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Metallic fuels hold numerous advantages over conventional uranium dioxide fuels and are a key component of several liquid metal-cooled advanced reactor concepts including sodium fast reactors. These fuels undergo rapid swelling during early burnup; consequently, they spend most of their reactor lifetime in a porous state. The presence of this porosity alters many of the mechanical properties of the fuel including creep impacting fuel deformation during axial swelling. This work investigates the creep behavior of the porous fuel using a spark plasma sintering technique. Creep tests were performed for the first time on porous α-phase uranium and uranium with 10 wt. % zirconium (U-10Zr) samples. The samples of α-phase uranium and U-10Zr were fabricated from depleted uranium by spark plasma sintering and subjected to uniaxial compressive creep testing. Calculated stress exponents were found to be 2.6 ± 1.6 and 5.7 ± 1.4 for α-U and U-10Zr, respectively, and calculated activation energies were found to be 61.6 ± 1.1 kJ / mol for α-U. The creep data were also used to evaluate existing porosity inclusive in creep models. [ABSTRACT FROM AUTHOR]

Excavation of underground engineering structures involving deeply buried water-rich soft rocks is generally carried out using the artificial freezing method. A series of undrained uniaxial and triaxial shear and creep tests were conducted on soft rocks under different confining pressures (0, 0.2, 0.5, and 1.0 MPa) at different freezing temperatures (room temperature, -5°C, -10°C, and -15°C). Test results indicate that the frozen soft rocks show strain softening characteristics. The stress—strain curve changes from a straight line to a curve as deviatoric stress constantly increases, while it decreases abruptly after the deviatoric stress reaches the peak and is slightly affected by the freezing temperature. At the same temperature, shear strength increases at a rate of 5.6 MPa/°C with increasing confining pressure; as freezing temperature decreases, the shear strength increases at 0.34 MPa/°C, and cohesion increases at 0.6 MPa/°C. Under the same confining pressure, the failure strain of soft rock decreases with the decrease of temperature. The Mohr-Coulomb (M-C) criterion can accurately describe the failure process of frozen soft rocks in the pre-peak stage, with a correlation coefficient greater than 0.98. Within the test stress range, soft rocks display attenuated stable creep deformation. Acoustic emission (AE) tests were conducted to further verify that the soft rocks show shear failure under load, with a shear plane showing an angle of 45° with the horizontal. The research findings provide technical support and theoretical reference for studying rock mechanical properties as well as for designing and carrying out underground freezing of rocks in a low-temperature environment. [ABSTRACT FROM AUTHOR]

As the pace of salt rock storage construction in China accelerates, suitable shallow storage sites are becoming scarce, as such, the utilization of deep salt deposits is a foregone conclusion. However, as salt deposits in China all contain a certain amount of impurities, triaxial multistage loading creep tests for deep salt rock with varying impurity contents were carried out to study the influence of impurity content and distribution on the creep properties and failure modes of salt rock. The isochronous stress–strain curves were used to calculate the long-term strength of the salt rocks with different impurity contents. The test results show that the higher the impurity content, the lower the steady-state creep rate, and the greater the long-term strength. Moreover, it was observed that cracks first appeared at the interface between the impurity and the salt rock, subsequently extending to the salt rock. Thereafter, a new nonlinear creep damage model considering impurity content was proposed by introducing the nonlinear viscoplastic damage body and using the fractional-order derivative theory. The proposed three-dimensional creep model was verified based on creep test data and compared with the traditional creep models. The proposed model has fewer parameters and increased fitting accuracy. Thus, this study contends that the proposed model can accurately simulate the entire creep process for impurity salt rock, which provides a theoretical basis for the safe operations in salt caverns containing impurities. Highlights: The triaxial multistage loading creep tests for deep salt rock with varying impurity contents were carried out. The influence of impurity content on steady-creep rate, creep deformation and long-term strength of salt rock were analyzed. A nonlinear fractional-order creep damage model for deep impurity salt rock was proposed. The proposed three-dimensional creep model is in good agreement with the test data and can accurately simulate the whole creep process of impurity salt rock. [ABSTRACT FROM AUTHOR]

In this research, the microstructure and precipitate characteristics of the dissimilar inertia friction welded (IFW) joints of deformed and powder metallurgy (PM) nickel‐based superalloys were studied using optical, scanning electron, and transmission electron microscopy. In addition, several creep tests were conducted. The high‐temperature mechanical properties of the IFW joints were systematically analyzed. Under the creep testing condition of 680°C, the specimens exhibited creep fracture at the thermomechanically affected zone (TMAZ) of the PM superalloys. Further, the failure lifetime is enhanced with a reduction in the applied creep loading. Owing to the IFW process, various γ′ precipitates and carbide distributions were observed in the various zones of a dissimilar IFW joint. Undissolved powder particle boundary (PPB) defects in the TMAZ of the PM superalloy initiated creep cracks under creep loading. Based on the experimental results and theoretical analysis, the creep fracture mechanisms of the dissimilar IFW joints were revealed. Thus, the findings of this study provide guidance for controlling the microstructures and properties of dissimilar deformed/PM nickel‐based superalloy IFW joints. [ABSTRACT FROM AUTHOR]

In the complex geological environment of deep mining area, water‐bearing soft rock is more prone to damage and destruction by low‐frequency disturbance. In this paper, the dynamic–static combination test was conducted on the basis of uniaxial compression test by using creep dynamic disturbance impact loading system and acoustic emission technique. The test results show that with the increase of the initial value of disturbance loading, the fracture morphology of sandstone gradually changes from a single major crack to multiple cracks coexisting, and some saturated sandstones lose the bearing capacity in the process of disturbance, presenting a cone‐shaped fracture surface. The increase of the initial value of the disturbance changes the bearing capacity of the sandstone, and the peak energy of acoustic emission reaches the maximum value when the initial value of the disturbance is 80% UCS. The results of the study can provide some reference for the stability analysis of deep water‐rich soft rock mines. [ABSTRACT FROM AUTHOR]

Magnesium (Mg) alloys, particularly AZ91, have gained significant attention due to their castability and lightweight properties. The present study investigates the effects of individual strontium (Sr) and combined calcium (Ca)–strontium (Sr) addition on the microstructure evolution and creep performance of AZ91 alloy. Alloys are prepared via squeeze‐casting and subjected to tensile creep tests. Scanning electron microscopy and X‐ray diffraction studies reveal Al2Ca and Al4Sr phases at the expense of the β‐Mg17Al12 phase. Further, thermodynamic analysis shows these phases have higher dissolution compared to the β‐Mg17Al12 phase. The AZ91 alloy with the combined addition of Ca and Sr demonstrates a much lower steady‐state creep rate compared to individual Ca‐ or Sr‐modified AZ91 alloys. Further analysis of the creep data indicates that dislocation climb‐controlled power‐law creep governs in both Sr‐ and Ca–Sr‐modified AZ91 alloy. Microstructural investigation on the postrupture sample indicates that needle‐shaped Al4Sr acts as a crack/cavity initiator, while a skeleton shape‐interconnected network consisting of Al2Ca and/or Al4Sr precipitates is effective in retarding crack propagation. The higher thermal stability of Al2Ca and Al4Sr phases, along with the grain size refinement, is found to be the major factors contributing to improved creep performance in Sr–Ca‐modified AZ91 alloy. [ABSTRACT FROM AUTHOR]

Creep tests are conducted on forged 617 M superalloy samples at 650, 700, and 750 °C at stresses ranging from 115 to 320 MPa. At 650 °C, a significant steady‐state secondary creep is observed, while at 700 and 750 °C limited secondary creep and prolonged tertiary creep are observed. Creep data analysis using power‐law creep approach estimates high‐stress exponents (n ≈ 13.4 at 650 °C, ≈11.5 at 700 °C, and ≈9.7 at 750 °C) and activation energy (Q ≈ 530.6 kJ mole−1). After incorporating threshold stress, the activation energy for creep is found to be ≈261 kJ mole−1. This is consistent with the activation energy for lattice self‐diffusion in the alloy. Transmission electron microscopy provides evidences affirming that climb‐controlled dislocation creep may be the operative creep mechanism. Ni3(Al, Ti) (γ′) precipitates and M23C6 carbides evolve during exposure at operating temperatures. These are observed to lead to enhanced creep resistance at 700 °C. Significant coarsening rate of γ′ precipitates are noted during exposure at 750 °C. This intensifies recovery processes and lowers creep threshold stress drastically. Extended tertiary creep prevails near the service conditions of this alloy, which is ascribed to instability in microstructure during creep. [ABSTRACT FROM AUTHOR]

The nanoindentation method is a widely utilized approach for characterizing the mechanical properties of materials at the nanoscale. In typical nanoindentation tests, the mechanical responses of materials are monitored while maintaining constant environmental factors, such as lighting and temperature, in order to ensure the reliability of the results. Here, we propose a testing method that switches the light conditions during a single nanoindentation creep test to detect slight changes in the mechanical response due to weak light illumination. To achieve this, a reference sample of fused silica was employed, which is insensitive to light, in order to compensate for the thermal expansion/contraction of approximately 1 nm due to the light environment. The calibrated results revealed the instantaneous suppressive influence of light illumination on the indentation creep behavior of ZnO. It was found that upon initiating illumination, the indentation creep rate decreased by 45%, whereas terminating illumination led to a dramatic 19.4‐fold increase in the creep rate. The effective testing pattern involving a “light switch” enables quantitatively visualizing the light illumination effects through the instant “jump” in the creep strain rate within a single test, facilitating the detection of minor and instantaneous effects of light environments on indentation creep behavior. [ABSTRACT FROM AUTHOR]

The most widely used method in the self-healing of hot mix asphalt is the capsule method. In this method, the capsules effect the mechanical properties of asphalt mixtures. In order to determine the effect of capsules on the mechanical properties of asphalt mixtures, capsules containing waste vegetable oil in four different ratios (0.25%; 0.50%; 0.75% and 1.00%) were added to the mixtures. The mechanical properties of asphalt mixtures with and without capsules were determined by applying the creep test at single stress (450 kPa). Thanks to these test results, after the capsules written in 4 different ratios were randomly distributed into the sample with Python code, the creep test was carried out under three different constant stresses (300, 450 and 600 kPa) using the finite element method. Finally, the Response Surface Method (RSM) analysis was carried out to evaluate the relationship between variables and permanent deformations, thus it was aimed to gain a statistical perspective to the study. As a result of the simulation, differences caused by the capsules were observed. Accordingly, it was determined that the addition of capsules increased the permanent deformation rate of asphalt mixtures. As a result of the RSM analysis, it is seen that the model performs the analysis with high accuracy. [ABSTRACT FROM AUTHOR]

The utilization of reclaimed asphalt pavement (RAP) in asphalt mixtures not only reduces production costs and resource consumption but also provides significant environmental benefits. Consequently, technology and methodologies used for asphalt pavement recycling, aimed at enhancing the utilization rate of RAPs, have emerged as prominent topics in both academic research and engineering practice. Given the complex thermal history and poor low-temperature performance (LTP) of RAP, investigating the effects of varying thermal histories of RAPs on the LTP of a mixture holds substantial practical significance for increasing the utilization rate of RAP in seasonally frozen regions. In this study, scanning electron microscopy (SEM), the thermal stress restrained specimen test (TSRST), the trabecular bending test, and the bending beam creep test (BBCT) are utilized to examine the effects of the indoor simulation methods that produce RAPs with varying thermal histories and contents on a recycled asphalt mixture (RAM) from both microscopic and phenomenological perspectives. Additionally, this research investigates the accuracy of predicting the LTP of RAMs using the Burgers model. The test results indicate that the LTP of an RAM is influenced not only by the RAP content and its thermal history but also by the ambient temperature. Regardless of the thermal history of the RAP, the LTP of an RAM tends to decrease as the RAP content increases. Different thermal histories of RAPs exert varying effects on the low-temperature viscoelastic behavior of an RAM. The UVRAP reduces the viscoelastic temperature range of an RAM by an average of 10.79%, whereas the THRAP increases it by an average of 2.16%. These effects can be attributed to the distinct micromorphology of the asphalt on the surfaces of RAPs with a varying thermal history. Specifically, a greater number of micropores and microcracks on the asphalt surface leads to a poorer LTP of RAMs. Additionally, the residuals of the Burgers model for predicting the LTP of an RAM with THRAP exceeded −2. However, the Burgers model demonstrates predictive capabilities for evaluating the LTP of an RAM filled with RAP from the same source or with a similar thermal history. [ABSTRACT FROM AUTHOR]

Hard structural planes mainly exist in rock slopes and their creep characteristics largely determine slope stability. Traditional models have some shortcomings in describing the creep characteristics of hard structural planes, such as poor adaptability and unclear physical meaning of parameters. In order to overcome these shortcomings, based on the creep failure mechanism of hard structural planes, an element combination model is adopted in the study. In the instantaneous deformation stage, the plastic deformation proportional coefficient n is introduced based on the strain rebound theory of loading-unloading tests. In the attenuation creep stage, the hardening coefficient C and creep index m are introduced. In the viscoelastic-plastic failure stage, the weakening factor k is introduced. By improving traditional elements, a new piecewise nonlinear constitutive relationship of hard structural planes is established and then the creep equation is obtained with integration method. The adaptability of the established model and the way to solve parameters are analyzed and the correctness of the model is proved theoretically. The data of creep tests of the prefabricated serrated interpenetrated green sandstone structural plane and the concealed non-interpenetrated marble structural plane are further fitted and verified, yielding a fitting result exceeding 0.95, thereby indicating a strong correlation. By optimizing the whole creep process of the hard structural plane in stages and demonstrating the difference in the creep mechanism of the hard structural plane at different depths in a rock mass in the high and low stress fields in the form of piecewise function, the physical meaning of the improved model is clearer. In addition, the improved model allows the higher accuracy of nonlinear characteristics in attenuation creep stage and acceleration creep stage and provides the theoretical basis for the stability analysis of rock slopes. [ABSTRACT FROM AUTHOR]

Creep behavior of an as-received, normalized, and tempered 9Cr-1Mo (P 91) steel and its secondary short-term normalized and short-term tempered counterpart at temperatures of 550 °C, 600 °C, and 650 °C, at stresses in the range of 80–260 MPa, has been studied. The secondary heat treatment leads to insignificant coarsening of the prior austenite grains but refines the martensitic lath sub-grains and the grain boundary M23C6 carbides and enhances the dislocation density compared to that of the as-received alloy. Tensile creep tests reveal that the creep life of the secondary heat-treated alloy is several folds higher than that of the as-received alloy. For both alloys, considering the effect of threshold stresses at different temperatures, an effective stress exponent neff of 4.5–5.5, and activation energies of 316.4 and 258.3 KJ mol−1, it indicates that the steady-state creep relaxation mechanism involves dislocation climb and annihilation. Microstructural characterization, before and after the creep tests, reveals that lath sub-grains and M23C6 precipitates in both alloys undergo significant coarsening, with the former leading to microstructural instability at the onset of the tertiary stage of creep. Deformation mechanisms in the steady-state regime are described as a balance between processes that impede and facilitate dislocation motion in the sub-grain interior. The interplay between energy minimization-induced sub-grain coarsening and Zener pinning of the boundaries by M23C6 is discussed in the context of microstructural instability-induced failure. [ABSTRACT FROM AUTHOR]

Gussasphalt is widely used for steel bridge deck pavements, but it is prone to rutting during the operational stage. This paper proposes a finite element-based method for predicting rutting in gussasphalt steel bridge deck pavements. Based on the Nanjing Yangtze River Fourth Bridge project, asphalt mixture specimens were prepared and tested in the laboratory. The viscoelastic-plastic constitutive model was fitted via dynamic modulus test and uniaxial repeated loading creep test results. Wheel track tests were conducted to validate the numerical model. The temperature gradient was obtained using actual environmental data and validated using actual data from buried thermocouples. Based on the equivalent conversion and simplification of traffic loads, the permanent deformation of the pavement layer was calculated using both the viscoelastic-plastic constitutive model and the time-hardening creep constitutive model. The viscoelastic-plastic constitutive model yields an average relative error of 25% and an absolute error of 0.57 mm, while the time-hardening creep constitutive model shows an average relative error of 40% and an absolute error of 1 mm. The results indicate that the viscoelastic-plastic constitutive model can more accurately predict the long-term rutting of the steel bridge deck pavement. [ABSTRACT FROM AUTHOR]

In this research, PET particles at levels of 0%, 3%, 6%, and 9% (by the weight of asphalt binder) were added to asphaltic mixtures containing 0%, 10%, 20%, and 30% of RAP, and then their effects on volumetric and Marshall properties, Indirect Tensile Strength (ITS), creep, and fatigue behaviour were explored. Results demonstrate that Marshall stability increases with RAP addition, but decreases with the introduction of PET particles. While the ITS improves with added RAP, the highest ITS value resulting from PET addition is observed at a 3% PET content. Mixtures containing 20% RAP and 3% PET exhibit the highest resistance against moisture-induced damage. Based on dynamic creep test results, resistance to rutting decreases as PET content increases, whereas it improves with added RAP. Stress-controlled fatigue tests revealed that RAP incorporation enhances the fatigue resistance of mixtures, with this improvement growing alongside higher RAP content. However, PET particles reduce this property. Ultimately, the study's results suggest that RAP materials can offset the negative effects of PET, and with regulated quantities of both PET and RAP materials, asphalt mixtures containing these waste materials can perform comparably to conventional mixtures. [ABSTRACT FROM AUTHOR]

The pursuit of robust research methodologies to forecast the rutting sensitivity of asphalt mixtures and pavements remains a challenge for the industry. An in-depth examination of the rutting behaviour of asphalt mixtures and pavements under varying influencing factors was conducted via indoor experiments and finite element simulations to investigate the evolution of rutting. This study leverages high-temperature test data derived from multiple stress creep recovery tests of asphalt mortar, complemented by pertinent theories (Burgers model) as the constitutive model. At the same time, a contact law is defined based on the thickness of the asphalt binder layer and increases the accuracy of the rutting simulation. Generate random aggregate asphalt mixture and surface layer models using Python scripts in finite element software. The results show that the simulation results are consistent with the experimental results, and the overall measured amplitude on site is lower than the numerical simulation value. Furthermore, the model parameters will be applied to a microscopic pavement model to study the mechanical response and rutting development of pavement structures under thermal-mechanical coupling. The meso numerical simulation method developed in this study serves as an effective tool for unraveling the high-temperature failure mechanism of asphalt mixtures. [ABSTRACT FROM AUTHOR]

The severe service environment of steel bridges put forward strict requirements for the deck pavement, especially the flexibility of paving materials. In this study, a new super tough resin-based concrete (STRC) was introduced and a comparative study of STRC and epoxy asphalt concrete (EAC) performance was conducted. Specifically, the high-temperature stability, low- and intermediate-temperature flexibility, fracture resistance, and fatigue properties were characterised by the dynamic creep test, beam bending test, semi-circular bending test, and semi-circular fatigue test, respectively. According to the results, at 70°C, the cumulative strain after 10,000 cycles of loading is about 2700μϵ and 900μϵ for STRC and EAC, respectively. At −10°C, the maximum tensile strain of EAC is only 2419 μϵ, which is significantly lower than that of STRC (17000 μϵ). For the cracking resistance, STRC exhibits larger total fracture energy, pre-peak and post-peak fracture energies, which indicates the excellent cracking resistance of STRC. Furthermore, the fatigue life and accumulated dissipated energy of STRC are higher than that of EAC. Besides, the tensile strain growth rate of EAC is significantly greater than that of STRC, which implies a lower crack propagation rate and better fatigue resistance of STRC. [ABSTRACT FROM AUTHOR]

The creep behaviour of dissimilar weld joint of 316LN SS-P91 steel when subjected to lower applied stresses (below 100 MPa) generally fails in a Type-IV pattern. The dissimilar weld joint was welded through shielded metal arc welding (SMAW) process with INCONEL as electrode, a nickel-based superalloy. An interrupted creep test was carried out at creep condition of 80 MPa −600 °C temperature. Interruption was done at two stages of creep, i.e. (a) mid of secondary and (b) start of tertiary. Microstructural evolution with respect to the hardness variation along various regions of P91 steel at interrupted and the failed specimen was done. A coarsening of hierarchical boundaries and M23C6 carbides was observed along HAZ region that has resulted with respect to time and temperature. [ABSTRACT FROM AUTHOR]

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This study investigates creep behavior of distribution transformer (DT) winding Western Union splice (WUS) joints with and without the use of solder. The creep strain and contact resistance were measured during the creep test, and the life of aluminum and copper wound DTs were calculated. Improper WUS joint increases resistance and creates hot-spot and sparking, which accelerates the steady-state creep rate of WUS joint along with the winding conductor, ultimately reduces the life of DT. This research contributes to the DT manufacturers and electrical industries by addressing a knowledge gap regarding the optimal number of turns and creep performance of DT winding WUS joints. The aluminum and copper winding WUS joints of 25 kVA DT were prepared using 18 and 14 turns, respectively, which were optimized by performing the tensile test. Creep test of winding joints was performed as per ASTM E139-11. Results exhibited a higher steady-state creep rate and more contact resistance of the aluminum winding WUS joints for elevated temperature and stress conditions. Soldering of WUS joints improved the creep life of aluminum wound DTs and showed a lesser increase in contact resistance during creep. The copper winding WUS joint at 140 °C temperature and 55 MPa stress shows that the creep life for DT is much higher compared to the creep life of DTs due to aluminum winding WUS joints with and without solder. [ABSTRACT FROM AUTHOR]

The reinforcement of cast Cantor's-type high-entropy alloys by MC carbides and their effect on the hot oxidation behavior were investigated. Three equimolar CoNiFeMnCr alloys without or with carbon and with either hafnium or tantalum were elaborated. Their as-cast microstructures were specified. Oxidation tests were carried out in air at 1100 °C. Flexural creep tests were performed at 1100 °C at 10 MPa. The carbide-free CoNiFeMnCr alloy was single-phased. The version with Hf and C added and the one with Ta and C added contained interdendritic eutectic script HfC and TaC carbides, respectively. After oxidation for 50 h at 1100 °C, all alloys were covered by a (Cr,Mn)2O3 scale with various proportions of Cr and Mn. HfO2 or CrTaO4 also formed. Oxidation resulted in a deep depletion in Cr and in Mn in the subsurface. Oxidation is much faster for the three alloys by comparison with chromia-forming alloys. Their bad oxidation behavior is obviously due to Mn and protection by coating is to be considered. The creep deformation of the carbide-free CoNiFeMnCr alloy was very fast. The creep resistance of the two versions reinforced by either HfC or TaC deformed much slower. The addition of these MC carbides led to a deformation rate divided by five to ten times. Now, creep behavior comparisons with commercial alloys are to be conducted. They will be performed soon. [ABSTRACT FROM AUTHOR]

Current designs of sealing systems for non-adhesive flexible pipe end-fittings primarily address short-term loading conditions, often overlooking the creep behavior of polyvinylidene fluoride (PVDF) and the material used in the sealing layer. Over time, the creep of PVDF, particularly at elevated temperatures, can lead to excessive reduction in the sealing layer's thickness, thereby compromising the sealing performance of the end-fittings. In this study, to address the creep-related issues in the sealing layer, the compression and compression creep tests of PVDF were conducted at different temperatures to establish the material's elastic-plastic constitutive relationship and develop a creep constitutive model based on the time hardening model. Using the pressure penetration method within ABAQUS software, a two-dimensional axisymmetric finite element model of the end-fitting sealing system was constructed, incorporating the effects of internal fluid pressure. This model was employed to analyze the sealing performance while accounting for the materials' creep behavior across varying temperature conditions. The results demonstrate that creep in the sealing layer occurs predominantly in the early stages post-installation. Furthermore, the API 17J standard, which stipulates that reduction in sealing layer thickness should not exceed 30%, is found to be conservative at high temperatures. In these conditions, although the thickness reduction exceeds 30% before the maximum contact pressure drops below the fluid pressure, no fluid leakage is observed. Thus, in the initial phase following installation, especially at elevated temperatures, monitoring for potential leakage is critical. This research is the first to quantify the long-term impact of PVDF creep behavior on the sealing performance of flexible pipe end-fittings through comprehensive experiments and simulation analysis. The findings provide both a theoretical foundation and practical guidance for enhancing the long-term sealing performance of flexible pipe end-fittings. [ABSTRACT FROM AUTHOR]

Used engine oil recycling produces acid sludge as a by-product of the acid-clay treatment. It is classified as hazardous waste material. This paper introduces a novel material named PS (powdery sludge) by functionalising the acid sludge. PS was used in a dry method to replace fine aggregates of the asphalt mixture. The effect of adding PS was investigated on the rheological behaviour of asphalt mastics by using dynamic shear rheometer for performing frequency sweep and multiple stress creep and recovery tests, bending beam rheometer, differential scanning calorimetry, and Fourier transforms infrared spectroscopy tests. Adding PS makes the mastic softer at low temperatures and stiffer at high temperatures, causing it up to 5 and 1.38 times more resistant to rutting and fatigue, respectively. Also, PS reduces temperature sensitivity, aging potential, and moisture sensitivity. Therefore, using PS as a replacement for siliceous aggregates in cold, moderate, and tropical regions is recommended. [ABSTRACT FROM AUTHOR]

In the realm of daily life, ensuring the safety of building structures and civil engineering projects remains a paramount research focus. The creep properties of materials significantly influence their long-term loading process. Specifically, creep load and creep time are pivotal factors that impact material creep damage, thereby playing a crucial role in assessing the safety of engineering endeavors and estimating aspects such as housing construction. This study undertakes creep damage tests on cement-based materials, subjecting them to varying creep loads and creep times, and subsequently conducts uniaxial compression tests on the specimens post-creep damage. The refined Nishihara model is employed for data fitting, facilitating the construction of a creep damage time-stress model. Concurrently, a Neural Network model is utilized to validate the experimental data. The findings indicate that both steady-state creep strain and steady-state creep rate exhibit discernible trends relative to creep load and creep time, effectively mirroring the alterations in creep damage experienced by the specimens. The refined Nishihara model proves adept at predicting and equating creep damage under diverse creep loads and creep times. Similarly, the trained Neural Network model demonstrates capability in measuring and estimating various creep damages. The study successfully explored the correlation between creep time and creep load, enabling the simulation of long-term creep damage within a shorter creep time and facilitating an analysis of its physical and mechanical properties, which is pivotal in predicting the safety of large-scale engineering projects. Concurrently, it advances research on material damage equivalence, offering insights and theoretical groundwork for developing a system to assess material damage equivalence under various damage conditions. [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]

The durability of geogrid reinforcement exhumed after 25 years from a sloped wall structure was examined through a comparison of the material properties of exhumed samples with technical data for the original product type. Visual and microscopic inspections found no evidence of installation damage. Analysis of strain increments in rapid loading creep tests to 10 000 h showed excellent agreement between the exhumed and original materials. The results of this study lend confidence in the use of isochronous load–strain–time data for predicting the long-term strain of geosynthetic-reinforced soil structures in design to a serviceability limit state. [ABSTRACT FROM AUTHOR]

Herein, we report a new method of introducing circumferential shear to polypropylene (PP) pipes via a self‐designed rotational shear system (RSS) with the addition of a β‐nucleating agent (TMB‐5). The prepared PP pipes exhibited remarkable enhancement in toughening and tensile strength over conventional PP pipes incorporating 0.025 wt% of the nucleating agent into the sheared sample increased the elongation at break to 243.30%. At 0.05 wt% nucleating agent content, an optimal tensile strength of 40.98 MPa was attained compared to 33.62 MPa for unsheared PP, and the elongation at break also reached 108.09%. In creep tests, the PP pipes prepared with nucleating agents and shear rotation exhibited a minimum displacement of 2.1 mm and the lowest creep rate of 3.23 × 10−5 mm/s. In addition, the samples also showed a high resistance to crack growth compared to conventional PP pipes with a crack initiation time of 24 h and a crack growth rate of 0.08 mm/s. Highlights: Reinforced and toughened PP pipes were prepared using a rotational shear system.The shish‐kebab structure and β‐crystals exhibited a synergistic effect.Both short‐term and long‐term mechanical properties were studied. [ABSTRACT FROM AUTHOR]

The polymer-alloy geocell sheets (PAGS) represent a novel geocell material developed to replace conventional geocell materials. Accelerated creep testing, a convenient and precise performance evaluation method, presents a viable alternative to traditional creep testing for obtaining long-term creep strains. Nonetheless, there is a lack of prediction and in-depth exploration of accelerated creep testing. This paper aims to assess the efficacy of using the non-linear three-component (NLTC) model to simulate the accelerated creep behavior of PAGS. The predictive accuracy of the NLTC model has undergone evaluation through a comparison between stepped isothermal method (SIM) accelerated creep experimental tests and numerical simulations. Subsequently, the validated NLTC model was employed to simulate the time-temperature superposition method (TTSM), time-stress superposition method (TSSM), and stepped isostress method (SSM) accelerated creep tests, thereby verifying its effectiveness in predicting all accelerated creep tests. The results indicate that the NLTC model can effectively simulate creep deformation induced by temperature increases, particularly the temperatures below 41 °C. Although some errors are observed at elevated temperatures, it is within the acceptable range of 17.4%. Numerical simulation results of TTSM, TSSM, and SSM tests also suggest the model's proficiency in simulating the accelerated creep behavior by temperature and creep load increasing. • The accelerated creep behavior of polymer-alloy geocell sheets was investigated through experimental and numerical methods. • The suitability of the non-linear three-component model for simulating accelerated creep behavior was verified. • The non-linear three-component model was utilized to simulate all types of accelerated creep tests. [ABSTRACT FROM AUTHOR]

The aim of the study is to contribute to understanding how prolonged exposure to high temperature and stress affects the morphology, size, and distribution of secondary phase precipitates in Inconel 625 manufactured by laser powder bed fusion. Creep tests were performed under a constant stress of 100 MPa at temperatures of 600 °C, 700 °C, and 800 °C. Samples creep tested at 600 °C and 700 °C were terminated after 2000 hours, while at 800 °C, the creep test was carried out until rupture. Isothermal annealing was carried out at temperatures of 700 °C and 800 °C for the same duration as creep tests. Microstructural analysis of creep-deformed and annealed samples was performed with the use of light microscopy, scanning, and transmission electron microscopy. The first-ever comparison of the evolution of precipitates in Inconel 625 LPBF after creep tests and annealing at 700 °C and 800 °C was shown. The qualitative and quantitative analysis revealed that the stress applied during creep tests leads to more pronounced nucleation of δ phase precipitates, although the growth of δ particles occurs more slowly compared to annealing. Furthermore, in creep-tested samples, the growth and coalescence of carbides and Laves phase particles were more intensive, compared to stress-free annealing, particularly at a temperature of 800 °C. Moreover, we show that the evolution of carbides and Laves phase particles along grain boundaries contributes to cavity and microcrack formation during high-temperature creep of Inconel 625 LPBF. [ABSTRACT FROM AUTHOR]

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Concrete exhibits long-term time-dependent behavior due to creep and shrinkage that impacts the safety and serviceability of high-rise buildings. These rheological effects are difficult to predict due to their random nature, dependence on environmental conditions, and loading history. Current methods include the use of creep and shrinkage tests of structure-specific concrete samples to update compliance and shrinkage, and sophisticated numerical models for prediction of the long-term structural behavior. However, creep and shrinkage tests are time-consuming, and simulation requires reliable numerical models and often proprietary solvers that are not available to the structural health monitoring (SHM) practitioner. Further, uncertainty propagation in complex numerical models is rarely seen in the relevant literature. In contrast, data-driven prediction methods using SHM data and simplified analytical models have shown to be successful for prestressed concrete bridges. In this work, we investigate calibration strategies of creep and shrinkage models using SHM data toward data-driven forecasting of long-term time-dependent behavior of high-rise buildings. A calibration strategy is identified that enables significant and consistent improvement of forecasting of long-term time-dependent behavior. It is also shown that continuous calibration can provide good predictions at least 30 days ahead. First-order analytical uncertainty propagation formulas are also provided. The calibration strategies are evaluated on data from two residential high-rise buildings in Singapore. Recommendations to the SHM practitioners are also given. [ABSTRACT FROM AUTHOR]

The procedure of high-temperature uniaxial сrеер testing for welded joints of “base-deposited metal” made of difficult-to-weld nickel-based superalloys of ZhS32 type, containing more than 60 vol. % of the strengthening γ΄-phase, has been developed. It allows using witness samples to estimate the сrеер strength level at temperatures of 975 and 1000°С for the conditions of restoration of the edges of serial blades of modern aircraft gas turbine engines by micro-plasma powder welding deposition process. Its development took into account the need to go to larger sizes and, accordingly, the higher restraint conditions of the welded workpieces for manufacture of samples for mechanical tests, compared to typical conditions of serial restoration of the blade edge in industry, and some methods for hot cracks prevention were also proposed. Its feature is the use of “dovetail” type grips for samples with the working part of 7.5-9.0 mm2, which allows significantly reducing their size. The proposed approach of choosing the shape and dimensions of the sample, the technique of preparing and forming the welded workpieces necessary for it by micro-plasma powder deposition allows significantly reducing the heat input, bringing the deposition modes of the witness samples closer to the industrial modes of serial restoration of the edges of blades of aircraft gas turbine engines. Due to that, it was possible to avoid the known manifestations of the tendency to crack formation during the deposition process and post weld heat treatment in the welded joints of the “base-deposited metal” of the nickel-based superalloys with directional crystallization, which are the workpieces for subsequent production of such witness samples. The developed procedure was tested to evaluate the creep strength of ZhS32 deposited metal samples and “50% base (ZhS26-VI or Zh32-VI) + 50% deposited (ZhS32) metal” samples at 975°C and 1000°C on the base of 40 hours holding and comparison of the relevant experimental data with the technical condition requirements for these cast nickel-based superalloys. 22 Ref., 3 Tabl., 11 Fig. [ABSTRACT FROM AUTHOR]

Introduction: The finite element modelling for vibrational behaviour of viscoelastic carbon nanotubes -carbon fiber reinforced polymer (CNT -CFRP)-based hybrid skewed shell structures under different hygrothermal conditions has been presented in this article. The carbon fiber as reinforcing phase and modified polymer (CNT dispersed) as matrix phase has been used for the CNT -CFRP hybrid composite material system characterization. Such CNT-CFRP made shell structure were further investigated using finite element modelling for the dynamic analysis. Objective: To investigate the vibrational and damping responses of viscoelastic CNT-CFRP made skewed shell structures under hygrothermal environment. Methods/Formulation: Dynamic mechanical analysis is used to conduct the creep test for nanocomposites (NCs) samples which were fabricated, as per ASTM-D4065 standard. Novel mathematical formulation has been developed utilising the obtained experimental results in strength of materials with rule of mixture for the determination of the viscoelastic properties of CNT -CFRP hybrid composite materials for different stacking sequences. Such obtained viscoelastic properties were used in finite element analysis for the skewed shell structures to evaluate vibrational and damping responses under hygrothermal conditions. The arbitrary coordinate system was considered for defining the skewed shell geometry with SSSS boundary condition, and finite element modelling has been done with Serendipity element with five degrees of freedom in all eight nodes, for Koiter's shell formulation and shape functions using first-order shear deformation theory considering the transverse shear effect based on the Mindlin's hypothesis. The frequency-dependant viscoelastic properties are directly used to obtain the frequency responses of the skewed shell panel employing fast Fourier transform (FFT), whereas the transient responses are determined by using inverse fast Fourier transform (IFFT). Results: It is evident that 8% CNT volume fraction with 45° skewing angle improves modal parameters significantly of the said structures even under severe hygrothermal conditions. Also, it has been observed that the stacking sequence of [− 45/ 45/-45/ 45] omits improved modal parameters compared to the other stacking sequences (i.e. [0/90] and [0/90/90/0]) considered in the study. Finally, it can be concluded that CNT has significant impact on stiffness and damping property of the CNT -CFRP hybrid, thick and thin skewed shell structures, which further can be improved and controlled by the inclusion of effective volume fraction of CNT in a conventional composite, and which is useful in most of the structural applications under the hygrothermal environment. Conclusion: The obtained hygrothermal-dependent viscoelastic properties of such CNT -CFRP material system were further used in different thick (a/h = 10) and thin (a/h = 100) skewed shell structures to determine their vibration and damping characteristics under hygrothermal environment. Parametric study has been carried out for natural frequency, skewing angle, CNT volume fractions and different stacking sequence effects on the vibration behaviour of different geometry of CNT -CFRP hybrid, thin and thick skewed shell structures under different hygrothermal conditions. Results confirmed that 8% CNT volume fraction with 45° skewing angle improves modal parameters significantly of the said structures even under severe hygrothermal conditions. [ABSTRACT FROM AUTHOR]

The impact of 0.5 wt% silver (Ag) addition on the creep performance of the as-cast AZ91 Mg alloy was examined through impression creep tests under stresses between 175 and 700 MPa and temperatures in the range 425–525 K. It was found that creep rates were reduced at all temperatures and stress levels following Ag addition. This improvement in creep resistance can be ascribed to a combination of microstructural modification along with reduction and a more homogenous dispersion of the β -Mg 17 Al 12 intermetallic phase. The effect of Ag on solid solution strengthening, the tendency of Ag atoms to abide on the β -Mg 17 Al 12 phase, and the emergence of the thermally stable Mg 4 Ag particles are regarded as other influential factors. These consequences indicate that Ag is an advantageous alloying element for enhancing high-temperature creep behavior of AZ91 alloy. The creep stress exponents and activation energies acquired for the alloys under investigation were in the range 4.9–6.2 and 92–125 kJ/mol, respectively. The observed reduction in creep activation energy with rising stress levels indicates the competition between two distinct creep mechanisms, namely dislocation climb governed by pipe and lattice diffusion; the former mechanism dominates at high stress levels, while the latter is predominant at lower stress levels. [ABSTRACT FROM AUTHOR]

Australian fast-grown Eucalyptus plantations have traditionally been used for pulp and woodchip production. However, given their large availability, there is a growing interest among researchers to explore their potential for structural applications as solid wood and engineered wood products. Cross-laminated timber (CLT) provides one option for this resource, which is supported by recent research on its reliable mechanical properties. However, due to its orthogonal arrangements of layers, CLT is more susceptible to time-dependent deformation, which is normally called the creep behaviour. Therefore, the investigation on the creep performance of CLT made from Eucalyptus nitens (E. nitens) becomes necessary. Time-independent factors including relative humidity (RH) and temperature of the surrounding environment, play important roles in affecting the creep behaviour of timber, so these factors were also considered in creep tests in this study. Six E. nitens CLT considering different modulus of elasticity (MOE) grades in different layers, and one strength-class C24 spruce CLT were tested in this study as a control. A non-linear mathematical modelling equation was developed based on the 500-day experimental creep results, which was then used to extrapolate the data to predict the longer-term creep behaviour over 50-year. The E. nitens CLT panels incorporating highest-MOE boards in the transverse layers are expected to have the lowest creep ratio (1.397) after 50 years, followed by the CLT panels with highest-MOE boards in longitudinal direction (1.411). However, the E. nitens CLT panels that incorporate the lowest-MOE boards in both longitudinal and transverse directions are expected to have the highest creep ratio (2.193) after 50 years, surpassed the controlled spruce CLT (1.659). This study revealed how different structural grade (modulus of elasticity) in different lamellas influenced the creep ratios under constant applied loads, as well as the long-term creep performance of CLT under varied relative humidity and temperature. • 1.4-year bending creep behaviour of CLT under varied environmental conditions. • Fast-grown plantation hardwood CLT vs traditional softwood CLT. • The influence of timber grade on creep. • Timber performance under load. • Moisture sorption effects on creep. [ABSTRACT FROM AUTHOR]

Many underground mining operations require the design of pillars that their long-term structural integrity under creep loading is essential for sustainable operation of mines and safety of personnel. Characterizing the mechanical behavior of rocks at different shapes over the long-term can assist in efficient design of underground pillars. Over the past 4 decades, a large number of studies have examined the shape effect and long-term behavior of rocks separately, while consideration of these two together is essential. Accordingly, a comprehensive investigation is needed to assess the influence of shape on the mechanical behavior of intact rocks under long term or creep loading. Thus, in this work, an extensive laboratory experiments were conducted on a shaly sandstone, known as “Gosford” sandstone, with various length-to-diameter or “slenderness” ratios under both quasi-static and creep compressive loadings. The uniaxial compressive tests were performed on a number of cylindrical samples with constant diameter of 54 mm and varying slenderness ratios of 0.5, 1, 2, and 4. Also, a set of single and multi-step creep experiments were carried out on the samples with different slenderness ratios. Eighteen cylindrical samples were subjected to single-step creep loading at the slenderness ratios of 1, 2, and 4 and their corresponding instantaneous strains, apparent secondary creep strain rates, axial creep strains at the failure and times to failure were analyzed. The results showed that a decrease in the slenderness ratio led to an increase in the uniaxial compressive strength (UCS) of tested samples under quasi-static loading. Also, under single-step creep loading, the samples with the slenderness ratios of 2 and 4 exhibited classical creep behavior including distinct primary, secondary, and tertiary phases, whereas samples with the 1:1 ratio demonstrated localized failure. The multi-step creep tests endorsed these findings in which, the samples with smaller slenderness ratios resulted in larger cumulative strains and higher apparent secondary creep strain rate at the various creep stress ratios (the ratio of applied stress over the mean UCS). Finally, it was concluded that the resulting failure patterns from the tested samples are highly shape dependent under both quasi-static and creep loading conditions. [ABSTRACT FROM AUTHOR]

To effectively predict and mitigate geotechnical engineering disasters resulting from the utilization of red-stratum mudstone as fill material in high-fill subgrade construction, an in-depth investigation of its creep behavior is essential. In this study, the effects of water content and initial void ratio on the creep behavior of red-stratum mudstone fill material were investigated through a series of scanning electron microscopy (SEM) tests and one-dimensional creep tests. A fractional-order element model and a novel elastic-viscoplastic (EVP) model considering the effect of particle breakage were proposed. The results indicate that upon water immersion, the red-stratum mudstone particles exhibit a rough honeycomb surface with a loose and irregular pore structure, increased microporosity and microcracks, leading to reduced particle strength. The creep process of red-stratum mudstone fill material can be divided into three stages, and the magnitude and rate of creep deformation are positively correlated with the vertical stress. Higher initial void ratios and water contents result in greater creep displacement and longer times to reach steady-state creep. The isochronous stress-strain behavior transitions from nonlinear to linear, reflecting the irreversible deformation mechanisms of particle sliding and breakage, which lead to continuous elastic-viscoplastic deformation of the red-stratum mudstone fill material. A fractional-order element model was proposed, which has a significantly better fitting effect than the classical Burgers model. Furthermore, based on the one-dimensional elastic-viscoplastic (EVP) model, considering the influence of initial void ratio and water content on the secondary consolidation coefficient (φ), and introducing particle breakage and stress-related compression parameter (λ), a novel EVP model was developed. Comparative analysis and validation test data confirm that both the fractional-order element model and the novel EVP model can accurately describe the creep behavior of red-stratum mudstone fill material. • The microstructure characteristics and creep mechanisms of red-stratum mudstone fill material are revealed through a series of scanning electron microscopy (SEM) tests and one-dimensional creep tests. • Unveiled the particle breakage effect of red-stratum mudstone fill material under the hydro-mechanical coupling effect and elucidated the evolutionary laws of the secondary consolidation coefficient. • A fractional-order element model and a novel elastic-viscoplastic (EVP) model considering the effect of particle breakage are proposed. • Both the fractional-order element model and the novel EVP model can accurately describe the creep behavior of red-stratum mudstone fill material. • The microstructural characteristics, macroscopic creep behavior, and constitutive modeling of red-stratum mudstone fill material can reveal the intrinsic mechanisms of deformation in high-fill subgrades. [ABSTRACT FROM AUTHOR]

In this study, the creep tests of three PM Ni-based superalloys with different Zr contents were carried out at 700 °C/780 MPa, 750 °C/550 MPa and 800 °C/400 MPa, respectively. The effect of Zr on creep deformation behaviors was studied by OM, SEM, EBSD and AC-STEM. The results show that the addition of appropriate Zr (0.1 wt.%) inhibits crack initiation and premature cracking, prolongates the creep rupture time, reduces the minimum creep rate, and increases the proportion of steady-state creep duration. However, excessive Zr content (0.5 wt.%) can promote the continuous precipitation of μ, σ, and Ni7Zr2 phases at the grain boundaries, which is easy to become a crack source and reduce the creep performance. In general, the alloy with 0.1Zr addition has high creep strength, low tendency of intergranular cracking at high temperature, and the best overall creep performance. This study provides a theoretical basis for the appropriate addition of Zr in PM Ni-based superalloys and provides some ideas for the optimization of alloy composition and design of novel PM Ni-based superalloys. [ABSTRACT FROM AUTHOR]

In the present work, two β-solidifying γ-TiAl based intermetallic alloys, Ti-43.5Al-4Nb-1Mo-0.1B (TNM) and Ti-43.5Al-6(Nb,Zr,Hf)-0.1B (TNZ) (at.%), have been comparatively studied. Two microstructural conditions per alloy, near duplex and near lamellar, were obtained in the alloys by isothermal upset forging and two-stage heat treatments. Microstructure examination revealed three phases (γ, α 2 and β(β o)) in both alloys but in the TNZ alloy the β(β o) phase content was less than 1 vol% in contrast to the TNM alloy, in which the β(β o) phase content was varied within 4–8 vol%. The near duplex conditions of the alloys were similar, whereas a coarser microstructure was obtained in the TNZ alloy with near lamellar structure. The tensile and creep tests revealed that the brittle-ductile transition in the TNZ alloy occurred at higher temperatures that correlated with an appreciably higher creep resistance of the TNZ alloy as compared to the TNM alloy. In the near lamellar condition, the TNZ alloy showed superior strength at 900–1000 °C as compared to known γ-TiAl alloys (e.g. UTS = 554 MPa at 950 °C). The oxidation resistance of the alloys in the near lamellar conditions was evaluated during exposure at 800 °C for 1000 h. The TNZ alloy showed higher oxidation resistance and thus generally appreciably higher high-temperature capability than the TNM alloy. It has been shown that the fundamental reason for different temperatures of the brittle-ductile transition and different creep and oxidation resistance of the alloys is the enhanced thermal stability of the microstructure of the TNZ alloy compared to the TNM alloy. [Display omitted] • Engineering TNM and recently designed TNZ γ-TiAl based alloys were investigated. • Near duplex and near lamellar conditions were obtained in the alloys. • Mechanical properties and oxidation resistance of the alloys were studied. • The TNZ alloy showed superior high-temperature capability. • Doping of the TNZ alloy provided improved thermal stability of microstructure. [ABSTRACT FROM AUTHOR]

In this study, hourly three-minute creep testing is used to elucidate the evolution of the viscoelastic behavior of cement pastes produced with ordinary Portland cement (OPC), limestone Portland cement (LPC), and limestone calcined clay cement (LC3), from 1 to 7 days after production. An innovative test evaluation protocol, accounting for shrinkage, is used to identify values of the elastic modulus, the creep modulus, and the creep exponent, without making assumptions. The S-shaped shrinkage evolution of the LC3 paste is explained by Portlandite dissolution and the associated redistribution of chemical shrinkage-induced compressive stresses to the remaining solid skeleton. The evolution of the elastic stiffness of the LC3 paste is explained by space filling by C-A-S-H phases. The small creep compliance of the LC3 paste is explained by C-A-S-H which creeps less than C-S-H, and by AFm phases which precipitate in nanoscopic slit pores between C-S-H structures, gluing viscous interfaces. [ABSTRACT FROM AUTHOR]

This study investigates the viscoelastic and fatigue performance of in-situ asphalt mortar under various aging conditions, utilizing the multiple stress creep and recovery test combined with energy-based methods. The objective is to analyze the stress-strain responses and energy dissipation characteristics of asphalt mortars from surface, middle, and bottom pavement layers. Hysteretic curves were constructed for each mortar, and both energy dissipation (enclosed area) and slope (the reciprocal of the unloading slope) were calculated. Results indicate as service life extends, the hysteresis curves shift leftward, and the enclosed area decreases, signifying a decline in performance. For a given type of mortar, prolonged service results in a leftward shift of the curves and a reduced enclosed area. Both the dissipated energy and the slope exhibit degradation with increased service age. Notably, this degradation is more pronounced in surface layer, which show greater decay than middle and bottom layer. The middle layer's aging rate is less than 54 % of the surface layer's characterized by dissipated energy and slope, suggesting slower aging dynamics and better long-term durability for the middle and bottom layers. Both dissipated energy and slope are effective indicators of asphalt pavement degradation. However, the 69 % decay difference in slope for the surface layer offers a more sensitive compared to the 2 % decay difference in dissipated energy. This work highlights the utility of MSCR and energy-based methods in evaluating the long-term performance of asphalt pavements. • Using energy dissipation analysis for MSCR to evaluate the viscoelastic and fatigue properties of aged asphalt mortar. • Suitable indicescan characterize field aging effects in pavement layers on asphalt mortar scale. • Accurate assessments of aged material performance enhance sustainable pavement management and reduce maintenance costs. [ABSTRACT FROM AUTHOR]

A new testing technique is developed as an index creep device for evaluating time-dependent responses of rocks. Rock samples from Çankırı, Tuzköy in Nevşehir and Kağızman in Kars Provinces of Türkiye and Oya tuff from Tochigi Prefecture in Japan with well-studied time-dependent properties are selected for index creep tests. The impression creep devices developed are capable of applying tip pressure up to 433 MPa for an indenter of 3 mm in diameter for index creep testing technique. Experimental results obtained from impression creep tests are compared with those from conventional creep tests and the suitability of impression creep tests as an index creep test is explored. The most critical issue in creep tests is the determination of stress level. This issue is investigated through experimental, theoretical and numerical methods. It is proposed that the short-term impression test can be utilized for determination of the stress level in impression creep tests. The experimental results clearly demonstrated that both conventional creep and index creep tests are quite comparable and similar type responses are observed and it is concluded that the impression creep technique can be utilized as an index creep test. [ABSTRACT FROM AUTHOR]

Numerous incidents and failures of bank slopes are caused by the creep behavior of sliding zone soil. During reservoir regulation, the pore water pressure in the sliding zone undergoes cyclic changes. Under such complex cyclic hydraulic conditions, the creep behavior may differ from that under the monotonic seepage condition, which is still poorly understood. In this paper, the Majiagou landslide in the Three Gorges Reservoir area is taken as a case study. Triaxial creep tests were first carried out to study the creep behavior of the sliding zone soil specimen under cyclic seepage pressure. Then, the nonlinear Burgers creep model was proposed to characterize the observed creep behavior of the sliding zone soil specimen, and the secondary development was performed based on FLAC3D software. Finally, the proposed model was applied to the Majiagou landslide to simulate its deformation under fluctuating reservoir water levels. The following results were obtained: (1) Under low deviatoric stress levels, cyclic seepage pressure causes the creep strain curve to fluctuate significantly. The decrease of seepage pressure leads to a reduction in pore pressure, resulting in a sharp increase in the strain rate of sliding zone soil. (2) The proposed model can well reflect the creep characteristics of sliding zone soil under cyclic seepage pressure. (3) During reservoir operation, the landslide deformation exhibits a step-like growth, and the proposed creep model can effectively simulate the retrogressive deformation characteristics of the Majiagou landslide. The research results provide the theoretical basis for the long-term stability of reservoir landslides under fluctuating water levels. [ABSTRACT FROM AUTHOR]