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Maintaining the geometrical stability of hot filament is a challenge in chemical vapor deposition (CVD) over a larger area since deformation varies the distance between the filament and the substrate and, consequently, destroys the uniformity of diamond deposition. Herein, Ta filament is straightened with a tensile stress ranging from 4.40 to 11 MPa to suppress deformation, and the stability during the CVD process of diamond film is evaluated. Scanning electron microscopy and energy dispersive X‐ray are further utilized to investigate the morphological and structural evolutions of Ta filament. Results show that straightened Ta filament maintains geometrical stability without any visible deformation or breakage and uniform deposition of diamond film is obtained through Ta filament undergone a transformation from Ta to Ta2C and then to TaC. At high deposition pressure (7 kPa) or a low concentration of methane (1%), the straightened Ta filament goes through a moderate transformation, which implies the cracks caused by rough transformation can be avoided, thus prolonging the lifetime of straightened Ta filament. These works provide significant guidelines for the large‐scale manufacture of diamond deposition. [ABSTRACT FROM AUTHOR]

Biaxially prestressed large concrete structures of the confinement building in nuclear power plants (NPPs) should meet the safety requirement for the extension of the service time. Long‐term delayed strains of concrete are one of the key factors determining the safety factor in these structures. This article presents 30‐year long in situ measurement results of strain evolution of confinement buildings in four different NPPs. The delayed strains are predicted at a material level using the next‐generation Eurocode‐2, and the influence of temperature as proposed by the fib model code 2010, making use of delayed strain characteristics of the corresponding concrete from a previous study. We found that the default law given in Eurocode underestimates the delayed strain. However, with the possibility of adjusting the shrinkage and creep laws, the prediction results fit with a good accuracy for the in situ measurement. [ABSTRACT FROM AUTHOR]

The long‐term behavior of slender (1/40) long‐span precast high‐strength concrete girders was experimentally investigated regarding their use as a competitive solution in relation to steel alternatives for highway overpasses. The time‐dependent effects of full‐scale girders has rarely been addressed, particularly the influence of creep and shrinkage of concrete with compressive strengths around 120 MPa. Two half‐scale girder specimens were produced using an economically optimized and high‐strength concrete mixture, nonfiber reinforced, designed only with conventional raw materials, currently available at Portuguese precast companies, and subjected to long‐term loading, with a magnitude of approximately 50% of the failure load in bending, during a period of 3.75 years. Using the same mixture, prismatic specimens were also produced and subjected to long‐term loading at 24 h and 7 days of age to assess both creep and shrinkage. Results show that the age of concrete at the loading day is of paramount importance regarding the time‐dependent effects. These are most relevant during the first days of loading and tend to stabilize from the 112th day of loading onward. The time‐dependent girder's mid‐span deflection at the end of the 3.75 years did not exceed more than 50% of the initial deformation. Comparison of results with those obtained with Model Code 2010 and the current version of Eurocode 2 shows that these underestimate strains and deflections due to creep, mostly because the short‐term development of these effects, occurring during the first days of loading, are not adequately represented. On the contrary, a sound agreement between experimental and theoretical values, both in short and long term, was obtained using the Auperin et al. approach. [ABSTRACT FROM AUTHOR]

This publication concerns the synthesis of a novel class of hybrid thermoset/thermoplastic elastomers, i.e., double cross‐linked polyisobutylene‐based polyurethanes (xPIB‐PUs), together with their processing and some key properties. These materials are designed to exhibit a combination of properties for indwelling medical applications, specifically for heart valve prostheses. The chemical cross‐links are introduced by well‐defined 3‐arm PIB stars fitted with HO‐end groups of molecular weights (MWs) of Mn = 3081 and 9000 g mole−1 and narrow MW dispersities (<1.3). Processibility of xPIB‐PU containing 70 wt% PIB (for biocompatibility and calcification resistance) is achieved by driving the syntheses to high conversions (>97%) close to but still below the gel point and completing the cross‐linking in heated molds. The processibility period (minutes) is controlled by controlling the MW of the cross‐linking agent in the 3081 to 9000 g mole−1 range. Blends of 3‐arm stars and linear bifunctional PIBs can also control the processibility period. The creep resistance of xPIB‐PU is significantly improved (from 13.2% to 5.5%) relative to physically cross‐linked PIB‐PU. xPIB‐PUs exhibit negligible permanent set (1–2%), and high Young's modulus (41 MPa). The stress/strain properties of xPIB‐PUs are also investigated. The data clearly show the contribution of two modes of cross‐linking. [ABSTRACT FROM AUTHOR]

In this study, high impact polystyrene (HIPS) materials was prepared by using a styrenic elastomer (10, 20, 30 wt%) and carbon nanotube (CNT) (3, 5, 7, 10 phr) by melt blending technique as alternative to commercial HIPS including polybutadiene rubber. The poly (styrene- b -isobutylene- b -styrene) (SIBS) was used as thermoplastic elastomer with polystyrene (PS) to improve its poor impact resistance and CNT was added to PS/SIBS blend matrix to maintain its strength and stiffness. The modulus, tensile strength and toughness values of the blends decreased while those of impact resistance increased in comparison to neat PS. The impact strength of PS20SIBS blend containing 20 wt% SIBS was found to be approximately 530% higher than pure PS. The nanocomposites of the PS20SIBS exhibited a decrease in the size of SIBS particles with increasing CNT compared to PS20SIBS. This was ascribed to the increased viscosity of PS matrix via CNT filler, preventing the coalescence of the elastomer domains. Compared to the PS20SIS, its nanocomposites showed higher strength, modulus and toughness, but lower impact strength. The toughness of the nanocomposite containing 5 phr CNT (PS20SIBS-5CNT), increased by 117% while its creep deformation decreased by approximately 40%, in comparison with PS20SIBS blend. Although PS20SIBS-5CNT exhibited lower impact strength than the PS20SIBS blend due to the dispersion of smaller SIBS particles in the PS matrix, it still increased the impact strength of pure PS by 188%. The PS20SIBS-5CNT nanocomposite, which improved impact strength and creep resistance with optimal toughness and tensile modulus can be used as a novel HIPS material that tunes the hardness-toughness/impact balance effectively. Moreover, the same nanocomposite was found to reach the conductivity threshold by exhibiting 106 times lower electrical resistance in comparison with that containing 3 phr CNT, leading to a conductive filer network with 5 phr loading of the nanotubes into the system. [ABSTRACT FROM AUTHOR]

Despite the common use of the standard linear solid model (SLSM) in viscoelasticity, the physical significance as well as the difference between the Maxwell and Kelvin forms of SLSM are still not clear. This paper demonstrates that each parameter of those two models has its specific physical meaning, and introduces the relationships allowing the transformations between those parameters. Regardless of their physical significance, those two models are equivalent in terms of their mathematical properties. Hence, no matter which model is chosen, consistent analysis results can always be obtained as long as the physical meaning of each parameter is accurately interpreted. [ABSTRACT FROM AUTHOR]

The increasing availability of mass timber panels has expanded the possibilities for using timber-concrete-composite (TCC) flat floors beyond the traditional TCC T-beams. While TCC floors often easily satisfy ultimate limit state requirements, their stiffness, vibration characteristics, and long-term performance are critical design considerations. This research aimed to validate the bending, vibration, and long-term performance for nine different TCC floor systems through full-size tests with a span of 5.8 m. The tested floor systems used laminated-veneer-lumber, laminated-strand lumber, and cross-laminated-timber (CLT) panels connected to a concrete slab with and without an interlayer. Three types of shear connections were employed: self-tapping screws; glued-in steel mesh; and a combination of STS and adhesive bond. First, the shear connection properties were determined via 54 small-scale push-out tests. Then, 18 floors were tested in bending and vibration shortly after fabrication, and an additional nine floors were subjected to service loading for 32 months under variable climatic conditions, after which they were subjected to bending and vibration tests. The results confirmed that the calculations based on the γ -method accurately predict the stiffness, natural frequency, and governing failure modes of TCC floors. The long-term exposure to service loading had minimal effect (within 10%) on resistance, stiffness, and natural frequency of TCC floors, except for the TCC using CLT, which showed the highest creep deflection and stiffness reduction among the tested configurations. [ABSTRACT FROM AUTHOR]

On the surface of complex landslide areas, other types of slope processes often occur in addition to the landslide movements themselves. However, in order to define the interrelationships or analyse their triggers, it is necessary to have chronological information on their past occurrence. In this study, a spectrum of tree-ring-based (dendrogeomorphic) approaches for spatio-temporal analysis of these processes is presented. The different approaches are applied to a selected complex landslide area with the presence of both creep and rockfall movements. Tree-ring-based data were obtained from standard increment cores as well as from tree roots exposed in tension cracks and from the modified surface of stumps. The presented approaches allowed not only chronological reconstruction of past activity processes but also reconstruction of their spatial activity and even estimation of the rate of displacements of selected landslide blocks. For each methodological approach, their advantages and limitations were evaluated. In addition, the obtained chronological data were used to evaluate potential triggers. The uniqueness of the tree-ring-based data was evident in detecting a wide variability in both the preparatory (up to 2-year periods with above-average rainfall in the case of landslides) and triggering factors themselves (3–5-day rainfall totals for landslides, extreme river discharges for activity tension cracks, or the influence of low temperatures during the winter season). Thus, this study provides a comprehensive overview of dendrogeomorphic approaches that can be used to obtain unique data on the spatio-temporal activity of processes in landslide areas in the past, estimating their rates and preparatory and triggering factors. [ABSTRACT FROM AUTHOR]

Vertical drain assisted by vacuum and/or surcharge preloading is an effective method for improvement of soft ground with high water content. A large settlement will occur, and the water flow may deviate from the Darcy's law. The creep is also non-negligible in estimating the long-term settlement of such soft ground. To accurately predict the consolidation process, this study develops an axisymmetric finite strain consolidation model based on Barron's free-strain theory incorporating the creep, radial and vertical flows, non-Darcian flow law, and void ratio-dependent hydraulic conductivity during the consolidation process. First, to mathematically validate the model and highlight the new model's features, the existing model not considering the creep and the non-Darcy flow is also adopted as a reference for comparison based on a benchmark simulation. Then, Rowe cell tests involving non-Darcian flow are simulated by the new model to experimentally validate the predictive performance. Furthermore, the model is applied to simulate the consolidation process of a long-term monitoring embankment to examine the applicability of the model for engineering practice. All results demonstrate that the model is capable of accurately describing the consolidation of soft soils with vertical drains under combined loading with features of creep and non-Darcy flow. • An axisymmetric finite strain consolidation model is developed, incorporating the extended 1D Yin–Graham EVP model and a non-Darcy flow law. • Consolidation governing equations including the radial and vertical water flow are solved using alternating direction implicit (ADI) method. • The model performance describing non-Darcian flow and creep is verified by comparing with physical model tests and long-term field test. [ABSTRACT FROM AUTHOR]

A shear‐transformation‐zone (STZ) model is proposed for time‐dependent behaviours of clay, in which the viscoplastic deformation is described by the evolution of a temperature‐like state variable. The model is featured by rate‐dependent dilatancy and a unique critical state stress ratio. In its present form, it has nine parameters, most of which can be handily calibrated, and can predict the rate‐dependent undrained shear strength, primary, and secondary creep, as well as stress relaxation for normally consolidated clay under complex stress paths using a single set of parameters. The capabilities of the model have been verified by available experimental results on five different clays. [ABSTRACT FROM AUTHOR]

The ductility and exhibition of the multiple, fine, self-controlled cracking of strain-hardening cementitious composites (SHCCs) under tension has made them attractive for enhancing the durability of civil infrastructure. These fine cracks are key to preventing the ingress of water and harmful chemicals into the structure and thereby achieving steel reinforcement. However, several studies have suggested that the short-term fine cracks shown in the laboratory may end up exceeding the acceptable crack widths that are specified in design codes when SHCC members are subjected to sustained constant loads. In real structures, however, the load is also shared by the steel reinforcement in the member, so the SHCC within may not be under a constant load; therefore, the crack widening will not be as severe. This study focuses on the creep behaviour of SHCCs when they are applied as an external layer on reinforced concrete to enhance durability. A novel approach to simulate various stress–strain regimes in such systems is developed by using a fixture to share a sustained moment exclusively between a reinforcement member and SHCC. The developed load-sharing system allows stresses within the reinforcement and SHCC to be monitored against time during the imposed loading, while ensuring access to the SHCC layer for instrumentation and monitoring of strain/cracking. The time-dependent widening of cracks in the SHCC layer is found to be much less significant than that under constant loading, so resistance to water/chemical penetration can still be ensured in the long term. The obtained information on the variation in stress, strain, and crack opening with time will be useful for the development of a general model for the creep behaviour of SHCC members. [ABSTRACT FROM AUTHOR]

Viscous behaviour is a significant characteristic of soil, and to accurately capture this behaviour, a piecewise-linear model called ACLC has been developed specifically for modelling one-dimensional large-strain consolidation of soft clay. ACLC takes into account both the long-term deformation and anisotropy of the soil. Furthermore, it incorporates various factors such as soil heterogeneity, self-weight, time-dependent loading, vertical flows, and seepage force. In ACLC, the settlement of the soil layer is a result of both the net outflow of fluid from the soil element and the development of soil creep. To describe the creep behaviour of the soil, ACLC employs two yield surfaces: the Current State Surface (CSS) and the Normal Consolidation Surface (NCS). The creep rates are calculated based on the associated flow rule. To ensure the accuracy of ACLC, it is validated using the enhanced CS2 model, oedometer tests conducted on Xiaoshan soft clay, and observed data from the Murro test embankment. Finally, the influence of ACLC parameters on the consolidation behaviour of clay is thoroughly investigated. This analysis helps to understand the role of these parameters and their impact on the overall consolidation process. [ABSTRACT FROM AUTHOR]

This paper examines the consolidation and settlement behaviour of soft clay deposits treated with granular columns (single and in groups). Two Rowe cell loading chambers were used to conduct the investigations on samples of kaolin and a local Belfast natural estuarine alluvium called 'sleech'. Tests were carried out on unreinforced samples and then reinforced samples with single and multiple column configurations. The test duration for each test was between 3 and 4 months, depending on the test material and the granular column configuration. The settlement reduction factors based on primary and secondary consolidation were examined. The study suggests that the effectiveness of granular columns at mitigating primary and/or secondary settlement is directly related to the loading intensity, the stress history and the creep characteristics of the subsoil. It was also found that the stress concentration ratio reduced with the stress level. Secondary consolidation also has some effects on the stress concentration ratio. [ABSTRACT FROM AUTHOR]

Applications of Bayesian updating commonly treat soil parameters as random variables. A significant issue with this is that soil parameters are highly subjective. Therefore, using traditional parameter-based models, Bayesian analysis starts from a subjective prior and it is unclear how this may influence the overall results of a study. In this paper, Bayesian updating is combined with a data-driven method, known as CRACA (i.e., CReep And Consolidation Analysis), for predicting the settlement of embankments on soft soil. Importantly, the method directly ingests measured oedometer data and, therefore, avoids the subjectivity involved in parameter selection. Because parameters are not used, scaling factors are introduced that account uncertainty associated with the laboratory measurements and the automated interpretation process. These factors have an initial value of unity (returning the prior) and are updated in a Bayesian framework as settlement monitoring data are revealed over time to improve future forecasts. The model was applied to an embankment case history and was shown to result in a rapid improvement in the accuracy and a narrowing of the 95% confidence interval as settlement monitoring data are revealed to the model. [ABSTRACT FROM AUTHOR]

Constitutive models in the literature for creep of frozen soil are based on the direct use of time counted from the onset of creep. An explicit time dependence in a constitutive equation violates the principles of rational mechanics. No change in stress or temperature is allowed for during creep, using the time-based formulations. Moreover, the existing descriptions need much verification and improvement on the experimental side as well. Creep behaviour of artificially frozen sand was evaluated experimentally. Novel testing methods were used, and new insights into the creep behaviour of frozen soil were gained. Creep rate under uniaxial compression was examined with different kinds of interruptions, like unloadings or overloadings. Experimental creep curves were presented as functions of creep strain. They were brought to a dimensionless form which describes the creep universally, despite changes in stress or temperature. Possible anisotropy of frozen soil was revealed in the creep tests on cubic samples with changes of the loading direction. Using the particle image velocimetry (PIV) technique, information on the lateral deformation and the uniformity of creep were obtained. Volumetric creep of unsaturated frozen soil under isotropic compression was demonstrated to be due to the presence of air bubbles only. [ABSTRACT FROM AUTHOR]

High-performance composites are subjected to different mechanical forces and stresses during their lifetime. Hence, knowledge of the time-dependent deformation at different temperatures is crucial for engineering applications. In this context, a polyetherimide/carbon fiber composite was analyzed via creep behavior from the glassy to the elastomeric state (30–250 °C). Creep tests were carried out under low-stress loads. An artificial neural network (ANN) was used to fit the curves for all tested temperatures. The ANN allowed excellent fit for all conditions independently of the curve shape, mainly for the glassy region, in which most of the analytical models did not fit well. This study is a growing and promising field in the materials science field due to the fact that it uses ANN as an alternative to fit creep behavior not fitted by usual analytical equations, which utilize closed-form solutions. Furthermore, it is expected that this study will allow the formulation of new equations and methods to determine the creep behavior at high stresses, for example. [ABSTRACT FROM AUTHOR]

This study examines the influence of weathering aging on the mechanical properties and durability of flax fiber‐reinforced polymer composites (FFRP) intended for outdoor applications. Employing an accelerated weathering environment replicating natural outdoor conditions, encompassing UV radiation, condensation, and water spray, the FFRP samples with 2 and 4 mm thicknesses underwent exposure durations of 0, 500, 1000, and 1500 h. Mechanical tests characterized tensile, flexural, and inner‐plane shear properties, while a custom‐made apparatus measured the long‐term tensile creep behavior. Additionally, scanning electron microscopy allowed for the observation of microscopic changes in fiber and matrix. The findings illustrate a consistent decline in tensile and flexural properties with increased weathering exposure, resulting in reductions of 17% and 38% in the tensile strength and modulus, and 24% and 52% in the flexural strength and modulus after 1500 h. Intriguingly, inner‐plane shear strength exhibited a slight increase after 500 h before a subsequent decrease. Furthermore, samples with the same thickness demonstrated an increased creep development with longer weathering durations. Despite this, the mechanical degradation rate induced by weathering was comparatively slower for thicker samples. Overall, the diminished mechanical properties of FFRP post‐weathering can be attributed not only to the polymer but also to the substantial role played by flax fibers in this process. Highlights: UV weathering degrades the mechanical properties of flax/polyester composites.Both the instantaneous elastic properties and the long‐term creep behavior are affected by weathering.Thickness influences the mechanical degradation of the composites caused by UV weathering.SEM confirmed UV‐water weathering resulted in the degradation of both natural fiber and polymer matrices. [ABSTRACT FROM AUTHOR]

Understanding viscoelastic behavior of dielectric elastomers for artificial muscle application is important to regulate actuation performance, response time, energy density, sensitivity, duty cycle, etc. The performance of elastomers is widely recognized as being influenced by various fillers, including functional particles and poly-reagents. However, the impact of fillers on the viscoelastic properties of VHB 4910 remains to be fully understood. In this work, a new range of particulate-polymer filled VHB elastomers are studied for the effects of barium titanate and Ketjenblack particles dispersed trimethylolpropane trimethylacrylate on viscoelastic properties. This followed characterization of stress-relaxation and creep behavior to realize the time-dependent mechanical performance. Also, the stress-softening and energy dissipation behavior are examined to find the number of cycles required to reach the equilibrium energy state. Viscoelastic properties of elastomer including elastic modulus, toughness, are found to significantly reduced as a result of modified poroelastic effects due to incorporated fillers. The mechanical properties of composites are evidenced to depend on the size of the particulates and the amount of polymer reagent within elastomer. Theoretical analysis comparing deformation, relaxation, and creep mechanisms in biomedical materials validates the potential of modified elastomers for use in soft actuation devices, particularly in the field of artificial muscles. This work may help in recognizing the strategies to tune viscoelastic behavior of microporous elastomers for potential applications in flexible electronics. [ABSTRACT FROM AUTHOR]

The thermal-mechanical response of the anode-supported planar solid oxide fuel cell (SOFC) during sintering is important for its manufacturing and in-service operation. The integrated micro/nano-indentation and finite element (FE) modeling method was used to characterize the Young's modulus, yield stress and creeping for the NiO-3YSZ anode and 8YSZ electrolyte at room temperature. Based on the real-time full-field deformation of the half-cell SOFC which was measured using the 3D digital image correlation (DIC), the FE simulation was used to estimate the stress response in a manner of sensitivity study. It shows that the half-cell SOFC warps towards the anode substrate during heating and points in the opposite direction during cooling. The warping deformation of FE simulation matches well with the DIC measurement. In addition, the maximum tensile stress in the electrolyte coat of the half-cell SOFC plate is about 207 MPa if assuming temperature-independence of creeping for the SOFC materials. • Real-time full-field displacement of the half-cell SOFC during sintering is measured. • The mechanical properties of the NiO-YSZ and 8YSZ materials are characterized. • The relation of creeping with the stress state of the FE analysis is validated experimentally. • The difference of creeping at 1200 °C for NiO-YSZ and 8YSZ is characterized. • The stress response during sintering and cooling is estimated, respectively. [ABSTRACT FROM AUTHOR]

Traditional concrete creep testing and prediction methods are cumbersome and time-consuming. In this study, the creep behavior of concrete modified with various supplementary cementitious materials (sludge and fly ash, 10–30 wt.%) was investigated and analyzed using the indentation tests and multiscale homogenization analysis. The study revealed that incorporating 10% water treatment sludge ash (WTSA) effectively enhanced concrete’s axial compressive strength and elastic modulus, while reducing its creep strain. This was mainly because adding 10% WTSA improved the compactness of concrete and increased the ratio of high density (HD) C–S–H in C–S–H gel and reduced the width of interfacial transition zone (ITZ). However, a higher content of WTSA admixture was observed to negatively impact the concrete properties. Furthermore, the creep behavior of concrete was predicted through multiscale homogenization calculations. Utilizing the nanoindentation technique, accurate predictions in the multiscale creep model can be obtained by differentiating and quantifying the volume fraction of the physical phase based on the characteristic indentation modulus. In contrast, the quantitative results of the physical phase obtained from the inverse convolution need to be corrected by thermogravimetric analysis and backscattered electrons to obtain a higher level of accuracy in creep prediction. [ABSTRACT FROM AUTHOR]

After the gas drainage borehole is formed in the coal seam, its stress deformation process is a creep process without the influence of mining. By arranging boreholes on coal samples and carrying out creep loading test of porous coal through rock mechanics testing machine, the creep process of boreholes in actual coal seams is simulated. The results show that the creep loading test results of drilled coal are quite different from those of conventional loading. Creep loading produces large deformation due to rheological and aging characteristics. Compared with non-porous coal, the yield of drilled coal occurs earlier and the yield platform is wider during creep loading. Also, the larger the borehole diameter, the deeper the borehole depth, and the lower the peak stress. The up dip angle is easier to destroy than the down dip angle. Compared with hard coal, soft coal produces greater deformation under smaller peak stress. The research results have guiding significance for drilling gas drainage in the soft coal seam. [ABSTRACT FROM AUTHOR]

This article presents a study carried out on a 2 kN·m torque transducer at the Central Office of Measures (GUM) and the Physikalisch-Technische Bundesanstalt (PTB). The weighted least squares method was used to generate the linear regression equations for this torque transducer. The Monte Carlo method and the law of uncertainty propagation were used to calculate the expanded uncertainty. In addition, a creep study was carried out at eight measurement points ranging from 200 N·m to 2000 N·m. The investigations showed that the highest readings of the torque transducer, expressed in electrical units as mV/V, occur within the initial few seconds of the test after the removal of the maximum reference torque. [ABSTRACT FROM AUTHOR]

In many settlement prediction methods, the creep settlement of shallow foundations on sand is either disregarded or accounted for using time correction factors that lack a reliable basis. These existing settlement correction factors for creep have mainly been derived from a restricted number of long-term settlement measurements and do not consider the influence of factors such as the load level, rate of load application and properties of the soil below the foundation. In this study, a newly proposed one-dimensional elasto-viscoplastic macro-element was used to investigate the factors influencing the time-dependent behaviour of shallow foundations on sand. The safety factor of the foundation, the creep characteristics of the soils and the duration of load application were found to have important effects on the post-construction settlement development. The simulation results were used to develop an enhanced settlement correction factor for creep, which takes into account the identified factors. The improved settlement correction factor was found to be comparable to existing ones when the safety factor of the foundation is 3. The effectiveness of the proposed settlement correction factor is demonstrated using creep settlement measurements from one field footing test and two case histories. [ABSTRACT FROM AUTHOR]

This study delves into the convergence of operators and the viscoelastic properties of fractal ladder and tree structures. It proves the convergence of fractal stiffness operators through operator algebra, revealing a fundamental connection between operator sequence limits and fractal operator algebraic equations. Our findings demonstrate that, as the hierarchical levels of these structures increase, their viscoelastic responses increasingly align with the fractional viscoelastic behavior observed in infinite-level fractal structures. We explore the similarity in creep and relaxation behaviors between fractal ladders and trees, emphasizing the emergence of ultra-long characteristic times in steady-state creep and pronounced tailing effects in relaxation curves. This research provides novel insights into the design of fractional-order viscoelastic structures, presenting significant implications for materials science and mechanical engineering. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of temperature variations on the creep and stress relaxation behavior of clay samples from London Bank Station. The independent and coupled effects of strain rate and temperature on one-dimensional (1D) stress–strain and stress relaxation responses were investigated based on a series of temperature-controlled constant rate of strain (CRS) compression–relaxation tests carried out at fast, intermediate, and slow displacement rates and over 20°C–55°C. The temperature effect on the creep index (Cα) was investigated based on a series of temperature-controlled multistage loading (MSL) oedometer tests. The results of the CRS compression–relaxation tests showed that with the increase in temperature, the coefficient of stress relaxation (Rα) decreases for samples that were loaded at fast and intermediate prerelaxation displacement rates (υ˙); however, it increases for samples loaded at the slow prerelaxation displacement rate. A decrease in υ˙ by a factor of 10 (i.e., from 0.010 to 0.001 mm/min) causes the Rα values to reduce by 55%–11% with the temperature increase. The increase in temperature caused an increase in Cα that were obtained from the MSL tests. The maximum value of Cα increased by 18% from 35°C to 45°C and by 37% from 45°C to 55°C. The temperature effects on other conventional parameters that included the preconsolidation pressure, and the compression and swelling indexes (Cc and Cs) were comparable with the findings reported in the literature. Comparing Cα that were obtained from the MSL tests and Rα that were obtained from the CRS tests supports the validity of Rα=Cα/Cc correlation for thermally influenced saturated reconstituted clays and that the time-dependent soil parameters could be obtained from relatively fast CRS compression–relaxation tests as an alternative to conventional time-consuming oedometer tests. [ABSTRACT FROM AUTHOR]

Single- and multi-stage isotropic creep tests including bender element and acoustic emission measurements are carried out to investigate the relationship between ageing and creep in dense silica sand. In the considered pressure range, the experimental results show an inversely proportional relationship between ageing and creep: the small-strain shear modulus increases with decreasing isotropic pressure,, while the axial creep strain and the acoustic emissions show the opposite pressure dependence. In the multi-stage creep test, the small-strain shear modulus increases monotonically, while the rates of axial strain, number of acoustic emissions and small-strain shear modulus decrease with time according to a power law. In the single-stage creep tests, the ageing and creep indicators initially evolve as in the multi-stage creep test, but then the small-strain shear modulus reaches a peak value and decreases with time thereafter. At the same time, the rates of axial strain, number of acoustic emissions and small-strain shear modulus deviate from the power law. A conceptual model assuming a time-dependent behaviour of the normal and shear forces at the particle contacts in order to explain the experimental observations qualitatively is proposed. Accordingly, an increase in small-strain shear modulus results from homogenisation of the force chains, while a decrease in small-strain shear modulus results from a temporary formation followed by a time-delayed collapse of strong force chains. [ABSTRACT FROM AUTHOR]

Pressure-assisted sintering models involve numerous closely correlated parameters that depend on temperatures, porosity, and microstructure development. Consequently, the identification of the model parameters is relatively lengthy and requires experiments to extract the underlying creep behavior (pressure/temperature dependent), shear, bulk sintering moduli that are porosity-dependent, and grain growth. Knowing that certain sintering mechanisms are grain-size dependent, it is very difficult to assess the densification behavior for the case of ceramics. We have already developed a sinter-forging method to assess independently all parameters for ceramics. However, this method implies numerous interruption tests to measure the specimen diameter evolution, and the capillarity forces were neglected. In this study, an instrumented microwave sinter-forging prototype avoiding highly repetitive interruption tests has been developed to record the specimen diameter evolution of submicronic alumina powder samples. The new method includes the effect of the capillarity forces on the identification equations, making the model more realistic for submicronic ceramics. The resulting model was tested on a finite element code for validation and to explore its stability for complex shapes. [Display omitted] • Pressure assisted sintering model assessment. • Identification including the capillarity forces. • Instrumented porous stage method insensitive to grain growth. [ABSTRACT FROM AUTHOR]

This work investigates the behavior and properties of corundum and mullite ceramics at high temperatures and during very long exposures in a controlled atmosphere. The motivation of the work lies primarily in advanced applications in nuclear energy technology, specifically in the search for materials for helium-cooled reactors of the 4th generation. The studied ceramic samples Al63, Al70, Al76, Al96, Al100, where the number indicates the mass percentage of Al 2 O 3 , were exposed for 1000 h at a temperature of 900 °C in gaseous atmospheres of helium, nitrogen and air. The properties of the exposed and unexposed samples were evaluated by measuring the bending strength at room temperature (CMOR), hot modulus of rupture at high temperature (HMOR), and isothermal creep, BET method, and using electron microscopy. The color changes induced by the reducing atmosphere and temperature were also interpreted using a simple thermochemical model. The CMOR measurement results show that all ceramic samples do not significantly change their properties due to long-term exposure. The detected deviations in the exposed samples from the unexposed ones can be considered random caused by the inherent heterogeneous structure. A similar conclusion also applies in the case of the HMOR measurement results, except for the results for the Al63 sample, where the drop in the strength of the exposed samples by approx. 37 MPa (20 %) may be related with the highest proportion of polyvalent oxide admixtures of all studied ceramics, i.e. 1.01 wt % Fe 2 O 3 and 0.52 wt % TiO 2. The change in color indicates that the iron and titanium present are being reduced. However, none of the conducted experiments indicate that changes in the redox state associated with the formation of oxygen vacancies would significantly reduce strength at high temperatures or increase creep in mullite ceramics. [ABSTRACT FROM AUTHOR]

Isothermal creep and sustained-peak low-cycle fatigue (SPLCF) tests were conducted on as-fabricated and precracked chemically vapor infiltrated (CVI) SiC-fiber-reinforced SiC-matrix (SiC/SiC) composites with Hi-Nicalon™-S fibers from 1200 to 1450 °C in air at stresses up to 150 MPa and for exposure times up to 400 hr. The creep behaviors were analyzed by using a modified Norton-Bailey equation. The residual in-plane tensile properties of those specimens that survived 300- to 400-hr runout were measured. Results indicate that the as-fabricated composites show better durability under creep than under SPLCF and retain a significant percentage of their in-plane tensile properties after runout. In contrast, durability and residual in-plane tensile properties of the precracked composites under similar creep and SPLCF testing conditions decreased with an increase in temperature as well as an increase in stress. Failure mechanism(s) and factors influencing durability of the composite are discussed. [ABSTRACT FROM AUTHOR]

Solute-induced transition of slip planes and changes of dominant slip system in single-phase (Ti,Zr)(B,C) solid solution ceramics are revealed experimentally based on the high temperature compressive creep tests and microstructure characterizations. The superior creep resistance of (Ti,Zr)(B,C) was confirmed by the steady-state creep rates of (Ti,Zr)(B,C) of 3.8 × 10−9-6.1 × 10−8 s−1 at 1400–1600 °C, a magnitude lower than that of TiB 2. The solid solution of Zr and C cause a transition of dominant dislocation slip system form basal plane to other slip systems with higher Peierls stress. Zr clusters around dislocations reduce local strain and dislocation energy, and create dislocation jogs with the same b of main dislocation but on different slip plane. As a result, dislocation slip along (0001) < 1 ̅ 2 1 ̅ 0 > are restrained and other slip systems with higher Peierls stress are prioritized in (Ti,Zr)(B,C), responsible for the significantly higher creep resistance than traditional diborides. This finding provides experimental evidence for the solute-induced transition of dislocation slip systems and highlight the significance of solutes in mechanical plastic behavior of multi-component ceramics. • (Ti,Zr)(B,C) single-phase solid solution has a remarkably higher creep resistance than the traditional mono-carbides and mono-borides at high temperatures. • The dislocation movements on basal plane are restrained and on other slip system with higher Perier stress are activated in (Ti,Zr)(B,C). • Dislocation configurations and densities of (Ti,Zr)(B,C) and TiB 2 are notably different. • Zr clusters are formed around dislocations, decrease local strain, and serve as pinning points to resist dislocation movements. [ABSTRACT FROM AUTHOR]

In this paper, the creep experiments of Nitrate Ester Plasticized Polyether (NEPE) propellant under eight different stress levels are carried out. The creep experimental data is discussed with different constitutive models, and it is found that the four parameters fluid constitutive model and the composite time-hardening constitutive model can be used to fit the experiment data better. The composite time-hardening constitutive model is more suitable to predict the long-term creep behavior based on the short-term creep behavior. The accuracy of the constitutive model is proved by comparing the predicted results with the experimental results. [ABSTRACT FROM AUTHOR]

Functionally graded (FG) materials have shown excellent thermoelastic and creep performance, being considered as excellent materials for cylindrical shells subjected to thermo-mechanical loads. This review provides a detailed account of thermoelastic and creep properties of FG cylindrical shells. A review of governing equations on properties of FG materials as well as thermoelastic response of materials is provided. In depth analysis of the works carried out on the thermoelastic and creep performance of FG cylindrical under different thermal and mechanical loads (such as internal/external pressure, axial loading, etc.) is then conducted. Results obtained so far indicate the superior creep performance of FG cylindrical shells. Although many studies have been carried on thermoelastic response of FG cylindrical shells, their creep properties under different loading is yet to be extended and is a subject of interest for the future researches. [ABSTRACT FROM AUTHOR]

In recent years, the depth of oil drilling has exceeded 9000 m, and the testing and evaluation of mechanical properties of ultra-deep rocks face great challenges. Obtaining complete core samples has lots of serious problems through ultra-deep drilling, so it is difficult to process standard rock samples for general tests to obtain the mechanical properties. In order to study the creep behaviour of deep rocks, we conducted continuous step holding nanoindentation creep experiments on carbonate rocks from the Tarim Oilfield in Xinjiang, China. We first investigated the effects of load and holding time on the creep behaviour; Furthermore, by calculating the stress exponent, the deformation mechanism is revealed; At last, four traditional creep models and fractional order Maxwell model were used for regression to explore the applicability of models in describing the creep behaviour. The results show the creep displacement is positively correlated with the load and holding time. Creep curves with different shapes were obtained in nanoindentation (named A1 and A2 respectively). The Burgers and the two-dashpot Kelvin model are in good agreement with experimental data under long holding time. The stress exponents of A2 are greater than 3, indicating that the creep mechanism of A2 is dislocation creep. [ABSTRACT FROM AUTHOR]

Vitrimer materials have attained great interest owing to their sustainable functions and distinctive physical properties. Compared with conventional cross‐linked materials, the thermoplastic‐like nature, such as the stress relaxation and creep at high temperatures, is outstanding, which is owing to the activation of the bond exchange in the cross‐linked network. The activation temperature of the bond exchange, so‐called topology freezing temperature (Tv), are treated as the important material parameters, and non‐isothermal (i.e., temperature‐ramp) creep test is one of the method to determine the Tv. This study investigates effects of network defects, that is, the breaking point of network connectivity, on the creep and Tv. The transesterification vitrimer samples with varying fraction of the network defects are designed using thiol‐epoxy click reaction, where the overall fraction of the bond exchange units, that is, the ester bond and hydroxyl group, is kept constant. Non‐isothermal creep tests are conducted with varying temperature‐ramp rate and applied stress levels, and the difference of Tv and creep behaviors at T > Tv are discussed in terms of network strand diffusion during bond exchange and chain elongation under stress. [ABSTRACT FROM AUTHOR]

The benefits of using glued laminated bamboo (GLB) as a structural material are numerous, such as its low weight, high specific strength, and low carbon footprint. However, as a viscoelastic material, GLB materials exhibit creep, which is a significant characteristic that needs to be considered. To ensure the safety and serviceability of structures that utilize GLB, it is essential to accurately estimate the long-term performance of GLB composites under external forces. This paper reports on an experimental investigation into the creep characteristics of GLB under tensile and compressive loads. The experiments were conducted at various load levels for a period of 500 h under a controlled environmental condition. The Burgers model and the five-parameter model were used to characterize creep behavior and predict the long-term deformation by extrapolating beyond the experimental period. The long-term deformation of the GLB may be overestimated by the Burgers model due to its constant creep rate for the viscous component. In contrast, the five-parameter model introduces a modification factor that results in a nonlinear viscous component, allowing a more accurate fit and a reasonable deformation estimate. Highlights • Creep characteristics of GLB were studied under tensile and compressive loads. • Burgers and five-parameter models were used to describe the creep behavior. • Extrapolation of Burgers model overestimates the creep deformation of GLB. • Five-parameter model provides reasonable deformation estimate for GLB. [ABSTRACT FROM AUTHOR]

We report the effect of particle surface roughness on creep deformation and subsequent strain recovery in dense colloidal suspensions. The suspensions are composed of hard-spherelike poly(methyl methacrylate) smooth (S) and rough (R) colloids with particle volume fractions ϕS = 0.64 ± 0.01 and ϕR = 0.56 ± 0.01, corresponding to a distance of 3.0% and 3.4% based on their jamming volume fractions (ϕ J S = 0.66 ± 0.01 , ϕ J R = 0.58 ± 0.01). The suspensions are subject to a range of shear stresses (0.01–0.07 Pa) above and below the yield stress values of the two suspensions (σ y S = 0.035 Pa , σ y R = 0.02 Pa). During creep, suspensions of rough colloids exhibit four to five times higher strain deformation compared to smooth colloids, irrespective of the applied stress. The interlocking of surface asperities in rough colloids is likely to generate a heterogeneous microstructure, favoring dynamic particle activity and percolation of strain heterogeneities, therefore resulting in higher magnitude of strain deformation and an earlier onset of steady flow. Strain recovery after the cessation of stress reveals a nonmonotonic recoverable strain for rough colloids, where the peak recoverable strain is observed near the yield stress, followed by a steep decline with increasing stress. This type of response suggests that frictional constraints between geometrically frustrated interlocking contacts can serve as particle bonds capable of higher elastic recovery but only near the yield stress. Understanding how particle roughness affects macroscopic creep and recovery is useful in designing yield stress fluids for additive manufacturing and product formulations. [ABSTRACT FROM AUTHOR]

To investigate the influence of temperature and humidity variations on creep in high-performance concrete beams, beam tests were conducted in both natural and laboratory settings. The findings indicate that the variations in creep primarily stem from temperature changes, whereas humidity changes have little influence on fluctuations in both basic creep and total creep. The influence of humidity on creep is more strongly reflected in the magnitude of creep. Functions describing the influence of temperature and humidity on the creep behavior of high-performance concrete (HPC) subjected to fluctuating conditions are proposed. The findings were employed to examine creep deformation in engineering applications across four places. This study complements the correction method for the creep of members under fluctuating temperature and humidity. This research application can provide a basis for the calculation of the long-term deformation of HPC structures in natural environments. [ABSTRACT FROM AUTHOR]

To study creep failure behaviors of jointed rock mass with seepage pressure as the main damage driving force, creep tests under multi-level loading of seepage pressure were conducted on sandstone with different joint dip angles. In addition, a memory-dependent nonlinear seepage–creep model was established for jointed sandstone. The results show that jointed sandstone experiences three creep stages (initial, steady-state, and accelerated creep stages) in creep tests under multi-level loading paths of seepage pressure. Jointed sandstone with joint dip angles of 30° and 60° undergoes shear failure, while that with the joint dip angle of 45° is subject to tensile–shear failure. Under the same seepage pressure, the sandstone with the joint dip angle of 45° has a greater creep rate in the steady-state creep stage than that with joint dip angles of 30° and 60°. In the volumetric compression stage, the permeability increases at the instant of applying each level of seepage pressure, followed by gradual reduction and stabilization of permeability. In the volumetric dilation stage, the permeability gradually rises. The theory of memory-dependent derivative reflecting the time memory effect was introduced to establish the memory-dependent nonlinear viscoelastic–plastic seepage–creep model for jointed sandstone. The results obtained using the theoretical model conform to the test data. Moreover, the creep failure criterion of the rock was proposed. The creep acceleration starts to increase from 0 and the critical steady state transitions to a non-steady state, suggesting that the rock will soon be damaged. The calculation formula for critical time corresponding to the critical steady state of creep was also deduced. The critical time to onset of creep can serve as an early warning of the creep failure of rocks. [ABSTRACT FROM AUTHOR]

A model for residually stressed viscoelastic bodies undergoing finite deformations is developed and applied to the study of time-dependent responses of spheres and cylinders to various stress and strain controlled tests. An approach based on the notion of natural configurations is employed. An appropriate free energy function is used, and a suitable dissipation function is adopted to obtain a constitutive model. This constitutive model is applied to the study of different boundary value problems of thick spheres and cylinders. The responses to various strain controlled tests are investigated, which includes the stress-relaxation test and a test for a time-dependent inflation–deflation cycle. Also, the response to creep test and step-stress test in thick viscoelastic spheres is investigated. Furthermore, the stretch-controlled responses of residually stressed viscoelastic cylinders to pure torsion and axial stretch are studied. Pure torsion involves an axial extension or compression known as the Poynting effect. The Poynting effect in residually stressed viscoelastic bodies, which does not appear to be studied in the literature, is investigated in detail here. It is noted that the magnitude of the angle of twist has a significant influence (sometimes involving a change of sign) on the observed Poynting effect. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) has been increasingly used for gas turbine (GT) components over the last decade. Many different components can be successfully designed, printed, and used in the gas turbine. However, there still exist questions on the use of AM components in hot-section areas. These components are typically fabricated from nickel-base superalloys that are known to have superior mechanical properties at elevated temperatures (e.g., creep and fatigue). Research over the last decade has been primarily focused on the printability of nickel-base superalloys, and there still exists a gap in understanding the high temperature processing-structure-properties-performance relationships of these alloy systems. This study evaluates the effect of processing methods, such as laser-based powder bed fusion (LBPBF) and electron beam powder bed fusion (EBPBF), on the resulting microstructure and time dependent mechanical properties of a nickel-base superalloy (ABD®900). Material after each build was subsequently heat treated using both near-solvus (at or slightly below the gamma prime solvus temperature) and super-solvus (above gamma prime solvus temperature) conditions. Multistep aging was then carried out to produce a bi-modal distribution of gamma prime precipitates as is typical in similar alloys. Microstructure was evaluated in both the as-built and fully heat-treated conditions for each processing technique. Mechanical testing was conducted to evaluate the effects of AM build methods, microstructure, and heat treatment on high temperature mechanical properties. The results show that there are several methods which can be used to improve the performance of components built using AM. The creep testing results for ABD900-AM clearly show an improvement in properties (rupture life and ductility) at all test conditions compared to testing in the prior AM alloy of the same class. A super-solvus heat treatment improved creep rupture strength by ∼3× in the LBPBF material compared to the near-solvus heat treatment. These findings provide directions for future studies to advance the overall state of gas turbine technology by enabling ABD®900-AM material and other AM alloys to be used in more innovative hot-section components. [ABSTRACT FROM AUTHOR]

The UK High Temperature Power Plant Forum have completed a long term cross-weld creep test programme on a Grade 92 steel pipe. This paper describes an analysis of the creep test data. The weld strength factor (WSF), i.e. the ratio of cross-weld strength to base material strength for a specified rupture time and temperature, is shown to be a unique function of a dimensionless parameter S, the creep test stress divided by ultimate tensile strength at the test temperature. The key practical finding is that, since a single universal cross-weld creep life parametric is applicable to all temperatures, long-term behaviour at service temperatures should reliably be predictable from short-term tests at accelerated temperatures. [ABSTRACT FROM AUTHOR]

In this paper, a new high-temperature methodology for determining the 'effective' corrosion rates of internal pressure-tested cladding tubes, based on the reduced creep failure times under exposure, is presented. The methodology has been developed to estimate the combined damage accumulation of corrosion and creep and to establish temperature limits for the use of 1515Ti claddings in high-temperature Lead-Bismuth-Eutectic (LBE). The results are compared to static corrosion rates determined from earlier test campaigns in stagnant LBE. All tests are conducted on 24% cold worked 1515Ti cladding tubes that are the SCK CEN reference material for the MYRRHA design efforts. The virgin material creep model that is the basis for the corrosion rate estimation, has been fitted on an extended creep failure database and a life-fraction rule is applied to accommodate for the life reduction caused by the sought 'constant' effective corrosion rate. [ABSTRACT FROM AUTHOR]

Regarding the application of the Monkman-Grant relationship to creep strength enhanced ferritic steels such as modified 9Cr-1Mo and 12Cr steels, there have been many reports showing that results tend to be an overestimation of the creep life in the long-term region. To address this issue, an author conducted a study to improve the estimation accuracy in the long-term region by the Monkman Grant relationship. Analysing the published creep test data for modified 9Cr-1Mo steel, the author found that the product of the minimum creep strain rate and rupture time (ƐMG) is not constant but depends on the loading conditions, which are test temperature and stress. Then, the author proposed an extended Monkman-Grant relationship considering the dependence of ƐMG on the loading conditions. When this model was applied to the data for modified 9Cr-1Mo and 12Cr steels, the creep life was predicted with good accuracy from the short-term to long-term regions. [ABSTRACT FROM AUTHOR]

P92 (9Cr-1.8W–0.5Mo-NbV) martensite steel is widely used in high-temperature pipes of ultra-supercritical boilers in China. During high-temperature operation, microstructural evolution of the heat affected zone (HAZ) across welded joint leads to type IV cracking failure. In this article, microstructural evolution and type IV cracking of P92 steel welded joint in an actual 605℃ supercritical boiler were analysed. The results show the cracking appeared in the fine-grained heat affected zone (FGHAZ). Laves phase and M23C6 phase clustered around the cavity. Their precipitation and coarsening promote the nucleation and growth of cavities. The Z phase was also observed in the heated affected zone. Compared with other zones, FGHAZ has lower dislocation density and more degeneration of tempered martensite lath, the coarsening of Laves phase and M23C6 phase is more severer in FGHAZ. These factors led to the deterioration of the creep properties and type IV cracking. [ABSTRACT FROM AUTHOR]

Base plate preheating is a relatively new strategy to influence the mechanical properties and microstructure of IN718. Base plate preheating was studied to reduce Niobium (Nb) segregation in the interdendritic region of IN718 superalloy and to improve mechanical properties through the laser powder bed fusion (L-PBF) process. Here, we compared experimental results for high-temperature (650℃) mechanical properties of specimens built with 200℃ (PH200) and 600℃ (PH600) preheated base plates. The as-built PH200 and PH600 specimens had relatively similar grain morphologies and orientations along the building direction. The PH200 specimen showed a cellular structure and higher Nb segregation at the interdendritic region, whereas the PH600 specimen had a dendritic structure and lower Nb segregation. The lower amount of Nb segregation in the PH600 specimen is mainly because of the cooling rate difference between specimens during the L-PBF process. The PH600 specimen exhibited slightly better tensile properties, longer creep life, and elongation than the PH200 specimen in both the as-built and heat-treated conditions. These differences mainly occurred due to differences in Laves and δ-phase fractions between the PH200 and PH600 specimens. The simulation result indicates that the temperature distribution in the block remains relatively uniform during the building process. [ABSTRACT FROM AUTHOR]

The tensile creep tests for two kinds of epoxy resin matrix composite laminates were performed under 25°C and 50°C. Results indicate that these materials deform in a time‐dependent manner, that is, the tensile strain increases within a short time after the tests began, and then decreases during most of the loading period. Such increase and decrease trends reflect the creep characteristic and effect of physical aging, respectively. A linear viscoelastic model is developed to include both the creep temperature effect and physical aging effect, starting from the Boltzmann superposition principle. In modeling, these two effects both contribute to the transient compliance and result in the increase and decrease of the transient compliance. Time–temperature/aging time superposition principle is adopted to deal with the influences of temperature and physical aging. This theoretical model is further implemented numerically within a finite element framework. To verify the newly proposed model, not only the experimental and numerical results of the tensile deformations of laminates are compared, but also the bending deformations of structural components made from the above laminates are analyzed. Highlights: Tensile creep tests were done for carbon fiber/epoxy laminates.The strain shows creep temperature and aging effect (TE and AE).New constitutive relation was proposed to describe the TE‐ and AE‐caused strains.Structural‐level flexure creep tests and simulation analyses were conducted. [ABSTRACT FROM AUTHOR]

Changes in grain size of two firn (density from ∼550 to ∼820–840 kg m−3) samples, extracted at Summit Greenland during their stress relaxation over 3 days were observed using optical micrographs. These changes were confirmed by both 3-D microstructural reconstruction images and plots of microstructural parameters vs. time, viz., the grain size increased with the decrease of pore size, the specific surface area, and the index of prevalent ice curvature. Building on studies of both the viscoelastic behaviour of firn deformation and the measured changes in grain size, a quadratic-based model is constructed to describe the evolution of grain size during the stress relaxation stage, where the grain growth is in relation to the microstructure, the relaxation time, and the threshold stress (an equilibrium residual stress at the grain size maximum, which forces the grain growth before the arrival of the grain size maximum). This model can be scaled up from laboratory samples to the glaciers and ice sheets, e.g. the time at the grain size maximum spanning across days to thousands of days, even to a geological age. In addition to the firn samples which have undergone the stress relaxation prior to laboratory tests, especially sensitive to the effect of grain size, should be calibrated, this work also sheds light on learning more about the mechanical behaviours and changes in grain size during the deformation of firn or other porous materials under interrupted or cycle load, particularly from the stress relaxation, irrespective of the compression, tension, or shear. [ABSTRACT FROM AUTHOR]

In this article, we investigate the creep mechanism of clay at the nanoscale. We conduct the molecular dynamics (MD) modeling of clay samples consisting of hexagonal particles under compression and shear. The MD simulations include oedometer creep, shear creep, direct shear tests, and stress relaxation. The numerical results show that the nanoscale creep mechanism of clay is related to particle rotation, translation, and stacking under different loading conditions. The clay sample under creep shows two types of particle arrangements, that is, the shifted face‐to‐face configuration and the face‐to‐edge configuration. The orientation angle of clay particles is computed to track the rotation of individual particles due to creep. The fabric variation of the clay under creep is characterized by the dihedral angle between the basal particle plane and the x‐y plane and the order parameter. It is found that the factors affecting the microstructure variation of the clay aggregate include stress levels, loading rates, and particle sizes. In the nanoscale shear creep test, the creep process comprises three stages, that is, primary, secondary, and tertiary. The microstructure change during creep depends on the initial alignment of clay particles. The clay creep under a more significant stress level results in a more considerable order parameter and a more orientated clay structure. [ABSTRACT FROM AUTHOR]

Development of load-bearing fiber reinforced plastic (hereinafter referred to as FRP) composite structures in civil engineering, exploited under high temperatures, such as industrial chimneys and gas ducts, requires the knowledge of their long-term behavior under constant and cyclic mechanical and temperature loads. Such conditions mean that the viscoelasticity of FRP should be considered along with the thermal aging effect. This research is devoted to the effects of thermal aging on the viscoelastic behavior of polymers. Two sets of experiments were conducted: creep tensile tests and cyclic heating in a constrained state. The Kelvin–Voigt viscoelasticity model was used to determine the rheological parameters of binder from experimental creep curves. Cyclic heating was used to compare the behavior of normal and thermally aged binders and to evaluate the possibility of temperature stress accumulation. Fourier-transform infrared spectroscopy was used for polymer's structural changes investigation. Both tests showed that non-aged glassed polymer (hereinafter referred to as GP) was prone to viscoelastic behavior, while the thermally aged GP lost viscosity and worked almost perfectly elastic. It was assumed that long heat treatment had caused changes in the inner structure of the GP, reducing the number of weak bonds and increasing the number of elastic ones. Therefore, the results show that the designing of FRP structures, exploited under thermomechanical load, requires using the elastic model while taking into account the properties of FRP after long-term heat treatment. [ABSTRACT FROM AUTHOR]

In this study, we examined at the grain-scale the normal contact behavior of rigid-soft interfaces via a series of micromechanical experiments, in which "rigid" refers to quartz particle and "soft" refers to polymeric granules composed of recycled rubber. Emphasis was placed on the influence of creep by quantifying the creep deformations at the composite interface subjected to long-term loading. The experimental data suggested that the creep behavior of the sand-rubber interface subjected to different normal loads is not deterministic and that there is a correlation between creep and elastic deformations. We also examined the applicability of available creep models to the specific creep problem and the parametric study highlighted the heterogenous features of the creep contact behavior of the sand-rubber samples, which is dependent on the elastic properties of the rubber and the irregular geometry of the contact area. The ground-truth dataset suggested the Burgers model is the most suitable contact model for the creep problem at the sand-rubber interface. The parameters of the Burgers model were also calibrated for further exploration of constitutive models to be used in discrete-based computer analyses. This modeling also provided fundamental insights to understand the physics of the problem. [ABSTRACT FROM AUTHOR]