Triaxial stress relaxation tests on Saskatchewan potash

1995 ◽  
Vol 32 (1) ◽  
pp. 11-21 ◽  
Author(s):  
Rui Chen ◽  
B. Stimpson
Keyword(s):  
Stress Relaxation ◽  
Constitutive Model ◽  
Underground Mining ◽  
Deformation Modulus ◽  
Constitutive Law ◽  
Loading Path ◽  
Triaxial Tests ◽  
Axial Deformation ◽  
Creep Limit ◽  
Reverse Loading

Relative to the study of creep, the stress relaxation phenomenon has been overlooked in research on salt rocks, especially with respect to the behavior of salt in deep underground mining environments. In the laboratory tests described in this paper, deformational properties of potash were first studied by performing reverse-loading tests that approximately simulate in situ loading paths during excavation of underground cavities. Potash relaxation properties were then investigated by multiple-stage, repeated relaxation tests along the reverse-loading path. Results show that potash behavior along a reverse-loading path is highly stress rate dependent and is reflected in the dependence of the initial axial deformation modulus, ductile point, and post-yield behavior on the rate at which the deviatoric stress is applied to the specimen. The inserted relaxation phases did not significantly affect the subsequent behavior of the potash, and therefore inserted relaxation tests are useful for investigating time-dependent behavior at various stages of deformation. A linear relationship exists between normalized stress drop and logarithm of time, which might imply that potash has no creep limit. Finally, an attempt was made to extend a uniaxial strain hardening constitutive law postulated by another researcher to include confining pressure, and the experimental data were found to approximately fit the proposed constitutive model. Key words : potash, stress relaxation, triaxial tests, constitutive model.

Prediction of Stress Relaxation in Power Plant Components Based on a Constitutive Model

2017 ◽  
Author(s):  
Y. Kostenko ◽  
K. Naumenko
Keyword(s):  
Power Plant ◽  
Stress Relaxation ◽  
Constitutive Model ◽  
Evolution Equations ◽  
Material Behavior ◽  
Assessment Procedure ◽  
Reliable Prediction ◽  
Inelastic Material ◽  
Plant Components

Many power plant components and joint connections are subjected to complex thermo-mechanical loading paths under severe temperature environments over a long period. An important part in the lifetime assessment is the reliable prediction of stress relaxation using improved creep modeling to avoid possible integrity or functionality issues and malfunction in such components. The aim of this work is to analyze the proposed constitutive model for advanced high chromium steels with the goal of predicting stress relaxation over the long term. The evolution equations of the constitutive model for inelastic material behavior are introduced to account for hardening and softening phenomena. The material properties were identified for 9–12%CrMoV steels in the creep range. The model is applied to the stress relaxation analysis of power plant components. The results for long-term assessment, which are encouragingly close to reality, will be presented and discussed. An outlook on further developments of the model and assessment procedure is also provided.

scholarly journals Microplane Constitutive Model and Metal Plasticity

2000 ◽  
Vol 53 (10) ◽  
pp. 265-281 ◽  
Author(s):  
Michele Brocca ◽  
Zdeneˇk P. Bazˇant
Keyword(s):  
Constitutive Model ◽  
Plastic Region ◽  
Constitutive Models ◽  
Flow Theory ◽  
Basic Structure ◽  
Steel Tube ◽  
Loading Path ◽  
Microplane Model ◽  
Metal Plasticity ◽  
Path Direction

The microplane model is a versatile constitutive model in which the stress-strain relations are defined in terms of vectors rather than tensors on planes of all possible orientations, called the microplanes, representative of the microstructure of the material. The microplane model with kinematic constraint has been successfully employed in the modeling of concrete, soils, ice, rocks, fiber composites and other quasibrittle materials. The microplane model provides a powerful and efficient numerical tool for the development and implementation of constitutive models for any kind of material. The paper presents a review of the background from which the microplane model stems, highlighting differences and similarities with other approaches. The basic structure of the microplane model is then presented, together with its extension to finite strain deformation. Three microplane models for metal plasticity are introduced and discussed. They are compared mutually and with the classical J2-flow theory for incremental plasticity by means of two examples. The first is the material response to a nonproportional loading path given by uniaxial compression into the plastic region followed by shear (typical of buckling and bifurcation problems). This example is considered in order to show the capability of the microplane model to represent a vertex on the yield surface. The second example is the ‘tube-squash’ test of a highly ductile steel tube: a finite element computation is run using two microplane models and the J2-flow theory. One of the microplane models appears to predict more accurately the final shape of the deformed tube, showing an improvement compared to the J2-flow theory even when the material is not subjected to abrupt changes in the loading path direction. This review article includes 114 references.

A Kinematic Hardening Finite Elements Model to Evaluate Residual Stresses in Shot-Peened Parts, Local Measurements by X-Ray Diffraction

2006 ◽  
Vol 524-525 ◽  
pp. 161-166 ◽  
Author(s):  
Choumad Ould ◽  
Emmanuelle Rouhaud ◽  
Manuel François ◽  
Jean Louis Chaboche
Keyword(s):  
Finite Elements ◽  
Residual Stresses ◽  
Shot Peening ◽  
Kinematic Hardening ◽  
Constitutive Law ◽  
Loading Path ◽  
Isotropic Hardening ◽  
X Ray Diffraction ◽  
X Ray ◽  
Local Measurements

Experimental analysis can be very costly and time consuming when searching for the optimal process parameters of a new shot-peening configuration (new material, new geometry of the part…). The prediction of compressive residual stresses in shot-peened parts has been an active field of research for the past fifteen years and several finite elements models have been proposed. These models, although they give interesting qualitative results, over-estimate, most of the time, the level of the maximal compressive stresses. A better comprehension of the phenomena and of the influence of the parameters used in the model can only carry a notable improvement to the prediction of the stresses. The fact that the loading path is cyclic and is not radial led us to think that a model including kinematic hardening would be better adapted for the modelling of shot peening. In this article we present the results of a simulation of a double impact for several constitutive laws. We study the effect of the chosen constitutive law on the level of residual stresses and, in particular, we show that kinematic hardening, even identified on the same tensile curve than isotropic hardening, leads to lower stress levels as compared with isotropic hardening. Furthermore, the overall shape of the stress distribution within the depth is significantly different for the two types of hardening behaviour. Further, in order to check the modelisations, local measurements were carried on with X-ray diffraction on a large size impact and correlated with the topography of the impact.

A novel constitutive model for multi-step stress relaxation ageing of a pre-strained 7xxx series alloy

2018 ◽  
Vol 106 ◽  
pp. 31-47 ◽  
Author(s):  
Jing-Hua Zheng ◽  
Jianguo Lin ◽  
Junyi Lee ◽  
Ran Pan ◽  
Chen Li ◽  
...  
Keyword(s):  
Stress Relaxation ◽  
Constitutive Model ◽  
Series Alloy

Thermodynamic-based cross-scale model for structural soil with emphasis on bond dissolution

2021 ◽  
Author(s):  
Wei Zhang ◽  
Jia-qiang Zou ◽  
Kang Bian ◽  
Yang Wu
Keyword(s):  
Constitutive Model ◽  
Bond Strength ◽  
Scale Model ◽  
Triaxial Tests ◽  
Natural Soil ◽  
Engineering Practice ◽  
Compression Tests ◽  
Strength Deterioration ◽  
Decomposed Granite ◽  
Completely Decomposed Granite

The immersion weakening effect of natural soil has always been a difficult problem encountered in geotechnical engineering practice. The bond dissolution is a common cause of soil strength deterioration, which remains not well understood yet. In this study, a thermodynamic-based constitutive model of structural soils based on the α model is first established, considering the bond strength by modifying the yield surface size and gradually reducing the bond strength with the development of plastic strain. Furthermore, by taking the meso-mechanisms of bond dissolution into account, the evolution rule of the free energy during the bond dissolution process is derived based on a homogenization approach, and a thermodynamic-based constitutive model of structural soil with bond dissolution is thereafter developed. By comparing with the results of one-dimensional compression tests and conventional triaxial tests, the model is verified to be capable of reflecting the gradual destructuration process of soil while loading. The comparison with triaxial test results of completely decomposed granite after different immersion durations and parametric studies show that based on the cross-scale energy equivalence, the model can well reflect the strength deterioration characteristics of completely decomposed granite with bond dissolution mechanisms at the mesoscale fully considered.

A novel constitutive model for stress relaxation of Ti-6Al-4V alloy sheet

2019 ◽  
Vol 161-162 ◽  
pp. 105034 ◽  
Author(s):  
Xuexi Cui ◽  
Xiangdong Wu ◽  
Min Wan ◽  
Bolin Ma ◽  
Yanling Zhang
Keyword(s):  
Stress Relaxation ◽  
Constitutive Model ◽  
Alloy Sheet

Viscoelastic Characterization of Fiber-Reinforced Elastomeric Composites at Finite Strain

2010 ◽  
Vol 123-125 ◽  
pp. 603-606
Author(s):  
Mohammad Tahaye Abadi
Keyword(s):  
Constitutive Model ◽  
Large Deformation ◽  
Finite Strain ◽  
Mechanical Response ◽  
Viscoelastic Model ◽  
Constitutive Law ◽  
Micromechanical Modeling ◽  
Fiber Reinforced ◽  
Material Parameters ◽  
Elastomeric Composites

A viscoelastic model is developed to describe the mechanical response of fiber-reinforced elastomeric composites at large deformation. A continuum approach is used to model the macroscopic mechanical behavior of elastomeric materials reinforced with unidirectional fibers, in which the resin and fibers are regarded as a single homogenized anisotropic material. The anisotropic viscoelastic constitutive model is developed considering transient reversible network theory. An efficient computational algorithm based on micromechanical modeling is proposed to relate the material parameters of constitutive model to the mechanical properties of composite constituents at finite strain. The microstructure is identified by a representative volume element (RVE) and it is subjected to large deformation with considering the conformity of opposite boundaries. The material parameters of the viscoelastic constitutive law are determined based on the response of heterogeneous microstructure which is examined under different loading conditions.

A Micromechanically Based Constitutive Model for the Inelastic and Swelling Behaviors in Double Network Hydrogels

2015 ◽  
Vol 83 (2) ◽  
Author(s):  
Yin Liu ◽  
Hongwu Zhang ◽  
Yonggang Zheng
Keyword(s):  
Constitutive Model ◽  
Strain Energy ◽  
Polymer Chains ◽  
Loading Path ◽  
Induced Anisotropy ◽  
Double Network ◽  
Strain Energy Density Function ◽  
Damage Process ◽  
Single Polymer Chain ◽  
Swelling Behaviors

This paper presents a micromechanically based constitutive model within the framework of the continuum mechanics to characterize the inelastic elastomeric and swelling behaviors of double network (DN) hydrogels, such as the stress-softening, necking instability, hardening, and stretch-induced anisotropy. The strain-energy density function of the material is decomposed into two independent contributions from the tight and brittle first network and the soft and loose second network, each of which is obtained by integrating the strain energy of one-dimensional (1D) polymer chains in each direction of a unit sphere. The damage process is derived from the irreversible breakages of sacrificial chains in the first network and characterized by the directional stretch-dependent evolution laws for the equivalent modulus and the locking stretch in the non-Gauss statistical model of a single polymer chain. The constitutive model with the optimized-material evolution law predicts stress–stretch curves in a good agreement with the experimental results during loading, unloading, and reloading paths for both ionic and covalent DN hydrogels. The deformation-induced anisotropy is investigated and demonstrated by the constitutive model for the free swelling of damaged specimen. The constitutive model is embedded into the finite-element (FE) procedure and proved to be efficient to model the necking and neck propagation in the plane-strain uniaxial elongation. Based on the procedure, the effects of imperfection and boundary conditions on the loading path and the material evolution during different stages of deformation are investigated.

Experimental Study on Mechanical Property of Thermo-Mechanical and Hydro-Mechanical Coupling Condition for a Sandstone

2006 ◽  
Vol 326-328 ◽  
pp. 1797-1800 ◽  
Author(s):  
Qing Chun Zhou ◽  
Hai Bo Li ◽  
Chun He Yang ◽  
Chao Wen Luo
Keyword(s):  
Pore Pressure ◽  
Deformation Modulus ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Underground Engineering ◽  
Coupling Condition ◽  
West China ◽  
Mechanical Coupling ◽  
North Water ◽  
Confining Pressures

The mechanical properties of rock under high temperature, high geostress and high pore pressure are the basic and important information to assess the safety of underground engineering in west China. Based on the environmental conditions of the west route of south-to-north water transfer project in west China, a series of triaxial tests at confining pressures (0 to 60MPa) and temperatures (25°C to 70°C) as well as pore pressure (0 to 10MPa) have been conducted for a sandstone. It is reported that under the temperatures varying from 25°C to 70°C, the strength of the rock increases with the increment of confining pressure, while the deformation modulus of the rock doesn’t change distinctly with the increment of confining pressures. It is also indicated under the temperatures condition in the experiments, when the confining pressure is lower than 40MPa, the strength of the rock increases with the increment of temperature, whereas when the confining pressure is higher than 40MPa, the strength of rock tend to decrease with increment of temperature. It is further shown that the strength decreases with increasing pore pressure, and the decreasing rates tend to decrease with the increment of confining pressures.

scholarly journals Further Insight into the Depth-Dependent Microstructural Response of Cartilage to Compression Using a Channel Indentation Technique

2013 ◽  
Vol 2013 ◽  
pp. 1-11 ◽  
Author(s):  
Ashvin Thambyah ◽  
Neil D. Broom
Keyword(s):  
Stress Relaxation ◽  
Axial Strain ◽  
Compressive Strain ◽  
Microstructural Analysis ◽  
Elastic Response ◽  
Axial Deformation ◽  
Aspect Ratios ◽  
The Matrix ◽  
Tissue System ◽  
Relaxation Responses

Stress relaxation and structural analysis were used to investigate the zonally differentiated microstructural response to compression of the integrated cartilage-on-bone tissue system. Fifteen cartilage-on-bone samples were divided into three equal groups and their stress relaxation responses obtained at three different levels of axial compressive strain defined as low (~20%), medium (~40%) and high (~60%). All tests were performed using a channel indenter which included a central relief space designed to capture the response of the matrix adjacent to the directly loaded regions. On completion of each stress relaxation test and while maintaining the imposed axial strain, the samples were formalin fixed, decalcified, and then sectioned for microstructural analysis. Chondron aspect ratios were used to determine the extent of relative strain at different zonal depths. The stress relaxation response of cartilage to all three defined levels of axial strain displayed an initial highly viscous response followed by a significant elastic response. Chondron aspect ratio measurements showed that at the lowest level of compression, axial deformation was confined to the superficial cartilage layer, while in the medium and high axial strain samples the deformation extended into the midzone. The cells in the deep zone remained undeformed for all compression levels.

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