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The short-term and long-term performance of bituminous geomembrane (BGM) seams are examined using both small-scale and large-scale tests. Different BGM products, different sustained tensile loads, different weld qualities, and different overburden stresses are examined. The BGM seams are shown to be very susceptible to creep rupture under sustained tensile loads. Time to rupture and strain at rupture for acceptable welds are both exponentially correlated with the sustained load, for the different BGM products examined. With the increasing tensile load from 5%, 10%, 20%, 30%, 40% of sheet maximum tensile strength, the time to rupture decreased from 30–50 days (5%), 5 days (10%), 0.8 day (20%), 0.2 day (30%), to 0.03 day (40%) and, the strain at rupture increased from 5%, 7%, 13%, 17%, to 20–30%. In large-scale tests simulating field conditions, the BGM seam creep ruptured within 24 days when the overburden stress was 20 kPa, and within ≤0.2 day when the overburden stress reached 50 kPa. The consequences of liquids or gases readily permeating through failed seam should be evaluated before using BGMs in an environment where tensile stresses can develop (e.g. due to differential settlement, subgrade irregularity, or downdrag). • first investigation of the creep rupture of different BGM seams at sustained tensile loading as small as 1 kN/m. • first evaluation of the creep behavior of different BGM seams under simulated field conditions. • first correlations of time to rupture and strain at rupture both with a wide range of sustained tensile loads. [ABSTRACT FROM AUTHOR]

To explore the creep characteristics of geomembrane under different tensile stresses, a series of creep tests were carried out on high-density polyethylene (HDPE) geomembrane specimens. For the interpretation and fitting of the experimental data, refined approximation functions were proposed. Particular attention was paid to the creep failure behavior under high tensile stresses, i.e., 70%, 80%, and 90% of maximum peak stress. To investigate the effects of size on the mechanical response, experiments with two different membrane thicknesses were conducted. The results obtained under high stress levels were compared with creep tests at medium and low stress levels. Depending on load level, different creep characteristics can be distinguished. In the secondary creep state, the creep velocity is higher for higher load levels. In contrast to the medium and low load levels, the geomembrane under high stresses underwent the tertiary creep stage after instantaneous deformation and primary and secondary creep stages. In some tests, it was observed that under very high stress levels, creep velocity does not necessarily follow the expected trend and creep rupture can occur within a short time. For numerical simulation, an improved mathematical model was proposed to reproduce in a unified manner the experimental data of the whole non-linear evolution of creep elongation under different stress levels. [ABSTRACT FROM AUTHOR]

Hyperbolic sine (HS) minimum creep rate equations combined with the Monkman-Grant equation are attractive for correlating time to rupture data because of their physical basis in dislocation creep theory, numerical stability, and conformance to physical boundary conditions at zero and infinite stress. In this study, uniaxial creep life data of Sanicro 25 and HR6W alloys were correlated to two recently published HS creep life equations with three commonly used objective functions. For each alloy, the correlation results (fit to the data and predicted strength at 100,000 h time to rupture) were essentially the same using either HS equation. Multiple equivalent solutions (same goodness of fit but different values of the fitting constants) were obtained with the HR6W data set. A discussion on obtaining initial estimates of fitting constants is provided as an Appendix. [ABSTRACT FROM AUTHOR]

In this paper, a unified physics-informed machine learning (PIML) model is proposed for the accurate prediction of the creep rupture life of oxide/oxide ceramic matrix composites (CMCs) by incorporating prior physical information and microstructure features. The collected dataset undergoes missing value imputation and standardization methods for processing. Key feature parameters that influence rupture life are identified through global sensitivity analysis. Furthermore, a high-throughput design module is developed to explore optimal composition under specific creep conditions, providing design guidelines for new materials in oxide/oxide CMCs. This study demonstrates that the predicted results consistently fall within the ±3 error bands. Improved life expectancy is attained with fiber modulus (220–290 GPa) and matrix modulus (>310 GPa). The transformation from expensive creep testing to low-cost exploration of modulus and proportional limit is achieved, offering theoretical support and analytical methods for the design of CMC components and the development of new materials for high-temperature applications. [ABSTRACT FROM AUTHOR]

The theory and methods for constructing equations (functions) of evolutionary damage and rupture of materials in the Kachanov model (creep rupture and fatigue rupture) are presented. In general, it is proved that the factorized Kachanov model is identical to the Palmgren-Miner rule, which is often not confirmed experimentally. To construct damageability functions adequate to the experimental data, new mathematical objects (potential and normalized potential) are introduced. If the entire history of changes in the damage variable is known in experiments, then the use of the potential makes it possible to construct a damageability function of any complexity without integrating the evolutionary equation (explicit method). For cases where only rupture moments are recorded in experiments, a criterion for the adequacy of the normalized potential is formulated and an implicit method for its construction is developed. It is supplemented with a recursive algorithm that generates an unlimited number of such potentials. The implicit method is illustrated by examples, following which the reader can construct a damageability equation for his material without a thorough study of the theory. [ABSTRACT FROM AUTHOR]

C276 superalloy is considered as a potential structural material for advanced nuclear reactor with good mechanical properties and corrosion resistance. High-temperature creep behaviour of C276 alloy was investigated in the temperature range of 650°C–700°C and at stresses of 140–430 MPa. A linear relationship was fitted between stress and minimum creep rate in the logarithmic coordinate system. The rupture time is analysed for life prediction in terms of isotherm extrapolation method, Monkman–Grant relation, and Larson–Miller parameter method, respectively. The isochronous stress–strain curves as a means of representing stress–strain–time relations under creep conditions were established by the parameter method. The fracture surface morphology of ruptured specimens was characterised by a scanning electron microscope to elucidate the failure mechanism. [ABSTRACT FROM AUTHOR]

The turbine section of turbojet engines operates above 900 °C. The cast Ni-based superalloy blades and vanes are used in this section. These components which are working in a very aggressive environment are usually applied with diffusion coatings. These coatings are used to increase oxidation resistance of parts and have evolved from plain aluminide coating to platinum-doped coating. Although the positive effect of platinum–aluminide coatings on the oxidation resistance of the superalloys is reported in several studies, the influence of this type of coatings on the mechanical properties of superalloys is somewhat challenging. This tutorial review of Pt–Al coatings covers: how they supply protection against cyclic oxidation, how they are employed, their microstructure characterization, and their influence on the mechanical behavior of Ni-based superalloys. The present review tries to collect all the available information on the subject and seeks the optimum correlation between Pt–Al coating characterization and mechanical/cyclic oxidation behavior of the coated superalloys. [ABSTRACT FROM AUTHOR]

Models of rupture data formulated recently by conventional methods for different heats of a 2.25Cr1Mo0.3 V pressure vessel steel are compared to models of the same data formulated by the P-NID (parametric, numerical isothermal datum) procedure. The alternative models are evaluated according to the accuracy with which they replicate the data. Confidence in the prediction of long-term properties from these models is discussed, and it is argued that major extrapolations may be considered reliable for models that satisfy the simple criteria of accuracy of the P-NID procedure. [ABSTRACT FROM AUTHOR]

This paper presents the results of a comprehensive effort to characterize the properties of Inconel 718 produced by a form of laser powder bed fusion (LPBF) additive manufacturing (AM) or three-dimensional (3D)-printing, subsequently subjected to hot isostatic pressing (HIP) and heat treatment according to standards F3055-14a and AMS 5663, respectively. Material property data, while broadly available for traditional Inconel 718 presentations (e.g., forgings or castings) is currently lacking for the 3D-printed material. It is expected that while limited in size, the experimental data sets presented provide sufficient information to glean the capability of LPBF Inconel 718. These include: (1) chemical composition, electron backscatter diffraction (EBSD), and X-ray energy dispersive spectroscopy (XEDS) characterization of 3D-printed material structure; (2) tensile properties--0.2% yield stress, ultimate stress, modulus of elasticity, and elongation to failure--based on 108 samples, as functions of temperature and sample print orientation; (3) creep rupture data including the Larson-Miller parameter, based on 21 samples; and (4) high cycle fatigue data based on 21 samples as a function of temperature. Results are compared to available standards and/or data for forged, cast, and other AM Inconel 718. A key observation of this study, based on the EBSD results, is that while the material appears to approach full recrystallization following heat treatment, there is a detectable fraction of the material that does not fully recrystallize, resulting in a material with mechanical properties (e.g., yield stress and creep rupture) measurably lower than those of forgings, but higher than those of castings. [ABSTRACT FROM AUTHOR]

The creep test of T91/Super304H joint is carried out at 610°C and 180–150 MPa. OM and SEM were used to characterize the microscopic changes before and after the joint creep, and the finite element simulation was carried out according to the actual operating parameters, which are used to analyze failure reason of the T91/S304H joint. Finally, the creep life prediction is carried out. The results show that the creep deformation of T91/S304H welded joints with nickel-based filler metal is controlled by the part of martensite T91. Meanwhile, the T91 heat-affected zone is the weak location of the joint. When the stress decreases, the creep life gradually increases, and the creep rupture changes from ductile fracture to brittle fracture. The distribution of Nb-containing phases improves the creep strength of S304H steel. In the process of high-temperature creep, stress concentration occurs between the coarser M23C6, the precipitated Laves phase and the matrix interface, which leads to the formation of creep holes and then gradually connected into cracks. The fracture mechanism is a typical type IV cracking model. The revised θ model can better predict the service life of T91/S304H welding. [ABSTRACT FROM AUTHOR]

• The remaining mechanical properties of bainitic 2.25Cr1Mo steel linearly decrease with Larson-Miller parameter. • The applied creep stress accelerates the softening of the steel. • The mechanism behind the degradation of the remaining strength of the steel is elucidated. • The application of remaining strengths in design and operation of SG is discussed. In this work, the microstructure and remaining mechanical properties of bainitic 2.25Cr1Mo steel plate used in steam generator of sodium cooled fast reactor during creep were systematically examined. Creep tests at 530 °C with a rupture time up to 18800 h reveals that the creep stress correlates linearly with the Larson-Miller parameter ( P LM ), while the creep plasticity is rather independent on P LM . The remaining strength parameters, such as yield strength (R P0.2), ultimate tensile strength (R m) and hardness (H), are found to linearly decrease with P LM , while the remaining plasticity is seen to increase. It suggests that the application of creep stress to the steel accelerates the softening of the material. During the creep process, the dislocation density in bainitic matrix decreases, while the number density of carbides increases, sacrificing the solution strengthening and leading to a continual reduction in the lattice parameter. Although abundant fine carbides precipitate after creep rupture, the remaining strength is however reduced. Instead, the weakening effect due to reduction in dislocation and solute content overwhelms the strengthening of precipitation, resulting in a degradation of the remaining strength. The obtained remaining mechanical properties are attempted to be applied in the design and operation assessment of steam generator. [ABSTRACT FROM AUTHOR]

Turbine blades (rotary parts) and vanes (stationary components) are made from nickel-based superalloys. The replacement of high-cost aviation/industrial blades and vanes is the most important task in the turbojet engine repair industry. These parts which are manufactured by the investment casting process withstand high temperatures and high stresses/strains during the service. Depending on the temperature and strain rate, creep failure occurs by various mechanisms in superalloys. Cavitation is one of the modes of creep failure. In order to facilitate creep life extension of hot section parts and reduce overhaul of engine costs, alloy rejuvenation procedures have been investigated and implemented over the past few years. This study introduces a method including hot isostatic pressing (HIPing) and a post-HIP heat treatment for recovering the creep strength of the cast polycrystalline nickel-based superalloy Rene®80. To certify the positive effect of introduced method on the renovation of creep properties, the creep rupture tests at 850±1 °C/360±2 MPa were assessed. As revealed by the results of this evaluation, the creep properties of Rene®80 can be recovered by HIP procedure (1205 °C /150MPa /4 h) in combination with a post-HIP heat treatment (1093 °C /4hr + 1054 °C /4hr + 845 °C /24hr). [ABSTRACT FROM AUTHOR]

This study investigates the damage, microstructure, and mechanical evolution of service‐exposed HP40NbTi radiant tubes of a steam reformer furnace. Tube failure was reported after 6‐year of working at 525°C–830°C in the form of visible longitudinal and transverse cracks. The microstructure was evaluated using optical and scanning electron microscopy equipped with energy‐dispersive X‐ray spectrum analysis. The carbide phase transformation was determined by the method based on the matrix dissolution technique and X‐ray diffraction. The results of this study showed that the primary cause of the longitudinal crack formation is the local overheating and the oxidation of the dendritic grain boundaries. The M7C3 carbide transforms completely into the metastable M23C6 phase during high‐temperature service. Metallographic examinations revealed the shrinkage cavities and creep voids that are nucleated on both Cr‐ and Nb‐carbides. The continuous oxide layers of Cr2O3 and SiO2 formed near the inner and outer tube surfaces and the matrix's chemical composition near the outer tube surface was found to be depleted of Cr and C. Mechanical properties are irregular across the samples. A little margin of safety is noted, while the complete ductility dip is detected at room temperature. The root cause analysis of the failure under investigation showed that the tube failed due to the creep. [ABSTRACT FROM AUTHOR]

HR3C (25Cr-20Ni-Nb-N) is a key material used in heat exchangers in supercritical power plants. Its creep properties and microstructural evolution has been extensively studied at or below 650 °C. The precipitation evolution in HR3C steel after creep rupture at elevated temperatures of 700 °C and 750 °C with a stress range of 70~180 MPa is characterized in this paper. The threshold strength at 700 °C and 750 °C were determined by extrapolation method to be σ 10 5 700 = 57.1 MPa and σ 10 5 750 = 37.5 MPa, respectively. A corresponding microstructure investigation indicated that the main precipitates precipitated during creep exposure are Z-phase (NbCrN), M23C6, and σ phase. The dense Z-phase precipitated dispersively in the austenite matrix along dislocation lines, and remained stable (both size and fraction) during long-term creep exposure. M23C6 preferentially precipitated at grain boundaries, and coarsening was observed in all creep specimens with some continuous precipitation of granular M23C6 in the matrix. The brittle σ phase formed during a relatively long-term creep, whose size and fraction increased significantly at high temperature. Moreover, the σ phases, grown and connected to form a large "island" at triple junctions of grain boundaries, appear to serve as nucleation sites for high stress concentration and creep cavities, weakening the grain boundary strength and increasing the sensitivity to intergranular fracture. [ABSTRACT FROM AUTHOR]

A model of Sanicro 25 creep rupture data is formulated by the P-NID procedure and compared to several conventional models. Convergence metrics are used to assess the reliability of these models in extrapolation. The results of similar studies for other high-temperature alloys are summarised, leading to a general recommendation for ensuring reliable extrapolation. [ABSTRACT FROM AUTHOR]

Modified hyperbolic sine minimum creep rate equations were used to correlate uniaxial minimum creep strain rate data of 1/2Cr-1/2Mo-1/4 V and Grade 22 steel alloys and to correlate creep life data of Grade 22 steel when coupled with the Monkman-Grant equation. Hyperbolic sine equations were selected because of their physical basis in dislocation creep and numerical stability. Both equations provided very good fits to minimum strain rate data over a wide range of temperatures and stresses. Reasonable correlations of a large Grade 22 creep life data set were obtained with goodness of fit nearly equivalent to those obtained with the Larson-Miller and Wilshire equations, and with more conservative predictions of long-term creep strength. However, all these equations provided a poor fit to the entire data set when only short-term data (tr < 5,000 h) were correlated, and they predicted lower long-term creep rupture strengths vs. the full data set correlations. [ABSTRACT FROM AUTHOR]

• Investigated the influence of sliver defects on the creep rupture life of nickel-based single crystal superalloys. • Revealed the damage mechanism of sliver defects on the creep life of single crystal superalloys through SEM and EBSD observations. • Developed creep constitutive equations for specimens containing sliver based on crystal plasticity theory, explaining the reasons for the decrease in sample life caused by sliver. • Predicted the damage tolerance of sliver defects with different orientations. Sliver defects are common casting imperfections in the preparation of single crystal blades, significantly impacting the high-temperature mechanical performance of blades and potentially leading to blade failure. A detailed study was conducted on the microstructure of sliver in the second-generation nickel-based single crystal superalloy CMSX-4, focusing on its influence on creep performance at 980 °C/250 MPa. Results indicate a substantial impact of sliver on the creep performance of single crystal superalloys, with a 26.37 % reduction in creep rupture time for samples with sliver compared to those without. Fracture analysis reveals that sliver primarily contributes to performance deterioration by promoting the extension of grain boundary microcracks through grain boundary sliding during the creep process, accelerating sample fracture. Utilizing crystal plasticity theory, a successful fit was achieved for the creep rupture life of samples with sliver, allowing the prediction of fracture life for samples with different orientations of slivers. Predictive results suggest that, for CMSX-4 alloy, the orientation of the sliver should be restricted to within 8°. [ABSTRACT FROM AUTHOR]

In the field of nuclear engineering, Printed Circuit Heat Exchangers (PCHEs) have become increasingly popular and the structural integrity assessment of these key power plant components is crucial. As part of the structural integrity assessment, creep rupture analysis considers the interaction of cyclic plasticity and creep behaviour, which is vital for components subjected to cyclic thermal-mechanical loads. The Linear Matching Method (LMM) framework has included a creep rupture module based on an extended shakedown algorithm, which has been adopted by several researchers. However, the current LMM framework mainly relies on linear extrapolation and requires users to provide a large amount of data points to estimate the rupture stress. This paper introduces a Unified Creep Rupture Equation (UCRE) for characterizing the creep rupture curves of diverse steel types. The UCRE is implemented in an extended shakedown algorithm and integrated into the LMM framework. The numerical method is validated through a comparative analysis, wherein the estimated rupture curves are compared with those provided in the ECCC data sheet, as well as against alternative numerical models. Shakedown and creep rupture analyses are then performed on a PCHE core. The proposed method facilitates the parametric study of changing materials and the process of material selection. Various geometric configurations are also considered and the proposed unitary cell model is verified by comparing the results with ones from full FE models. The UCRE has been proved to be an accurate engineering tool for the prediction of rupture strengths while the LMM framework has gained improved usability and versatility for engineering applications. • A numerical procedure to predict rupture strengths for a wide range of steel. • Proposed method is verified by comparing with alternative numerical models. • Direct method-based creep rupture analysis using the Linear Matching Method framework. • Parametric study on a Printed Circuit Heat Exchanger core based on a unitary cell model. [ABSTRACT FROM AUTHOR]

The relevance of incorporating "threshold stress" in models for the dependence of rupture time on applied stress is discussed in the context of data for 2.25Cr1Mo and 1CrMoV steels, with particular reference to a recent publication on this subject (Evans, 2023) [1]. • Highlights of "Concerning the use of 'threshold stress' in the modelling of creep rupture data". • Reviews recently published rupture models including threshold stress. • Examines validity of threshold stress in those models of rupture data. • Presents and compares alternative models excluding threshold stress. [ABSTRACT FROM AUTHOR]

The fatigue properties of lithium hydride (LiH) are crucial to its application as neutron shielding and moderating at elevated temperatures. The dynamic fatigue tests of LiH were investigated with the notched 3-point bend (3 PB) specimens over ranges of loading rates at RT up to 400 °C. At RT, the results showed that slow crack growth (SCG) occurred prior to failure as the minor deviation from linearity to nonlinearity in the load-deflection curves. In addition, the fracture strength of LiH decreased with decreasing stress rate and the SCG zone gradually became smaller with higher stress rates, indicating evident dynamic fatigue phenomenon. However, the trends were quite different at 200, 300 and 400 °C due to accumulative creep damage for low stress rates at elevated temperatures. With increasing temperature and decreasing stress rate, there existed a transition of the dominated failure mechanism, from SCG to creep rupture. Evidence of very small SCG zone could also be detected at the notch for the failure dominated by creep rupture. • Lithium hydride (LiH) shows obvious dynamic fatigue phenomenon and the slow crack growth parameter is determined to be 15.787 at room temperature. • A transition in the dominated failure mechanism, from slow crack growth (SCG) to creep rupture, is found with increasing temperature and decreasing stress rate in the dynamic fatigue tests. • Evidence of very small SCG zone could also be detected at the notch for the failure dominated by creep rupture. [ABSTRACT FROM AUTHOR]

The alloying elements that control the creep rupture life of low carbon steel in the region of inherent creep strength were investigated by a data-driven model selection method. The experimental data published in NRIM Creep Data Sheet No. 7B was used. A model in which the Larson–Miller parameter is expressed as a linear sum of the logarithmic stress and the chemical composition of alloying elements was proposed on the basis of the analysis of the experimental data. There were 1023 ( = 2 10 − 1) candidate models containing one or more of the 10 alloying elements, and they were compared using two model selection methods: 10-fold cross validation (CV) and posterior probability based on Bayesian inference. The 10-fold CV suggested that Mo must be included in the model to improve the predictivity of the unknown data. A comparison among the Bayesian posterior probabilities of the candidate models showed that the Mo-only model has a predominantly high posterior probability of 79.76% compared with the other models. Furthermore, other element terms that co-occur with Mo evenly appeared in the top list after the Mo-only model, indicating that only Mo is crucial for increasing the posterior probability. From these results, it is concluded that the Mo-only model is the most appropriate as a data generation model. The selected Mo-only model was confirmed to have high predictivity of the creep life. [ABSTRACT FROM AUTHOR]

Creep deformation is one of the life time limiting reasons for gas turbine parts subjected to stresses at elevated temperatures. In this study, creep rupture behavior of uncoated and platinum-aluminide coated Rene®80 has been determined at 760°C/657 MPa, 871°C/343 MPa and 982°C/190 Mpa in air. For this purpose, an initial layer of platinum with a thickness of 6µm was applied on the creep specimens. Subsequently, the aluminizing coatings were formed in the conventional pack cementation method via the Low Temperature-High Activity (LTHA) and High Temperature-Low Activity (HTLA) processes. Results of creep-rupture tests showed a decrease in resistance to creep rupture of coated specimen, compared to the uncoated ones. The reductions in rupture lives in LTHA and HTLA methods at 760°C/657 MPa, 871°C/343 MPa and 982 °C/190 MPa were almost (26% and 41.8%), (27.6% and 38.5%) and (22.4% and 40.3%), respectively, compared to the uncoated ones. However, the HTLA aluminizing method showed an intense reduction in creep life. Results of fractographic studies on coated and uncoated specimens indicated a combination of ductile and brittle failure mechanisms for all samples. Although the base failure mode in substrate was grain boundary voids, cracks initiated from coating at 760°C/657MPa and 871°C/343. No cracking in the coating was observed at 982°C/190MPa. [ABSTRACT FROM AUTHOR]

Four sets of experimental data of a minimum creep rate of P91 in different range of stress (from 1.1 to 350 MPa) were compiled for the calibration of the linear + power law and modified sine law. An investigation was conducted to examine the accuracy of both laws in different range of stress. It appears that modelling result of linear + power law fitted experimental data well in low and high stress level while modified sine law fits experimental data in all stress level. The predicted results from narrow ranges of stress indicates that linear power law requires data from both high and low stress levels to make a prediction, modified sine law could make prediction on a wider range of stress with data from a narrow range of stress. This conclusion could help research on predicting low stress level's data with experimental data from high stress level. [ABSTRACT FROM AUTHOR]

In the present study, the creep rupture behaviour and microstructural evolution of 2195-T84 Al-Li alloy are investigated at different tensile stresses. It is found that as the applied stress during the creep rupture process increases, the corresponding creep strain and creep rate significantly increase. Moreover, the evolution of microstructures, including precipitates, dislocation density and creep cavities at different stages is characterized using a transmission electron microscope (TEM), X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The main strengthening precipitates are identified as T1 (Al2CuLi) and θ′ (Al2Cu) phases. Obtained results show that as the applied stress increases, T1 and θ′ phases are gradually coarsened. This coarsening is more pronounced for θ′ phase. Furthermore, the creep cavities are mainly distributed at the interface between the insoluble second phase particles and the matrix, and their average sizes gradually increase as the applied stress increases. Meanwhile, the density and size of dimples on the fracture surface gradually decrease as the applied stress increases. Moreover, the main fracture mechanism changes from transgranular dimple fracture to quasi-cleavage fracture. Based on the microstructural evolution, a novel set of unified creep rupture constitutive model is proposed. The established model incorporates the evolution of microstructures, including the dislocation density, average length of T1 and θ′ precipitates and creep cavitation, and correlates microstructural variables with creep rate. The results calculated by the constitutive model are in good agreement with the experimental data, which validates the proposed model. [ABSTRACT FROM AUTHOR]

Uniaxial creep life data is still used to estimate long-term creep strength and maximum allowable design stresses for structural materials. Many 'single-line' equations have been developed to correlate uniaxial creep life data, such as the Larson-Miller Parameter (LMP) and Wilshire (WS) equations; few are derived from the physics of creep. Some forms of these equations can be mathematically inconsistent with the behaviour of metals at high temperatures, making them potentially unreliable predictors of long-term life. Two modified hyperbolic sine minimum creep rate equations combined with the Monkman-Grant equation were used to correlate uniaxial creep life data of Sanicro 25 and HR6W, and then calculate their long-term creep strength. A modified hyperbolic sine equation was selected because it has a physical basis in dislocation creep and is numerically stable. It was found that the modified hyperbolic sine equations fit the experimental data as well as the LMP and WS equations. [ABSTRACT FROM AUTHOR]

Ductility of metallic materials has practical importance in evaluating structural integrity against ductile fracture or creep rupture but it changes in a more complicated fashion than strength. In order to provide a means to predict the ductility under arbitrary conditions, a model applicable to wide ranges of temperatures and loading conditions was developed. This model consists of an equation describing the dependency on temperature and strain rate in a combined way and a power-law function of stress but emphasis is placed on the former which has two terms representing the behaviour at high and low temperatures. Based on the experimental data from various tests on four materials, effectiveness of the model was demonstrated. Relations between equivalent stress and equivalent strain rate defined in conjunction with the ductility model were also modelled by a similar equation with two terms, allowing the accurate prediction of the ductility in a purely analytical way. [ABSTRACT FROM AUTHOR]

In addition to strain, inelastic strain energy is often used for estimating damage due to inelastic deformation. In order to compare with the approach using inelastic strain, rupture strain energy density was modelled as a function of temperature and strain rate or energy density rate for four materials, using similar equations. It was found that these energy-based approaches provide an equally good performance in modelling the temperature- and strain rate-dependency of rupture energy density as in the strain-based approach. Using the equivalent stress vs. equivalent strain rate relations developed in the companion paper simultaneously, the rupture energy density under various conditions could be estimated with a reasonable accuracy. It was also found that the employment of a common value for the thermal activation energy for all materials does not deteriorate the quality of modelling significantly thus allowing a direct comparison of the characteristics of different materials on the same ground. [ABSTRACT FROM AUTHOR]

In this study, VVER‐1000/V446 nuclear reactor modeling using RELAP5/SCDAP3.4 code to investigate the reactor core behavior during severe accident conditions in a LBLOCA scenario along with station‐black‐out (SBO) is carried out. The analyses are performed in two stages, before and after the core heat up, without considering operator's action on the accident management. Fuel assemblies in the core are grouped into five based on average power peaking factors and are modeled in SCDAP code. For each group a corresponding channel is modeled in RELAP5 code plus a bypass channel. In the first stage, the study of ECCS and KWU tanks efficiency to keep the reactor core in the safe condition, the calculation of the elapsed time before the reactor core heat up and the estimation of available time for operator's action to avoid core degradation, are investigated. In the second part the results of Hydrogen production rate, cladding oxide thickness, cladding damage level, release of fission products into the coolant are studied. Analysis of the scenario by the code shows the production of around 350kg Hydrogen with the maximum rate of about 1kg/s and releasing a large amount of FPs in the order of 10kg. The results also demonstrate that the operators have ∼3 h before the fuel rod cladding rupture and ∼2.5 h before the inception of exothermic steam‐zirconium reaction. Finally, using a geometric mesh for the lower plenum and applying the COUPLE code, the results show that the core slumping into the lower plenum and the lower plenum rupture occur at 17561 and 18370 seconds after the onset of accident, respectively. [ABSTRACT FROM AUTHOR]

Tension and creep rupture behaviors of Alloy 617 after a year of thermal ageing at 900 °C were investigated in comparison with those of unaged (virgin) material. Tension tests were carried out under a controlled strain rate of 5.85 × 10−4 (1/s) from room temperature to 950 °C, and creep tests were conducted with different stresses at 900 °C. Tensile and creep rupture properties were obtained, then creep microstructures and the oxidation layer were measured and analyzed. The mechanical properties of Alloy 617 aged for a year showed effects of thermal damage. The mechanical properties were reduced in terms of tensile and creep strengths compared with the unaged. However, the tensile and creep rupture elongation increased. The reduction of creep life (or strength) in the aged material was caused by the rapid creep strain rate, which resulted from material softening due to thermal aging. In the micro-hardness values, the aged material decreased by approximately 26 % compared with the unaged one. The aged material formed a Cr2O3 layer of approximately 20 µm thickness on its outer surface. The outer and internal oxide-layer thickness revealed a typical trend of a parabolic increase. [ABSTRACT FROM AUTHOR]

To investigate the creep behavior of recycled asphalt pavement (RAP)as backfill material at different construction temperatures,with considerations of viscosity and temperature sensitivity of asphalt, the direct shear and direct shear creep tests on RAP specimens were conducted at 0°C and 50°C.The direct shear test results show that at given compaction temperature, the shear strength is increased with increasing of vertical stress, and the shear strain corresponding to the maximum shear stress is increasesd.The shear strength is increased with the increasing of compaction temperature. The direct shear creep tests results show that at given shear stress ratio, the time to creep rupture is increased with the increasing of compaction temperature. Under the same compaction temperature, the time to creep rupture is increased with the increasing of vertical stress. The critical shear stress ratio is increased linearly with the increasing of compaction temperature. The modified creep model is proposed with considering the effect of compaction temperature by revealing the quantitative variation law for each parameter of the empirical three-parameter creep model. The construction of RAP as backfills is recommended in the summer to achieve high compaction temperature and increase the critical stress ratio for improving creep resistance. [ABSTRACT FROM AUTHOR]

Scaling effects governing the creep behaviour of unnotched and uncracked metallic specimens are investigated by applying similarity considerations and fractal modelling to experimental results provided in the literature. The focus is on stress rupture tests conducted at elevated temperatures on Cr-Mo-V steel cylindrical bars of different sizes. The observed specimen-size effects on the versus tR creep resistance diagrams are interpreted in terms of incomplete self-similarity and fractal weakening (lacunarity) of the specimen reacting cross-section. That leads to a scale-invariant (fractal) formulation of the creep rupture law in terms of renormalized stress. [ABSTRACT FROM AUTHOR]

The creep rupture behaviours and microstructural changes of a modified 9Cr-1Mo heat-resistant steel were investigated at 853 K. Analysis of creep results suggests that dislocation climb is the dominant deformation mechanism with true stress exponent of 5 under the present conditions. Based on the microstructural analysis, strengthening contributions from M23C6 carbides and MX carbonitrides were clarified. The M23C6 carbides can promote grain boundary strengthening by exerting Zener pinning forces, whereas MX carbonitrides can enhance the creep strength by interacting with mobile dislocations to induce threshold stress. Besides, softening of the steel is related not only to the decrease of dislocations, but also the coarsening of precipitates and substructures. The value of creep damage tolerance factor is close to 6.6, which further confirms that the creep damage is mainly attributed to the microstructural degradations, such as the coarsening of precipitates and substructures and decrease of dislocations. [ABSTRACT FROM AUTHOR]

This paper presents the study of creep-fatigue interaction damage and creep rupture limit for 9–12% Cr steam turbine rotor under coupled cyclic thermal-mechanical loadings that alter in phase and out of phase. The investigation is implemented using the Linear Matching Method (LMM) and based on the newly developed creep-fatigue and creep rupture evaluation procedures. Latest experimental creep data of FB2 which belongs to 9–12% Cr heat-resistant steel family is employed to calculate creep-related damage and creep rupture bearing capacity of steam turbine rotor. Various factors that affect creep and fatigue damage of steam turbine rotor are analyzed and discussed, including dwell period and rotating speed of rotor. From the parametric studies, the damage locations and cycles to failure induced by creep and fatigue mechanism are presented respectively. Moreover, through creep rupture analyses for varying desired fracture time, the novel creep rupture curves under multi-type double-cyclic-loading conditions are given and further compared with cyclic plasticity failure curve. These surrogate-model analyses offer a deep understanding of structural responses of steam turbine rotor under long-term high temperature operation and provide critical loading conditions to be referenced for smooth running. • Study of creep-fatigue interaction damage and creep rupture limit for 9–12% Cr steam turbine rotor. • Various advanced direct methods including the extended Direct Steady Cycle Analysis are adopted and presented. • Important creep rupture limit and trend under multi-type double-cyclic-loading are established. • Parametric studies to evaluate the effects of various factors on damage behaviour induced by creep and fatigue mechanism. • Deep understanding of structural responses of steam turbine rotor under long-term high temperature operation. [ABSTRACT FROM AUTHOR]

An advancement can be seen in ultra-thin coatings used for the enhancement of material durability and lifespan. Among candidate materials, copper is used in various applications, such as micro sensors, nuclear fuel waste deposition canisters, and International Thermonuclear Experimental Reactor first walls. However, it is easily susceptible to metal creep, due to its exposure to harsh environments. In this study, graphene, a promising ultra-thin material, is tested as a single-layer coating substance used to enhance the creep property of copper. For measuring creep life, the small punch creep test methodology is adopted. Results show that, remarkably, the creep lifetime of copper increases by up to 19% with the use of the graphene coating. In testing, the heat-treated copper specimen without graphene was fractured at 45 hours, while the graphene-coated copper specimen was fractured at 55.4 hours. The finite element method also supports the experimental results obtained. [ABSTRACT FROM AUTHOR]

This addendum to Reliable analysis and extrapolation of creep rupture data, Int J Press Vessels Pip 2017 , covers matters that were insufficiently addressed in the original article. Uncertainties that obscure evaluation of the P-NID procedure by analysis of multi-batch data are addressed by blind testing the procedure for individual batches of an 18%Cr steel, Type 316 SS. Uncertainties that arise in the extrapolation of near-linear rupture curves are addressed by the inclusion of temperature dependence in parametric stress equations. The use of Tensile Strength data as equivalent short-term rupture data is demonstrated and discussed. • Discusses testing the reliability of an extrapolation procedure by modelling data for individual batches of material. • Shows that P-NID models of short-term data for individual batches of 18%Cr steel predict long-term data accurately. • Discusses difficulties in extrapolating data that show a near-linear relationship between log stress and log rupture time. • Illustrates the advantages of a model that includes a temperature-dependent parametric stress. • Discusses and demonstrates the use of UTS data as equivalent short-term rupture data. [ABSTRACT FROM AUTHOR]

The effects of shear stress level and vertical stress on creep characteristics of recycled asphalt pavement (RAP) material were investigated by a series of direct shear creep tests. The results show that the yield shear stress level of RAP is about 0. 73. The specimens at shear stress level greater than the value are observed creep rupture during the tests, and the time of creep rupture initiation is decreased with the increasing of stress level. On the contrary, the specimens are stable when the stress level is lower than the value. The variation of shear strain rate with time in log-log scale shows a series of decreasing parallel lines and can be well predicted by the three-parameter empirical creep model for soils. The vertical stress has slight influence on three model parameters but has great effect on the time of creep rupture. Under the same shear stress level, the shear strain is increased with time. The specimen with low vertical stress firstly undergoes creep rupture at low shear strain, and the shear strain at the time of failure is increased with the increasing of vertical stress. The shear strain rate under lower vertical stress is decreased faster to the minimum value than those of higher vertical stress. [ABSTRACT FROM AUTHOR]

Abstract In past decades, molybdenum (Mo) has demonstrated the potential to replace tungsten (W) in designing lighter nickel-based single crystal superalloys with enhanced creep resistance. In this research, three groups of nickel-based single crystal superalloys are designed and prepared by tuning the Mo:W ratio. The experimental observations show that the primary and secondary dendrite arm spacings are both independent on Mo:W ratio, but the γ/γ′ eutectic volume fraction decreases as Mo:W ratio increases. The electron probe microanalysis reveals that Re, W and Co segregate to dendrite core regions, while Al, Ti, Cr, Mo and Ta to interdendritic regions. The microsegregation of Ta, W and Re are gradually relieved with increasing Mo:W ratio. Atom probe tomography results further indicate that Cr and Mo are depleted in γ/γ′ eutectics, leading to the enrichment of Cr and Mo at interdendritic regions away from γ/γ′ eutectics. Creep rupture results show that the rupture life at 1040 °C/145 MPa is improved as Mo:W ratio increases. [ABSTRACT FROM AUTHOR]

Highlights • A new model was proposed to reasonably predict creep life. • The notch weakening effect was found in the brazed joint. • The creep life increases with notch angle increases while it decreases with notch radius increases. • The brazed joint under multiaxial stress was mainly fractured by intergranular brittle mode. Abstract The brazed components operating at high temperature inevitably suffer from multiaxial creep under multiaxial stress. In this study, the creep strain, fracture and failure mechanisms of HastelloyC276-BNi2 brazed joint under multiaxial stress were studied by experiment and finite element modeling (FEM). A new damage evolution model was put forward to estimate the creep fracture behavior of brazed joint under multiaxial stress. And the influences of notch angle and radius were also discussed. The notch weakening effect was exhibited in the brazed joints. The creep life is not only dependent on the creep fracture strain but also on notch type. The proposed creep damage evolution model can reasonably reflect the relationship between creep fracture ductility and multiaxiality. The predicted creep life by proposed model agrees very well with the experimental results. Most importantly, the fracture mechanisms of brazed joint under multiaxial stress were revealed and the creep damage evolution was well interpreted by FEM. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

The influence of fireside corrosion on creep rupture of a Ni-Fe based model alloy was investigated by comparing the rupture life, fractography and microstructure of specimens in fireside corrosion and air. Results showed that the rupture life at 140 MPa in fireside corrosion is only 40% of that in air. The internal sulfidation along grain boundaries promoted the initiation of intergranular cracks, and was responsible for the premature rupture. The surface collapse in fireside corrosion was attributed to the outward propagation of internal cracks, while surface cracks in air originated from the formation of recrystallized grains in the surface layer. • The creep rupture life of a new Ni-Fe based superalloy in different environment was investigated. • The internal cracks caused by internal sulfidation accounts for the surface collapse in fireside corrosion. • The premature rupture in fireside corrosion is attributed to the increase of internal creep cracks. • The surface intergranular cracks initiate in the recrystallization layer in air. [ABSTRACT FROM AUTHOR]

Background The creep-fatigue damage in low-cycle regime has been described by a strain-based creep-fatigue equation through integrating creep effect into fatigue damage. Need There is a need to develop a creep-fatigue equation which describes the stress-controlled creep-fatigue behaviour in high-cycle regime. Approach This stress-based creep-fatigue equation was developed through superposing a fatigue mechanism with a creep mechanism. This creep-fatigue equation was then validated on GP91 casting steel. The creep-fatigue data were transformed to the reference condition and collapsed into one power-law curve with good quality. Outcomes This result verified the formulas of the fatigue component and the creep component, and demonstrated the method of extracting the coefficients. The full-range characteristic of this creep-fatigue equation is discussed. In addition, the introduction of the compatibility presents a better description of the reference condition. Originality A new creep-fatigue equation is provided with demonstrably good ability to cover the full range of conditions from the pure-fatigue condition to the pure-creep condition for the high-cycle regime. The method of extracting the coefficients is also provided. [ABSTRACT FROM AUTHOR]

A micro-mechanism based void growth model involving the void shape change during the creep deformation is proposed, referring to the traditional Cocks–Ashby (C–A) model framework, for multiaxial power-law creep rupture prediction. Accordingly, an improved prediction for creep lifetime and multiaxial creep ductility are derived. Results indicate that the creep life and creep ductility are significantly affected by the void shape evolution in the low stress triaxiality range. By contrast, such an effect could be neglected under the situation of high stress triaxiality. In addition, a large fraction of creep ductility is consumed during the tertiary creep stage. A good agreement has been achieved between the proposed model and the collected experimental data. [ABSTRACT FROM AUTHOR]

The research work explores the microstructure evolution and creeps rupture behavior of the shielded metal arc welded joint of reduced activation ferritic/martensitic P91 steel plate in the as-welded and different states of post weld heat treatment (PWHT). Two types of heat treatments were employed including (i) post weld heat treatment (PWHT) at 760 °C for 2 h and finally air cooled and (ii) re-austenitizing at 1040 °C for 60 min and air-cooled and tempered at 760 °C for 2 h, followed by air cooling (PWNT). The P91 steel plates were received in the cast and forged condition having fully tempered lath martensite with lath blocks, packet boundaries and prior austenite grain boundaries (PAGBs). In this research, microstructural evolution at fracture frontier of crept P91 weld sample, creep rupture life and effect of creep exposure time on microstructure evolution in the fine-grained heat affected zone (FGHAZ) were studied. The results show a dominating effect of PWNT treatment on fracture behavior and creep rupture life of the P91 welded joints. PWNT treatment results in negligible hardness variation across the transverse section of the weld joint. The creep rupture life of PWNT specimen was 594.895% higher as compared to that of PWHT specimen and 142.7% higher than that of the as-welded specimen for the similar condition of creep exposure (620 °C/150 MPa). In PWHT condition, the most common type IV cracking was observed. However, it was eliminated in PWNT specimens and fracture occurred form the base zone. The fracture frontier of crept PWNT specimen showed a higher amount of creep cavities that can be attributed to the formation of Laves phase. [ABSTRACT FROM AUTHOR]

This paper studied the creep rupture behavior of Hastelloy C276-BNi2 brazed joint by experimental. Based on a series of creep rupture tests at 600 °C under 110–250 MPa, a relation between the stress and rupture time was achieved to evaluate the creep life of brazed joint. The results show that all the brazed joints were fractured in brazed seam immediately after the second creep stage. The creep model, fracture behavior and failure mechanism are dependent on the level of applied stress. The creep behavior of the brazed joint should be depicted by two-regime Norton (2RN) creep model rather than single Norton model. The creep damage tolerance factor was used to identify the cause of creep damage. From low to high stress level, the failure mode is changed from intergranular brittle to transgranular ductile fracture due to the increases of damage tolerance factor with applied stress increases. [ABSTRACT FROM AUTHOR]

Background Creep and fatigue damages in metals are known to interact and then lead to aggregated damage. While models exist for fatigue, creep and creep-fatigue, no models cover all 3 load regimes. Also, a heat treatment-related parameter is not well included in most creep-fatigue models. Need There is a need to develop a creep-fatigue equation, which covers the full loading regime from pure fatigue to pure creep, and creep-fatigue. Also needed is inclusion of a heat treatment-related parameter. Approach The unified creep-fatigue equation was started from the Coffin-Manson equation and integrated with the Manson-Haferd parameter. This equation was validated on Inconel 718. Outcomes The method of deriving the coefficients and the formula of the creep function are demonstrated, and the resulting equation shows a good ability to describe the grain-size effect and the fully integrated characteristics. Originality Original contributions of this work are the development of a new formulation to represent creep, fatigue and creep-fatigue in metals. Also the inclusion of grain size-which is a proxy for heat treatment-in the formulation of this equation and in a proposed modified Manson-Haferd parameter. [ABSTRACT FROM AUTHOR]

The present study examines the physical models for predicting long-term creep strengths at different application temperatures using creep parameters determined from short term creep tests for the modified 9Cr-1Mo steel, which is a candidate material for design and construction of Gen-IV nuclear power plants with a specified service life of minimum 60 years. It is demonstrated that the complex stress and temperature dependence of minimum creep rate of this steel grade can be rationalised in a simple manner on the basis of the new power law creep equation that incorporates the tensile strength σ TS . The activation energy of creep determined on this basis does not depend on stress and the stress exponent depends only on the stress ratio σ/σ TS region but not on temperature. This allows the new power law equation to be used in combination with Monkman-Grant relationship to predict long-term (60 years) creep strengths and lifetimes at different application temperatures using creep parameters determined from creep tests lasting less than 6000 h. The reliability of these predictions is discussed and the causes for possible over-predictions are considered. It is also shown that the previously observed stress dependence of activation energy of creep is simply the consequence of the conventional method by which this parameter is determined and hence has no physical significance. The change in stress exponent in respective stress ratio σ / σ TS regions is not due to the change in creep mechanism but may be attributed to microstructure changes under creep load in respective σ / σ TS ranges. [ABSTRACT FROM AUTHOR]

Oxide dispersion strengthened (ODS) steels are considered as potential candidates for future Gen-IV reactors core structural applications. Ti is added to this alloy to refine the dispersoid and facilitates formation of Y-Ti-O complex oxides. Optimisation of Y 2 O 3 and Ti content in these ODS steels governs size and stoichiometry of the dispersoids. Equal amount of both Ti and Y 2 O 3 content resulted in formation of finer and stable Y-Ti-O dispersoids. In this study two varieties of ODS alloys are synthesized: one with 0.35 wt% Ti and Y 2 O 3 while another with 0.2 wt% Ti and Y 2 O 3 by mechanical milling followed by SPS. The microstructure and microtexture of these two varieties of ODS steels were compared with modified 9Cr 1Mo (P91) steel. The creep-rupture studies reveal that the ODS steels have better creep-rupture life as compared to P91 steel, and the steel with 0.35 wt% Ti and Y 2 O 3 , possess superior mechanical properties. [Display omitted] • 10 h milling duration found to be optimum for synthesis of 9Cr ODS steel. • Microtexture of 9Cr ODS steels was comparable with modified 9Cr- 1Mo (P91) steel. • ODS steels have better creep-rupture life as compared to P91 steel. • For ODS steel, optimum content of Y 2 O 3 and Ti content should be 0.35 wt% each. [ABSTRACT FROM AUTHOR]

The P-NID (Parametric, Numerical Isothermal Datum) method of extrapolating creep rupture data has been applied to the four large datasets recently analysed by the European Creep Collaborative Committee in order to re-evaluate its own recommended procedure. It is demonstrated from an analysis of these and other datasets that the P-NID method provides a very reliable basis for extrapolation. [ABSTRACT FROM AUTHOR]

In order to optimize the creep rupture strength of Sanicro 25 welded joints, the precipitates in Sanicro 25 welded joint base metal are investigated based on the microstructural evolution during creep at 973 K, and the contribution of precipitates to the precipitation strengthening is calculated. The precipitates in the as-received Sanicro 25 welded joint base metal are primary NbCrN and MX, and creep results in the precipitation of secondary NbCrN, Cu-rich particles and M23C6. Secondary NbCrN is extremely fine and stable during creep. The precipitation strengthening of secondary NbCrN, Cu-rich particles, M23C6, and MX greatly contributes to the high creep rupture strength of Sanicro 25 welded joints. At least 58% of precipitation strengthening is contributed by secondary NbCrN and 28% is contributed by Cu-rich particles. Secondary NbCrN and Cu-rich particles are the key precipitates in improving the creep rupture strength of Sanicro 25 welded joints. [ABSTRACT FROM AUTHOR]

To avoid the dependency on origin of time, an improved damage law for creep rupture of clays is proposed considering the accumulated inelastic deviatoric strain as a measure of damage, instead of incorporating time directly. This law is incorporated into an existing anisotropic elastoplastic-viscoplastic bounding surface model for clays. The performance of the damage law was demonstrated via the simulations of creep rupture tests on undisturbed clays, and generally a good agreement between model simulations and test data was obtained. Discussions on the creep rupture parameters were followed and further improvement was suggested. At present when high quality test data for creep rupture is very limited, the proposed damage law could serve as a practical way to model creep rupture of clays. [ABSTRACT FROM AUTHOR]

Creep rupture tests and tensile tests of Ti-22Al-25Nb alloy with bimodal size lamellar O phase microstructure were carried out at 650 °C and 700 °C. The fracture surface analyses indicate that the tensile fracture originated from the center of the cylinder sample while the creep rupture started at the surface. The different fracture mechanism of creep rupture samples is ascribed to the orthorhombic cases (O cases). It is found that the sub-surfaces of the creep rupture samples were enriched with the element oxygen. The interstitial oxygen, an alpha stabilizer for titanium alloys, promoted the transformation from B2 phase to O phase. Thus the sub-surfaces contained more acicular O phases than the substrates. The sub-surfaces with more O phase component are named as O cases. The dissolved interstitial oxygen and the added O phase component increased the strength but reduced the ductility and the toughness in the O cases. It was the incompatibility of the creep strains between the O cases and the substrates that made the creep rupture to originate at the surfaces. [ABSTRACT FROM AUTHOR]