Stage Of Creep Deformation Research Articles

Viscoelastic creep model and parameter inversion of bond interface in steel plate reinforced tunnel lining

The interface filler material (epoxy resin) used for reinforcing tunnel linings with steel plates exhibits time-dependent mechanical properties, commonly referred as creep behavior. The creep behavior of the filler material will significantly influence the long-term service performance of the reinforced tunnel, especially considering the design service life scale of 100 years. This paper presents an experimental test and mathematical modelling to illustrate the creep mechanical behavior of bond interfaces within shield tunnels reinforced with steel plates. It was observed that in the initial moments of stress application, the bond interface demonstrates an instantaneous response through elastic strain and on-set of creep deformation stage at maximum stress value. Three stages can be characterized in the creep deformation process: the decay creep stage, the steady-state creep stage and the accelerated creep stage. In the accelerated creep stage, the bond interface rapidly deteriorated after experiencing 90 % of the ultimate shear stress for 186 hours or 90 % of the ultimate tensile stress for 96 hours. Based on the fractional-order calculus theory and drawing inspiration from the modeling principles of classical component combination models, a constitutive equation that accurately characterizes the creep mechanical behavior of the bond interface between steel plates and concrete linings was formulated. The model parameters are inversely computed using the principle of least squares and the accuracy of this model is validated through a comparison with the results of the creep tests.

Damage creep model of viscoelastic rock based on fractional derivative and experimental verification

Exploring the creep law of sandstone provides a theoretical basis for evaluating the long-term stability of geotechnical engineering projects in red beds. Based on a conventional triaxial test of sandstone, a progressive loading triaxial creep test is conducted. The deformation characteristics and laws of each sample in different deformation stages are summarized, and the laws relating steady creep rate, stress and time are analyzed. On this basis, a nonlinear viscoelastic‒plastic creep model based on fractional derivative theory and damage theory is established. According to the nonlinear fitting results, the parameter sensitivities are analyzed. The results verify the rationality of the model; this model has a good fitting effect for each creep deformation stage, especially for the accelerated creep stage. The constitutive relationship of the model is simple, clear and easily applicable. The research results provide a reference for studying the long-term stability of geotechnical engineering projects.

Deformation Characteristics and Stability Prediction of Mala Landslide at Miaowei Hydropower Station under Hydrodynamic Action

In recent years, with the completion of the construction of large-scale hydropower projects in China, a series of engineering geological problems that occurred during the operation of the hydropower station have become an important issue affecting the normal operation of hydropower stations. Landslides on reservoir slopes triggered especially by water storage and other factors related to the construction of hydropower stations seriously affect the normal operation of the hydropower station and lead to other geological disasters. Research indicates that many reservoir-area landslides are triggered by hydrodynamic forces resulting from water level fluctuations in hydroelectric power stations. The Mala landslide of Miaowei Hydropower Station in the Lancang River Basin of China is taken as the engineering example to study the influence of hydrodynamic forces on the deformation characteristics and stability trends of the landslide. This paper explores the formation mechanism and influencing factors of the Mala landslide by conducting a field investigation of the Mala landslide and analyzing the monitoring data. Additionally, this paper also discusses the impacts of water storage, rainfall, and engineering construction on landslide induction. It is considered that the evolution of the Mala landslide from the initial stage of water storage to the current state mainly includes four stages: small-scale bank collapse stage, creep deformation stage, accelerated sliding stage, and uniform sliding stage. Moreover, the changes in the trend of landslide stability are analyzed using the two-dimensional finite element method. The research results provide a valuable reference for understanding the formation mechanism and predicting the deformation of reservoir landslides, which has considerable engineering practical significance.

Thermal-hydraulic-mechanical coupling mechanical behavior and acoustic emission characteristics of deep sandstone

Based on the deep in situ mining environments with ?three high?, a triaxial compression experiment of water-saturated sandstone under the conditions of 150?C, 110 MPa confining stress and 105 MPa pore water stress was carried out. The results show that the creep deformation stage produces a surge in acoustic emission energy when the radial deformation of sandstone changes from expansion to rapid compression, and the sandstone is sheared by a single crack when it is damaged. From deformation monitoring and acoustic emission energy analysis, the thermal-hydraulic-mechanical (THM) coupling environment will cause irreversible changes to the internal stress distribution, pore structure and mineral framework of sandstone. In the THM coupling experiment, the irreversible impact of the rock sample due to the long-term simulation of the "three high" environment and the difference caused by the impact on the final experimental results should be considered.

Displacement Back Analysis of Reservoir Landslide Based on Multi-Source Monitoring Data: A Case Study of the Cheyiping Landslide in the Lancang River Basin, China

Landslides that occur in the littoral zone of a reservoir can directly damage the hydraulic structures and threaten the lives and property around the reservoir. Due to the spatial variability and heterogeneities of rock mass, a limited amount of data obtained from laboratory and in situ tests cannot comprehensively characterize the mechanical properties of rock and soil masses. Therefore, displacement back analysis is often performed to determine the mechanical parameters of rock and soil masses. The spaceborne Interferometric synthetic aperture radar (InSAR) has proved to be a powerful tool for geodesy in the measurement of landslide movement. However, InSAR can only measure the surface motion of the landslide without the subsurface information. This study uses multi-source monitoring data in the landslide displacement back analysis, including surface InSAR and an internal borehole inclinometer. The identified material parameters and finite element simulation are used to predict the landslide deformation. The case study of the Cheyiping landslide located in the Lancang River basin demonstrates the necessity and feasibility of using multi-source monitoring data in landslide displacement back analysis. The Cheyiping landslide is currently in the creep deformation stage. The decrease in shear strength of rock masses due to the rheological deformation and the change in reservoir water level are the internal and external factors leading to excessive landslide deformation. The numerical modeling can accurately simulate the landslide movement using the identified material parameters. By combing multi-source monitoring data and numerical modeling, the reservoir landslide deformation analysis can help evaluate the landslide deformation state and stability, which is vital for reservoir risk mitigation and the sustainable development of hydropower resources.

Viscoelastic mechanical performance of dense polyurethane mixtures based on dynamic and static modulus testing and creep testing

Asphalt mixtures are pavement materials that are susceptible to permanent deformation due to the weakening of asphalt at high temperatures. Aimed at finding a new binder with less temperature sensitivity, this paper presents two types of dense polyurethane mixtures, Stone Matrix polyurethane (SMPU-13) and Superpave polyurethane mix (SUPU-20), in which the polyurethane binder was used to replace asphalt binder. The dynamic modulus, phase angle, static modulus, and creep properties of the two polyurethane mixtures and Stone Matrix Asphalt (SMA-13) were compared to display whether the polyurethane mixtures possess better viscoelasticity. It is found that the residual dynamic moduli of the polyurethane mixtures are greater than 8000 MPa and their phase angles are not higher than 6° at 60 °C, while the dynamic modulus of SMA-13 has declined to 189 MPa at 50 °C with its phase angle being about 30°. The dynamic modulus test results show that the two dense polyurethane mixtures are viscoelastic materials dominated by elastic characteristics within the normal working temperature and loading frequency of the pavement, and their mechanical properties are more stable than those of the asphalt mixture. There is a linear correlation between the dynamic modulus and the static modulus of the polyurethane mixtures when the temperature is higher than 20 °C. And the two moduli can be transformed into each other through an established formula. The creep curves of the two polyurethane mixtures exhibit only the first two stages of creep deformation, with the third stage not appearing within a comparatively long loading time, indicating better resistance to permanent deformation.

Evaluation of Monkman–Grant strain as a key parameter in ductility exhaustion damage model to predict creep rupture of grade 92 steel

Conventional strain-based numerical prediction assumes that failure occurs when ductility is exhausted or accumulation of creep strain reaches the critical failure strain. Due to instability at the onset of rupture, the failure strain value appears to be scattered and leads to the erroneousness in prediction. In this paper, a new local constraint-based damage model incorporating the Monkman–Grant ductility, as a measure of strain during uniform creep deformation stage, was implemented into a Finite Element (FE) model to predict the creep damage and rupture of Grade 92 steel under uniaxial and multiaxial stress states. The prediction was applied on plain and notched bar specimens with various notch acuities. The uniaxial stress-dependent Monkman–Grant (MG) failure strain was adopted in the FE to simulate the influence of the constraints which were induced by the creep damage. The implication of reduced failure strain in long-term creep time on the rupture prediction is discussed. The multiaxial MG failure strain of the notched bar, which has a lower value than uniaxial failure strain due to the geometrical constraint, was estimated based on the linear inverse relationship between normalised MG failure strain and normalised triaxiality factor. It was found that the results obtained from the proposed technique were in good agreement with the experimental data within the scatter band of ± factor of 2. It was shown that MG failure strain can be used as an alternative to strain at fracture. MG strain outweighed strain at fracture because the determination of its value only required short-term testing to be performed. In most cases considered in the present investigation, the rupture-type fracture was predicted, however, there was evidence that under high constraint and low stress, stable crack propagation occurred before fracture. The location of the maximum creep damage was found to be dependent on the creep time, geometry or acuity level of the specimen. For sharp notch specimen, the failure was initiated near the notch root, however, as the notch radius increased, the initiation location moved further away towards the specimen centre.

DEFORMATION CHARACTERISTICS AND INSTABILITY MECHANISM OF LARGE MONOCLINAL LAYERED NEOGENIC BEDROCK LANDSLIDE IN THREE GORGES RESERVOIR AREA

This paper take the Jiaodingfeng Ⅱ landslide in Wushan County of the Three Gorges Reservoir area as an example and combines the reservoir water level changes and geological environment conditions data. It analyzes the deformation characteristics,formation mechanism and development trend of the landslide in detail. It uses field survey and mapping,UAV,engineering geological drilling,surface and deep displacement monitoring and other techniques. The volume of the landslide is about 250×104 m3. It is a large monoclinal neogenic bedrock landslide. The height difference between the front and rear edges of the landslide is about 380 m. The leading-edge shear outlet is high and steep and is located below the reservoir water level. The deep monitoring data show that there are two sliding zone in the water-level-fluctuation zone. The two zones are located between 12.0~17.0 m and 25.0~30.0 m from the slope. At present,the landslide is in the creep deformation stage. Under the influence of landform,stratigraphic structure,deterioration of the water-fluctuation zone and water,the vertical displacement continues to increase. The front deterioration zone has a high possibility of sliding failure and instability,and there is a risk of landslide surge disaster chain. It is suggested to carry out continuous observation and research on the deterioration system of the fluctuation zone in the reservoir area to improve the ability of identification and early warning of new landslide disasters in the reservoir area.

Validation of the mechano-bactericidal mechanism of nanostructured surfaces with finite element simulation

The mechano-bactericidal property of nanostructured surfaces has become the focus of intensive research toward the development of a new generation of antibacterial surfaces, especially in the current era of spreading antibiotic resistance. However, the mechanisms underlying nanostructured surfaces mechanically damaging bacteria remain unclear, which ultimately limits translational potential toward real-world applications. Using finite element simulation technique, we developed the three-dimensional thin wall with turgor pressure finite element model (3D-TWTP-FEM) of bacterial cell and verified the reliability of this model by the AFM indentation experiment simulation of the cell, and the cell model is able to simulate suspended bacterial cell and the process of cell adhering to the flat and nanopillar surfaces. Since bacterial cells suffer greater stress and deformation on the nanopillar surfaces, a two-stage model of the elastic and creep deformation stage of the cells on the nanostructured surfaces was developed. The calculations show that the location of the maximum stress/strain on the cells adhered to the nanopillar surfaces is at the liquid-cell-nanopillar three phase contact line. The computational results confirmed the ability of nanostructured surfaces to mechanically lyse bacteria and gave the effect of nanopillar geometry on the efficiency and speed of bacterial cell rupture. This study provides fundamental physical insights into how nanopillar surfaces can serve as effective and fast mechanical antimicrobial materials.

Evaluating the creep characteristics of recycled construction waste materials under saturated and dry condition

The creep deformation characteristics of recycled construction and demolition waste (CDW) filler are important factors affecting its road performance. In this paper, a series of laboratory tests are carried out on CDW filler, including gradation test, compaction test, California bearing ratio (CBR) test, and creep test, and the road performance of different ratios of recycled CDW filler is systematically studied. The mechanical properties of different ratios of CDW materials can meet the requirements of subgrade filler in the specification. Through the creep test, it can be seen that the elastic-plastic deformation speed of CDW material is fast and the duration is short. The creep deformation stage is opposite. Combined with the theoretical analysis, it is found that the t/e-t curve under each stress level has a good linear relationship. The relationship between strain and time is hyperbolic, and the relationship between parameters A, B, and load is a power function. The creep process belongs to attenuation creep, which conforms to the Kelvin model.

Study on the Deformation Mechanism of Reservoir Landslides Considering Rheological Properties of the Slip Zone Soil: A Case Study in the Three Gorges Reservoir Region

Reservoir water level fluctuation is one of the main extrinsic factors that could change the stress field in landslides, as well as the mechanical strength of geomaterials, hence affecting the deformation and stability of landslides. The largest reservoir landslide in the Three Gorges Reservoir area was selected for a case study. The impact of reservoir water level fluctuation is represented by the dynamic change in the underground seepage field and was thereby analyzed with numerical modeling. The deformation behavior considering the rheological properties of the slip zone soil was studied. The sudden change in the displacement–time curve was selected as the failure criterion for the investigated landslide. The evolution process of the accelerated deformation stage was divided into slow acceleration, fast acceleration, and rapid acceleration stages. The Huangtupo landslide is characterized by a retrogressive landslide and is currently in the creep deformation stage; the deformation mechanism and deformation characteristics are closely related to the reservoir water level fluctuation. Research was carried out by means of field investigation, in situ monitoring, and numerical simulation to provide a true and reliable result for stability evaluation.

A grain-based time-to-failure creep model for brittle rocks

Long-term stability analysis and stand-up time prediction of underground excavations are important in engineering design and construction. A Time-to-Failure (TtoF) creep model is proposed for the simulation of lifetime of intact brittle rock under uniaxial and triaxial loading conditions. In the TtoF model, the grain-based modeling approach using UDEC is adopted to describe the heterogeneity and micro-fractures of rock. The time-dependent deformation behavior of a grain cell is assumed to obey the Burgers creep model. The viscosity coefficient of the Maxwell component is modified to relate it to stress. The time to enter the acceleration creep deformation stage is considered as a function of the stresses and the strength parameters of the grain cell. A damage index is defined as a function of the strength parameters and the center-driving-stress ratio at a given time. Degradation of grain boundary is considered to measure the roughness corrosion of contact. The validity of the TtoF model is verified using laboratory uniaxial and triaxial compression test data of brittle rocks. The model can be useful for investigating time-dependent deformation behaviors of brittle rock and determining stand-up time of rock structures.

On the effect of thermo-mechanical treatment on creep deformation and rupture behaviour of a reduced activation ferritic-martensitic steel

Creep deformation and rupture behaviour of a reduced activation ferritic-martensitic (RAFM) steel subjected to thermo-mechanical treatment (TMT) is studied and compared with those of conventional normalized and tempered (N + T) steel. In TMT processing, the steel is warm rolled and aged in austenite phase field at 973 K before the martensite transformation on cooling and is then tempered at 1038 K. The TMT processing renders the steel with higher dislocation density, refinement in lath structure and large quantity of finer M23C6 and MX precipitates than those in the N + T steel. Creep tests are carried out at 823 K over the stress range 180–300 MPa. TMT processing of the steel decreases its minimum creep rate (ε˙min) with corresponding increase in time to onset of tertiary stage of creep deformation, rupture life (tr) and creep rupture ductility (εf). The stress exponent value (n), obtained from minimum creep rate vs. stress plot, increases upon TMT processing, indicating high resistance to creep deformation than in the N + T steel. Resisting stress as estimated based on the Lagneborg and Bergman method is found to increase on TMT processing and is associated with high damage tolerance parameter, defined asλ=εf/(ε˙min.tr). Enhanced creep deformation and rupture strength of the TMT steel, compared to N + T steel, is attributed to the microstructural refinement. Post-creep microstructural investigations show higher microstructural stability of the steel on TMT processing and are in line with the observed high damage tolerance parameter (λ), longer time to onset of tertiary creep and rupture life.

Analysis of creep deformation and damage behaviour of 304HCu austenitic stainless steel

ABSTRACTCreep deformation, damage and rupture behaviour of 304HCu austenitic stainless steel have been studied at temperatures 923, 973 and 1023 K over the stress range 100–240 MPa. The material exhibited relatively short primary stage of creep deformation followed by secondary (steady-state creep) stage and relatively extensive tertiary stage of creep deformation. The transient creep deformation is analysed based on the Garofalo relationship, The variations of (i) rate of exhaustion of transient creep creep rate and time to onset of secondary creep and (ii) initial creep rate with were found to obey power-law relationship with powers close to unity, thereby facilitating the development of master transient creep curve. The variation of with stress and temperature obeyed Dorn’s equation modified with back stress concept. The time to onset of tertiary creep is found to be proportional to rupture life (tr) while the damage tolerance factor decreased with increase in tr. In view of the prolonged tertiary creep, associated with microstructural change and intergranular creep cavitation, Kachanov–Rabotnov model has been used to assess the creep damage behaviour of the steel. The damage assessment coupled with finite-element analysis closely predicted the creep deformation and rupture life of the steel.

An experimental study of seepage properties of gas‐saturated coal under different loading conditions

AbstractIn order to supply benefits for safe production of coal underground and efficient exploitation of coalbed methane, a self‐developed gas seepage experimental device considering gas adsorption and desorption was proposed to study the seepage properties of gas‐saturated coal in this paper. A series of gas seepage experiments under different loading conditions were carried out to investigate the change rules of permeability of gas‐saturated coal. The experimental results covered the significant effects of confining pressure, gas pressure, temperature change, creep stress, and complete stress‐strain process on the seepage laws of gas‐saturated coal. The experimental results showed that the permeability of gas‐saturated coal is strongly sensitive to the effective stress and decreases with the increase of the effective stress. Under the fixed confining pressure, the permeability of gas‐saturated coal showed an obvious Klinkenberg effect, but the Klinkenberg effect would no longer be evident once the gas pressure was larger than 1.0 MPa. And the change law of permeability of gas‐saturated coal with temperature was mainly reflected in the comprehensive effect of thermal stress and effective stress on the control of pore deformation. Under the complete stress‐strain loading conditions, the change rules of permeability were mainly dependent on the failure mode of gas‐saturated coal. And the change rules of permeability, for the condition of triaxial creep stress, were relied on the stage of creep deformation. The deformation at decay creep stage was responsible for a steady permeability after the failure of gas‐saturated coal, while the deformation at nondecay creep stage was responsible for a rapid increase of permeability after the failure of gas‐saturated coal. The results in this work can offer some helpful suggestions for efficiently exploring coalbed methane in the future.

Effect of thermo-mechanical treatment on tensile properties of reduced activation ferritic-martensitic steel

Effect of thermo-mechanical processing on tensile behaviour of reduced activation ferritic martensitic (RAFM) steel has been assessed and compared with those of the normalized and tempered steel. The thermo-mechanical treatment (TMT) was carried out by performing hot rolling and ageing in the austenite phase field, air cooled followed by tempering. TMT of the steel increased its hardness compared to the normalized and tempered condition. Tensile strength of the steel increased on TMT over the investigated temperature range of 300–923 K and more importantly was accompanied with increase in ductility. The strength increase on TMT was accomplished with the refinement of microstructure of the steel having finer martensite lath size and intra-granular precipitates. The tensile flow behaviour of steel has been assessed in the frame work of Voce's constitutive equation. The strength related parameters of the constitutive equation i.e. initial stress and saturation stress increased on TMT, while the recovery related parameter (nv) decreased marginally. The enhancement of tensile strength and ductility of the steel on TMT is considered due to microstructural refinement and its enhanced stability as reflected in appreciable lower relaxation and creep rates and the delayed in onset of tertiary stage of creep deformation.

Microstructure evolution in L12 hardened Co-base superalloys during creep

Abstract

Creep deformation and fracture behaviour of modified 9Cr-1Mo steel in flowing liquid sodium environment

The creep deformation and rupture behaviour of modified 9Cr-1Mo ferritic steel in flowing liquid sodium has been studied at 873K over a stress range of 130–160MPa and compared with those tested in air environment. In the flowing sodium environment, the steel exhibited better creep deformation and rupture strength than those in air environment. The onset of tertiary stage of creep deformation has delayed in sodium environment over that in air environment, which led to the decrease in minimum creep rate. Also the rate of tertiary creep strain accumulation was lower in sodium environment than that in air, leading to the increase in rupture life. The steel failed in ductile dimple fracture mode in both the testing environments. The steel exhibits relatively higher creep damage tolerance in sodium environment than in the air environment. Minimal oxidation was observed in the specimens creep tested in sodium environment. The near absence of oxidation of the steel in sodium environment delayed on onset of tertiary stage of creep deformation and decrease the rate of tertiary creep strain accumulation, leading to the increase in creep deformation and rupture strength.

A study of Triaxial creep test and yield criterion of artificial frozen soil under unloading stress paths

The triaxial shear test method with consolidation, low temperature freezing, and radial unloading was applied to simulate the mechanics process of the unloading process of deep artificial frozen clay during the excavation of a freezing mine shaft. The triaxial unloading creep test on artificial frozen clay showed that the first and second stages of the creep deformation occur only when the deviatoric stress is low and that creep deformation accounts for >70% of the total deformation. The third stage of creep deformation occurs only when the stress level exceeds a certain critical value, and is characterized by the frozen soil undergoing a large plastic flow, with breaking for 3 to 5h. The creep strength envelope at low confining pressure is linear, in compliance with the Mohr-Coulomb strength criterion, and the critical stress value in the third stage can be described with the improved Zienkiewicz-Pande parabolic yield criterion.

Extrapolation of Imaginal Minimum Creep Rate in Compression by a Concept of SATO-Index

Creep characteristics of alloys and compounds have been evaluated mainly by the minimum creep rate or the steady-state creep rate, and by its stress and temperature dependences. In some cases, however, direct comparison of the minimum creep rate or the steady-state creep rate are not practically easy due to difficulties of experiment, i.e., a long duration of primary stage of creep deformation. The minimum creep rates are not always precise representative value, which is directly evaluated from experiments. It should be valuable, if one could estimate the minimum creep rate from creep curve in primary stage. I have proposed a method of quantitative evaluation of creep curve based on the evaluation of strain rate change and its strain dependence during creep [1-3]. The value that reflects a shape of creep curve is named “Strain Acceleration and Transition Objective-Index (SATO-Index)” [4]. SATO-Index and related differential equation show a strain dependence of strain rate and lead entre creep curve by numerical integration. This concept provides quantitative information of shape of each creep curve, and information of the entire creep curve. In this paper, examples of evaluation and extrapolation of creep rate from primary stage in compression are presented. It is concluded that the extrapolation with the concept of SATO-Index reasonably provides imaginal minimum creep rate. Usability of extrapolation of creep curve by the concept is presented.