scholarly journals An Improved Nishihara Model for Frozen Loess considering the Influence of Temperature

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Xin Li ◽  
Enlong Liu ◽  
Bingtang Song ◽  
Xingyan Liu
Keyword(s):  
Creep Behavior ◽  
Microscopic Analysis ◽  
Confining Pressure ◽  
Deviatoric Stress ◽  
Frozen Soil ◽  
Experimental Results ◽  
Creep Process ◽  
Model Parameters ◽  
Creep Tests ◽  
Deviator Stress

A series of triaxial creep tests under the constant confining pressure are performed on frozen loess specimens, and the creep behavior of the frozen loess with respect to variations in both temperature and deviator stress is examined. Experimental results illustrate that the frozen loess specimens present the attenuation creep at the lower deviatoric stress, whereas the nonattenuation creep under the higher deviatoric stress level, and with a drop in the temperature, the deviator stress value which the exhibition of nonattenuation creep needs will increase under the constant confining pressure condition. According to the microscopic analysis on deformation characteristics in the creep process of frozen soil, both temperature and external stress will cause the hardening and weakening effects, affecting the creep properties of frozen loess. By introducing the hardening variable and damage variable to consider the hardening and weakening effects of the frozen loess, an improved Nishihara model is proposed. The correlations between model parameters and the temperature as well as deviator stress are determined. The comparisons between model predictions and experimental results show that the improved creep constitutive model proposed here can not only describe the whole creep process well, but also reveal the influences of the temperature and deviator stress on the creep behavior of frozen loess, which demonstrate its accuracy and usefulness.

Combined constitutive model for creep and steady flow rate of frozen soil in an unconfined condition

2017 ◽  
Vol 54 (7) ◽  
pp. 907-914 ◽  
Author(s):  
Guofang Xu ◽  
Chong Peng ◽  
Wei Wu ◽  
Jilin Qi
Keyword(s):  
Constitutive Model ◽  
Strain Rate ◽  
Steady Flow ◽  
Flow Rate ◽  
Creep Behavior ◽  
Frozen Soil ◽  
Creep Process ◽  
Model Parameters ◽  
Creep Failure ◽  
Creep Tests

A combined constitutive model is developed for the creep behavior of frozen soil in an unconfined condition. The model is obtained by coupling two stress- and time-dependent models, which are responsible for the primary and tertiary creep stages. The model parameters are dependent on temperature and can be readily determined from the strain rate–time curves at two creep stresses. The model performance is demonstrated by simulating the complete strain–time and strain rate–time curves (including primary, secondary, and tertiary stages) of frozen sand and frozen clay in uniaxial creep tests under different creep stresses. Moreover, two equations are obtained from the combined model. One shows a good capability in describing the relationship between creep strength and the time to creep failure. The other makes an excellent prediction of the steady flow rate in a typical creep process. Both equations can reflect the effects of stress and temperature on the creep behavior of frozen soil.

scholarly journals Nonlinear Viscoelastic–Plastic Creep Model Based on Coal Multistage Creep Tests and Experimental Validation

Energies ◽  
2019 ◽  
Vol 12 (18) ◽  
pp. 3468 ◽  
Author(s):  
Junxiang Zhang ◽  
Bo Li ◽  
Conghui Zhang ◽  
Peng Li
Keyword(s):  
Creep Behavior ◽  
Physical Property ◽  
Creep Model ◽  
Creep Process ◽  
Creep Tests ◽  
Model Based ◽  
Nonlinear Viscoelastic ◽  
Improved Model ◽  
And Control ◽  
Plastic Creep

The development of fractures, which determine the complexity of coal creep characteristics, is the main physical property of coal relative to other rocks. This study conducted a series of multistage creep tests to investigate the creep behavior of coal under different stress levels. A negative elastic modulus and a non-Newtonian component were introduced into the classical Nishihara model based on the theoretical analysis of the experimental results to propose a nonlinear viscoelastic–plastic creep model for describing the non-decay creep behavior of coal. The validity of the model was verified by experimental data. The results show that this improved model can preferably exhibit decelerating, steady state, and accelerating creep behavior during the non-decay creep process. The fitting accuracy of the improved model was significantly higher than that of the classical Nishihara model. Given that acceleration creep is a critical stage in predicting the instability and failure of coal, its successful description using this improved model is crucial for the prevention and control of coal dynamic disasters.

Tensile and Compressive Creep Behavior of IN718 Alloy Manufactured by Selective Laser Melting

2020 ◽  
Vol 986 ◽  
pp. 102-108 ◽  
Author(s):  
Zhen Xu ◽  
Chuan Guo ◽  
Zhen Rong Yu ◽  
Xin Li ◽  
Xiao Gang Hu ◽  
...  
Keyword(s):  
Creep Behavior ◽  
Chemical Potential ◽  
Creep Process ◽  
Tension Stress ◽  
Creep Tests ◽  
Compressive Creep ◽  
Large Size ◽  
Stress Orientation ◽  
Evolution Of Microstructure ◽  
Tension Compression Asymmetry

Tensile and compressive creep behavior of SLMed IN718 alloy under 973K (700°C) were investigated. Crept samples were analyzed by SEM and TEM to expose evolution of microstructure, precipitates and dislocation structure during the creep process. Results show that initial creep rate under compression is higher than under tension for the same creep conditions. Minimum creep rates are approximately the same both in tensile and compressive creep tests. The different creep behaviors may be related to the fact that tension stress promotes precipitations of fine needle-like γ′′ phases, while compression stress promotes precipitations of large size δ phases. The tension-compression asymmetry owns to the increment of chemical potential varying with the stress orientation.

scholarly journals Viscoelastic Damage Characteristics of Asphalt Mixtures Using Fractional Rheology

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5892
Author(s):  
Qipeng Zhang ◽  
Xingyu Gu ◽  
Zilu Yu ◽  
Jia Liang ◽  
Qiao Dong
Keyword(s):  
Damage Evolution ◽  
High Stress ◽  
Creep Damage ◽  
Asphalt Mixtures ◽  
Creep Process ◽  
Model Parameters ◽  
Creep Tests ◽  
Steady Stage ◽  
Stress Levels ◽  
Different Temperatures

The mechanical behavior of asphalt mixtures at high stress levels are characterized by non-linear viscoelasticity and damage evolution. A nonlinear damage constitutive model considering the existence of creep hardening and creep damage mechanisms in the entire creep process is proposed in this study by adopting the fractional rheology theory to characterize the three-stage creep process of mixtures. A series of uniaxial compressive creep tests under various stresses were conducted at different temperatures to verify the model. The results indicated that the model predictions were in good agreement with the creep tests. The relationship between the model parameters and applied stresses was established, and the stress range in which the mixture exhibited only creep consolidation was obtained. The damage to the asphalt mixture was initiated in the steady stage; however, it developed in the tertiary stage. A two-parameter Weibull distribution function was used to describe the evolution between the damage values and damage strains at different stress levels and temperatures. The correlation coefficients were greater than 0.99 at different temperatures, indicating that a unified damage evolution model could be established. Thus, the parameters of the unified model were related to material properties and temperature, independent of the stress levels applied to the mixtures.

scholarly journals The Effect of Specimen Size and Test Procedure on the Creep Behavior of ME21 Magnesium Alloy

Crystals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 918
Author(s):  
Bettina Camin ◽  
Maximilian Gille
Keyword(s):  
Magnesium Alloy ◽  
Creep Behavior ◽  
Test Procedure ◽  
Primary Creep ◽  
Creep Process ◽  
Transport Sector ◽  
Creep Tests ◽  
Miniature Specimen ◽  
Heat Treated ◽  
A Minor

Lightweight constructions and materials offer the opportunity to reduce CO2 emissions in the transport sector. As components in vehicles are often exposed to higher temperatures above 40% of the melting temperature, there is a risk of creep. The creep behavior usually is investigated based on standard procedures. However, lightweight constructions frequently have dimensions not adequately represented by standardized specimen geometries. Therefore, comparative creep experiments on non-standardized miniature and standardized specimens are performed. Due to a modified test procedure specified by a miniature creep device, only the very first primary creep stage shows a minor influence, but subsequently, no effect on the creep process is detected. The creep behavior of hot extruded and heat treated ME21 magnesium alloy is investigated. It is observed that the creep parameters determined by the miniature and standard creep tests are different. As the deviations are systematic, qualitatively, evidence of the creep behavior is achieved. The creep parameters obtained, and particularly the creep strain and the strain rate, show a higher creep resistance of the miniature specimen. An initial higher number of twinned grains and possible multiaxiality in the gauge volume of the miniature specimen can be responsible.

scholarly journals Creep Strain Analysis and an Improved Creep Model of Granite Based on the Ratio of Deviatoric Stress-Peak Strength under Different Confining Pressures

2021 ◽  
Author(s):  
Li Qian ◽  
Jianhai Zhang ◽  
Xianliang Wang ◽  
Yonghong Li ◽  
Ru Zhang ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Creep Behavior ◽  
Viscosity Coefficient ◽  
Deviatoric Stress ◽  
Peak Strength ◽  
Creep Model ◽  
Secondary Creep ◽  
Creep Tests ◽  
Underground Powerhouse ◽  
Confining Pressures

Abstract Creep refers to the deformation of rock with time under long-term applied stress, which occur in most underground engineering. The creep behavior of granite in Shuang jiangkou underground powerhouse in Western Sichuan Province, China, was studied by creep tests. Based on test results, a new parameter DPR, the ratio of deviatoric stress to peak strength, is proposed. DPR is found to be a key parameter to describe creep parameters such as instantaneous elastic modulus, creep elastic modulus, and viscosity coefficient of rock under different confining pressures. Creep tests show that instantaneous elastic modulus increases with the increase of DPR. Creep elastic modulus increases when DPR changes from 0.54 to 0.7004, but decreases when DPR is from 0.7004 to 0.88, indicating fractures in rock closes firstly and then new fractures are generated. The viscosity coefficient of the rock increases first and then decreases with the increase of DPR, and when DPR = 0.7171, viscosity coefficient is maximum, indicating the time for rock to reach stability is the longest in creep tests. By introducing DPR and confining pressure into creep model, which interconnect creep parameters in a unified expression, an improved generalized Kelvin creep model is proposed which can accurately describe the primary and the secondary creep behavior of granite under given deviatoric stresses and confining pressures.

scholarly journals Study on the Creep Behaviors of Interactive Marine-Terrestrial Deposit Soils

2019 ◽  
Vol 2019 ◽  
pp. 1-14
Author(s):  
Zhen Yan ◽  
Gang Li ◽  
Jinli Zhang ◽  
Rui Zhang
Keyword(s):  
Creep Behavior ◽  
Axial Strain ◽  
Nonlinear Creep ◽  
Creep Tests ◽  
Creep Equation ◽  
One Dimensional ◽  
Consolidation Pressure ◽  
Deviator Stress ◽  
Consolidation Coefficient ◽  
Triaxial Creep

The interactive marine-terrestrial (IMT) deposit soils were formed in the complex depositional environment; their mechanical properties are different from the other deposits. The creep behaviors of Dalian clayey soils were studied according to one-dimensional creep tests and drained triaxial creep tests. Based on the creep test results, the empirical model was established to describe the one-dimensional creep behavior and triaxial creep behavior, respectively. The results showed that Dalian deposits have typical nonlinear creep behavior. With the increasing of consolidation pressure, the strain is increased, the stability time is extended, and the demarcation point between primary and secondary consolidation is more obvious. The deposits belong to medium to high secondary compressibility soil, and the secondary consolidation coefficient is decreased with the increasing of consolidation time and increased with consolidation pressure increasing. The ratio between secondary consolidation coefficient and compression index at different depths changes from 0.033 to 0.058, which conform to Mesri conclusion. Under low deviator stress, the creep processes showed the characteristic of attenuation creep and shear contraction. However, it showed the characteristic of acceleration creep, shear contraction, and shear dilatancy under damage deviator stress. The axial strain rate decreased with the increasing of creep time and increased with the deviator stress increasing, while the deviator stress has little effect on the m values. The tests results agree well with the calculation results, which showed that the creep equation is suitable for describing the creep behaviors of Dalian interactive marine-terrestrial deposits.

scholarly journals Creep Mechanics of the High-Stress Soft Rock under Grade Unloading

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Shunjie Huang ◽  
Xiangrui Meng ◽  
Guangming Zhao ◽  
Yingming Li ◽  
Gang Liu ◽  
...  
Keyword(s):  
Constitutive Model ◽  
Creep Test ◽  
Creep Behavior ◽  
High Stress ◽  
Soft Rock ◽  
Confining Pressure ◽  
Deviatoric Stress ◽  
Axial Pressure ◽  
Accelerated Creep ◽  
Test Process

In order to study the creep behavior of deep soft rock, gritstone was chosen as the research subject, and a rock triaxial rheometer (Rock 600-50) and acoustic emission (AE) system (SH-II) were used to carry out the grade unloading confining pressure creep test under a high-stress level. The test results showed that the lateral creep behavior of the gritstone was more prominent than the axial creep under the initial high confining pressure. Under the same confining pressure, the creep strain rate (the direction the same as strain) of the gritstone decreases with the increase in axial pressure. As shown by the AE count, AE signals were generated throughout the entire test process, indicating that the creep was a “microdynamic” process. The creep behavior was characterized by a significant confining pressure effect. As the confining pressure was decreased, the degree of creep increases significantly. During the test, the AE energy increased on the whole but decreases during the creep phase. During the entire test process, the overall energy in the constant deviatoric stress grade unloading of the confining pressure was 45% higher than that in the constant axial pressure grade unloading. The degree of failure of the rock was different in these two unloading creep tests, and the constant axial pressure grade unloading of the confining pressure entails greater damage than the constant deviatoric stress grade unloading of the confining pressure. The main reason was that the former had a lower confining pressure level and longer creep process than the latter, and the sample was mainly characterized by creep damage and large cumulative damage, while the latter features mainly unloading damage. Through the inversion of the Burgers constitutive model and nonlinear damage constitutive model for the creep test curve, the nonlinear constitutive equation can better fit the accelerated creep stage, which suggested that this model can describe the accelerated creep characteristics of the high-stress soft rock.

scholarly journals Nonlinear Creep Behavior and Viscoelastic-Plastic Constitutive Model of Rock-Concrete Composite Mass

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Yang Liu ◽  
Da Huang ◽  
Baoyun Zhao ◽  
Chen Wang ◽  
Duofeng Cen
Keyword(s):  
Mechanical Properties ◽  
Creep Rate ◽  
Composite Structures ◽  
Testing Machine ◽  
Confining Pressure ◽  
Creep Process ◽  
Nonlinear Creep ◽  
Creep Tests ◽  
Triaxial Compressive Strength ◽  
Confining Pressures

The joint force deformation of rock-concrete composite structures is different from that of simple rock specimens or concrete specimens, such as the tunnel surrounding rock-lining concrete, dam foundations, and concrete. In order to study the creep mechanical properties of rock-concrete composite structures under long-duration load, the TFD-2000 microcomputer servo triaxial creep testing machine is used to carry out step loading creep tests on rock-concrete composite specimens (hereinafter referred to as composite specimens) under different confining pressures (including the confining pressures σ3 = 0 MPa). The creep test results show that, under the same confining pressure, when axial deviatoric stress is applied step-by-step according to 10%, 20%, 30%, 40%, 50%, and so forth of the UCS (σ3 = 0 MPa) and TCS (triaxial compressive strength) of the composite specimens, the failure stress that the specimen can bear is closely related to the confining pressure. When the confining pressures are 0 MPa, 7 MPa, 15 MPa, and 22 MPa, respectively, the failure stresses that the composite specimens can bear are 60% (corresponds to 0 MPa), 50%, 30%, and 20% of the TCS under the current confining pressures, respectively. Under the same confining pressure, the initial creep rate of the composite specimen on each step shows a U-shaped change trend. Meanwhile, the instantaneous creep rate and failure creep rate of the specimen increase as the confining pressure increases. When the failure creep rate is excluded, the initial creep rate of other stepped loads at the same confining pressure level decreases step-by-step. The improved Nishihara model can better describe the whole creep process of rock-concrete composite specimens, especially in the accelerating creep step. The testing data and research results in this paper can serve as references for further research on mechanical properties of rock-concrete composite structures.

scholarly journals Creep Behaviors of Methane Hydrate-Bearing Frozen Sediments

Energies ◽  
2019 ◽  
Vol 12 (2) ◽  
pp. 251 ◽  
Author(s):  
Yanghui Li ◽  
Peng Wu ◽  
Xiang Sun ◽  
Weiguo Liu ◽  
Yongchen Song ◽  
...  
Keyword(s):  
Strain Rate ◽  
Methane Hydrate ◽  
Axial Strain ◽  
Confining Pressure ◽  
Creep Tests ◽  
Creep Stage ◽  
Long Term Stability ◽  
Deviator Stress ◽  
Strain And Strain Rate

Creep behaviors of methane hydrate-bearing frozen specimens are important to predict the long-term stability of the hydrate-bearing layers in Arctic and permafrost regions. In this study, a series of creep tests were conducted, and the results indicated that: (1) higher deviator stress (external load) results in larger initial strain, axial strain, and strain rate at a specific elapsed time. Under low deviator stress levels, the axial strain is not large and does not get into the tertiary creep stage in comparison with that under high deviator stress, which can be even up to 35% and can cause failure; (2) both axial strain and strain rate of methane hydrate-bearing frozen specimens increase with the enhancement of deviator stress, the decrease of confining pressure, and the decrease of temperature; (3) the specimens will be damaged rather than in stable creep stage during creeping when the deviator stress exceeds the quasi-static strength of the specimens.

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