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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.)

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 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]

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]

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]

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]

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]

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]

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]

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 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 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]

Copyright of Journal of Mining & Metallurgy. Section B: Metallurgy is the property of Journal of Mining & Metallurgy 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.)

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]

Copyright of Journal of Jiangsu University (Natural Science Edition) / Jiangsu Daxue Xuebao (Ziran Kexue Ban) is the property of Editorial Department of Journal of Jiangsu University (Natural Science Edition) 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.)

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]

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]

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]

Copyright of Journal of Jiangsu University (Natural Science Edition) / Jiangsu Daxue Xuebao (Ziran Kexue Ban) is the property of Editorial Department of Journal of Jiangsu University (Natural Science Edition) 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.)

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]

This paper contributes to understanding how installation damage of geosynthetics influences their long-term response and design. A geotextile and a geogrid were exhumed after installation under real conditions; their long-term tensile behaviour was investigated using conventional creep and creep rupture tests. Reduction factors for installation damage, creep and their combined effect were computed. The main aim of the paper was to assess how the long-term response of the geosynthetics was influenced by installation damage and whether it would be necessary to update current design approaches. The installation damage affected the mechanical response of both geosynthetics; important strength reductions were observed, particularly for the most severe installation conditions. The results indicate that, contrary to what has been reported in the literature, the creep rupture response of the geotextile changed after installation damage. When tested under similar creep loads (fraction of the sample tensile strength), both geosynthetics exhibited reduced potential for creep rupture and smaller strains at the end of primary creep. Changes in stiffness were less important than those for strength, for both short- and long-term response. There was synergy between installation damage and creep; the traditional approach to design was unsafe for the geotextile and slightly conservative for the geogrid. [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]

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]

Recycled asphalt pavement (RAP) can be beneficially used as alternative construction material in geotechnical applications, but characterizing its creep response is important to account for potential viscous effects attributable to the material's asphalt content. Effects of elevated temperature (35 and 50°C) on creep behavior of compacted RAP specimens were investigated through temperature-controlled triaxial compression tests at sustained deviator stresses. RAP compacted at room temperature (22°C) and subjected to deviator stress at elevated temperature showed creep strain and strain rate that systematically increased with increasing temperature. Time to creep rupture decreased with increasing temperature. Compaction at elevated temperature resulted in denser specimens and reduced creep strain and strain rate. Temperature effects were incorporated into a creep model that may be used to estimate strain rate of RAP at elevated temperatures. Construction of structural fills containing RAP is recommended during warm months of the year to minimize subsequent creep strain and potential for creep rupture. [ABSTRACT FROM AUTHOR]

The increased thermal efficiency of fossil power plants calls for the development of advanced creep-resistant alloy steels like T92. In this study, microstructures found in the heat-affected zone (HAZ) of a T92 steel weld were simulated to evaluate their creep-rupture-life at elevated temperatures. An infrared heating system was used to heat the samples to 860 °C (around AC1), 900 °C (slightly below AC3), and 940 °C (moderately above AC3) for one minute, before cooling to room temperature. The simulated specimens were then subjected to a conventional post-weld heat treatment (PWHT) at 750 °C for two hours, where both the 900 °C and 940 °C simulated specimens had fine grain sizes. In the as-treated condition, the 900 °C simulated specimen consisted of fine lath martensite, ferrite subgrains, and undissolved carbides, while residual carbides and fresh martensite were found in the 940 °C simulated specimen. The results of short-term creep tests indicated that the creep resistance of the 900 °C and 940 °C simulated specimens was poorer than that of the 860 °C simulated specimens and the base metal. Moreover, simulated T92 steel samples had higher creep strength than the T91 counterpart specimens. [ABSTRACT FROM AUTHOR]

Research of a metal of the stop valve case (SVC) of the K-300-23.5 LMZ turbine (steel grade 15Kh1M1FL), destroyed after operation for 331000 hours, is performed. It's chemical composition and properties are determined as follows: a short-term mechanical tensile stress at 20°C and at elevated temperature, critical temperature, fragility, critical crack opening at elevated temperature, and long-term strength. Furthermore, nature of the microstructure, packing density of carbide particles and their size, and chemical composition of carbide sediment are estimated. A manifestation of metal properties for the main case components by comparison with a forecast of the respective characteristics made for the operating time of 331000 hours is tested. Property-time relationships are built for the forecast using statistical treatment of the test results for the samples cut out from more than 300 parts. Representativeness of the research results is proved: the statistical treatment of their differences are within the range of ±5%. It has been found that, after 150000 hours of operation, only the tensile strength insignificantly depends on the operating time at 20°C, whereas indicators of strength at elevated temperature significantly reduce, depending on the operating time. A brittle-to-ductile transition temperature (BDTT) raises, a critical notch opening changes in a complicated way, a long-term strength reduces. It has been found empirically that the limit of a long-term strength of the SVC metal at 540°C and the operating time of 10 hours is almost 1.6 times less than the required value in the as-delivered state. It is possible to evaluate a service life of the operating valves with the operating time of more than 330000 hours with respect to the long-term strength of the metal taking into account the actual temperature and stress. Guidelines for the control of similar parts are provided. [ABSTRACT FROM AUTHOR]

The multi-axial creep strength of circumferential welds in power piping, including failure mode and failure life against a wide range of stress ratios and stress levels, was newly examined in this paper. The creep rupture behaviour of modified 9Cr–1Mo steel (9Cr–1Mo–VNb steel; ASME P91) pipe with a circumferential weld subject to combined internal pressure and axial load was experimentally investigated at 650 °C. The test results, with several kinds of stress ratios of macroscopic axial and hoop stress can be summarised as follows. Along with the increased stress ratio (axial/hoop), both failure location and failure mode changed from a base metal failure caused by hoop stress to an FGHAZ (fine-grained heat affected zone) failure due to axial stress. The stress ratio where the failure mode changed was ‘0.8’. Strength reduction in FGHAZ failure by axial stress should be considered in the structural design of circumferential welds. A series of FEM creep analysis was carried out to discuss the relation of the failure mode to both the local stress distribution and the damage. The failure mode variation along with the increase in the stress ratio is also discussed based on simplified ductile creep failure analysis. [ABSTRACT FROM PUBLISHER]

Microstructures of the heat-affected zone (HAZ) of a Gr. 91 steel weld were simulated to evaluate their effects on the creep life of the weld at elevated temperatures. The Ac and Ac temperatures of the Gr. 91 steel were determined by a dilatometer to be at 867 and 907 °C, respectively. An infrared heating system was employed to heat the samples to 860 (STOT), 900 (ICHAZ) and 940 °C (FGHAZ) for 1 min, followed by cooling to room temperature. The simulated specimens were then subjected to conventional post-weld heat treatment (PWHT) at 750 °C/2 h. After the PWHT, the tempered ICHAZ specimen had a shortest creep life among the specimens tested at 650 °C/60 MPa. Moreover, the simulated specimen heated to 860 °C (STOT) was more likely to fracture at 615 °C/80 MPa than others. [ABSTRACT FROM AUTHOR]

The creep behavior of a nickel-base superalloy, Alloy 617, which is considered as a candidate material for the very high temperature gas cooled reactor, was studied. Creep rupture tests were carried out at 800°C, 900°C and 1000°C in static and flowing helium environments as well as in air. Creep rupture life in static helium was longer than that in air, while it was shorter in flowing helium environments. Microstructure observation of the creep tested specimens showed that the shorter creep rupture life in flowing helium was associated with the thicker oxide layer, greater decarburization depth, and deeper internal oxidation happened during the creep tests. The degree of such oxidation damage was quantified for the creep tested specimens and correlated with the creep rupture life in different environments. [ABSTRACT FROM AUTHOR]

The cross dissimilar welds between T92 martensitic steel and S30432 austenitic steel were crept at 625 °C with different applied stresses, and the creep deformation and microstructure behaviors were characterized. The results revealed that the creep deformation behavior of dissimilar weld joint was controlled by its martensitic T92 part due to the Ni-based filler metal employed. The fracture positions of crept dissimilar welded joints were located in base metal of T92 steel as the applied stress over than 140 MPa. The fracture type was mainly caused by plastic deformation and characterized by dimples and surface necking. In contrast, as applied stress was <140 MPa, fractured location was transferred into the fine-grained heat-affected zone of T92 part identified to be the intergranular brittle fracture. This phenomenon was controlled by creep deformation and related to undissolved carbides, fine grain size and constraint effect induced by creep deformation inconsistent in this zone. [ABSTRACT FROM AUTHOR]

In this study, creep experiments on smooth and circumferential V-type notched round bars were conducted in GH3536 Ni-based superalloy at 750 °C to identify notch strengthening effect in notched specimens. FE analysis was carried out, coupled with continuum damage mechanics (CDM), to analyze stress distribution and damage evolution under multiaxial stress state. The creep deformation of smooth specimens and the rupture life of both smooth and notched specimens showed good agreement between experimental results and FE analysis predictions; the creep rupture life for the notched specimen was successfully predicted via the 'skeletal point' concept. Both creep damage analysis and the observed fracture morphology suggest that creep rupture started first at the root in the V-type notched specimens, and shifted to the region close to the notch root when the notch was relatively shallow compared to U-type notched specimens. [ABSTRACT FROM AUTHOR]

Creep behavior is one of the most critical factors determining the failure life of components at elevated temperature. Turbine rotor shaft is subjected to such elevated conditions. The creep behavior of rotor grade steel 28CrNiMoV59 was studied at elevated temperatures from 550 to 650 °C and at stress levels varying from 120 to 300 MPa. Tensile tests were conducted to determine the basic properties. Microstructural and chemical analyses were performed to characterize the as received material. Creep rupture data were determined from experimental results. These results were used to calculate the creep constants at elevated temperature which are used in time-temperature parametric (TTP) methods. Different TTP methods like, Larson-Miller, Orr-Sherby-Dorn and Manson-Haferd, were analyzed to check their suitability for extrapolation of creep rupture data of (28CrNiMoV59) steel. [ABSTRACT FROM AUTHOR]

The fusion zone is usually the weakest link in austenitic steel weld joints and it is usually in this region where damage initiates during creep deformation. The heterogeneity in microstructure of the fusion zone enhances the complexity in understanding the damage evolution during creep exposure. The major source of heterogeneity in the microstructure is the weld thermal cycle, which the weld joint is inevitably subjected to during multi-pass welding. Subsequent thermal cycles are likely to alter the microstructure of the previously deposited fusion zone thereby influencing the mechanical properties of the joints. In this study, the effect of thermal cycle on creep rupture behaviour of 316LN SS weld joint has been studied. Weld joints were fabricated by two welding processes-activated tungsten inert gas (ATIG) and shielded metal arc (SMA) welding. In case of ATIG weld joints, the creep properties of single and dual-pass weld joints were compared and for the SMAW joints, the comparison was made between weld joints made with two different electrode sizes. In ATIG weld joint, the subsequent thermal cycle in the dual pass weld joint improved its creep rupture life. In the case of the SMAW joint, the weld joint made with larger electrode, which was subjected to less number of thermal cycles exhibited better creep properties. The weld thermal cycle induces a 'thermo-mechanical treatment' and changes the morphology of delta ferrite in the previously deposited fusion zone which has a synergistic role in dictating the creep rupture life of the 316LN SS weld joints. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to determine the feasibility of identifying the creep rupture of reactor cladding tubes using acoustic emission technique (AET). Design/methodology/approach – The creep rupture tests were carried out by pressuring stainless steel capsules upto 6 MPa at room temperature and then heating continuously in a furnace upto rupture. The acoustic emission (AE) signals generated during the creep rupture tests were recorded using a 150 kHz resonant sensor and analysed using AE Win software. Findings – When rupture occurs in the pressurized capsule tube representing the cladding tube, AE sensor attached to a waveguide captures the mechanical disturbance from the capsule and these data can be advantageously used to identify the creep rupture event of the cladding tube. Practical implications – The creep rupture data of fuel clad tube is very important in design and for smooth operation of nuclear reactors without fuel pin failure in reactors. Originality/value – AE is an advanced non-destructive evaluation technique. This technique has been successfully applied for on-line monitoring of creep rupture of the reactor cladding tube which otherwise could be detected by thermocouple readings only. [ABSTRACT FROM AUTHOR]

The creep rupture of a long rod subjected to tension in an aggressive medium is considered. Using a diffusion equation where the diffusion coefficient D is a monotonically decreasing function of concentration c of the medium, the diffusion penetration of elements of the aggressive medium into the material of the rod is modeled. On the border between the rod and external medium, a condition of mass transfer is assumed. The approximate method put forward for solving the diffusion equation is based on the introduction of a diffusion front. Two stages of the diffusion process are considered: penetration of the front and saturation. A comparison between solutions of the diffusion equation for proposed D(c) functions is performed. The influence of D(c) on the creep rupture of a tensile rod is evaluated using the Rabotnov kinetic theory of creep and creep rupture. [ABSTRACT FROM AUTHOR]

This paper aims to identify the creep mechanisms of high tenacity (HT) polyester industrial fiber under different loads. In-situ synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) tests were conducted on a 1000 D HT fiber during the creep and creep recovery process with a low load (15 N) and a medium load (50 N) as well as creep rupture process with a high load (60 N). The measured creep strain-time curves comprised tensile zone (I), creep deformation zone (II) and creep recovery/rupture zone (III). The SAXS indicated that the macroscopic initial creep strain in zone I and creep deformations in zone II were attributed to conformation transition from gauche to trans in amorphous region, increasing the amorphous orientation and long period. Irreversible portion of conformation changes accounts for the small unrecoverable plastic creep strain after removing 15 N load in zone III. The initial creep strain in zone I and creep deformations in zone II of the 50 N creep process were bigger than the microscopic long period strain, because amorphous layers had conformational transformation and microfibril slippage which also produced a higher unrecoverable plastic creep strain in zone III. The long period increased significantly at the beginning of rupture zone with 60 N due to fragmentation of amorphous tie molecular. The disappearance of lamellar peaks at the end of rupture zone implied destruction of periodic lamellar structures, for the entire breakage of amorphous chains. The WAXS suggested that the crystal structure was stable under the creep loads. [ABSTRACT FROM AUTHOR]

A set of creep rupture data, for which two independent investigators have previously published models, is re-examined using the recently proposed parametric numerical isothermal datum (P-NID) approach to modelling. It is shown that neither of the existing models can be presumed reliable in extrapolation. In contrast, P-NID models are found to represent the data with much greater accuracy and to satisfy appropriate criteria for reliability in extrapolation. According to the principles of this approach, the close correspondence between the P-NID models and the data justifies extrapolation in rupture time at mid-range and lower test temperatures in excess of 15-fold. This expectation is confirmed by excluding from the analysis all data at more than 7% of the longest known rupture life, then comparing the resultant extrapolation to the excluded data. The success of the procedure suggests a potential for greatly reducing the extent of rupture testing necessary to produce reliable extrapolation to times of practical interest. This is demonstrated for a set of data including simulated results at intermediate temperatures. The study shows a potential reduction to less than one-tenth of the aggregate test time conventionally considered necessary. The analysis of further sets of rupture data shows how a P-NID model may reliably be extrapolated even when the material behaviour necessitates a model partitioned according to temperature range, or exhibits instability. Limited investigation indicates that, for a given material, creep strain data are consistent with parametric models for rupture data and may be extrapolated over similar intervals. [ABSTRACT FROM AUTHOR]