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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]

Copyright of Iron Steel Vanadium Titanium is the property of Iron Steel Vanadium Titanium Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, the nonlinear creep behaviour of additive-manufactured carbon fibre-reinforced polyethylene terephthalate (CF-PET) is characterised using experimental, theoretical and computational methods. The experimental approach investigates the influence of infill orientations on the creep deformation of the material. For the study, samples at 0°, 45○, and 90° infill orientations are produced with 90% infill density using fused filament fabrication (FFF). The infill orientation parameter highly influences the creep behaviour. Increasing the infill orientation from 0° to 90° monotonically improves the creep resistance of the material, which can be explained by orientation of the fibre-matrix reinforcement towards the uniaxial stresses. Surface examinations of creep-ruptured samples via scanning electron microscopy (SEM) reveal that a combination of matrix failure, fibre pull-out, fibre-matrix debonding, inter-layer debonding, and the presence of voids cause the fractures. Based on the experimental data, the primary and secondary creep responses are modelled theoretically and computationally. The theoretical model is based on the dependence of the material's creep on stress and time parameters at the transient and steady state stages. Combined stress and time functions are used to model the creep of the material. Parallelly, two-dimensional (2D) finite element (FE) analyses are made on COMSOL Multiphysics to model the creep computationally. The approach is based on the superposition of Norton's and Garofalo's creep models with predefined time hardening property. The results of the modelling are in good agreement with the experimental findings, showing a maximum of 1.04 % for the theoretical, and 2.9 % for the computational approaches.

Creep rupture tests were conducted on 67 thin-walled DD6 specimens, with thicknesses ranging from 0.35 mm to 1.50 mm, at temperatures of 760 °C, 850 °C, 980 °C, and 1100 °C, revealing a log-linear relationship between rupture lifetimes and specimen thicknesses. Micro-CT observations identified an inhomogeneous distribution of creep micropores around dendrites as a contributing factor to the thickness debit effect. Based on the reliability mathematical method, a possible explanation was proposed for the parabolic law relationship between rupture times and specimen thicknesses. In addition, a thickness debit characterization parameter (TDP) was derived to quantify the trend of creep property degradation as thickness decreases. The TDP equation effectively predicted the creep rupture lifetimes of DD6 thin-walled specimens mostly within a scatter band factor of 2.

By using state-of-the-art characterisation techniques including atom probe tomography and atomic resolved elemental mapping, we successfully probed the site occupation evolution associated with composition change in γ′, during 1100°C creep of a fourth generation Ru-bearing Ni-based superalloy. It is quantified that, W and Ru maintain unchanged site preference after creep rupture, while interestingly, the rest elements especially Co, Ta and Re show a weakened preference at both α- and β-sites in the γ′ lattice. This indicates the overall reduced γ′ ordering degree and thus the possible decrease in planar fault energies, which further facilitates dislocation shearing in γ′.

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.

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]

By using state-of-the-art characterisation techniques including atom probe tomography and atomic resolved elemental mapping, we successfully probed the site occupation evolution associated with composition change in γ′, during 1100°C creep of a fourth generation Ru-bearing Ni-based superalloy. It is quantified that, W and Ru maintain unchanged site preference after creep rupture, while interestingly, the rest elements especially Co, Ta and Re show a weakened preference at both α- and β-sites in the γ′ lattice. This indicates the overall reduced γ′ ordering degree and thus the possible decrease in planar fault energies, which further facilitates dislocation shearing in γ′. Associated with the tremendous mass transfer during high-temperature creep, the site-occupation scenario in the γ′ lattice evolves as that, the preference at both α- and β-sites for Co, Ta and Re weakens while that of W and Ru remains nearly unchanged, indicating the overall decrease in ordering and thus the easier dislocation shearing in γ′. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Mechanics is the property of Chinese Journal of Applied Mechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Creep rupture as a failure mechanism during a severe accident in a PWR is of particular importance as it can lead to releasing radioactive materials into the environment. Following a severe accident, the decay heat transferred to other parts of the reactor cooling system can result in the heat-up of RCS structures and failure of vulnerable pressure boundaries. SBO without operator actions accident (TMLB sequence) is considered one of the most likely scenarios threatening the integrity of the RCS pressure boundary. In addition to PWR plant modeling, in this sequence, the location of rupture in the RCS depends on the type of natural circulation phenomenon of the reactor's primary side. This research investigates the sensitivity analysis of steam generator tube rupture (SGTR) and RCS hot-leg to the type of natural circulation, i.e. con-current and countercurrent, using the MELCOR code. The results of two models of con-current and countercurrent natural circulation show when the countercurrent natural circulation phenomenon is predominant, the RCS hot leg creep rupture occurs earlier than SGTR. However, the SGTR occurs earlier than any other part of RCS due to the concurrent natural circulation phenomenon. Moreover, the amount of materials released to different parts of the plant and the environment has been estimated for both models. The results show that about 18 kg and 145.76 kg of radioactive aerosol and fission product vapor materials are ejected to the containment following the rupture for con-current and countercurrent natural circulation models, respectively. On the other hand, in the con-current natural circulation, about 136.33 kg of radioactive aerosol and fission product vapor materials are released into the environment through the main steam line safety valve.

The macroscopic creep properties of negative electrodes in lithium-ion batteries and their estimation methods have been investigated based on the microscopic structure of the electrode. Tensile and creep tests were conducted on a negative electrode consisting of carbon powder and polyvinylidene fluoride (PVDF) binder. The stress-strain curve, the time history of the tensile strain, and the creep rupture time were measured in these tests and estimated using the simple model proposed in this study. The proposed model approximates the alignment of carbon particles as body-centered cubic (bcc) or face-centered cubic (fee). The external load on the model was supported by a PVDF binder located between carbon particles. The test results showed that PVDF binder mechanical properties affect the macroscopic mechanical properties of the negative electrode, including the creep properties. The stress-strain curve and time history of the tensile strain were located between the upper and lower limits of the proposed model. The tensile strength and creep rupture time agree with the lower limit of the proposed model. [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]

Fatigue strength, relaxation, and creep rupture strength of carbon-fiber-reinforced polymer (CFRP) strands were evaluated experimentally, and their impact on bridge beam design was investigated. The long-term relaxation of CFRP strands was evaluated by loading CFRP test specimens under different environmental conditions and monitoring prestress loss over time. Creep rupture strength of CFRP strands after I million hours of sustained stress exposure was predicted by loading and monitoring CFRP test specimens under a range of sustained stress levels for an extended time. The fatigue strength of CFRP strands was established by cyclically loading CFRP test specimens using different stress amplitudes. In addition, and as a benchmark for fatigue evaluation, low-relaxation steel and stainless steel strand test specimens were prepared and cyclically loaded within the fatigue test matrix. Test results showed that fatigue strength of CFRP strands is superior to that of low-relaxation steel and stainless steel prestressing strands. In addition, the one-million-hour relaxation loss of CFRP strands is approximately 2% for a wide range of initial stress levels. Furthermore, the one-million-hour creep rupture strength is at least 88% of the average tensile strength of the strands. Extended exposure to environmental conditions did not seem to affect the tensile capacity of CFRP strands. [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]

The premature creep rupture of cast reformer tubes made of HP-Nb steel due to short-term overheating, was investigated. Investigation was performed on specimens from ruptured, cracked, and uncracked tubes and included metallography, mechanical testing, and SEM/EDX analysis. It was found that accidental short-term overheating, after 5 years of normal operation, caused rapid tertiary creep, manifested by the formation of dense cavities and cracking, which eventually led to the premature creep rupture of several tubes of the reformer. Creep cavities formed preferentially at M7C3 carbides but also at M23C6 and MC carbides while crack propagation took place along the interdendritic carbide network. It appears that the radial direction of the columnar grains from the inside to outside diameter orients the grain boundaries perpendicular to the hoop stress, a situation which degrades creep rupture resistance. An analysis based on the Larson–Miller parameter confirmed the premature creep rupture of the tubes due to overheating.

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]

Abstract Cross-laminated timber (CLT) has been used extensively in timber construction. CLT panels are typically used in roofs and floors that carry a continuous load, and it is important to examine the long-term loading capacity of CLT. However, studies that focus on the long-term loading capacity of CLT are limited. To this end, we conducted long-term out-of-plane bending tests on seven-layer CLT made from Japanese larch (Larix kaempferi) under constant environmental conditions, investigated creep performance and duration of load, and experimentally analyzed creep rupture behavior. The mean estimated relative creep after 50 years was 1.49. The sample showed a satisfactory resistance to creep as a building material. The duration of load of most of the specimens in this study was shorter than the conventional value of small clear wood specimens. Specimens had a lower duration of load capacity than solid lumber. According to the results of survival analysis, a loading level of 70% or more caused the initial failure of specimens. Creep rupture of most of the specimens occurred at less deflection than displacement at failure in the short-term loading test. Additional studies focusing on the effects of finger joints, transverse layers, and width of a specimen on creep rupture behavior are suggested.

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]

In this study, we proposed an optimal foam tape design for the assembly of curved display modules using topology optimization. We constructed the lifetime prediction model of the foam tape by verifying the correlation between the stress and the failure time with the revised power model. Two optimal designs were derived through a 2‐step topology optimization process by constructing constraints with a life prediction model. We manufactured the curved display module using the optimal design and verified its performance. [ABSTRACT FROM AUTHOR]

The initiation, expansion, and penetration of microscopic cracks in rock is the macroscopic manifestation of creep. This paper investigates mechanical creep characteristics and fracture evolution processes in rock masses with different fracture angles, lengths, and rock bridge dip angles. Single fractures, dual parallel fractures, and fracture groups are considered. The approach comprises discrete element simulation based on continuum mechanics, utilizing the continuous and discontinuous software, GDEM. Single-fracture rock masses are characterized by a progressive fracture development mode dominated by tensile shear failure. The rate of creep and fracture magnitude both increase according to fracture length. With increasing fracture inclination angle, creep rate and fracture magnitude increase and decrease. The creep rate and degree of rupture are highest for fractures inclined at 30°. The dual-fracture rock mass exhibits both tensile crack failure and compressional shear failure. Creep rates are highest, and rupture effects are most apparent at rock bridge inclination angles of 90°. If the rock bridge is too long or too short, the stable creep stage is prolonged, but the creep acceleration stage intensifies due to interaction between fracture-bounded rock masses. The failure mode, in this case, involves collective failure by tension fractures and compressional shear. Creep rate and fracture magnitude increase with the number of fractures, which accelerates rock mass deformation to a certain extent. However, when the number of fractures reaches a certain threshold, a relatively stable structure may become established, slowing down the creep rate, especially during the creep acceleration stage. This study can provide a theoretical basis and reference for investigating the creep rupture law of rock mass engineering and the prevention and control of fractured rock mass geological disasters.

• 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 effect of grain size on the mechanical properties and creep rupture of 253 microalloyed (MA) austenitic stainless steel (ASS) was investigated. The cold rolling process with a 53% reduction in thickness was applied to the steel followed by annealing at 1100 °C over 0, 900, 1800, and 3600 s to obtain grain sizes of 32.4, 34.88, 40.35, and 43.77 µm, respectively. Uniaxial tensile and micro-Vickers hardness tests were carried out to study the effect of grain size on mechanical properties at room temperature. The creep rupture test was performed at 700 °C under a load of 150 MPa. The results showed that there was a correlation between grain size, mechanical properties, and creep rupture time. The fine initial grain size showed relatively good mechanical properties with a short creep rupture time, while the coarse initial grain size produced low mechanical properties with a long creep rupture time. The initial grain size of 40.35 µm was the optimum grain size for a high value of creep rupture time due to the low hardness and elongation values at room temperature and low creep ductility value. The intergranular fracture was found on the initial grain size below 40.35 µm, and a mixed mode of intergranular and transgranular fracture was found on the initial grain size above 40.35 µm after the creep rupture test. [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.

The mechanism governing de-oxidation of vanadium metal is regarded as fundamental knowledge; however, it has not been elucidated in existing literature. In this paper, the thermodynamic data of V-H-O systems were summarized, and the Gibbs free energies of the main compounds were calculated. Consequently, the de-oxidation limits of different reductants in a VO system were evaluated, namely: Si, Al, and Mg. It was observed that Si could not remove an O content of less than 7.27 wt% from V. However, Al was the stronger reducing agent; it could remove O contents of up to 0.01 and 0.1 wt% at 800 and 1050°C, respectively. Nevertheless, Mg exhibited the best reducing properties as it could remove less than 0.01 wt% of O at 1100°C. The addition of H2 rendered the V-O solid solution unstable to a certain extent, thereby indicating that H2 facilitated de-oxygenation. Furthermore, the results obtained by analyzing the equilibrium conditions were in accordance with the results of the de-oxidation limit in the V-O system. In other words, this study demonstrated that oxygen in vanadium can be effectively controlled by changing the reductant dosage and temperature.

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]

Non-destructive and destructive techniques were used to document and model crack formation in acetal resin nuts used for household toilet water supply lines. The morphologies of creep rupture and overload failure were documented using optical microscopy and scanning electron microscopy (SEM). The forensic investigation stemmed from litigation between a homeowner, plumbing contractor, and parts supplier related to a failure at a single residence. Fortuitously, 447 fittings in service for approximately two years under similar conditions were available for examination. In many properly installed fittings, cracks had initiated at the notch created by the sharp thread root radius, as predicted by engineering mechanics and finite element analysis. This study found that the cracks had propagated via plastic creep. [ABSTRACT FROM AUTHOR]

Cross-laminated timber (CLT) has been used extensively in timber construction. CLT panels are typically used in roofs and floors that carry a continuous load, and it is important to examine the long-term loading capacity of CLT. However, studies that focus on the long-term loading capacity of CLT are limited. To this end, we conducted long-term out-of-plane bending tests on seven-layer CLT made from Japanese larch (Larix kaempferi) under constant environmental conditions, investigated creep performance and duration of load, and experimentally analyzed creep rupture behavior. The mean estimated relative creep after 50 years was 1.49. The sample showed a satisfactory resistance to creep as a building material. The duration of load of most of the specimens in this study was shorter than the conventional value of small clear wood specimens. Specimens had a lower duration of load capacity than solid lumber. According to the results of survival analysis, a loading level of 70% or more caused the initial failure of specimens. Creep rupture of most of the specimens occurred at less deflection than displacement at failure in the short-term loading test. Additional studies focusing on the effects of finger joints, transverse layers, and width of a specimen on creep rupture behavior are suggested. [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 this study, an experimental creep crack growth rate (CCGR) of austenitic steel AISI 316L was predicted from the creep constant values and Nibkin Smith Webster (NSW) method. The experimental CCGR data were obtained from the CCG test under four different load conditions ranging from 6000 to 7000 N at 525 oC. The creep constants, A and n were obtained from the uniaxial creep rupture test under various load conditions, ranging from 180 to 225 Mpa at 525 oC. The creep constants were determined both from the minimum and average creep strain rate data. By applying the creep constants and NSW method, the predicted CCGR curve was generated and compared with the experimental CCGR curve. The result showed that the predicted CCGR curve based on the minimum creep strain rate data was found to be close to the experimental CCGR curve. The significant portion of creep crack growth’s lifetime of austenitic steel AISI 316L was occupied by the crack propagation (steady stage) period rather than crack initiation and/or fracture periods. In addition, plane stress and strain conditions could also be determined from the predicted CCGR curve. It was observed that the experimental CCGR curve was located near the plane strain condition where no deformation occurred in the lateral direction.

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 σ105700= 57.1 MPa and σ105750=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.

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]

The effect of grain size on the mechanical properties and creep rupture of 253 microalloyed (MA) austenitic stainless steel (ASS) was investigated. The cold rolling process with a 53% reduction in thickness was applied to the steel followed by annealing at 1100 °C over 0, 900, 1800, and 3600 s to obtain grain sizes of 32.4, 34.88, 40.35, and 43.77 µm, respectively. Uniaxial tensile and micro-Vickers hardness tests were carried out to study the effect of grain size on mechanical properties at room temperature. The creep rupture test was performed at 700 °C under a load of 150 MPa. The results showed that there was a correlation between grain size, mechanical properties, and creep rupture time. The fine initial grain size showed relatively good mechanical properties with a short creep rupture time, while the coarse initial grain size produced low mechanical properties with a long creep rupture time. The initial grain size of 40.35 µm was the optimum grain size for a high value of creep rupture time due to the low hardness and elongation values at room temperature and low creep ductility value. The intergranular fracture was found on the initial grain size below 40.35 µm, and a mixed mode of intergranular and transgranular fracture was found on the initial grain size above 40.35 µm after the creep rupture test.

In order to reveal the creep failure behavior of novel modified 310S austenite steel welded joints, the creep life and microstructure evolution of the 310S austenite steel welded joints were investigated in this study. The rupture life was assessed to estimate the damage of the welded joint based on creep rupture tests performed at 600 °C in the stress range of 170–238 MPa. Compared with WM, HAZ facilitated the occurrence of creep failure in long term creep due to the combination of a smaller hardness value, a more heterogenous microstructure accompanied by coarsened M23C6, a larger grain size, higher KAM and Schmid factor. Discontinuous Laves phases appeared near the boundaries between the δ-ferrite and γ-austenite grains in the WM, and dislocation strengthening and precipitation strengthening were observed near the boundary in the BM. Furthermore, segregation elements were detected by APT and EDS adjacent to the boundary. Cr and C segregation near grain boundaries weaken the creep resistance in long term creep service.

Creep tests were carried out on notched plate specimens of nickel-based superalloy GH4169 with different stress concentration coefficients. It was found that the duration of the first stage of the creep curve increases with the increase of stress concentration coefficient, while the fracture ductility decreases with the increase of stress concentration coefficient. To predict the life of notched plate specimens, four constitutive models were used to analyze the stress and strain of the notches. It was found that the average Von Mises equivalent stress (AVES) on the minimum notch section first decreases and then increases with the creep time, resulting in a minimum value. The minimum average Von Mises equivalent stress (MAVES) is considered as the characteristic stress of notched specimens in this paper. The creep life equation is fitted according to the results of creep tests of smooth specimens, and then the predicted life of notched specimens is obtained by substituting the minimum average Von Mises equivalent stress of notched specimens into the creep equation. The prediction results of the four constitutive models are within 2 times the dispersion band, and the three-stage model is within the 1.5 times dispersion band.

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]