composite materials. Traction-traction (R = 0.1) fatigue tests at 250 °C are carried out on Carbon/polyimide [45]6 8-harness satin woven composites under three different environments (air, 2 bar N2, 2 bar O2). Part I is specifically devoted to image based damage characterization by employment of Digital Image Correlation (DIC) and Micro-Computed Tomography (µ-CT) techniques. For the used samples, intra tow matrix cracks along fibres on the external plies are the first damage form at the ply-scale. Damage evolution on the sample surface can be followed during the test (in situ) by using 2D DIC. Moreover, fatigue tests are periodically interrupted to perform µ-CT scans to characterize and quantify the damage in the volume of the samples. The obtained results prove that the damage assessment methods presented in this work are suitable for environmentally-assisted fatigue tests on composite materials.

High temperature fatigue of carbon/polyimide 8-harness satin woven composites. Part II: Environmental effects

This paper focuses on high temperature fatigue of Carbon/polyimide 8-harness satin woven composite materials. Traction-traction (R = 0.1) fatigue tests at 250 °C are carried out on Carbon/polyimide [45]6 8-harness satin woven composites under three different environments (air, 2 bar N2, 2 bar O2). Part II is specifically devoted to the study of the environmental effects occurring during high temperature fatigue: strain, mechanical properties and damage evolution are characterized by Digital Image Correlation (DIC) and µ-Computed Tomography (µCT) techniques. The rich characterisation of damage extent and orientation can be naturally integrated within the context of a damage-dependent behaviour models. The effect of the environment is assessed through a description of thermo-oxidation phenomena occurring at high temperatures.

Creep and high temperature fatigue performance of as build selective laser melted Ti-based 6Al-4V titanium alloy

The present work focuses on the room and high temperature low-cycle fatigue and creep testing of Ti-6Al-4V manufactured by selective laser melting (SLM) or laser-based powder bed fusion process (LBPF). The fatigue specimens were tested in a strain control mode with the as-built and machined surfaces, evaluating the influence of the surface roughness on the fatigue performance. This helps in understanding the potential negative influence of a surface defect/roughness on the fatigue performance of the complex components produced by SLM (in as-built state), where surface machining may not be possible due to geometrical constraints. The fatigue fractures at room and high temperature were investigated with the help of a scanning electron microscope. The creep tests were performed at three different temperatures with as-built SLM samples, demonstrating an equivalent or better performance when compared to their counterparts produced by hot-forging.

Laboratory Experimental Research on Foamed Warm Mix Asphalt Mixture Road Property

To verify the foamed warm mix asphalt mixture road property, the article formed foaming warm mix asphalt mixture, Sasobi-LM warm mix asphalt mixture, ordinary hot mix asphalt mixture test piece, comparative analysis of different asphalt mixture The resistance of high temperature to rutting, shear resistance, resistance of low temperature crack, water stability and fatigue properties, and comparative economic analysis. The results show that the resistance of low temperature crack, water stability and shear resistance of foamed warm asphalt mixture surpass Sasobi-LM warm asphalt mixture, but slightly lower than ordinary asphalt mixture; The resistance of high temperature rutting and fatigue resistance of the mixture is lower than that of Sasobi-LM warm mix asphalt mixture; through economic analysis, the economical efficiency of foamed warm mix asphalt mixture surpasses the economical efficiency of the Sasobi-LM warm mix asphalt mixture, lower than the ordinary hot mix asphalt mixture, it is recommended to choose construction in special areas.

A New 3D Creep-Fatigue-Elasticity Damage Interaction Diagram Based on the Total Tensile Strain Energy Density Model

Fatigue damage, creep damage, and their interactions are the critical factors in degrading the integrity of most high-temperature engineering structures. A reliable creep-fatigue damage interaction diagram is a crucial issue for the design and assessment of high-temperature components used in power plants. In this paper, a new three-dimensional creep-fatigue-elasticity damage interaction diagram was constructed based on a developed life prediction model for both high-temperature fatigue and creep fatigue. The total tensile strain energy density concept is adopted as a damage parameter for life prediction by using the elastic strain energy density and mean stress concepts. The model was validated by a great deal of data such as P91 steel at 550 °C, Haynes 230 at 850 °C, Alloy 617 at 850 and 950 °C, and Inconel 625 at 815 °C. The estimation values have very high accuracy since nearly all the test data fell into the scatter band of 2.0.

Unveiling the Re effect in Ni-based single crystal superalloys

Single crystal Ni-based superalloys have long been an essential material for gas turbines in aero engines and power plants due to their outstanding high temperature creep, fatigue and oxidation resistance. A turning point was the addition of only 3 wt.% Re in the second generation of single crystal Ni-based superalloys which almost doubled the creep lifetime. Despite the significance of this improvement, the mechanisms underlying the so-called “Re effect” have remained controversial. Here, we provide direct evidence of Re enrichment to crystalline defects formed during creep deformation, using combined transmission electron microscopy, atom probe tomography and phase field modelling. We reveal that Re enriches to partial dislocations and imposes a drag effect on dislocation movement, thus reducing the creep strain rate and thereby improving creep properties. These insights can guide design of better superalloys, a quest which is key to reducing CO2 emissions in air-traffic.

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.

Gradation Design and Performance Evaluation of High Viscosity Asphalt Mixtures

The property of asphalt binder plays an important role in the performance of asphalt mixture. The natural rubber additive (NRA) was recommended as a modifier in the preparation of high viscosity asphalt (HVA) binder. Then, the gradation named LASTIKA‐13 was adopted to design the high viscosity asphalt mixture (HVAM) according to the orthogonal test analysis and the optimized gradation. The performance of the proposed HVAM was evaluated through a series tests including the permanent deformation at high temperature, moisture stability, low‐temperature cracks, and bending fatigue test. The results indicate that the proposed modified asphalt binder shows a comparable property with the conventional modified asphalt binder. The proposed HVAM with the NRA modifier has a superior performance to other conventional mixtures in the temperature susceptibility and resistance to moisture damage. Furthermore, the proposed HVAM was less sensitive to the temperature change and has good performance in terms of resistance to low‐temperature cracks, bonding characteristics, and fatigue behaviors.

Effect of Organic Montmorillonite on Properties of High-viscosity Modified Asphalt

In order to investigate the effect of organic montmorillonite (OMMT) and its content on properties of high-viscosity modified asphalt, a series of laboratory tests were carried out through zero shear viscosity (ZSV) at 60 °C, rutting factor, ductility at 5 °C, and fatigue factor to analyze high-temperature, low-temperature and anti-fatigue properties of high-viscosity modified asphalt with different OMMT contents. The results show that OMMT/high-viscosity modifier (HVM) composite modification can improve obviously high-temperature performance and fatigue resistance of high-viscosity modified asphalt, but the best improvement effect can be achieved only when adding proper amount of OMMT. The addition of a small amount of OMMT has little effect on low-temperature performance of high-viscosity modified asphalt, but when the content of OMMT exceeds 4%, its low-temperature performance will decrease significantly. The addition of OMMT can improve the temperature sensitivity of high-viscosity modified asphalt’s high-temperature performance, but reduces the temperature sensitivity of its fatigue resistance.