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This paper aims to present the determination of the creep behaviour of a globular microstructure aluminium 7075 alloy semi-solid metal feedstock billets under a constant temperature of 250 °C. Globular microstructures are often preferred in thixoforming processes due to their unique properties and favourable mechanical and high-temperature applications. Less attention has been given to globular microstructure even though the contribution of microstructure to creep behaviour is essential. Therefore, for this test, globular microstructure aluminium 7075 alloy feedstock billets were produced by the direct thermal method. The creep tests were conducted at different stress ranges from 30 to 70 MPa, and the effect of globular microstructure was examined. The results showed that the globular microstructure had the least deformation and the lowest creep rate at a longer deformation time. The fracture surface of the samples was then analysed with scanning electron microscopy (SEM). The microstructural changes that occurred during the test were investigated. SEM analysis revealed that the globular microstructure of the feedstock billet exhibits fewer voids and defects due to a uniform microstructure. The strain exponent value of globular microstructure billets was found to be at n = 4.6 in the stress range between 30 and 70 MPa at a constant temperature. This study is expected to provide an understanding of the creep behaviour of globular microstructures at high temperatures and high-stress conditions. [ABSTRACT FROM AUTHOR]

The Japan Atomic Energy Agency has been developing 9Cr-oxide dispersion strengthened (ODS) steel as a fuel cladding material for sodium-cooled fast reactors (SFRs). Previous studies have formulated the creep rupture equation for 650°C–850°C. However, little data have been obtained above 850°C, and no equation has been formulated. This study conducted creep tests to evaluate creep strength at 700°C–1000°C. Two creep test methods, the internal pressure and ring creep tests under development, were used, and the validation of the ring creep test method was conducted. The results showed that 9Cr-ODS steel undergoes almost no strength change due to the matrix's phase transformation, and a single equation can express a creep rupture strength from 700°C to 1000°C. In validating the ring creep test method, analysis clarified the effect of stress concentration on the specimen. Plastic deformation occurs at high initial stress and may lead to early rupture. The results will be essential for future creep testing and evaluation of neutron-irradiated 9Cr-ODS steel. [ABSTRACT FROM AUTHOR]

Abstract For dissimilar metal welds (DMWs) involving nickel-based weld metal (WM) and ferritic heat resistant steel base metal (BM) in power plants, there must be an interface between WM and BM, and this interface suffers mechanical and microstructure mismatches and is often the rupture location of premature failure. In this study, a new form of WM/BM interface form, namely double Y-type interface was designed for the DMWs. Creep behaviors and life of DMWs containing double Y-type interface and conventional I-type interface were compared by finite element analysis and creep tests, and creep failure mechanisms were investigated by stress-strain analysis and microstructure characterization. By applying double Y-type interface instead of conventional I-type interface, failure location of DMW could be shifted from the WM/ferritic heat-affected zone (HAZ) interface into the ferritic HAZ or even the ferritic BM, and the failure mode change improved the creep life of DMW. The interface premature failure of I-type interface DMW was related to the coupling effect of microstructure degradation, stress and strain concentrations, and oxide notch on the WM/HAZ interface. The creep failure of double Y-type interface DMW was the result of Type IV fracture due to the creep voids and micro-cracks on fine-grain boundaries in HAZ, which was a result of the matrix softening of HAZ and lack of precipitate pinning at fine-grain boundaries. The double Y-type interface form separated the stress and strain concentrations in DMW from the WM/HAZ interface, preventing the trigger effect of oxide notch on interface failure and inhibiting the interfacial microstructure cracking. It is a novel scheme to prolong creep life and enhance reliability of DMW, by means of optimizing the interface form, decoupling the damage factors from WM/HAZ interface, and then changing the failure mechanism and shifting the failure location.

Understanding mechanical performance evolution and failure mechanism of solid oxide fuel cell stack (SOFCs) during long-term operation period are essential to prolong operation life and advance commercialization. In this study, based on the structural mechanical model, the evolution characteristics of thermal stress, failure probability, strains, and deformation of SOFCs fueled by partially pre-reformed CH 4 during 3000 h' operation are revealed. It's found the maximum thermal stresses of anodes, sealants, and frames/ICs decease respectively by 82.9%, 74.1%, and 88.4%, while those of electrolytes and cathodes firstly fluctuate then increase. The failure probabilities of sealant and anode decrease by 6∼10 orders of magnitude, while increase by 1 order of magnitude and 1.5 times for electrolyte and cathode. 300 h later, sealant may fracture by creep strain, while the component most likely to fail due to thermal stress changes from sealant to cathode. The maximum deformation of positive electrode-electrolyte-negative electrode (PEN) locates in anode of cell 15. It is suggested creep resistance of sealant be improved to avoid creep fracture, mechanical strength of cathode/sealant be increased to decrease failure probability, and the temperature unevenness be decreased to avoid larger deformation. • A large-scale SOFC stack with high geometry-resolution constructed. • Temperature field obtained by multiphysics models. • Long-term mechanical performance evolution characteristics elucidated. • Locations susceptible to failure disclosed. • Failure mechanism revealed and rational suggestions given. [ABSTRACT FROM AUTHOR]

For dissimilar metal welds (DMWs) involving nickel-based weld metal (WM) and ferritic heat resistant steel base metal (BM) in power plants, there must be an interface between WM and BM, and this interface suffers mechanical and microstructure mismatches and is often the rupture location of premature failure. In this study, a new form of WM/BM interface form, namely double Y-type interface was designed for the DMWs. Creep behaviors and life of DMWs containing double Y-type interface and conventional I-type interface were compared by finite element analysis and creep tests, and creep failure mechanisms were investigated by stress-strain analysis and microstructure characterization. By applying double Y-type interface instead of conventional I-type interface, failure location of DMW could be shifted from the WM/ferritic heat-affected zone (HAZ) interface into the ferritic HAZ or even the ferritic BM, and the failure mode change improved the creep life of DMW. The interface premature failure of I-type interface DMW was related to the coupling effect of microstructure degradation, stress and strain concentrations, and oxide notch on the WM/HAZ interface. The creep failure of double Y-type interface DMW was the result of Type IV fracture due to the creep voids and micro-cracks on fine-grain boundaries in HAZ, which was a result of the matrix softening of HAZ and lack of precipitate pinning at fine-grain boundaries. The double Y-type interface form separated the stress and strain concentrations in DMW from the WM/HAZ interface, preventing the trigger effect of oxide notch on interface failure and inhibiting the interfacial microstructure cracking. It is a novel scheme to prolong creep life and enhance reliability of DMW, by means of optimizing the interface form, decoupling the damage factors from WM/HAZ interface, and then changing the failure mechanism and shifting the failure location. [ABSTRACT FROM AUTHOR]

Historically, reduction of area has been neglected during uniaxial creep tests, and engineering rather than true stress-strain and strain rate have been considered. In high load accelerated tests, there is an increasing error associated with the engineering stress and strain, hence this assumption is no longer valid. In this work, uniaxial creep tests on Type 316H austenitic stainless steel at 480–550 °C have been analysed for both engineering and true stress–strain and strain rate. Significantly higher stresses and lower minimum strain rates were determined from true stress-strain rate relationships for as-received 316H. These differences diminish as the material is strain hardened, limiting plastic loading strains and reducing creep ductility. The true stress-strain rate analysis method is shown to be more accurate, however, the engineering stress-strain analysis predicts higher creep strain rates for a given stress and is the more conservative measure for component lifetime assessments. [ABSTRACT FROM AUTHOR]

Timber architectures have arisen as sustainable solutions for high-rise and long-span buildings, assisting in implementing a circular economy. The creep strain dissipation of laminated veneer lumber (LVL) was investigated in this work to understand the inherent creep behaviors of LVL derived from natural wood. The results demonstrated a significant loading regime dependency of the creep behaviors of LVL. Coupled creep strain dissipation that transits/is parallel to the wood–adhesive interface was proven in the creep deformation of flat-wise and edge-wise bent LVL. In contrast, the creep strain dissipated considerably along the wood–adhesive interface when the LVL was subjected to axial compression creep. Further investigation into the morphologies of LVL after creep revealed that direct contact between the loading plane and wood–adhesive interface could be a plausible trigger for the accelerated deformation and the resultant plastic deformation of the LVL after creep. We believe that this work provides essential insights into the creep strain dissipation of LVL. It is thus beneficial for improving creep resistance and assisting in the long-term safe application of LVL-based engineered wood products in timber architectures. [ABSTRACT FROM AUTHOR]

One of the most important elements for animal transportation is the packaging that ensures the safety and health of the transit. During the transport of live small animals, such as day‐old chickens, the animals may only stay in the boxes for a very limited period, in this case, 48 h. Therefore, it is important to be able to model the strength behaviour of these boxes concerning packaging material requirements and sustainability. The aim of this study was to determine the short‐ and relatively long‐term strength of day‐old chicken packages to better estimate packaging design and to use these data to establish an analytical creep model with suitable parameters that adequately approximate the measured data. Two types of packages were tested, and two types of creep models were used to model the creep strain‐time graphs. The creep behaviour of the two samples was tested at four different uniaxial load cases, with consistent environmental conditions during the tests (23°C and 50% relative humidity [RH]). At the two highest loads, both samples failed before the 48‐h cycle, indicating a significant difference in box strength between short‐term and long‐term load tests. The secondary creep strain rate increases with the magnitude of the compressive load. When comparing the two creep models for both box types, the Power law provided the best accuracy at the 50% of box compression test (BCT) load case, while at the other three load cases, the Andrade law showed better predictions. [ABSTRACT FROM AUTHOR]

In mechanical structures exposed to high temperatures, such as turbine blades for power generation, cracks are detected during in-service inspections. However, there is a risk of fracture owing to the relatively rapid rate of crack propagation, even when a large safety factor is in force. Therefore, a technique is required to estimate the creep-strain distribution before crack initiation and to predict the remaining service life. An inverse analysis method, based on the eigenstrain methodology, has been proposed to estimate the three-dimensional creep-strain distribution using non-destructively measured surface displacements. Three-dimensional creep-strain distributions can be estimated even when the relationship between the creep strain and displacement is non-linear. Through iterative calculations, this method converges to a solution with relatively high estimation accuracy, however, a method for estimating actual complex creep-strain distributions is needed. In this study, a method was proposed to improve the convergence of the iterative calculations. Its effectiveness was demonstrated by numerical analysis using a torsional geometry model that could be used to describe an actual turbine blade. Many unknown values were assumed so that relatively complex creep-strain distributions could be estimated. Convergence calculations were performed to improve the estimation accuracy through iterative calculations, even when displacement measurement errors were considered. The estimation accuracy was improved by using more actual measurements in the inverse analysis.

In this paper, the phenomenon of creep compliance and the creep Poisson's ratio of a 3D-printed Sierpinski carpet-based fractal and its bulk material (flexible resin Resione F69) was experimentally investigated, as well as the quantification of the change in the viscoelastic parameters of the material due to the fractal structure. The samples were manufactured via a vat photopolymerization method. The fractal structure of the samples was based on the Sierpinski carpet at the fourth iteration. In order to evaluate the response of both the fractal and the bulk material under the creep phenomenon, 1 h-duration tensile creep tests at three constant temperatures (20, 30 and 40 °C) and three constant stresses (0.1, 0.2 and 0.3 MPa) were conducted. A digital image correlation (DIC) technique was implemented for strain measurement in axial and transverse directions. From the results obtained, the linear viscoelastic behavior regime of the fractal and the bulk material was identified. The linear viscoelastic parameters of both fractal and bulk materials were then estimated by fitting the creep Burgers model to the experimental data to determine the effect of the fractal geometry on the viscoelastic properties of the samples. Overall, it was found that the reduction in stiffness induced by the fractal porosity caused a more viscous behavior of the material and a reduction in its creep Poisson's ratio, which means an increase in the compliance of the material. [ABSTRACT FROM AUTHOR]

Creep of clayey soils is defined as the time-dependent deformation under sustained stresses, due to viscous behavior of the soil skeletons. The creep behavior of soil is influenced by several main factors, such as time, temperature, soil type, soil structure, stress history, stress state, and drainage conditions. Soft foundations of low embankments exhibit significant time-dependent effect on deformation in decades after construction, and there is a lack of simple method for predicting the creep rate of overconsolidated soft clay under plain strain condition. In this study, plane strain triaxial test have been conducted to investigation volumetric, axial and lateral creep strain of saturated soft clay. The experimental results show that the volumetric creep strain of soil specimens subjected to static loading increases with the increasing magnitude of external load, and it depends on the amplitude of pre-consolidation load, a larger preconsolidation load value is associated with a significantly reduced volumetric creep strain. The variation of axial strain and lateral strain are similar with variation of volumetric creep strain for both normally and overconsolidated state, but the rate of variation decreases significantly when the soil transitions into an overconsolidated state. In addition, the test results show that the excess pore pressure develops and increases rapidly to reach the peak values as soon as the external loads was applied on the specimen and then decreases gradually to a stable value of zero during creep deformation stage of soil. [ABSTRACT FROM AUTHOR]

Chalks are non-clastic type of carbonate sedimentary rocks. Any applied axial load would lead to a deformation of the sediments by the depletion of the pore fluids. This results in compaction which is a process in which the compressive strength of the rock is exceeded and plastic deformation occurs, resulting in irreversible reduction of porosity. In this work, a time-dependent deformation in chalks known as creep is presented. A reduction from 30 MPa to 5 MPa pore pressure in 100 minutes (0.25 MPa/min) was termed rapid loading. The same pressure was depleted for about 8333 minutes (0.003 MPa/min) and regarded as a slow loading. At the lower value of 5 MPa, the samples were left to deform under constant stress for some time. It was observed that when loaded rapidly, the deformation accumulated at the creep stage was higher; observed mainly at the transient creep phase, compared to when loaded slowly. The results of the experiments show that other parameters such as uniaxial compaction modulus both in the elastic and plastic regions, creep strain and creep rate are all loadingrate dependent. Hence, it could be inferred that if creep is porosity dependent, then it is load-rate dependent. Also, creep rate is highest for rapid loading and lowest for slow loading, while values for intermediate loading were in-between. The loading rate has to be widely different for variations in accumulated strains to differ with time. [ABSTRACT FROM AUTHOR]

Despite the fact that densified mixture design algorithm (DMDA) has been identified as a promising tool for green concrete mix design, its use in real practice has still been minimal worldwide. Due to the lack of precise information on DMDA computation in earlier studies, this work proposes DMDA including fly ash and ground granulated blast‐furnace slag as a viable way to improve the long‐term performance of green concrete. To encourage the use of DMDA, this study offers a detailed description of the DMDA mix design, as well as a step‐by‐step standard operating procedure and an empirical example of the computation. Assessments of the long‐term performance of green mixtures (self‐consolidating concrete and high‐performance concrete) and ordinary Portland cement concrete (designed using the conventional method of American Concrete Institute, ACI) were made. Performances of the ACI (O6000 mixture) and DMDA concretes (S6000 and H6000 mixtures) were then compared in terms of compressive strength, elastic modulus, shrinkage, and creep strain. As a result, all of the concrete samples attained the target strength of above 41 MPa (6000 psi) after only 28 days. Moreover, compressive strength, elastic modulus, shrinkage, and creep strain increased significantly in all of the concretes over curing time. Importantly, the experimental results confirmed that both types of DMDA concrete exhibited higher compressive strength and better long‐term performance than the ACI concrete under elastic modulus, creep, and shrinkage aspects. [ABSTRACT FROM AUTHOR]

In this work, time and temperature-dependent viscoelastic properties, i.e., creep and stress relaxation of synthetic fabrics have been studied using the dynamic mechanical analyser. Three different fabric materials viz. polyester (PET), polypropylene (PP) and Nylon 6,6 (PA) were used and tests were carried out at a wide range of temperatures from 35 to 110 °C with an interval of 15 °C after each test. Thereafter, the master curve for each fabric is generated at 35 °C using the time–temperature superposition (TTS) principle which extrapolates short time experimental data to a longer time scale by shifting experimental curves of different temperatures toward the reference temperature (35 °C) and superimposes them to obtain a smooth master curve. From the creep study, it is observed that PET fabric is expected to give greater creep resistance with minimal deformation in creep strain of about 39% followed by 53% in PA and 128% in PP even after 10 years. Besides, in the stress relaxation study, relaxation modulus for all fabrics tends to decrease with increasing temperature. It is found that PA fabric showed a slow reduction of relaxation modulus even after 10 years, which gives about 55% reduction followed by PET (68%) and PP (75%) from its initial value. In addition, true stress versus time curves showed that a higher true stress value in PA followed by PP and PET is referring to its higher relaxation modulus. It was found that initial modulus, glass transition temperature (Tg) and crystallinity of fibre plays an important role in determining creep and stress relaxation behaviour of the fabrics. On the other side, the correlation between experimental data and theoretical data ascertains the use of viscoelastic Burger's model and Weibull distribution equation model for creep and stress relaxation. [ABSTRACT FROM AUTHOR]

The reaction coils of high-temperature ethylene production plants are operated under extremely harsh conditions: long-term impact of high temperatures (900–1100°C), internal pressure (up to 0.7 MPa), periodic heating and cooling. The rated service life of coils is 100,000 hours. However, reaction tubes are often rejected after 4000 to 6000 hours of operation due to inadmissible shape change (axial bending). Studying the microstructure and mechanical properties of several metal samples of rejected tubes of pyrolysis furnaces showed that their service properties are close to those of as-received tube metal and that the carburization of and damage to the near-surface layers are insignificant. Therefore, the most likely causes of premature failure of reaction tubes are the design and operational factors. The stress–strain state of a standard 125 × 10 mm tube, 10 m long, under an axial load was numerically analyzed using a viscoelastic problem formulation for various boundary conditions and temperature distributions over the surface. MSC.Marc finite-element software system was used. The input data were the results of processing test data on creep and stress rupture of as-cast cylindrical 45Cr26Ni33Si2Nb2 alloy specimens with gage length equal to five times the diameter at temperatures of 900–1100°C. The most probable causes of irreversible shape change (transverse bending) of reaction tubes were identified. [ABSTRACT FROM AUTHOR]

Creep strain versus time curves (creep curves) have traditionally been described with the help of empirical models where a number of adjustable parameters are involved. These models are simple to use, but they cannot be applied for prediction. For understanding the general behavior of primary and tertiary creep, they are still useful. In fact, the phi model can represent primary creep, and the Omega model tertiary creep for a number of materials. However, in recent years, basic analytical models have been formulated that can predict and describe creep strain data without using fitting parameters. In the paper, a review of these models is given. A number of applications of the models are also given. It is demonstrated that the basic models can quantitatively predict observations. They also provide derivations of some empirical findings. [ABSTRACT FROM AUTHOR]

In order to study the effect of graded loading rate on creep characteristics of anthracite, the effects of graded loading rate and stress level on instantaneous strain, creep strain and creep rate of coal samples were analyzed by triaxial creep tests of anthracite under four different graded loading rates. The results show that at the same stress level, the higher the graded loading rate is, the smaller the instantaneous strain is and the larger the creep strain is, but the increasing trend of creep strain gradually slows down; at the same loading rate, with the increase of the creep stress level, the instantaneous strain of coal samples shows an overall decreasing trend of rapidly decreasing-slowly decreasing-increasing, while the creep strain of coal samples shows an overall increasing trend of basically unchanged-slowly increasing-rapidly increasing; the change process of creep rate can be divided into three stages: rapid decay, slow decay and stability, at the same stress level, the higher the graded loading rate is, the higher the maximum creep rate is, and the faster the creep rate decays.

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The service life of mechanical structures is influenced by the inelastic strain generated during manufacturing and operation. Therefore, non-destructive estimation of three-dimensional inelastic strain is essential to ensure structure safety even during operation. Accordingly, an inverse problem method was proposed to estimate the inelastic strain over the entire component based on the eigenstrain theory using non-destructively measured surface displacement. However, this method assumes micro-deformation, in which the causal inelastic strain and resulting displacement are linearly related. In practice, the value of inelastic strain is large, which results in large deformation and a nonlinear effect on displacement determined by the magnitude of the inelastic strain. This study considers the inverse problem of estimating the creep strain in a turbine blade for power generation from the displacement caused by the creep strain and proposes a method to derive the exact solution even for large deformation problems. Numerical simulations using a simplified turbine model show that the estimates converge to the correct solution value with relatively high accuracy in the absence of measurement errors. Moreover, the result of the iterative calculations used in the proposed method converge around the correct value, even in the presence of measurement errors in the displacement by the laser displacement meter.

Timber architectures have arisen as sustainable solutions for high-rise and long-span buildings, assisting in implementing a circular economy. The creep strain dissipation of laminated veneer lumber (LVL) was investigated in this work to understand the inherent creep behaviors of LVL derived from natural wood. The results demonstrated a significant loading regime dependency of the creep behaviors of LVL. Coupled creep strain dissipation that transits/is parallel to the wood–adhesive interface was proven in the creep deformation of flat-wise and edge-wise bent LVL. In contrast, the creep strain dissipated considerably along the wood–adhesive interface when the LVL was subjected to axial compression creep. Further investigation into the morphologies of LVL after creep revealed that direct contact between the loading plane and wood–adhesive interface could be a plausible trigger for the accelerated deformation and the resultant plastic deformation of the LVL after creep. We believe that this work provides essential insights into the creep strain dissipation of LVL. It is thus beneficial for improving creep resistance and assisting in the long-term safe application of LVL-based engineered wood products in timber architectures.

In this paper, the phenomenon of creep compliance and the creep Poisson’s ratio of a 3D-printed Sierpinski carpet-based fractal and its bulk material (flexible resin Resione F69) was experimentally investigated, as well as the quantification of the change in the viscoelastic parameters of the material due to the fractal structure. The samples were manufactured via a vat photopolymerization method. The fractal structure of the samples was based on the Sierpinski carpet at the fourth iteration. In order to evaluate the response of both the fractal and the bulk material under the creep phenomenon, 1 h-duration tensile creep tests at three constant temperatures (20, 30 and 40 °C) and three constant stresses (0.1, 0.2 and 0.3 MPa) were conducted. A digital image correlation (DIC) technique was implemented for strain measurement in axial and transverse directions. From the results obtained, the linear viscoelastic behavior regime of the fractal and the bulk material was identified. The linear viscoelastic parameters of both fractal and bulk materials were then estimated by fitting the creep Burgers model to the experimental data to determine the effect of the fractal geometry on the viscoelastic properties of the samples. Overall, it was found that the reduction in stiffness induced by the fractal porosity caused a more viscous behavior of the material and a reduction in its creep Poisson’s ratio, which means an increase in the compliance of the material.

Creep strain versus time curves (creep curves) have traditionally been described with the help of empirical models where a number of adjustable parameters are involved. These models are simple to use, but they cannot be applied for prediction. For understanding the general behavior of primary and tertiary creep, they are still useful. In fact, the phi model can represent primary creep, and the Omega model tertiary creep for a number of materials. However, in recent years, basic analytical models have been formulated that can predict and describe creep strain data without using fitting parameters. In the paper, a review of these models is given. A number of applications of the models are also given. It is demonstrated that the basic models can quantitatively predict observations. They also provide derivations of some empirical findings.

In a quest to drastically reduce the cost of production of electrical energy and the dire need to meet the increasing demand for electricity, power generation steam pipings are exposed to different steam loading conditions. The different daily loading conditions/cycles are known to impact the creep behaviour and the pattern of stress relaxation in the steam piping., the creep response and stress relaxation of P92 steam piping subjected to different loading conditions were simulated using a finite element (FE) technique Abaqus CAE/2020 was used to estimate the creep behaviour and stress relaxation of the piping while fe-safe/Turbolife was used in the computation of the creep damage and useful life of the pipe. Comparing the different conditions of operation, faster or swifter stress relaxation and higher creep strain were observed in the piping subjected to steady-state in relation to the analyses encompassing cyclic loadings. The piping's useful creep life when subjected to cyclic loading is lower than that obtained when subjected to steady-state analysis. Thus, any form of cyclic loading of steam piping greatly reduces its useful creep life. [ABSTRACT FROM AUTHOR]

This research analyses the strain behaviour of fibre-reinforced concrete (FRC) in the event of a creep episode. The analysis of creep experienced by FRC specimens during the test reflects better performance than that predicted by the EHE-08 standard. The authors propose a formulation for the evaluation of creep strain undergone by FRC. During the research, the evolution of the modulus of elasticity of FRC after a creep episode is analysed. After the test campaign, it can be concluded that FRC loaded at an earlier age stiffens after a creep episode. After the creep test is completed, the delayed elastic strain undergone by FRC is analysed and it is observed that FRC loaded at an earlier age undergoes less deformation. The authors propose a formulation for the evaluation of the delayed elastic strain undergone by FRC after a creep episode. [ABSTRACT FROM AUTHOR]

The goal of the study is determination of the regularities of changes in cyclic strains and related deformation diagrams attributed to the existence of time dwells in the loading modes and imposition of additional variable stresses on them. Analysis of the obtained experimental data on the kinetics of cyclic elastoplastic deformation diagrams and their parameters revealed that, in contrast to regular cyclic loading (equal in stresses), additional deformations of static and dynamic creep are developed. The results of the studies are especially relevant for assessing the cyclic strength of unique extremely loaded objects of technology, including nuclear power equipment, units of aviation and space systems, etc. The experiments were carried out on samples of austenitic stainless steel under low-cycle loading and high temperatures of testing. Static and dynamic creep deformations arising under those loading conditions promote an increase in the range of cyclic plastic strain in each loading cycle and also stimulate an increase in the range of elastoplastic strain owing to active cyclic deformation. At the same time, the existence of dwells on extrema of stresses in cycles without imposition of additional variable stresses on them most strongly affects the growth of plastic strain ranges in cycles. Imposition of additional variable stresses on dwells also results in the development of creep strains, but their growth turns out to be somewhat less than in the presence of dwells without stresses imposed. The diagrams of cyclic deformation obtained in the experiments are approximated by power dependences, their kinetics being described in terms of the number of loading cycles using corresponding temperature–time functions. At the same time, it is shown that increase in the cyclic plastic deformation for cycles with dwells and imposition of additional variable stresses on them decreases low cycle fatigue life compared to regular loading without dwells at the same stress amplitudes; moreover, the higher the values of static and dynamic creep, the greater decrease in low-cycle fatigue life. This conclusion results from experimental data and analysis of conditions of damage accumulation for the considered forms of the loading cycle using the deformation criterion of reaching the limit state leading to fracture. [ABSTRACT FROM AUTHOR]

In the present work, a combination of experimental and numerical procedure is proposed to study the effects of different hygrothermal conditions on the creep strain, viscoelastic properties of nanocomposites, and mechanical properties of such nanocomposite-based carbon fiber–reinforced polymer (CFRP) hybrid composite materials. Ultrasonic probe sonicator is used to randomly disperse the multiwalled carbon nanotubes into an epoxy to minimize agglomerations. Dynamic mechanical analysis is employed to conduct the creep tests under different hygrothermal conditions of such nanocomposite samples. The Findley power law is used to obtain the long-term creep behavior of nanocomposite materials. Prony series is used to determine the viscoelastic properties of nanocomposite material in the frequency domain. Coefficient of moisture expansion (CME) is independent of moisture concentration; thus, CME of the nanocomposite is also determined. Strength of materials and Saravanos–Chamis micromechanics (SCM) have also been utilized to obtain the mechanical properties of such hybrid composite materials under different hygrothermal conditions. It has been found that the inclusion of multiwalled carbon nanotubes in the nanocomposite and hybrid composites improves storage modulus and loss factor (i.e., tan δ) compared to the conventional CFRP-based composite materials under hygrothermal conditions. [ABSTRACT FROM AUTHOR]

In this paper, a new constitutive model of SnAgCu lead-free solder, which covered the low-temperature and elevated-temperature creep properties, was constructed according to the thermomechanical property test under a wide range of temperatures (−40 to 120 °C). This model was then implemented to the finite element model for simulation of the cyclic creep deformation of Sn3Ag0.5Cu solder in a chip inside the microelectronic power module (MPM). The accumulated creep strain of the solder layer was calculated and used to predict the thermo-mechanical fatigue life of the MPM. The applicability of the life prediction method was evaluated through a cross-check of the present results with that obtained by a double power model in the literature, as well as the thermo-mechanical fatigue test results. It was found that the thermo-mechanical fatigue lives, estimated by the accumulated creep strain and creep strain energy density from the established hyperbolic sine power law, are closer to the test results than that estimated by the double power law. The presented model can be seen as an improvement on the existing constitutive models of SnAgCu lead-free solder.

Creep properties of altered granite were changed due to water level rise and fall in the tailings ponds. In this paper, the effects of water influx-lost cycles on the creep properties were tested. The axial load was applied with the 30%, 40%, 60%, 75% and 100% of the triaxial compressive strength, the rock creep test results showed that: (1) Significant creep effects of altered granite subjected to water influx-lost cycles, the creep stages were included decay creep stage, steady creep stage, and accelerated creep stage. It was found that the creep strain gradually increases with of the number of water influx-lost cycles increases, and the ratio of the maximum creep strain to total strain can reach 10.42%. (2) The degradation of long-term strength of altered granite subjected to water influx-lost cycles was studied, the long-term strength was decreased from 32.13 to 5.46 MPa. The relationship between the long-term strength and number of cycles was indicated by an exponential function. It was found that water influx-lost cycles have adversely effects on the long-term stability of the tailing pond slope, and the research results are of great significance to the prevention of slope engineering disasters. [ABSTRACT FROM AUTHOR]

Mechanical performance analysis is important for ensuring the long-term reliability of solid oxide fuel cells (SOFCs). Thermal-mechanical models are constructed to conduct time-dependent mechanical performance analysis of SOFC stack with temperature field obtained by multiphysics modeling. The volume-averaged temperature field is used as comparison. The creep strains are examined with a time step of 10 h for 10,000 h. It reveals: (1) Uniform temperature significantly decreases the stresses, strains, failure probabilities of all stack components. (2) The failure probability of sealant reduced rapidly and the sealant becomes mechanically safer for long-term operation. (3) Creep strain is dominant for anode/sealant/interconnect, but negligible for electrolyte/cathode. All components are predictably safe against strain failure for 100,000 h (4) Creep strains of stack components interact with each other. Coupled analysis of creep strains of anode/sealant/interconnect is mandatory, but the creep strains of electrolyte/cathode may be neglected for studying mechanical evolutions. • In-depth analysis of thermal-mechanical evolutions of stack components during 10,000 h. • Creep strain as the mechanism for long-term safety of sealant clearly demonstrated. • Close coupling of creeps and stress relaxations of different components revealed. • Strong effect of temperature field on stress/strain and their evolutions illustrated. [ABSTRACT FROM AUTHOR]

This work summarizes the prediction models for creep strain taken place in concrete under compression as well as under tension and shear. In literature, many researchers have carried out experimental studies on creep, RILEM has gathered these experimental results within a computerized data bank. This work briefly reviews the most widely used models and can predict observations up to 5000 days assessed by ACI209R-1992 Model, B3 Model, CEB C99 Model, GL 2000 Model, BS 8110 (1985), and AS3600 (1988). Since creep is one of the most important time dependent property of concrete as it increases cracking and harmfully distresses the function, durability, and structural appearances. The objective of this work is to understand the behavior of concrete when creep strain takes place at different ages by incorporating spread sheets which simplify the calculations for engineers when estimating the creep strain for the design purpose. Based on RILEM data bank, most of the studies confirms that GL2000 Model is the closest to the experimental results. [ABSTRACT FROM AUTHOR]

Steam piping is one of the major components of power generation plant because of its use in conveying steam from the boiler to the turbines compartment. Over time, these pipings are subjected to diverse operating conditions in an attempt to meet the daily electricity demand. Hence, the useful creep life of the piping is drastically affected. In this study, finite element technique was used to investigate the influence of diverse operating cycles on the useful life of P92 steam piping. Faster stress relaxation with a characteristic higher creep strain was observed in the steady-state analysis as compared to those involving daily cycles. However, the rate of creep damage accumulation and the computed useful life under the different operating conditions computed using fe-safe/Turbolife software show that any form of daily shift has a detrimental effect on the useful life of steam piping. [ABSTRACT FROM AUTHOR]

Improving creep ageing behavior and mechanical properties of Al–Zn–Mg–Cu alloys via different pre-aging temperature, using the creep ageing test, room-temperature tensile test and transmission electron microscopy observation. A pre-aging temperature of 120 °C markedly improved the mechanical properties of the samples, including a tensile strength of 605.2 MPa, yield strength of 583.4 MPa, and elongation of 13.8 %. Pre-aging generated a "peak age region" during creep ageing, advantageous for extending the ageing time and enhancing creep strain without compromising strength. Detailed microstructure and mechanical performance characterizations were employed to discuss and unveil the strengthening mechanisms. The results additionally illustrated that pre-aging effectively reduces creep strain, as compared to the T4 sample, by minimizing vacancy concentration. Furthermore, pre-aging can manipulate lattice distortion and creep strain by facilitating atom diffusion, and a larger lattice with a pre-aging temperature of 100 °C results in higher creep strain. Moreover, elevating the pre-aging temperature (120 °C) reduces vacancy concentration, thereby inhibiting the phase transformation from η′ to η precipitates. This led to the attainment of a desirable microstructure consisting of η′ precipitate with high density and dispersed distribution, significantly enhancing the strength of the alloy. Hence, a new method is provided for the manufacture of large-scale panel component with excellent mechanical properties. [ABSTRACT FROM AUTHOR]

Polymer materials, such as extruded polystyrene (XPS), polyurethane (PU) and polystyrene (EPS), are extensively used as thermal insulators in cold regions to protect the engineering from frost damage. However, the performance degradation caused by freeze-thaw cycles (FTC) of polymer material has not been fully quantified. To fill this gap, a series of experiments were carried out by taking XPS board as the test material. After the XPS board was subjected to hundreds of FTC, the volumetric water absorption, thermal conductivity, uniaxial compressive strength and Young's modulus as well as creep strain were measured and analyzed. The results demonstrate that the volumetric water absorption and thermal conductivity change slightly with the FTC. After 400 times of FTC, the volumetric water absorption increased within only 0.1% and the thermal conductivity decreased within 9 × 10−4 W⋅(m⋅K)−1. Additionally, the uniaxial compressive strength and Young's modulus decrease with the increasing of FTC, and the effect of FTC on Young's modulus is mainly concentrated in the first 50 times. The creep behavior of XPS board belongs to decay creep and the exponential function can describe the creep process well. The results obtained in this study may help us to understand the degradation of XPS board and provide references for the design of controlling engineering damages caused by FTC in cold regions.

The results of creepage research of cylindrical elements from soil cement subjected to constant compressive stress of different values are discussed. The Portland cement of the type 40 MPa, belozem as a pulverescent clay sand (belozem carbonate mixture)and ordinary pipeline water are used for the soil cement mixture. It's shown that analytical dependence between creepage stresses and creepage strains for soil cement elements can be done successfully taking into account known dependences applicable for cement concrete elements. Utter an opinion that during the practical calculation of the deformation mode for special elements and different parts of soil cement constructions taking into account the material creepage, the above-mentioned analytical dependences can be applicable. [ABSTRACT FROM AUTHOR]

Co-base superalloys show attractive properties for the strengthening of γ'-Co3(Al,W) precipitates. Directional coarsening of γ' precipitates under external stress forms the rafting morphology, which plays a crucial role in the creep property. The microelastic theory, coupled with the crystal plasticity model, is utilized to study the rafting behavior during the early stage of creep in Co-Al-W superalloys. High W content and large eigenstrain can produce a lower creep strain of early stage, for the subdued plastic deformation in the γ matrix. Driving forces of element redistribution during rafting are compared among the chemical, interfacial and elastic contribution, in which the elastic contribution is dominant in rafting. With the change in creep stress from 197 MPa to 297 MPa, the element redistribution is strengthened, and the rafting is accelerated in Co-10 Al-9 W (at.%) alloy. Elements redistribution in the rafting process widens the γ/γ' interface. In contrast, the width of γ/γ' interface along the rafting direction begins to decrease when the coalescence of γ' precipitates happens. The straight-forward insight on the element diffusion during rafting and the related creep properties guides the composition design and rafting behavior prediction of this novel Co-Al-W superalloy.

The physical depreciation of electric and thermal stations and heating networks is determined by a sharp decrease in the rate of renewal of fixed assets. This article proposes an attempt to assess the residual life of a technical device (steam line) using a characteristic criterion, i.e., the creep strain of the pipe material. [ABSTRACT FROM AUTHOR]

This research analyses the strain behaviour of fibre-reinforced concrete (FRC) in the event of a creep episode. The analysis of creep experienced by FRC specimens during the test reflects better performance than that predicted by the EHE-08 standard. The authors propose a formulation for the evaluation of creep strain undergone by FRC. During the research, the evolution of the modulus of elasticity of FRC after a creep episode is analysed. After the test campaign, it can be concluded that FRC loaded at an earlier age stiffens after a creep episode. After the creep test is completed, the delayed elastic strain undergone by FRC is analysed and it is observed that FRC loaded at an earlier age undergoes less deformation. The authors propose a formulation for the evaluation of the delayed elastic strain undergone by FRC after a creep episode.