scholarly journals Features and Constitutive Model of Gypsum’s Uniaxial Creep Damage considering Acidization

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Wei Chen ◽  
Wen Wan ◽  
Senlin Xie ◽  
Wenlong Kuang ◽  
Wenqing Peng ◽  
...  
Keyword(s):  
Hydrochloric Acid ◽  
Constitutive Model ◽  
Stress Level ◽  
Failure Modes ◽  
Failure Time ◽  
Acid Corrosion ◽  
Creep Damage ◽  
Nonlinear Creep ◽  
Creep Tests ◽  
Acidic Groundwater

Acidic fluids cause rock erosion and further endanger the safety of rock engineering, especially the corrosion of pillars by acidic or weakly acidic groundwater. In this paper, the rock samples in the gypsum mining area were taken as the research object. Uniaxial compression creep tests were carried out under neutral water, pH=6 and pH=5 hydrochloric acid solutions, respectively. Meanwhile, the specimens before and after saturation were observed by an electron microscope scanner. The results show that (1) the gypsum specimens with pH=5 hydrochloric acid were damaged at the first stress level, while that with pH=6 and pH=7 were destroyed at the second stress level. The failure modes of the three groups were basically the same, with cleavage and end damage of different degrees. The difference is that the failure time of the former is earlier than that of the latter, which indicates that the stronger acidity causes greater corrosion on the creep of the samples. (2) From the perspective of microstructure, the samples saturated in the neutral aqueous solution and dry state are compact and complete in structure, and the whole is relatively homogeneous. However, after saturating in the acid solution, the samples significantly increased dense pores with large size and loose structure. Due to the rapid increase, the surfaces of the samples are almost like “holes”. (3) A new nonlinear creep constitutive model was established by connecting Burgers model with nonlinear viscoplastic body (NVPB) model in series, which can well describe the creep characteristics of gypsum rocks under acid corrosion.

A nonlinear creep damage model for salt rock

2018 ◽  
Vol 28 (5) ◽  
pp. 758-771 ◽  
Author(s):  
Fei Wu ◽  
Jie Chen ◽  
Quanle Zou
Keyword(s):  
Test Data ◽  
Damage Model ◽  
Creep Damage ◽  
Nonlinear Creep ◽  
Salt Rock ◽  
Creep Tests ◽  
Nonlinear Constitutive Equation ◽  
Damage Constitutive Model ◽  
Creep Damage Model ◽  
Actual Stress

In the creep tests, stress is no longer a constant and increases gradually under the influence of damage occurring during accelerating creep, which is a slow-loading process rather than a conventional creep. With the accumulation of the damage over time, the actual stress increases greatly. The increased actual stress not only generates loading strain but also causes the steady creep rate to rise. This coupling possibly explains why salt rock presents nonlinear accelerating characteristics at the accelerating creep stage. In this work, the constraint of the present creep concept was overcome by assuming that the acceleration creep phase is a coupling process of loading and creeping. Furthermore, we demonstrate that the total strain in this phase is equal to the sum of loading strain and creeping strain. A new nonlinear constitutive equation for creep was then derived, and the mechanisms underlying the nonlinear accelerating characteristics emerging at the stage of accelerating creep are further explained. A step-loading experiment on salt rock was performed for a period of six months. The characteristics of accelerating creep appeared in the last step of loading. This new nonlinear creep damage constitutive model was used to fit and analyze the test data. Obtained results show that this model fits well to these test data and also favorably represents the nonlinear characteristics of accelerating creep, thus supporting the model’s validity.

Time-Temperature-Stress Equivalence Applied to Accelerated Characterization of Creep Behavior of Viscoelastic Polymer

2007 ◽  
Vol 353-358 ◽  
pp. 1386-1389 ◽  
Author(s):  
Rong Guo Zhao ◽  
Wen Bo Luo ◽  
Chu Hong Wang ◽  
Xin Tang
Keyword(s):  
Temperature Stress ◽  
Stress Level ◽  
Creep Compliance ◽  
Superposition Principle ◽  
Test Duration ◽  
Nonlinear Creep ◽  
Creep Tests ◽  
Test Technique ◽  
Compliance Curve ◽  
Stress Superposition

Temperature induced change, and stress induced change as well, in intrinsic timescale were investigated by nonlinear creep tests on poly(methyl methacrylate). With four different experimental temperatures, from 14 to 26 degrees centigrade, time-dependent axial elongations of the specimen were measured at seven different stress levels, from 14 MPa to 30 MPa, and modeled according to the concept of time-temperature-stress equivalence. The test duration was only 4000 seconds. The corresponding temperature shift factors, stress shift factors and temperature-stress shift factors were obtained according to the time-temperature superposition principle (TTSP), the time-stress superposition principle (TSSP) and the time-temperature-stress superposition principle (TTSSP). The master creep compliance curve up to about two-year at a reference temperature 14 degrees centigrade and a reference stress 14 MPa was constructed by shifting the creep curves horizontally along the logarithmic time axis using shift factors. It is shown that TTSSP provides an effective accelerated test technique in the laboratory, the results obtained from a short-term creep test of PMMA specimen at high temperature and stress level can be used to construct the master creep compliance curve for prediction of the long-term mechanical properties at relatively lower temperature and stress level.

scholarly journals Study of Creep Mechanical Properties and A Rheological Model of Sandstone under Disturbance Loads

Processes ◽  
2021 ◽  
Vol 9 (8) ◽  
pp. 1291
Author(s):  
Xiaofeng Li ◽  
Zhixiang Yin
Keyword(s):  
Mechanical Properties ◽  
Constitutive Model ◽  
Creep Deformation ◽  
Failure Time ◽  
Liaoning Province ◽  
Deformation Pattern ◽  
Peak Strain ◽  
Creep Tests ◽  
Strength Failure ◽  
Triaxial Creep

The stress environments of rock masses are complex. To explore the mechanical properties of sandstone under earthquake or disturbance loads, laboratory triaxial creep tests under different disturbance loads were conducted on sandstone from Fuxin, Liaoning Province, China. Given the disturbance load, a creep deformation pattern for sandstone was analyzed, and the influence of the disturbance load on the mechanical properties of rock was considered. Thus, a constitutive model of rock under creep disturbance load was established. The results show that (1) the creep curve can be divided into four stages: attenuation creep, steady creep, disturbance creep, and acceleration creep; the increment of disturbance creep varies for different disturbance loads and the larger the disturbance load, the larger the disturbance creep deformation; (2) with increasing disturbance loads, the long-term strength, failure time, and elastic modulus of sandstone decreases linearly, while the peak strain increases; and (3) considering the influence of the disturbance load and introducing an acceleration element to modify the Nishihara model, a constitutive model describing the whole deformation process of sandstone under creep disturbance load was established. The accuracy of the model was verified by test data and provides a theoretical basis for rock mass stability analysis.

scholarly journals Nonlinear Creep Damage Constitutive Model of Concrete Based on Fractional Calculus Theory

Materials ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1505 ◽  
Author(s):  
Cong Zhang ◽  
Zhende Zhu ◽  
Shu Zhu ◽  
Zhilei He ◽  
Duan Zhu ◽  
...  
Keyword(s):  
Sensitivity Analysis ◽  
Fractional Calculus ◽  
Constitutive Model ◽  
Fractional Order ◽  
Creep Damage ◽  
Creep Process ◽  
Structural Development ◽  
Nonlinear Creep ◽  
Concrete Creep ◽  
Damage Constitutive Model

Concrete creep has become one of the major problems that threatens concrete structural development and construction. However, a reasonable and accurate calculation model for numerical analysis is the key to control and solve the creep deformation of concrete. To better describe the concrete nonlinear creep damage evolution rule, the visco-elasticity Plasticity Rheological Theory, Riemann Liouville Theory and Combined Model Theory are quoted, and the Able dashpot is used to reconstruct fractional-order soft-body composite elements to propose the expression of the stress-strain relationship of the elastomer, visco-elasticity plasticity body, and Viscoplasticity body, considering the evolution of the concrete compression damage process. A nonlinear creep damage constitutive model of concrete, based on fractional calculus theory, is conducted, and the parameters of the specific calculation method of the model are given. The influence of stress level σ, fractional order n and material parameter α on the concrete creep process is determined by a sensitivity analysis of the model parameters. The creep process and deformation amount of concrete in practical engineering can be effectively controlled by the results of the proposed sensitivity analysis. The research results can be used to provide guidance and reference for the safe construction of concrete engineering in actual practice.

scholarly journals An investigation of the nonlinear creep damage accumulation of different materials: Application of a novel damage model

2021 ◽  
Author(s):  
Xu Zhao ◽  
Xuming Niu ◽  
Yingdong Song ◽  
Zhigang Sun
Keyword(s):  
Damage Accumulation ◽  
Failure Modes ◽  
Damage Model ◽  
Evolutionary Process ◽  
Creep Damage ◽  
Experimental Result ◽  
Nonlinear Creep ◽  
The Novel ◽  
Proposed Model ◽  
Damage Accumulation Model

Variable creep load is one of the most important failure modes for hot-component of aero-engine. To accurately predict creep damage and remaining life, a novel nonlinear creep damage accumulation model is proposed based on the Wilshire function and isodamage line, which takes the influence of load history into account and uses ultimate tension strength to compensate the temperature effect. Experimental result of tests on four kinds of material were utilized to verify the accuracy of the proposed model and to compare it with existing models. It was determined that the novel model was better at predicting damage accumulation than all others model. Furthermore, the proposed model elucidates the evolutionary process of creep damage, and four cases of damage evolution process are discussed.

Creep Properties and Damage Study of Ni-Based Alloy C276 at High Temperature

2011 ◽  
Vol 328-330 ◽  
pp. 1143-1148 ◽  
Author(s):  
Xue Ping Mao ◽  
Qi Guo ◽  
Sheng Yuan Zhang ◽  
Su Yang Hu ◽  
Dao Gang Lu ◽  
...  
Keyword(s):  
High Temperature ◽  
Stress Level ◽  
Creep Damage ◽  
Primary Creep ◽  
Type I ◽  
High Temperature Creep ◽  
Fuel Cladding ◽  
Creep Tests ◽  
Temperature Creep ◽  
Creep Characteristic

One of the two challenges about Supercritical Water-Cooled Reactor is material, especially for the fuel cladding. High temperature creep tests of Ni-based alloy C276, one of the candidate materials for the fuel cladding, were carried out at 650°C~750°C, with stress 130MPa~430MPa. The effects of temperature and stress on creep were investigated, the change laws of steady state creep rate with stress and time to rupture were analysed, and creep damage factors were separately calculated based on Kachanov’s formula and Norton’s formula. The results indicate that there exist two types of primary creep characteristics in C276: Type I creep characteristic at lower stress level and Type II at higher stress level respectively. C276 shows excellent high temperature creep resistance, and Kachanov’s damage factors D vs normalized time are basically coincident at 650°C, 700°C and 750°C. The damage obtained by Norton’s formula starts at about 40% of lifetime, and the damage factors calculated by Kachanov’s formula are relatively conservative.

Predicting the Time to Failure in Heavily Loaded Masonry Specimens with the Acoustic Emission Technique

2010 ◽  
Vol 133-134 ◽  
pp. 217-222 ◽  
Author(s):  
Els Verstrynge ◽  
Luc Schueremans ◽  
Dionys Van Gemert
Keyword(s):  
Acoustic Emission ◽  
Failure Time ◽  
Event Rate ◽  
Creep Damage ◽  
Time To Failure ◽  
Creep Tests ◽  
Strain Monitoring ◽  
Specimen Processing ◽  
Term Creep

This paper presents the results of a research project in which the knowledge on testing of creep damage in masonry and acoustic emission (AE) monitoring are combined. Results from different types of creep tests are combined to investigate whether AE monitoring could predict the failure time of the masonry specimens. In previous work, it was observed that the AE event rate is related to the time to failure of the specimen. Processing of the results of new tests enables to update the previously found relation between AE event rate and failure time and to indicate a confidence interval for predictions made with this model. Additionally, the question can be raised whether temporary monitoring could detect unstable damage accumulation and predict failure. Therefore, the results of long-term creep tests are analysed and compared with data from strain monitoring. The results indicate that in most cases, the failure can be predicted.

Nonlinear creep damage constitutive model for soft rocks

2016 ◽  
Vol 21 (1) ◽  
pp. 73-96 ◽  
Author(s):  
H. Z. Liu ◽  
H. Q. Xie ◽  
J. D. He ◽  
M. L. Xiao ◽  
L. Zhuo
Keyword(s):  
Constitutive Model ◽  
Creep Damage ◽  
Nonlinear Creep ◽  
Soft Rocks ◽  
Damage Constitutive Model
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