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In this research, a 3D multiscale model was applied for the analysis of long-term deformation of mudstone under high stress. Firstly, Voronoi tessellation generating and cohesive elements inserting programs were developed by Python-driven ABAQUS to establish a multiscale numerical analysis platform. In addition, creep damage effects for high stress were investigated through tests. Extended Drucker–Pranger model with strain hardening creep was developed for the calculation of mudstone viscoelastic plasticity. Finally, the creep damage model was integrated with multiscale analysis platform to evaluate the creep process of samples. The results verified that the developed model was effective in multiscale numerical analysis. [ABSTRACT FROM AUTHOR]

In this work, we provide a theoretical framework to evaluate the beneficial effect of solute segregation on the creep behaviour of nanocrystalline materials. We choose copper as the model system and employ the Murdoch and Schuh model to identify Cu–3Zr as a binary system with high thermal stability in its nanocrystalline state. The effect of the segregation of Zr on the grain boundary diffusivity was evaluated using the Hondros and Henderson model. The effect of solute segregation on threshold stress for vacancy emission and absorption at the grain boundaries was evaluated using the Mohamed model. Using these in conjunction with the Bird Mukherjee Dorn equation for creep allowed us to compare the diffusional creep behaviour of nc copper and nc Cu–3Zr. The nc Cu–3Zr system with a grain size of 49 nm demonstrated a higher creep resistance compared to nc Cu bearing a similar grain size. However, the creep resistance of both systems was found to be significantly inferior when compared to the conventional coarse-grained Cu bearing a grain size of 1 μm. [ABSTRACT FROM AUTHOR]

Full-scale physical modelling was used to evaluate the response of modular polymer stormwater collection structures when subjected to design-truck loading that was sustained for 1 week (i.e. a parked vehicle) and when buried with minimum soil cover. Surface loading was applied on a steel load pad that simulates one-half of the AASHTO design-truck single-axle that was held constant for 1 week to assess the stability of the buried system and demand on the platen and column components of the modules to allow independent load rating of the buried structure. No collapse or limiting state occurred. The 1-week creep buckling resistance was found to be nearly four times the factored column demand to 1-week loading for both module types. New insight into the time-dependent behaviour of the soil–structure system was gained by comparing the buried response to creep tests conducted on isolated columns and platens. The response of the buried soil–structure system was less severe than unconstrained creep. Column loads were found to not increase with time. Bending deflections increased by 1.04 to 1.26 times when buried rather than by 3.0 to 3.4 times for unconstrained creep as platen creep when buried was greatly restrained by the soil. [ABSTRACT FROM AUTHOR]

Analytical and numerical solutions for the problem of geosynthetic-reinforced fills over a void have been the subject of investigation for the last four decades. A common feature of this prior work is that all methods have treated the analytical solutions as deterministic. While the treatment of some input parameters must be taken as deterministic, there are other parameters that have uncertainty. Furthermore, the underlying mechanistic models for load and resistance terms in the limit state equations for the reinforced fill over a void problem can be expected to have different accuracy. This paper revisits the problem of geosynthetic-reinforced fills over voids from a probabilistic point of view for reinforcement tensile strain, tensile strength, and geosynthetic stiffness limit states. Particular attention is paid to the method used to select the isochronous stiffness of the reinforcement and the associated uncertainty in the magnitude of that value. The paper demonstrates how the factor of safety from deterministic past practice can be linked quantitatively to the reliability index used in contemporary probabilistic design. Finally, the paper demonstrates the advantage of using product-specific constant-load creep test results to maximise margins of safety for strength and stiffness limit states in both deterministic and probabilistic frameworks. [ABSTRACT FROM AUTHOR]

In Enhanced Geothermal Systems (EGS), rock fractures in the reservoir are often subjected to cyclic changes in effective stress at elevated temperatures, causing permeability variations. In this study, the effect of cyclic normal stress on permeability evolution of rough fractures in Gonghe granite at elevated temperature was investigated through flow-through experiments. The results show that the fracture permeability decreases with increasing normal load and partially recovers as the normal load releases. Under a constant normal stress, the fractures gradually close, exhibiting viscoelastic-plastic behavior that can be characterized using the Nishihara model. Based on these characteristics, a fracture-creep deformation model has been developed considering the stress history using a combination of the Hopkins fracture closure model and the Nishihara model. This study investigated the effects of cyclic stress on the internal geometric features of fractures at elevated temperature, calculated the fracture deformation and the corresponding permeability during the loading and unloading process, and validated the accuracy of the proposed model. The study reveals the primary mechanisms responsible for fracture permeability evolution under cyclic effective stress at elevated temperatures, providing valuable insights for the sustainable development of EGS. Highlights: The viscoelastic–plastic behavior of rough fractures in Gonghe granite subjected to cyclic normal stress has been demonstrated in the flow-through experiments. A fracture-creep deformation model for a single rough fracture is developed considering the stress history using a combination of the Hopkins fracture closure model and the Nishihara model. The fracture permeability is calculated according to the geometric characteristics of the fracture, which has been validated by laboratory permeability measurements. [ABSTRACT FROM AUTHOR]

Creep in rocks refers to the gradual deformation of rock material over time under the influence of constant stress. Characterizing these deformations is of great importance for engineering design, geotechnical assessment, mining operations, geological studies, and understanding natural hazards. While laboratory experiments and a variety of numerical approaches have offered explanations for microcrack interaction and damage accumulation under the three stages of creep (primary, secondary and tertiary) in conventional creep experiments, the micromechanisms of the fractures produced in brittle creep and its dependency on the applied stress have not been explored in detail. The present study focused on investigating the fracturing mechanisms that occur during creep-induced fracturing at different stress levels and estimation of the source parameters and energy budget components. A series of uniaxial compression creep experiments have been conducted at different stress level ratios (70%, 75%, 80% and 85%), to the unconfined compressive strength (UCS) of double-flawed Barre granite specimen. Creep measurements were complemented with the Acoustic Emission (AE) measurements. The creep-induced fractures were classified into double-couple (DC), compensated linear vector dipole (CLVD) and isotropic (ISO) components using the AE moment tensor decomposition technique. The results show that non-double-couple sources dominated during creep at all the specified stress levels; however, their proportions decreased as the stress level was increased. The source parameters estimation indicated a significant increase in the magnitude of the events and the radiated seismic energy with increasing levels of stress and a slight increase in the evaluated source radius and stress drop with increasing stress levels. This study contributes to the existing knowledge of creep-induced fracturing by providing insights into the fracturing mechanisms and the radiated seismic energy produced, which can be helpful for the development of improved models and strategies for rock engineering and geoscience applications. Highlights: Tensile cracking is the dominant mechanism in all stress levels. Radiated seismic energy and radiation efficiency increased during creep with the increase in the applied stress. The decay rate during primary creep increases with the increase in the applied stress. [ABSTRACT FROM AUTHOR]

This study explores a new composite material enhanced with biocarbon from Selenicereus undatus (dragon fruit) and pineapple fibers, set in a sturdy vinyl ester base. We used a green method, pyrolysis, to obtain the biocarbon, adding an eco-friendly aspect to our work. Following the strict ASTM standards, we crafted the composites using the hand layup method to ensure quality and consistency. Our findings reveal that the composite named VPB3, with its specific mix of 2% biocarbon and 40% pineapple fiber, shows outstanding mechanical strength, achieving high marks in tensile, flexural, and compression strengths, along with significant impact resistance. However, increasing the biocarbon content in another composite, VPB4, slightly lowered these properties due to the clumping of biocarbon but improved hardness and wear resistance. VPB3 also exhibited excellent fatigue resistance, while VPB4 showed reduced creep and better hydrophobic properties. Overall, our research highlights the benefits of adding biocarbon and pineapple fibers to composites, enhancing their strength, durability, and environmental resistance. The use of these natural fibers not only improves the material's performance but also contributes to a more sustainable approach to composite manufacturing. [ABSTRACT FROM AUTHOR]

The objective of this work was to produce and use green pea pod lignin for improving the thermal stability, flammability, and creep resistance of pineapple fibre-reinforced epoxy composite. The lignin macromolecules are derived from waste green pea pods via thermo-chemical process and used as reinforcement. The composites were made using the compression moulding method followed by post curing at 120°C. The prepared composites are then machined for testing according to ASTM standards. The results of this research demonstrate that the decomposition temperature of the composite known as EF is improved by the incorporation of pineapple woven mats by a volume of 40%. Comparing to all the composite designations, the EFL3 offers the least loss of weight, the highest decomposition temperature (approximately 420°C), the highest storage modulus (about 7.5 GPa), and the lowest loss tangent (0.6). Accordingly, the EFL3 composite designation has been reported to have the lowest combustion rate of 5.88 mm/min and the highest DSC value of 0.6 mW/mg. However, the creep strain is reduced when adding lignin by 0.5, 1.0, and 2.0 vol. %. These eco-friendly waste converted green pea pod lignin strengthened pineapple fibre-epoxy composites could be used in high thermal applications including automotive insulation panels and domestic infrastructure. [ABSTRACT FROM AUTHOR]

Masjed Soleyman rockfill dam, with a height of 177 m, has experienced significant settlement during its construction, impoundment and operation stages. A possible contributing factor in the excessive deformation is the weak conglomerate rockfill material used in building the dam shells. This research work focuses on the experimental study of the mechanical behavior of the conglomerate rockfill material of the dam shells, including the point load, Brazilian, oedometer, and direct shear tests. The results of the point load and Brazilian tensile tests showed moisture and size effects, and suggested that the strength of the rockfill made of this rock falls within the medium to weak range. The oedometer test results demonstrated that the specimen moisture, density, gradation and applied stress impact the particle breakage, strain, and saturation collapse of the rockfill material. Our findings suggest that the excessive dam settlement and saturation collapse (wetting deformation) could have been substantially decreased and controlled by wet compacting the rockfill layers during the dam construction. It was shown that particle breakage in the direct shear tests is greater than that in the oedometer tests, suggesting that for dams with excessive shear deformation (like Masjed Soleyman Dam), a more realistic estimate of particle breakage can be obtained using either direct shear test or triaxial tests. The ratio of strain to particle breakage index was revealed to be independent of the applied stress and moisture content of the specimen, but it was affected by the material gradation and density. [ABSTRACT FROM AUTHOR]

Pressure tubes (PTs) play an important role in the safe and efficient operation of Nuclear Power Plants (NPPs) as they contain the fuel bundles and provide structural integrity. Creep has been identified as one of the main degradation mechanisms of PTs, which are made widely of Zr-Nb alloys. The creep curve of a material gives an insight into the nature of its creep behavior. In the present investigation, accelerated creep experiments were conducted on Zr-2.5Nb PT alloy in the stress and temperature range of 22–58 MPa and 600–850 °C, respectively. Two data-driven models, namely Radial Basis Function Neural Network (RBFNN) and Least Square Fit (LSF) were developed to simulate the non-linearity of the creep curves. Applied stress, test temperature, and time to failure were taken as the input parameters for the models. It was observed that although the LSF could predict the primary creep zone, it failed to predict the transition between the secondary and tertiary creep region. However, the creep curves predicted by the RBFNN model were in close agreement with the experimental results, having a confidence level of ≈ 0.99. Two separate sets of creep experiments were also done later to verify the accuracy of the proposed models. The results from the study established the ability of the RBFNN technique to simulate the complex behavior of the creep curves. [ABSTRACT FROM AUTHOR]

This study investigated the long-term creep behavior of concrete in drilled shafts using conventional and soft-cutting head techniques, focusing on their propensity for internal defects and crack propagation under sustained loading. Triaxial creep tests were performed on concrete specimens subjected to multistage loading to examine the axial- and radial-creep responses associated with each cutting-head method. The findings reveal that concrete prepared with conventional cutting heads exhibits a higher susceptibility to creep failure, attributed to an increased presence of internal defects. In contrast, specimens using soft-cutting heads demonstrated reduced axial- and radial-creep deformations. Concrete cured in laboratory conditions and those cut with soft-cutting heads at various elevations predominantly experienced shearing failures, whereas specimens with soft-cutting heads positioned at higher elevations were more prone to radial tension-shear failures. Considering the Burgers model and fractional-order theory, we introduce a one-dimensional nonlinear damage creep model, alongside a more comprehensive three-dimensional damage creep model. Validation of these models confirms their effectiveness in describing the creep behavior of concrete under different cutting-head disturbances. Importantly, our analysis suggests that the role of soft-cutting head methods on the integrity of cast-in-place concrete piles is comparatively minimal. This insight underscores the potential for optimizing pile-head breaking techniques to mitigate creep-related failures in concrete structures. [ABSTRACT FROM AUTHOR]

The aim of this work is to study the behaviour of a structural adhesive in an aggressive setting such as the marine environment. For this purpose, an ageing procedure is carried out under marine environmental conditions and a comparison of the properties before and after the process is performed. This is especially important as the characteristics of an adhesive can be heavily affected by factors such as temperature and humidity. For the assessment of the mechanical properties of the material bulk tensile tests are conducted, digital image correlation (DIC) is also employed to obtain parameters such as Poisson's ratio or Young's modulus. A dynamic mechanical analysis (DMA) is also carried out, on which the time-temperature superposition principle (TTS) is applied to make a long-term prediction of the behaviour of the adhesive, constructing the master curves for dynamic loads by means of a frequency test and for sustained loads through a creep test. This ageing procedure has led to a reduction in the strength of the material, but has also made it more ductile and flexible, while the master curve obtained from the frequency sweeps shows a smaller dependence of frequency in the aged material and the master curve obtained from the creep tests shows a similar behaviour for both the aged and unaged material. [ABSTRACT FROM AUTHOR]

Low friction can lead to poor adhesion conditions between the rail and wheel, which is detrimental to rail vehicle operation and safety. Up to date knowledge of the rail-wheel friction level is currently not available across rail networks, meaning planning mitigation strategies is difficult. This paper presents a real-time friction coefficient estimation algorithm based on a feed-forward neural network (FNN). Unlike conventional methods, the FNN does not depend on slip/adhesion curves or creep force models, and only requires wheelset longitudinal acceleration and speed. The wheelset acceleration and friction measurements are obtained by running a two-car rail vehicle on a friction-modified track with five different levels of friction conditions at four different vehicle speeds. Four different FNNs are trained for four speed conditions, and their estimation performance were validated by training multiple FNNs and testing them in each speed case using new sets of data. Validation results show that the average mean absolute errors from the four FNNs remains below 0.0083. [ABSTRACT FROM AUTHOR]

Measurements of slope displacements can be effective tools for the early warning of the collapse of slopes under excavation in construction projects in mountainous areas, while evaluating of instability based on measured displacement has not yet been accomplished for slopes under excavation. Measurements of displacements on sandy soil slopes under multistep excavation were made, and the measured data were analyzed to determine the characteristics of creep deformation of the slope during and after the excavation and to establish a procedure for evaluating instability of the slope under excavation in this paper. The following facts were derived from the examination of the measured data. Displacement was generated significantly in the latter stage of excavation, and it was generated not only during excavation but also after excavation. The ratio of the displacement after excavation to that from the start of the excavation to the start of the next excavation became larger as the displacement developed immediately before failure. It indicates that creep displacement after the excavation was more significant at latter excavation just prior to failure. The normal displacement converged to constant as the shear displacement increased under a steady state immediately before the failure in direct shear conditions, and the normal displacement can be an indicator of the instability of the slope. The normal displacement cannot remain constant when the inclination of the slope surface is different from that of the slip surface in the excavated slope in this paper. Different indicators are necessary in this case. The angle α between the slope surface and synthetic displacement (RD) on the slope derived from measured data was introduced instead of normal displacement. The synthetic displacement (RD) on the slope indicated the scalar of the synthesis of the displacements normal and downward to the surface of the slope and surface displacement. It converged to constant after excavation immediately before failure, and shear displacement showed an accelerative increase for constant α. This indicated that the angle α could be an indicator of the instability of the slope. This result showed that the angle α being constant indicated that the stress condition was almost in failure and the displacement increased acceleratively. Further examinations based on the measured data on other slope under excavation should be necessary for confirming the results in this paper based on only a case of experiment. [ABSTRACT FROM AUTHOR]

In this work, an alkali-activated municipal solid waste incineration (MSWI) fly ash-based filling material was prepared with MSWI fly ash as the raw material and slag as the auxiliary material. The filling body experiences long-term creep, which may have a direct effect on the stability of the overlying strata of the mine goaf. The long-term mechanical properties of the fly ash-based filling materials were tested with a triaxial rheological apparatus. First, uniaxial creep testing was carried out at five levels of axial stress: 50%, 60%, 70%, 80% and 90% of the uniaxial compressive strength (UCS). Then, triaxial creep testing was carried out by considering the geological environment of the goaf. The creep characteristics of fly ash-based filling materials under a three-dimensional stress state were explored. The results indicate that (1) under different stress levels, the creep curves of fly ash-based filling materials can be divided into three types: decelerated creep‒stable creep, decelerated creep‒constant creep, and decelerated creep‒constant creep‒accelerated creep. (2) The total creep deformation of the fly ash-based filling material is 0.46 ~ 0.78%, which is similar to the creep deformation of soft rock. The instantaneous deformation during loading contributes most of the total deformation. (3) The polymerization products generated in the fly ash-based filling material system can effectively cement the raw material particles, and the presence of gel can effectively delay the accelerating creep process of the material. (4) A nonlinear fractional-order model composed of an Abel dashpot can fully describe the complete process of decelerating creep-constant creep-accelerating creep. [ABSTRACT FROM AUTHOR]

Nickel-based superalloys are typically employed for high-temperature applications. One well-known degradation mechanism is the rafting of the γ′-phase. In this study, it was investigated, whether a high current impulse treatment is suitable to induce changes in element distribution that are opposite to those observed during the rafting process. Thus, samples of CMSX-4 were treated with high current impulses up to 4 kA/mm2. Energy-dispersive x-ray spectroscopy measurements showed changes in element distribution due to these treatments. The changes in element distribution were observed to become more pronounced with increasing current density and partly counteracted those induced by prior creep. The extent of the compositional changes also depends on the element. Variations in the Al and Ta content showed stronger tendencies than, e.g., Cr, Co and W. [ABSTRACT FROM AUTHOR]

Ethylene propylene diene monomer (EPDM) rubber is used in critical sectors such as national defense, military, and aerospace. However, it has performance limitations under high temperatures, affecting its dynamic mechanical properties, creep, and stress relaxation. To overcome these limitations, rare earth cerium oxide (CeO2) was incorporated as a filler into EPDM in this study, which enhances its properties and makes it suitable for the demanding applications. It could be seen that the CeO2‐enriched EPDM has significantly improved mechanical characteristics at elevated temperatures. The Young's modulus of CeO2‐enriched EPDM increased by about 100 %, while the energy storage modulus reaches a maximum increase of around 140 % at 165 °C. The addition of CeO2 improves its damping properties, provides better creep and stress relaxation resistance, and results in greater residual strain recovery. At room temperature, the impact on the stress relaxation rate at 50 % strain is minimal for the material EPDM, and it is almost negligible for the material EPDM/CeO2.These findings demonstrate that CeO2‐enriched EPDM has enhanced performance under high‐temperature conditions. Under elevated temperature conditions, EPDM enriched with CeO2 exhibits enhanced mechanical properties, superior creep resistance, and stable stress relaxation behavior, rendering it more adept at withstanding the rigorous conditions encountered in aerospace applications. [ABSTRACT FROM AUTHOR]

Understanding the impact of creep on the long-term mechanical features of concrete is crucial, and constructing an accurate prediction model is the key to exploring the development of concrete creep under long-term loads. Therefore, in this study, three machine learning (ML) models, a Support Vector Machine (SVM), Random Forest (RF), and Extreme Gradient Boosting Machine (XGBoost), are constructed, and the Hybrid Snake Optimization Algorithm (HSOA) is proposed, which can reduce the risk of the ML model falling into the local optimum while improving its prediction performance. Simultaneously, the contributions of the input features are ranked, and the optimal model's prediction outcomes are explained through SHapley Additive exPlanations (SHAP). The research results show that the optimized SVM, RF, and XGBoost models increase their accuracies on the test set by 9.927%, 9.58%, and 14.1%, respectively, and the XGBoost has the highest precision in forecasting the concrete creep. The verification results of four scenarios confirm that the optimized model can precisely capture the compliance changes in long-term creep, meeting the requirements for forecasting the nature of concrete creep. [ABSTRACT FROM AUTHOR]

In structures where prestressing plays a vital role, predicting stress losses is essential to demonstrate their robustness. After presenting the equations of the next-generation Eurocode 2 (EC2), the delayed deformations of the containment vessels of EDF nuclear power plants are predicted. In the first step, the parameters of the laws are recalibrated based on the measurements of the containments, considering a temperature higher than 20 °C. The application to 17 containments allows for the definition of a safety coefficient to be applied to shrinkage and creep to ensure that the delayed deformations evaluated for the design will be conservative. In the second step, the parameters of the equations of creep and shrinkage are calibrated on laboratory results, and an analytical model using these parameters is applied to 5 containments. All the results show that it is possible to predict the behavior of prestressed structures provided that the parameters of the equations controlling the delayed deformations are calibrated either on measurements of these structures or laboratory tests. Considering the variability of concretes, safety coefficients are proposed to guarantee that the predicted deformations cover 95% of the deformations of concrete of a given strength. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department 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.)

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering 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.)

Microstructure, tensile property and creep performance of a novel powder metallurgy nickel-based superalloy FGH4113A were systematically studied under two different prepared conditions. The experimental results show that the yield strengths and ultimate tensile strengths of the designed superalloy of A3-HIP and A3-HEX excess 1200 and 1650 MPa at room temperature, respectively, and still reach 900 and 1050 MPa at 800 °C. The 0.2% creep lifetime of A3-HEX is longer than that of A3-HIP. Prior particle boundaries are responsible for inferior creep property of A3-HIP. FGH4113A shows excellent tensile property, which is better than that of René104 and RR1000. The strengthening mechanism shows that superior strength of FGH4113A is attributed to precipitation strengthening. [ABSTRACT FROM AUTHOR]

This is a first report on profilometry‐based indentation plastometry (PIP) at high temperature (HT), covering both thermal characterization and issues for obtaining stress–strain curves. The heating system has a relatively low thermal inertia, reaching 800 °C within about 10 min, while both indentation (≈20 s) and cooling (≈20 min) are also quick. This capability is useful in terms of limiting exposure of the sample to prolonged periods at HT, and hence avoiding the formation of thick oxide layers (which can affect indent profiles and hence inferred stress–strain curves). There is good general consistency between stress–strain curves obtained via HT‐PIP and those from tensile testing. However, the possibility of creep (time‐dependent deformation) affecting the outcomes (of both types of test), particularly at higher temperatures, should be borne in mind. Creep has a characteristic effect on tensile curves, which can often be confirmed and investigated by changing the imposed strain rate. It can also be revealed by carrying out the HT‐PIP testing with different penetration velocities or by monitoring the shape of the load–displacement plot. [ABSTRACT FROM AUTHOR]

Calcareous sand has been widely used as a construction material for offshore projects; however, the problem of foundation settlement caused by particle crushing cannot be ignored. Although many methods for reinforcing calcareous sands have been proposed, they are difficult to apply on-site. In this study, a permeable polyurethane polymer adhesive (PPA) was used to reinforce calcareous sands, and its mechanical properties after reinforcement were investigated through compression creep, direct shear, and triaxial shear tests. The reinforcement mechanism was analyzed using optical microscopy, CT tomography, and mercury intrusion porosimetry. The experimental results indicate that there is a critical time during the compression creep process. Once the critical time is surpassed, creep accelerates again, causing failure of the traditional Burgers and Murayama models. The direct shear strength of the fiber- and geogrid-reinforced calcareous sand reinforced by PPA was approximately nine times greater than that without PPA. The influence of normal stress was not significant when the moisture content was less than 10%, but when the moisture content was more than 10%, the shear strength increased with an increase in vertical normal stress. Strain-softening features can be observed in triaxial shear tests under conditions of low confining pressure, and the relationship between the deviatoric stress and strain can be described using the Duncan–Chang model before softening occurs. The moisture content also has a significant influence on the peak strength and cohesive force but has little influence on the internal friction angle and Poisson's ratio. This influence is caused by the different PPA structures among the particles. The higher the moisture content, the greater the number of pores left after grouting PPA. [ABSTRACT FROM AUTHOR]

Using adhesively bonded joints is an effective strategy for achieving lightweight designs. However, understanding the long‐term performance of these bonded joints remains a critical concern. Creep is a time‐dependent phenomenon induced by sustained mechanical loads, which can lead to viscous strain in adhesive materials. This strain has the potential to cause cracking in bonded structures over time. This study aims to investigate the creep and post‐creep behaviors of adhesively bonded aluminum joints, focusing on two crucial parameters: creep load level and creep duration. Butt adhesive joint (BAJ) specimens were fabricated and exposed to varying creep loads and times. Subsequently, quasi‐static tensile tests were conducted to assess the residual mechanical properties. The results indicated that higher creep loads resulted in increased creep deformations at constant creep durations. Furthermore, a downward trend was observed in the residual tensile mechanical properties of BAJ specimens following creep. Specifically, higher creep load levels and longer times led to more pronounced reductions in joint strength, strain, and stiffness. These reductions in joint mechanical properties were corroborated through joint fracture surface analysis. Additionally, mathematical models were developed using response surface methodology (RSM) to predict the experimental joint residual mechanical properties under different creep loads and times. Highlights: Investigation of creep and post‐creep behaviors in adhesive joints.Higher creep load levels result in greater joint permanent deformations.Impact of higher creep load levels and durations on joint failure strength.Decreasing in the joint deformability and stiffness after creep. [ABSTRACT FROM AUTHOR]

The one-dimensional consolidation analysis of clays considering creep compression is a classical issue in soil mechanics and geotechnical design. The major debate lies in how to predict the consolidation settlement for a thick layer in the field using parameters obtained from a thin specimen from the laboratory. Different hypotheses have been advocated, based on which various methods and constitutive models have been developed. However, there are still some questions unaddressed and concepts inconsistently used, which may mislead engineers in the selection of methods/models and may result in settlements underestimated on a risk design side. In this paper, a state-of-the-art review and a thorough comparison study are performed on the existing methods and models for the consolidation analysis of clays exhibiting creep, from theoretical derivations to numerical simulations in comparison with soil test data. An in-depth discussion is carried out on several key issues related to the thickness effects on the time-dependent compression behaviour of clays. The arguments of Hypothesis A and Hypothesis B are revisited based on the current development of constitutive theories. Three existing elastic visco-plastic (EVP) models that consider the creep compression implicitly during the whole consolidation process can perform well in predicting the settlement of clay layers with different thicknesses, and are in line with Hypothesis B. It is concluded that using existing EVP models based on porous-media continuum mechanics is a rigorous scientific method (also called "rigorous" Hypothesis B method), which is superior to the old Hypothesis A method which has logic errors and may result in unsafe underestimation of settlements. [ABSTRACT FROM AUTHOR]

Large deformation is a kind of geological hazard in the construction of soft rock tunnels, which hinders construction, threatens workers' safety, and raises project costs. Accurately obtaining the large deformation characteristics and patterns of tunnels is the prerequisite for taking targeted support measures. First, a viscoelastic–plastic model that can simulate both the short-term strain-softening effect and the long-term creep effect was proposed to investigate the large deformation features of soft rock tunnels. Then, a sophisticated model for creep parameter inversion was developed using the support vector machine, genetic algorithm, and particle swarm optimization. Finally, the deformation, stress, plastic zone, and internal forces in the lining of a large deformation tunnel were determined using the proposed constitutive model and the creep parameters obtained by inversion. As the creep displacement only makes up 14.4–23.2% of the total displacement, the results demonstrate that the elastic–plastic displacement is much more than the creep displacement. Notably, the connection between the top and middle benches has the most pronounced horizontal movement, accompanied by a significant strain-softening effect, which ultimately becomes the weak point in the support system. The excavation disturbs the surrounding rock, causing a high-stress zone and a low-stress zone, with the interface located around the junction of the elastic and plastic zones. The bending moment is positive at the wall waist and negative at the vault and arch waist. In addition, there is a progressive rise in the bending moment from negative to positive at the arch foot. [ABSTRACT FROM AUTHOR]

Wax is a prevalent lubrication material extensively employed in various engineering applications. Understanding the degradation characteristics of the waxy lubrication layer under diverse stress variables and levels is crucial for ensuring system security and reliability. Due to the unclear mechanism governing the degradation of the waxy lubrication layer under different stress variables, existing degradation models are unsuitable for modeling waxy lubrication layer degradation data. To address this challenge, we propose a functional data‐driven method leveraging dense observations of waxy degradation. Through extensive simulations and a case study, we demonstrate the superior performance and effectiveness of the proposed approach. [ABSTRACT FROM AUTHOR]

Copyright of Beton- Und Stahlbetonbau is the property of Wiley-Blackwell 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.)

Carbon fibre reinforced polymer (CFRP) laminates nano-enhanced with carbon nanofibers (CNFs): 0.75 wt% and 0.5 wt% of epoxies Sicomin and Ebalta, respectively, were manufactured and their static and viscoelastic behaviour analyzed. After 180 min, the bending stress decreases and creep displacement increases over time, with Ebalta nano-enhanced resin laminates with CNFs showing the best results. A strong dependence of creep behaviour and stress relaxation is obtained with the applied stress level. The results show that laminates produced with pure Sicomin resin increased creep displacement by 1%, for a bending stress of 200 MPa, and 2 times greater for the bending stress of 700 MPa. The viscoelastic behaviour of CFRP composites nano-enhanced with CNFs was accurately predicted by the Kohlrausch-Williams-Watts (KWW) model and Findley power law. [ABSTRACT FROM AUTHOR]

Refractory High entropy alloy (RHEA) is a potential material for coating gas turbine blades and pipeline due to its high-temperature mechanical and chemical properties. In this paper, a series of new NbTiCrFeMoX (x = 0.2, 0.4, 0.6, 0.8, 1) RHEAs were coated on GTD-111 nickel base superalloy by the laser cladding method. The effects of the Mo amount on the microstructure and tensile, creep, corrosion, and wear properties were investigated. XRD results showed that the microstructure of all five coatings included the B2 regular phase, the BCC irregular phase, C14-Laves (FeTi2), and C15-Laves (Cr2Nb). However, with the increase of Mo from 0.2 to 1, the amount of the BCC phase increased from 24.1 to 29.5%, the C14 phase increased from 55.1 to 61.4%, and the amount of the C15 phase decreased from 11.2 to 1.8%. The yield strength increased by increasing the volume fraction of BCC and C14-Laves phases from 328 MPa for the Mo0.2 sample to 685 MPa for the Mo1 specimen. The same factor increased the creep life of RHEA from 43 to 54 h under a force of 450 N and temperature of 800 °C by increasing the places of dislocation locking. The simultaneous presence of the BCC solid solution and Laves phase was one of the factors that reduced the coefficient of friction during the wear test from 0.63 to 0.44 with increasing Mo. Electrochemical tests in 3.5 wt% NaCl solution showed that the RHEAs showed significant corrosion resistance. Specimen Mo1 with the smallest Icorr (1.6103 × 10–6 A cm2) and the highest Ecorr (− 1.2025 V) showed the best corrosion resistance. [ABSTRACT FROM AUTHOR]

Dissimilar metal welded (DMW) joint plays a crucial role in constructing and maintaining ultra-supercritical (USC) nuclear power plants while presenting noteworthy environmental implications. This research examines different welding techniques utilized in DMWJ, specifically emphasizing materials such as P91. The study investigates the mechanical properties of these materials, the impact of alloying elements, the notable difficulties encountered with industrial materials, and the concept of buttering. The USC nuclear power plants necessitate welding procedures appropriate for the fusion of diverse metal alloys. Frequently employed methodologies encompass shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and flux-cored arc welding (FCAW). Every individual process possesses distinct advantages and limitations, and the choice of process is contingent upon various factors, including joint configuration, material properties, and the desired weld quality. The steel alloy known as P91, which possesses high strength and resistance to creep, is extensively employed in advanced ultra-supercritical (AUSC) power plants. P91 demonstrates exceptional mechanical characteristics, encompassing elevated-temperature strength, commendable thermal conductivity, and notable resistance against corrosion and oxidation. The presence of alloying elements, namely chromium, molybdenum, and vanadium, in P91, is responsible for its improved characteristics and appropriateness for utilization in (AUSC) power plant applications. Nevertheless, the utilization of industrial materials in DMW joint is accompanied by many noteworthy concerns, such as the propensity for stress corrosion cracking (SCC), hydrogen embrittlement, and creep deformation under high temperatures. The challenges mentioned above require meticulous material selection, process optimization, and rigorous quality control measures to guarantee the dependability and sustained effectiveness of DMW joint. To tackle these concerns, a commonly utilized approach referred to as buttering is frequently employed. When forming DMW joint in nuclear facilities, it is customary to place a buttering coating on ferritic steel. This facilitates the connection between pressure vessel components of ferritic steel and pipes of austenitic stainless steel. The primary difficulty in DMW joint manufacturing is in mitigating the significant disparity in material characteristics resulting from carbon migration and metallurgical alterations along the fusion interface between ferritic steel and austenitic stainless steel. The process of buttering entails the application of a compatible filler material onto the base metal before the deposition of the desired weld metal. The intermediate layer serves as a mediator, enhancing the metallurgical compatibility, diminishing the probability of fracture, and enhancing the overall integrity of the joint. Buttering is still a new research area with a wide scenario of scope in terms of development, which could revolutionize developing high-temperature. These long-term sustainable joints could serve under critical conditions like AUSC power plants and reduce CO2 emissions by increasing the overall efficiencies of the systems. [ABSTRACT FROM AUTHOR]

One of the few synthetic resins from petroleum-based sources that are biodegradable and can reduce the environmental pollution is polyvinyl alcohol (PVA). PVA film is non-toxic, transparent, and biocompatible in line with green ecologically friendly requirements. It is completely biodegradable and possesses good mechanical properties, chemical resistance, and gas barrier. PVA's hydroxyl groups, however, decrease its mechanical and thermal properties and make it water-soluble, which limits its use. However, it is possible to control the water solubility or absorption by partially cross-linking the polymer chains. This work aims to enhance the mechanical properties while making an insoluble film through cross-linking with oxalic acid (OA). In the present investigation, PVA film was cross-linked with OA (with variable weight percentage (wt%) of OA) to limit its ability to absorb moisture. Tensile testing was utilized to evaluate the mechanical properties of the films, revealing their ultimate tensile strength, % elongation, and Young's modulus. With increase in wt% of OA, % elongation of PVA-based films decreases, whereas maximum tensile strength was observed at 10 wt% of OA configuration. In comparison to neat PVA, the differential thermo-gravimetric analysis peak migrated towards the higher temperature side with an increase in the OA concentration. The peak value of tan δ curve also increased and shifted towards higher temperature side as the OA concentration increased. This concludes that prepared films have high damping coefficient and can absorb impact load. Finally, the films' creep-recovery behaviour was also examined in detail. To represent the potential application of these films as packaging materials, anti-microbial tests were also conducted. [ABSTRACT FROM AUTHOR]

A significant effort in optimizing the chemical composition and powder metallurgical processing led to preparing new-generation ferritic coarse-grained ODS alloys with a high nano-oxide content. The optimization was aimed at high-temperature creep and oxidation resistance at temperatures in the range of 1100–1300 °C. An FeAlOY alloy, with the chemical composition Fe–10Al–4Cr–4Y2O3 (wt. %), seems as the most promising one. The consolidation of the alloy is preferably conducted by hot rolling in several steps, followed by static recrystallization for 1 h at 1200 °C, which provides a stable coarse-grain microstructure with homogeneous dispersion of nano-oxides. This represents the most cost-effective way of production. Another method of consolidation tested was hot rotary swaging, which also gave promising results. The compression creep testing of the alloy at 1100, 1200, and 1300 °C shows excellent creep performance, which is confirmed by the tensile creep tests at 1100 °C as well. The potential in such a temperature range is the target for possible applications of the FeAlOY for the pull rods of high-temperature testing machines, gas turbine blades, or furnace fan vanes. The key effort now focuses on expanding the production from laboratory samples to larger industrial pieces. [ABSTRACT FROM AUTHOR]

A polyol bonding agent (BA) was utilized to enhance the mechanical properties of propellant with low aluminum content. Through scanning electron microscope (SEM) and X‐ray photoelectron spectroscopy (XPS) analysis, it was discovered that BA can physically bond to the surfaces of ammonium perchlorate (AP) and hexogen (RDX). The results of mechanical testing showed that the use of BA can significantly improve the mechanical properties of propellants. Specifically, as the amount of BA increases, the maximum tensile strength (σm) of the propellant also increases, the fracture elongation (εb) initially increases and then decreases, the "dewetting ratio" continuously decreases, and the creep resistance of the propellant also increases. At a BA content of 0.2%, the σm of the propellant reaches 0.6 MPa, the εb exceeds 50%, and the "dewetting ratio" is less than 1.1. [ABSTRACT FROM AUTHOR]

Throughout the entire operational lifespan of a solid rocket motor, the propellant grain experiences creep due to gravitational forces, potentially influencing the motor′s reliability. To enhance the efficiency of creep tests for solid propellants, short‐term (3000 seconds) creep tests were conducted on nitrate ester plasticized polyether (NEPE) propellant at stress levels of 0.15 MPa, 0.20 MPa, 0.25 MPa, and 0.30 MPa using both the step stress method (SSM) and the conventional constant creep test (CCT). Furthermore, mid‐term (10000 seconds) and long‐term (7 days) creep tests were conducted. Based on the traditional generalized Kelvin model, the Saint‐Venant body was incorporated to derive a visco‐elastic‐plastic model with overstress considered, and constitutive model parameters were determined through data fitting. The findings demonstrate the efficacy of the constitutive model in well characterizing propellant creep behavior. According to the model, the yield stress of NEPE propellant was determined to be 0.2302 MPa, representing a significant 64.03% reduction compared to its design strength. This insight holds relevance for structural integrity analysis and the evaluation of solid motor storage life. [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.)

Capillary evolution at bicrystal UO2 grain boundaries is characterized using in situ transmission electron microscopy. The discontinuous nature of the densification process, both particle rotation and axial strain, along with the large activation stress for densification support a hypothesis that grain boundary strain in UO2 follows nucleation rate limited kinetics at low to intermediate stresses, that is, less than ≈108Pa$ \approx {10}^8\ {\mathrm{Pa}}$. The temperature dependence of the average activation stress for sintering agrees well with analysis of bulk sintering data and creep data reported within the literature when analyzed in the context of a grain boundary dislocation nucleation rate limited kinetic model. [ABSTRACT FROM AUTHOR]

A process of plastic deforming polymer blanks is developed involving polytetrafluoroethylene (PTFE) and carbon fibers of the UVIS-AK-P grade. The production process is explored from the standpoint of increasing the strength and resistance to creep. The relationship is found between the physics, mechanical, and tribotechnical parameters and the structural composite properties. The composites obtained using various schemes of plastic deforming polymer blanks differ in the character of deformation under tension. They develop different structures and feature various wear patterns. A multidirectional approach to plastic deforming blanks based on PTFE allows obtaining isotropic polymer materials featuring improved strength properties and better resistance to deformation under load. [ABSTRACT FROM AUTHOR]

This technical document discusses the development of elastic-viscoplastic deformation models for salt rocks. The study focuses on the behavior of salt specimens under compression and analyzes fracture criteria and plastic flow rules. Creep tests were conducted to study transient effects, and a mathematical model was constructed and calibrated using experimental data. The document provides equations, parameters, and results for different viscoplastic models and numerical simulations. The research was funded by the Ministry of Science and Higher Education of the Russian Federation. [Extracted from the article]

Synthetic fibers deforming over time can be a concern in structural design, particularly in serviceability limit states. Short-term pullout tests are commonly used to predict fiber–matrix interactions, but even in this case, an individualized evaluation of the pullout behavior of single fibers oriented parallel to the load direction may not be sufficient to predict the efficiency of the composite. In the present work, short- and long-term pullout tests were performed with fibers oriented at angles of 15°, 30°, and 45° to the direction of the load to investigate the influence of macro synthetic fibers orientation on fiber–matrix interactions. In short-term tests, optical microscopy images were obtained on the pulled-out fibers to correlate the surface degradation of the fibers with the stress versus strain curves. In quasi-static pullout (short-term), small reductions in pullout strength were observed for all fibers and angles, in addition to an intensive degradation of their surfaces owing to the significant snubbing effect of this type of fiber. In contrast, for the long-term tests, a creep reduction was observed with increasing fiber inclination angle caused by the creep reduction of the fiber due to non-axial loading and additional force components produced by the deviation of the axial force. The parameters of Burgers rheological model were written as a function of the fiber orientation angle, with excellent adjustment to the experimental data. [ABSTRACT FROM AUTHOR]

The combination of acoustic emission and electrical potential monitoring methods holds promise for monitoring and warning of rock bursts due to its comprehensive reflection of the damage process. However, the response features during the creep failure process remain unclear. In this paper, a coal creep test was conducted using a combination of electric potential and acoustic emission monitoring. The response characteristics were analyzed, their multifractal characteristics were analyzed, and the joint response mechanism was explored. This research demonstrated a significant correlation among acoustic emission and electrical potential signals and creep deformation and failure. At the start of loading, a brief increase in both signals was observed. As deformation progressed, the signals became steady, and their intensity and fluctuation notably increased during accelerated creep failure. Quantitative analysis of acoustic emission count rates and electric potential intensity during creep processes revealed a quadratic relationship of acoustic emission count rates with stress and strain variations, in addition to an exponential correlation with mean electric potential intensity. Additionally, the statistical analysis of the multifractal characteristics before coal sample instability and failure revealed consistent trends in the characteristic values of Δα and Δf(α), with initial decrease followed by slight fluctuations, culminating in a sudden abnormal change preceding failure. Finally, leveraging the mechanisms of acoustic emission and electrification under load, this study discusses the multifractal characteristics of acoustic-electric signals and verifies their complementary roles in accurately predicting coal rock creep failure. These studies provide essential theoretical groundwork and references for improving dynamic disaster monitoring in coal mines. [ABSTRACT FROM AUTHOR]

Concrete bridge deck cracking can cause serious serviceability issues during a bridge's design life and compromise a bridge's structural strength. Early age concrete bridge deck cracking occurs within a month of the concrete deck being placed and prior to live load application. It can typically be attributed to two factors: (1) construction practices; and (2) concrete shrinkage. This article examines the continuous deck placement sequence approach and its influence on early age concrete bridge deck cracking. Although the continuous deck placement process is commonly used, studies related to stresses induced during this process and the potential for deck cracking when using this construction method are very limited to work conducted overseas. Consequently, a time-dependent analysis considering the continuous bridge deck placement sequence at a steel composite bridge is presented in this article to help explain possible causes of early age bridge deck cracking. The modular ratio approach discussed in the Eurocode 4 is incorporated to approximate the early age concrete elastic modulus. To show the significance of using a continuous placement sequence, tensile stresses along the bridge length centerline are compared with the allowable tensile stress at two times, six and twenty-seven days after the bridge deck construction is initiated. Additionally, the article includes a simplified approach for calculating maximum bridge thermal stresses. The study results in this article will serve to aid engineers in understanding possible factors resulting in early age bridge deck cracking when a continuous deck placement sequence is used for bridge deck construction. Practical Applications: Early age bridge deck cracking can typically be attributed to construction practices and concrete shrinkage. Most bridges are constructed using a sequential deck placement where the concrete bridge deck is placed in discontinuous segments in an order to minimize tensile stresses developing in the concrete bridge deck. Conversely, a continuous deck placement entails placing the concrete bridge deck from one end of the bridge to the other end continuously. Contractors prefer using a continuous deck placement because of the method's reduced construction time. The Arkansas Department of Transportation (ARDOT) has identified early age concrete bridge deck cracking at a disproportionate number of continuous steel girder bridges constructed using a continuous deck placement. Early age concrete bridge deck cracking develops when tensile stresses in the concrete bridge deck exceed the concrete's tensile strength. During the bridge construction phase, concrete self-weight, construction loads, and thermal shrinkage are the primary load contributors to early age concrete bridge deck tensile stress. Since most continuous girder steel bridges consist of multiple short spans, early age concrete bridge deck tensile stress is primarily due to resistance to thermal shrinkage. An equation is derived in the article to calculate an approximate value for the thermal shrinkage stress. Thermal shrinkage cracking is averted by implementing proper curing methods to ensure the concrete tensile strength exceeds the induced tensile stress. Proper curing includes moist curing and minimizing moisture loss by using concrete curing blankets. [ABSTRACT FROM AUTHOR]

Risks associated with large landslides pose a severe threat to human life and property. Hence, the creep phase, the signal before the occurrence of large landslides, plays a significant role in the safety of mountainous areas. However, the mechanism of movement in the creep phase remains unclear. In this study, landslide events were divided into six blocks based on a thermo-poro-mechanical model. Blocks represent different landslide areas, which cannot be viewed collectively because of their varying external environments or intrinsic properties. We found that the phases of movement (stationary, creep, and rapid) of different blocks differed. Dividing the landslide into blocks may compensate for the disadvantage that a single sliding body model cannot reflect local creep. Additionally, friction strengthening and weakening were considered in this model. Friction strengthening refers to the phenomenon in which the friction coefficient increases with velocity, whereas friction weakening refers to the phenomenon in which the friction coefficient decreases with velocity. In this study, friction strengthening and weakening occurred before and after the critical velocity, respectively. Our findings suggest that the rapid movement of a landslide is mainly affected by the friction-weakening stage and the thermal-pressure generation stage. Furthermore, the former has a more profound influence than the latter. Notably, this model shows that the creep phase is controlled by friction strengthening. This study is expected to stimulate new ideas for landslide prediction. Highlights: The creep phase is controlled by frictional strengthening. Rapid movement of landslides is affected by friction weakening and thermopressure. Multi-block models are better suited to studying local creep. Different instincts for landslide areas should be considered comprehensively. [ABSTRACT FROM AUTHOR]

The creep behavior of rocks has been broadly researched because of its extensive application in geomechanics. Since the time-dependent stability of underground constructions is a critical aspect of geotechnical engineering, a comprehensive understanding of the creep behavior of rocks plays a pivotal role in ensuring the safety of such structures. Various factors, including stress level, temperature, rock damage, water content, rock anisotropy, etc., can influence rocks' creep characteristics. One of the main topics in the creep analysis of rocks is the constitutive models, which can be categorized into empirical, component, and mechanism-based models. In this research, the previously proposed creep models were reviewed, and their main characteristics were discussed. The effectiveness of the models in simulating the accelerated phase of rock creep was evaluated by comparing their performance with the creep test results of different types of rocks. The application of rock's creep analysis in different engineering projects and adopting appropriate creep properties for rock mass were also examined. The primary limitation associated with empirical and classical component models lies in their challenges when it comes to modeling the tertiary phase of rock creep. The mechanism-based models have demonstrated success in effectively simulating the complete creep phases; nevertheless, additional validation is crucial to establish their broader applicability. However, further investigation is still required to develop creep models specific to rock mass. In this paper, we attempted to review and discuss the most recent studies in creep analysis of rocks that can be used by researchers conducting creep analysis in geomechanics. Highlights: Creep constitutive models for rocks were reviewed, and their main characteristics were discussed. The applications of creep analysis in geomechanics were explained, and some engineering projects were mentioned. The back analysis techniques using long-time measured monitoring data were successfully used for finding rock mass creep parameters. [ABSTRACT FROM AUTHOR]

Copyright of Petroleum Geology & Oilfield Development in Daqing is the property of Editorial Department of Petroleum Geology & Oilfield Development in Daqing 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.)

The thin-wall effect of single crystal superalloys refers to the phenomenon that when the thickness of the sample and the part is less than 1 mm, the lasting life is reduced, the creep rate is increased and other mechanical properties are significantly attenuated. With the development of the internal cooling structure of advanced aero-engine single crystal blade parts, the structural thickness of some areas decreases, making it a typical thin-walled structure. Thus, it is of great engineering significance to consider the thin-wall effect in the thin-wall region during the design and manufacture of blades. Creep performance is one of the most important properties of superalloys for turbine blade application. This paper summarizes the thin-wall effect in creep performance of the superalloys as well as some advanced experimental equipment in the study of thin-wall effect. Research on thin-wall debit effect of superalloys can be divided into two categories, one is the cause of thin-wall debit, including the relative enhancement of oxidation, more significance in anisotropy, changes in micro structure and the initiation or growth of defects, and the factors that influence the thin-wall debit effect including experimental conditions (temperature, stress, etc.), the processing methods (casting, machining), geometric shape (rectangular cross-section, ring cross-section, film cooling holes). Research on thin-wall debit effect is within the scope of engineering application, as a part of "component level/analog component level" in "building block" verification and evaluation technology, thin-wall debit effect research under service environment or near-service environment conditions is more valuable for application. For this purpose, a variety of advanced experimental equipment platforms have been developed to simulate one or several coupled service conditions (high temperature, high pressure, corrosion/erosion, centrifugal loading) of the blade in the engine. Future research on thin-wall effects should be carried out under conditions closer to actual service conditions by preparing specimens according to the actual blade manufacturing process and conducting experiments on the equipment that simulates the service environment. [ABSTRACT FROM AUTHOR]

Fractional differential viscoelastic models can describe complex material behaviours and fit experimental data well; however, the physical significance of model parameters is difficult to express. In this study, the fractional differential Maxwell, Kelvin, and Zener models were used to fit the short-term creep compliance curves of polymethyl methacrylate at different ageing times. The model fits were in good agreement with the experimental data. As the ageing time increased, the fractional differential Zener model showed a relative increase in the modulus parameter of the spring and a relative decrease in the modulus parameter reflecting the viscosity of the spring-pot, which indicated that physical ageing made the material more elastic. The relaxation time of the material increased, which indicated that the physical ageing reduced the free volume of the material, hindered the movement of molecules/segments, and increased the time required for the material to reach equilibrium. The fractional order of the model decreased, which reflected the phenomenon that physical ageing reduced the creep compliance of the material. Using the relaxation time as the time scale, the creep curves at different ageing times under the same stress level could be superimposed, naturally presenting the time–ageing time equivalence principle. [ABSTRACT FROM AUTHOR]

The creep of bamboo scrimber is an important factor to be considered in engineering applications. Simply using the creep test method not only consumes a lot of time and money, but also cannot be extended to the full stress level. Therefore, in this paper, the short-term creep tests of bamboo scrimber under different stress levels (30% and 40%) and ambient temperatures (30°C–70°C) were carried out. The multicomponent Kelvin-Voigt model and generalized Maxwell shear relaxation model of bamboo scrimber were established. The Maxwell-3 shear relaxation model was used as the constitutive model of bamboo scrimber, and the creep finite-element model of bamboo scrimber under parallel-to-grain compression was established, which verified the creep constitutive model of bamboo scrimber. The results showed that the shear relaxation modulus exhibited a significant decrease during the unstable creep stage, reaching a maximum reduction of 62.0%. It showed nonlinear for the effect of ambient temperature on the compression creep of bamboo scrimber, and the creep rate near the glass transition temperature was significantly higher than that at other temperatures. The fitting coefficients, R -square of creep compliance models, were sorted as KV-4 and KV-5>KV-3>Burgers>KV-2. The fitting coefficients, R -square of the generalized Maxwell model of shear relaxation modulus, were sorted as Maxwell-4 and Maxwell-3>Maxwell-2>Maxwell-1. The simulated creep displacement error of the two specimens was 2.8% and 0.1%, respectively, which verified the accuracy of the numerical simulation method. The paper proposed creep behavior and a constitutive model for bamboo scrimber under parallel-to-grain compression, which holds significant theoretical implications for its widespread application. [ABSTRACT FROM AUTHOR]

The objective of the current work was to investigate the creep behavior of functionalized graphene (f-GNF)-epoxy nanocomposite. Time and temperature-dependent mechanical behaviors were investigated by performing creep tests at three different stress levels and two different temperatures. Graphene produced by the electric arc discharge method was functionalized with Triton X-100 by a non-covalent method. Then, f-GNF-epoxy nanocomposites are produced by using the Three Roll Milling (3RM) method to eliminate nanofiller agglomeration. By performing quasi-static compression tests, stress levels for creep tests are determined as 50, 100, and 200 MPa to guarantee the viscoelastic deformation regime, around yield, and the viscoplastic deformation regime, respectively. The results indicate significant creep resistance in the nanocomposite with 0.1 wt% f-GNF. Depending on temperature and stress level, the effect of f-GNF is more pronounced at higher stresses and temperatures. f-GNFs have a significant effect on inhibiting the mobility of polymer chains, resulting improvements in the creep modulus. This indicates that thermally activated processes controlling the creep rate are in part inhibited by the presence of f-GNF. In the creep tests carried out for 2 h, a maximum improvement of 85% was observed in the creep modulus of epoxy-nanocomposite compared to pure epoxy at room temperature. [ABSTRACT FROM AUTHOR]