Creep Data Research Articles

Effects of supercritical CO2 on viscoelastic properties of shales

Laboratory uniaxial compression creep tests, with differential stress of 30 MPa hold for 3 h, were performed on Chang-7, Longmaxi (LMX) and Barnett shales to study the influence of SC-CO 2 on short-term viscoelastic properties. To this end, the wet shale samples were treated with SC-CO 2 with a pressure of 30 MPa and a temperature of 110 °C for 14 days. We analyzed the creep data using the fractional Maxwell model. To investigate microscopic structural alterations, the surface morphology of the same location, before and after SC-CO 2 -water exposure, was examined by SEM images. Compared with dry shales, dynamic and static elastic moduli decreased by up to 25.02% and 55.83%, respectively, but the creep deformation increased by 200% for LMX and Chang-7 shales, and 500% for the Barnett shale treated by SC-CO 2 . Compared to dry sample, there is an increase in calculated fractional orders of 0.02, 0.07, 0.22 for SC-CO 2 treated samples, indicating that SC-CO 2 treatment is likely to enhance shale creep. SEM investigation confirmed physicochemical mechanisms responsible for the observed elastic damage and creep enhancement, including mineral dissolution and swelling caused by SC-CO 2 . This work would further improve our current understanding of the time-dependent deformation of shale under chemical-mechanical coupling effects during CO 2 capture utilization and storage.

Microstructural evolution mediated creep deformation mechanism for the AlCoCrFeNi2.1 eutectic high-entropy alloy under different testing conditions

The AlCoCrFeNi2.1 high-entropy alloys (HEAs) with a unique eutectic microstructure of soft L12 and rigid B2 exhibit outstanding mechanical performance at both ambient and high temperatures. However, their high-temperature creep data are not available, which restricts their industrial application under extreme environments. For this, the current work investigated the effect of microstructural evolution on the creep behavior and deformation mechanism of the AlCoCrFeNi2.1. The creep tests were performed at 700–900 °C with a stress ranging from 0.2 to 0.6 times of the high-temperature yield strength. Detailed microstructural examination and theoretical analysis were conducted to explore the creep mechanism. The results showed that the precipitation behavior was responsible for the accelerated steady creep-strain rate and reduced creep life when performed at 800–900 °C, compared to 700 °C. The creep deformation mechanism and fracture behavior at 800–900 °C were also found to exhibit discrepancy with those at 700 °C, with the aid of calculating the stress exponents, activation energies, Larson-Miller and Orr-Sherby-Dorn parameters. Based on the creep data and microstructural examination conducted, the predominant creep deformation mechanism was uncovered for different testing conditions. The current work performed will be beneficial to understand the high-temperature deformation behavior of the AlCoCrFeNi2.1 EHEAs. The basic data acquired will also offer a guarantee for the application of EHEAs.

The mechanical behavior of metal-halide perovskites: Elasticity, plasticity, fracture, and creep

Wide ranging mechanical properties — elasticity, plasticity, fracture, and creep — most relevant to the mechanical reliability of perovskite solar cells (PSCs) are systematically investigated. High quality bulk single-crystals of the commonly studied metal-halide perovskites (MHPs) relevant to PSCs are fabricated and studied: CH3NH3PbBr3 (MAPbBr3) and CH3NH3PbI3 (MAPbI3). The first direct measurement of MHP Young's modulus (E) using uniaxial compression reveals E<100> of 13.1 ± 1.3 and 10.6 ± 1.0 GPa for MAPbBr3 and MAPbI3, respectively. The Vickers micro-hardness H(100) of MAPbBr3 and MAPbI3 is 0.54 ± 0.02 GPa and 0.76 ± 0.05 GPa, respectively. The Vickers micro-indentation fracture toughness KIC of MAPbBr3 and MAPbI3 is estimated at 0.20 ± 0.03 MPa⋅m0.5 and 0.18 ± 0.03 MPa⋅m0.5, respectively. The stress-exponent, n, extracted from nanoindentation creep data is ∼8 and ∼10 for MAPbBr3 and MAPbI3, respectively. The trends in these properties are discussed. These properties are best estimates and are recommended for use in future mechanical behavior and reliability analyses of MHPs and PSCs.

Modified version of Monkman-Grant equation for Gr.91 by incorporating “strain to minimum creep rate” parameter

A modified version of the Monkman-Grant equation, which can provide a more accurate means of predicting creep rupture life than the standard Monkman-Grant formula, has been investigated for Gr.91 using creep data in the NIMS Creep Data Sheets at 450–725 °C. The maximum time to rupture tr was 1.2 × 105 h. The tr versus minimum creep rate ε˙min plot, which is called the Monkman-Grant relation, deviates downward at low stresses and long times. The difference between the maximum and minimum tr at a same ε˙min becomes more significant with decreasing stress and increasing test duration. Better correlation of the tr with the ε˙min is not obtained by the replacement of tr with (tr/εr), where εr is the total or rupture strain. The magnitude of data scattering is larger in the (tr/εr) versus ε˙min plot than in the tr versus ε˙min plot. The (tr/εm), where εm is the strain to minimum creep rate, is inversely proportional to the ε˙min over a wide range of stress, temperature and test duration and the magnitude of data scattering is only a little bit even at low stresses and long times. The (tr/εm) versus ε˙min plot gives us more reliable relation for Gr.91 than the tr versus ε˙min and (tr/εr) versus ε˙min plots.

An integrated unified elasto-viscoplastic fatigue and creep damage model with characterization method for structural analysis of nickel-based high-temperature structure

This paper proposes an integrated unified elasto-viscoplastic fatigue and creep damage model with modified hardening equations to simulate the elasto-viscoplasticity, primary-secondary and tertiary creep, relaxation, cyclic softening, temperature-dependency, and creep-fatigue interaction (CFI) damage. For this purpose, we integrate the creep damage and fatigue damage model into the viscoplasticity-damage model to predict tertiary creep and cyclic softening behavior caused by creep and fatigue damage modes. Interaction effects between each damage mode are considered by the creep-fatigue interaction (CFI) damage scheme. This paper also introduces a genetic algorithm-based integrated characterization method that can effectively optimize material input parameters of the unified elasto-viscoplastic-damage material model with limited experimental data. Implicit Euler's backward iteration scheme is adopted to improve the convergence and accuracy of solutions. The proposed material model is implemented in UMAT for finite element (FE) analysis of high-temperature structures under cyclic-dwell loading. Experimental data of tensile, dwell, creep, and cyclic loading at various temperatures are used to verify the model. Finally, full-scale turbine blade FE analysis is performed under anisothermal conditions. The proposed material modeling framework can also be utilized for other high-temperature structures, such as power plants, leading-edge nose cones, etc.

Nanoindentation creep behavior of diverse microstructures in a pre-strained interstitial high-entropy alloy by high-throughput mapping

Time-dependent plastic deformation, also known as creep, can occur in high-melting-point materials at room temperature when subjected to submicron plastic contact (e.g., components in micro-electronic mechanical systems) due to the extremely high stress conditions. Previous investigations of creep behavior at submicron scale mainly focus on uniform microstructures, whereas recently developed high-performance structural materials usually show complex microstructural heterogeneities. Here, we demonstrate a high-throughput nanoindentation approach to unveil the creep behavior of locally diverse microstructures, via a case study on an interstitial high-entropy alloy (iHEA). The prototype iHEA specimen was firstly pre-strained by severe cold-rolling to achieve diverse microstructure features including dense dislocations, nanotwins and nanograins. Nanoindentation mapping with 144 indents is conducted to collect creep data from all types of diverse microstructures, followed by systematical calculations based on power-law analysis. Then intuitive contour maps of nanohardness (H), strain rate (ε˙) and stress exponent (n) are attained. The individual creep mechanism of each microstructure variant is evaluated by correlating local microstructure features with corresponding creep responses from these contour maps. With the increase of n value for different sample regions, the ε˙ value inversely reduces and the corresponding dominant creep mechanism gradually converts from diffusion-mediated mode to dislocation-controlled one. The presence of nanograins and nanotwins significantly hinders dislocation interactions and promotes stress-induced diffusion. This work verifies that nanoindentation creep behavior is highly correlated with local microstructure features, and the mapping approach is feasible for evaluating creep-resistance of locally diverse microstructures under extremely high-stress conditions.

Brittle Creep and Failure: A Reformulation of the Wing Crack Model

AbstractWe propose a reformulation of the wing crack model of brittle creep and failure. Experimental studies suggest that the mechanical interactions of sliding and tensile wing cracks are complex, involving formation, growth, and coalescence of multiple tensile, shear and mixed‐mode cracks. Inspired by studies of failure in granular media, we propose that these complex mechanical interactions lead to the formation of micro shear‐bands, which, in turn, develop longer wing cracks and interact with a wider volume of rock to produce larger shear bands. This process is assumed to indefinitely continue at greater scales. We assume that the original wing crack formalism is applicable to micro shear‐band formation, with the difference that the half‐length, a, of the characteristic micro shear band is allowed to increase with wing crack growth. In this approach, the functional relationship of a with the wing crack length l embodies the entire process of shear band formation, growth and interaction with other shear bands and flaws. We found that the function a(l)/a(0) = 1 + (l/λ)q, where λ and q are constant parameters, generated creep curves consistent with published creep data of rocks. Similar accord was also obtained with experimental brittle failure data. Furthermore, we found that the Mohr‐Coulomb behavior emerged from our model, allowing estimation of the cohesion and angle of internal friction in materials for which λ and q are independently known.

Design of a new 11Cr martensitic steel and evaluation of its long-term creep rupture strengths

A new grade of 11 wt% Cr steel was designed in which no nitrogen was added to minimise the driving force of the Z-phase formation and hence to maximise the stability of the fine MX precipitate particles. But, 6 wt% Co was added to completely suppress the δ-ferrite formation in the matrix. The creep data were measured in the range of 650–725 °C at different stresses and rationalised on the basis of a new creep model, which revealed that the effect of stress on creep was equivalent to that of temperature. The model parameters so determined was used to predict the 100,000 h creep rupture strengths. The results showed that these long-term creep rupture strengths were higher than those for the P92 Steel, which is a 9 wt% Cr and the strongest steel grade among commercial 9–12 wt% Cr steels at present. The reliability of the long-term creep rupture strength predictions for the new steel is also analysed.

Influence of loading history on creep behavior of rock salt

Creep is a vital factor that affects the long-term stability of gas storage salt caverns. When we conduct a laboratory creep test of rock salt, compared with the single-stage loading method, the multi-stage loading method is used more frequently as it eliminates the discreteness of the sample. However, the early loading history affects the later creep behavior when the multi-stage loading method is used. To study the influence of loading history on the creep behavior of rock salt, the multi-stage loading triaxial creep test of rock salt and synchronous acoustic emission test were performed. Then, the numerical sample is established based on the laboratory test results and the discrete element numerical simulation is carried out. Single-stage loading and multi-stage loading creep tests were carried out on the initial numerical samples, respectively. Finally, the multi-stage loading data processing methods were compared using numerical simulation data. The results indicate that: (1) the improved multi-stage loading data processing method works well and it is recommended to use this method to process the multi-stage loading creep data. (2) Cracks are more developed in multi-stage loading sample, which experienced an early loading history, than in samples under single-stage loading. The damage accumulation in rock salt leads to its mechanical properties deterioration, which makes the creep deformation more prone to occur in the later stage. (3) The steady-state creep rate of rock salt is independent of loading history, only related to stress and temperature. The effect of damage accumulation in the loading history is mainly reflected in the transient strain and the strain in the transient creep phase. The study is helpful to further understanding the influence of loading history of rock salt on its creep, and provides an important basis for the design, construction, and operation of gas storage salt caverns.

Characterization of creep properties and the microstructure of a service-exposed low alloy CrMoV steel steam pipe

The effect of service degradation on the microstructure and creep properties of a 0.5%Cr-0.5%Mo-0.3%V steel steam pipe after an accumulated service time of 77,900 h was investigated and analysed. For comparison purposes, additional experiments and analyses were carried out on the same pipe in the as-received (service unused) conditions. The results of the microstructural analysis and the short-term creep testing confirmed that the high creep resistance of the investigated steel is caused predominantly by the dispersion of fine vanadium carbides, providing an effective precipitation hardening of the steel matrix. However, the microstructure is not in an equilibrium state, and as the size of the vanadium carbides and the accompanying mean interparticle spacing increase during the creep, the detrimental effect of vanadium carbide coarsening leads to a significant weakening in the precipitation hardening and, consequently, a decrease in the creep resistance. No creep cavitation was observed in the service-exposed steel. The short-term creep testing of the service-exposed and unused states of the steel was carried out in the power-law (dislocation) creep regime. Analysis of the creep data did not reveal any change in the operating creep deformation mechanisms as a response to the structural processes occurring during the long-term service. Instead, changes in the kinetics of creep flow and fracture were found.

Viscoelastic Influence on the Board Level Assessment of Wafer Level Packages Under Drop Impact and Under Thermal Cycling

Abstract Structural components such as printed circuit boards (PCBs) are critical in the thermomechanical reliability assessment of electronic packages. Previous studies have shown that geometric parameters such as thickness and mechanical properties like elastic modulus of PCBs have a direct influence on the reliability of electronic packages. Elastic material properties of PCBs are commonly characterized using equipment such as tensile testers and used in computational studies. However, in certain applications viscoelastic material properties are important. Viscoelastic influence on materials is evident when one exceeds the glass transition temperature of materials. Operating conditions or manufacturing conditions such as lamination and soldering may expose components to temperatures that exceed the glass transition temperatures. Knowing the viscoelastic behavior of the different components of electronic packages is important in order to perform accurate reliability assessment and design components such as PCBs that will remain dimensionally stable after the manufacturing process. Previous researchers have used creep and stress relaxation test data to obtain the Prony series terms that represent the viscoelastic behavior and perform analysis. Others have used dynamic mechanical analysis in order to obtain frequency-domain master curves that were converted to time domain before obtaining the Prony series terms. In this paper, nonlinear solvers were used on frequency domain master curve results from dynamic mechanical analysis to obtain Prony series terms and perform finite element analysis on the impact of adding viscoelastic properties when performing reliability assessment. The computational study results were used to perform a comparative assessment to understand the impact of including viscoelastic behavior in reliability analysis under thermal cycling and drop testing for Wafer Level Chip Scale Packages.

A general steady-state creep model incorporating dislocation static recovery for pure metallic materials

In this work, a mechanistic steady-state creep model is proposed for pure metallic materials to characterize the evolution of macroscopic creep strain rate as a function of the testing temperature and applied stress. Dislocation-dominated and diffusion-dominated creep are both addressed in the developed creep model, which is able to effectively characterize the phenomena of “first-power-law” creep, “five-power-law” creep and “power-law-breakdown” creep. Thereinto, the dislocation-dominated creep behavior is systematically analyzed by considering the evolution of dislocations, which includes dislocation multiplication, strain-rate dependent dynamic recovery and time-related static recovery. Main attentions are focused on the description of dislocation static recovery that covers the annihilation of dislocations induced by the creep mechanisms of dislocation climb and thermally related dislocation glide during the long term plastic deformation. A novel form of the dislocation mobility is deduced that not only considers the effect of dislocation climb and glide, but also takes into account the contribution of mechanical work on atomic diffusion. Moreover, the latter is noticed to be the dominant reason resulting in the transition from “five-power-law” creep to “power-law-breakdown” creep. In order to verify the developed model, creep data of six metallic materials with different crystalline structures is considered to compare with the theoretical results. Good agreement is achieved for all these data over a wide range of temperature and stress, which indicates that the model can well characterize the deformation behavior during the steady-state creep stage. In addition, the contribution of dislocation multiplication, dynamic recovery and static recovery to the evolution of dislocation density is further discussed at different temperatures and stresses, which can facilitate the comprehension of the fundamental creep mechanisms of metallic materials.

An advanced mean field dislocation density reliant physical model to predict the creep deformation of 304HCu austenitic stainless steel

Physical based creep modelling enables to understand the life-limiting factors that are required for a safe and economic operation of power plant components. Thus, herein an improved physical approach to address the creep behavior of 304HCu austenitic stainless steel is presented. This approach combines a dislocation density reliant physical model with a continuum damage mechanics (CDM) model. Two different dislocation densities: mobile and forest, and dislocation mean free path are used to describe the substructure in order to model the creep strain. The original Orowan’s equation for estimating creep strain rate is modified employing CDM based softening parameters to take account of damage causing tertiary creep. The model is advantageous in the sense that with the ongoing creep, the evolution of different variables that are dislocation densities, dislocation mobility, dislocation velocity, internal stress, effective stress and damage evolution is tracked and discussed thoroughly. Furthermore, the model output is corroborated with experimental creep data of 304HCu steel. The predicted values of forest dislocation density, mobile dislocation density, mean free path, internal stress, effective stress, dislocation mobility and dislocation velocity are in the range of 7.91 × 1011 – 1.01 × 1013 m−2, 8.16 × 1010 – 4.56 × 1011 m−2, 9.35 – 9.80 µm, 11.70 – 35.50 MPa, 86.0 – 165.0 MPa, 1.68 × 10−9 – 2.11 × 10−7 Pa−1s−1 and 6.48 × 10−11 – 7.45 × 10−9 m/s, respectively, at the end of simulation.

Impression creep behavior of different zones in friction stir welded ZE41 magnesium-rare earth alloy

The ability of the impression tests to obtain localized creep data is exploited to study the creep behavior of the friction stir welded (FSWelded) joints made on 15 mm thick plates of ZE41 magnesium alloy. The three zones of the FSWelded joint, Nugget zone (NZ), Thermo-Mechanically Affected Zone (TMAZ), and Heat Affected Zone (HAZ), were divided into ten different parts and their local steady-state creep behavior was studied. Impression tests were carried out at stresses of 350, 400, and 450 MPa and temperatures of 513 K, 533 K, and 553 K. Optical and SEM micrographs were used to study the microstructure of various zones of the FSWelded joint both before and after the impression test. Power law was used to obtain the creep exponent (n) and activation energy (Q) for different parts of the weld and the weld zones as a whole. The creep exponent was found to vary from 3.6 to 10.45 and the activation energy from ∼81 kJ/mol to ∼226 kJ/mol. The creep rate was found to vary between the upper and lower surfaces of the weld zones and also among the advancing and retreating sides. The weak zone was found to be temperature-dependent and varied when the temperature or stress changes. Within the parameters studied, the lower part of the TMAZ on the AS showed poor creep resistance at a lower temperature, while the lower part of TMAZ on the RS showed poor creep resistance at higher temperatures. The upper part of the TMAZ on the RS showed better creep resistance throughout the range of temperatures studied. To rationalize the high n and Q values, the threshold stress approach and the Eyring relationship were adopted. Using the threshold approach, creep exponents of 4.87 and 5.17 were obtained for TMAZ and HAZ, respectively. Using Eyring hyperbolic sine relationship, single activation energies of 143.5 kJ/mol and 261.5 kJ/mol were obtained for TMAZ and HAZ, respectively. Based on the obtained n and Q values, it is proposed that two mechanisms, namely climb and cross-slip of dislocations, are operative in the creep of the ZE41 FS weld joint. However, the dominant/rate controlling mechanism could not be arrived at conclusively.

Accelerated qualification of creep-resistant materials using a datum temperature method (DTM) to calibration

In this study, the datum temperature method (DTM) is applied to the Wilshire-Cano-Stewart (WCS) model to predict rupture time, minimum-creep-strain-rate, and creep deformation. The datum temperature method (DTM) is an alternative calibration approach that can be applied to existing models to improve accuracy and extrapolation reliability. The availability of creep data is limited due to the time and costs associated with testing. Often data is not available at desired operating conditions or creep life. Although accelerated testing methods have been developed, there is still a need to extrapolate creep data to conditions of interest. Conventional time-temperature-parametric (TTP) models have been used but the need for a decision which TTP model to use for specific materials, the point of convergence, and the inflection points limit their applicability. As an alternative, the DTM is proposed, where all data is transferred to a datum temperature for ease of calibration. In this study, the DTM is combined with the novel continuum damage mechanics based WCS model. To accomplish this, a single heat of alloy P91 from the National Institute of Material Science (NIMS) is considered and the WCS model is calibrated by DTM, and post-audit validated using the remaining heats of materials and an additional creep deformation dataset from Kimura. This calibration approach allows the model to predict rupture, minimum-creep-strain-rate, and creep deformation from a single datum temperature and single heat. It is found that DTM can significantly reduce the time for materials qualification and effort needed for model calibration.

High-temperature creep properties of 9Cr-ODS tempered martensitic steel and quantitative correlation with its nanometer-scale structure

ABSTRACT The Japan Atomic Energy Agency (JAEA) has been developing 9Cr-oxide dispersion strengthened (ODS) tempered martensitic steel (TMS) as a candidate material for use in the fuel cladding tubes of sodium-cooled fast reactors (SFRs). The creep property is essential for the fuel cladding tube of SFR; the reliable prediction of in-reactor creep-rupture strength is critical for implementing the 9Cr-ODS TMS cladding tube in the SFR. This study investigated the quantitative correlation between the creep properties of 9Cr-ODS TMS at 700°C and the dispersions of nanosized oxides by analyzing the creep data and the material’s nanostructure. The possibility of deriving a formula for estimating the in-reactor creep properties of 9Cr-ODS TMSs based on an analysis of the nanostructure of neutron-irradiated 9Cr-ODS TMSs was also discussed. The creep properties of 9Cr-ODS TMS at 700°C closely correlated with the dispersion of nanosized oxide particles. The correlation between creep-rupture lives and nanosized oxide particle dispersion in 9Cr-ODS TMS was determined using existing creep models. The elucidation of correlation between the stress exponent of secondary creep rate and the nanostructure is essential to enhance future modeling reliability and formulation.

Application of a modified hyperbolic sine creep rate equation to correlate uniaxial creep data vs. stress and temperature for creep resistant low chrome steel alloys

ABSTRACT Modified hyperbolic sine minimum creep rate equations were used to correlate uniaxial minimum creep strain rate data of 1/2Cr-1/2Mo-1/4 V and Grade 22 steel alloys and to correlate creep life data of Grade 22 steel when coupled with the Monkman-Grant equation. Hyperbolic sine equations were selected because of their physical basis in dislocation creep and numerical stability. Both equations provided very good fits to minimum strain rate data over a wide range of temperatures and stresses. Reasonable correlations of a large Grade 22 creep life data set were obtained with goodness of fit nearly equivalent to those obtained with the Larson-Miller and Wilshire equations, and with more conservative predictions of long-term creep strength. However, all these equations provided a poor fit to the entire data set when only short-term data (tr < 5,000 h) were correlated, and they predicted lower long-term creep rupture strengths vs. the full data set correlations.

Effect of Post-Processing Heat Treatments on Short-Term Creep Response at 650 °C for a Ti-6Al-4V Alloy Produced by Additive Manufacturing

Post-processing heat treatments of Ti-6Al-4V parts produced by additive manufacturing are essential for restoring the peculiar martensitic structure that originates from the extremely high cooling rates typical of this technology. In this study, the influence of a 1050 °C annealing on a Ti-6Al-4V alloy, produced by additive manufacturing, on the minimum creep rate dependence on applied stress and temperature, was investigated at 650 °C. Experimental data obtained after two different subcritical annealings were also considered for comparison purposes. The analysis of the experimental creep data demonstrated that the alloy annealed at the highest temperature exhibited lower creep rates. The improved creep response was attributed to the combined effect of the presence of extended α-β interfaces and of a small volume fraction of Ti3Al particles.

Creep Life Prediction of 10CrMo9-10 Steel by Larson-Miller Model.

Creep is defined as the permanent deformation of materials under the effect of sustained stress and elevated temperature for long periods of time, which can essentially lead to fracture. Due to very time-consuming and expensive testing requirements, existing experimental creep data are often analyzed using derived engineering parameters and models to predict and find the correlations between creep life (time to rupture), temperature and stress. The objective of this study was to analyze and compare different numerical algorithms by using the Larson–Miller parameter ( extrapolation model. Calculations were performed using the classical equation where different values of parameter were selected, as well as using a modified equation in which parameter was stress dependent . The impact of two different approaches of extrapolation and correlation functions (linear and polynomial) applied to fit the model was also investigated. A detailed analysis was performed to choose the best extrapolation fit function and error tolerance. The numerical algorithm implemented was validated through creep rupture testing performed on 10CrMo9–10 steel at 600 °C (873 K) and 80 MPa. Creep model behavior analysis proved that different values of can significantly change the estimated time to rupture. An excellent response of the model was obtained by considering polynomial dependency when parameter was assumed to be 18, especially for the temperature range from 773 to 873 K. Promising results were also achieved when parameter was taken as stress-dependent, but only for linear fitting, which requires further analysis. However, at validation stage it turned out that only the linear extrapolation function and taken as a constant value provided adequate time-to-rupture prediction. In the case of = 18, estimated time was slightly overestimated (~8%) and for = 20 it was underestimated by 27%. In all other cases error largely exceeded 50%.

Study on Shear Creep Characteristics and Creep Model of Soil-Rock Mixture Considering the Influence of Water Content

Water content has a significant effect on the creep properties of soil-rock mixtures (SRM). Multi-loading shear creep tests are carried out on SRM samples with different water contents. The test results show that deformation gradually increase with increasing water content, while long-term strength gradually decrease with increasing water content. The deformation mechanism shows that increasing of water content causes the change of rock particles at on the shear surface from fracture to rotation. Based on the creep test results, a modified Burgers model considering the water content is proposed by the empirical relationship between the parameters of the traditional Burgers model and the water content. And the results predicted by the modified Burgers model agree well quite well with the experimental creep data.