Negative creep of soils

2020 ◽  
Vol 57 (1) ◽  
pp. 1-16 ◽  
Author(s):  
Yang-Ping Yao ◽  
Yu-Fei Fang
Keyword(s):  
Three Dimensional ◽  
Yield Function ◽  
Time Dependent ◽  
Flow Rule ◽  
Test Results ◽  
Current Yield ◽  
Compression Tests ◽  
Creep Tests ◽  
Negative Creep ◽  
Over Time

After unloading, the deformation of soils cannot be stable immediately, but continues to expand over time even under constant pressure. In this paper, the expansive deformation over time when effective stress is kept constant is defined as the negative creep, while the compressive creep is described as the positive creep. The division between positive creep and negative creep is named the stable normal compression line (SNCL), on which the stress–strain behaviour of the soil is time-independent. Based on the concept of the SNCL and test results, a new formula for creep is proposed. This formula is simple in form and has less parameters, and both negative creep and positive creep can be well predicted. By incorporating this formula into the current yield function of the unified hardening model, a new time-dependent current yield function is built. Combining the yield function, a flow rule, and transformed stress method, a new three-dimensional time-dependent constitutive model considering both positive and negative creep for clays is derived and presented. The new model is then validated by test results, including multistage loading oedometer tests, triaxial undrained creep tests, and triaxial undrained compression tests at the constant strain rates.

scholarly journals A Nonlinear Creep Damage Model Considering the Effect of Dry-Wet Cycles of Rocks on Reservoir Bank Slopes

Water ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2396
Author(s):  
Xingang Wang ◽  
Baoqin Lian ◽  
Wenkai Feng
Keyword(s):  
Three Dimensional ◽  
Influential Factor ◽  
Time Dependent ◽  
Secondary Development ◽  
Nonlinear Creep ◽  
Test Results ◽  
Creep Tests ◽  
New Model ◽  
Dependent Behavior ◽  
Rock Creep

Water has a crucial effect on the time-dependent behavior of rocks. The long-term cyclical fluctuations of reservoir water level lead to dry–wet (DW) cycles of rocks on reservoir bank slopes, making this influential factor more complex. To deeply understand the time-dependent behavior of rocks under DW cycles, argillite from the reservoir bank slope of Longtan Hydropower Station was used to perform a series of triaxial creep tests. Subsequently, based on analysis of creep test results after different DW cycles, a damage nonlinear Burgers viscoelastic-plastic (DNBVP) model considering the effect of saturation–dehydration cycles was proposed by introducing a nonlinear viscoplastic body and a damage variable describing DW cycles. Then, the three-dimensional creep equations of the new model were derived and its creep parameters were identified. Comparison between the theoretical curves and the test results shows that the theoretical curves of the DNBVP model were able to describe rock creep tests results after different DW cycles. Furthermore, by comparing classical creep models with the proposed model, it was found that the DNBVP model can accurately reflect the nonlinear characteristics of rocks at the accelerated creep stage. Finally, the sensitivity of the DNBVP model was analyzed and discussed, and three-dimensional central difference expressions necessary for secondary development of the new model were also derived in detail. The proposed new model with secondary development may provide a basis for improving the geotechnical design of reservoir bank slopes and the control of reservoir bank landslides.

scholarly journals Elasto-Plastic Analysis of 3D Frames with Generalized Yield Function

2014 ◽  
Vol 14 (1) ◽  
pp. 5301-5311
Author(s):  
Harpal Singh
Keyword(s):  
Three Dimensional ◽  
Bending Moment ◽  
Yield Function ◽  
Inelastic Interaction ◽  
Flow Rule ◽  
Biaxial Bending ◽  
Concrete Frames ◽  
Plastic Analysis ◽  
Interaction Surface ◽  
Gauss Points

Three dimensional three node elasto-plastic finite element has been presented. Hinges have been assumed to form at the points of integration (Gauss points) which are distributed over the length of the element. One integration point at the center and the other two near the ends. The inelastic interaction between biaxial bending moment, torque and axial force has been considered by means of generalized yield interaction surface and a flow rule with strain hardening has been associated. The element is more effective where the location of hinges is not known in advance. The concept has been applied successfully on three dimensional steel and reinforced concrete frames

scholarly journals Experimental Study on Time-Dependent Changes in Rheological Properties and Flow Rate of 3D Concrete Printing Materials

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6278
Author(s):  
Hojae Lee ◽  
Eun-A Seo ◽  
Won-Woo Kim ◽  
Jae-Heum Moon
Keyword(s):  
Rheological Properties ◽  
Flow Rate ◽  
Test Specimen ◽  
Three Dimensional ◽  
Time Dependent ◽  
Flow Properties ◽  
Layer Width ◽  
Binder Ratio ◽  
Water To Binder Ratio ◽  
Over Time

Three-dimensional concrete printing (3DCP) materials require a relatively low water-to-binder ratio (W/B) of 0.3 or less to ensure their buildability and flow properties are sufficiently maintained after mixing. In this study, the rheological properties of 3DCP materials with W/B 0.28 were evaluated up to 60 min after mixing, and the yield stress and plastic viscosity were analyzed over time. A gradual decrease in flow rate with time was observed during the transport of 200 kg of material per batch through a 20 m hose. To examine the time-dependent changes in flow rate and layer volume, a 2200 mm × 1000 mm test specimen was printed. The dependence of the layer width over time during the printing process was measured and analyzed. The experimental analyses showed that the flow rate and layer volume of the 3DCP material gradually decreased with time after mixing, which was correlated with the rheological properties.

The mechanism of deformation and fracture in potash rock

1988 ◽  
Vol 25 (2) ◽  
pp. 262-278 ◽  
Author(s):  
Emery Z. Lajtai ◽  
E. J. Scott Duncan
Keyword(s):  
High Stress ◽  
Volumetric Strain ◽  
Strain Curve ◽  
Time Dependent ◽  
Compression Tests ◽  
Creep Tests ◽  
Initiation Point ◽  
Potash Salt ◽  
Measured Strain ◽  
Lateral Creep

Specimens of potash rock from the Rocanville mine of the Potash Corporation of Saskatchewan were subjected to uniaxial compression tests and to time-dependent creep tests under static, uniaxial loading.During the first cycle of loading, the main sources of the measured strain are compaction and dilation at grain boundaries and consolidation of the clay phase. The crystals of halite and sylvite deform elastically at low stress and in a brittle manner at high stress. There is little, if any, evidence for constant-volume plastic deformation at any level of uniaxial stress.The stress–strain curve can be divided into three parts, each representing a different dominant deformational process: a low-stress quasi-elastic, an intermediate-stress ductile, and a high-stress brittle mechanism. The three parts are separated by the yield point (1–8 MPa) and the crack initiation point (10–13 MPa). The strength of the Rocanville potash specimens ranged between 15 and 18 MPa.The deformation of potash rock is strongly time dependent. There is evidence for the existence of all three stages of creep: transient, steady-state, and tertiary. There is very little interrelationship between the axial and lateral creep strains; the volumetric strain is negative at low stress and positive (dilatant) at high stress, but rarely, if ever, constant. Key words: creep, dilatant, ductile, elastic, fracture, microfracture, plastic, potash, salt.

Study of the Size Dependence of Time-dependent Plastic Deformation of Gold Micro-pillars and Micro-spheres

2013 ◽  
Vol 1580 ◽  
Author(s):  
AZM Ariful Islam ◽  
Robert J. Klassen
Keyword(s):  
Plastic Deformation ◽  
Constant Load ◽  
Time Dependent ◽  
Dislocation Slip ◽  
Compression Tests ◽  
Creep Tests ◽  
Jump Frequency ◽  
Single Plane ◽  
Pillar Diameter ◽  
Micro Pillars

ABSTRACTIn this study the length scale dependence of the operative mechanisms of time-dependent plastic deformation was studied using room temperature compression tests performed on Au micro-pillars and micro-spheres of 1.0 to 5.0 µm diameter. All the samples tested displayed deformation that had a component of random strain jumps. In the case of the Au micro-pillars, the frequency of the strain jumps showed a bilinear dependence upon pillar diameter with the frequency being larger, and more sensitive to diameter, when the pillar diameter was small (and τR was high). We suggest that this indicates a transition from deformation occurring by deformation on multiple slip planes to deformation occurring predominantly by single-plane dislocation slip when the pillar diameter is less than 2 µm.The strain jump frequency during the constant-load micro-pillar creep tests showed a linear dependence upon τR. Creep tests performed on the micro-spheres of 5.0 µm diameter displayed displacement jump frequency that was essentially independent of the applied load while the jump frequency increased with increasing load for the smaller 2.5 µm diameter micro-spheres. We suggest that this difference is related to the volume of the micro-sphere. When the volume is small, the component of the deformation that occurs by a stochastic dislocation glide process is increased and becomes strongly dependent upon the magnitude of the local shear stress.

Elastoplastic Constitutive Modeling for Reinforced Concrete in Ordinary State-Based Peridynamics

2020 ◽  
Vol 36 (6) ◽  
pp. 799-811
Author(s):  
Tianyi Li ◽  
Xin Gu ◽  
Qing Zhang ◽  
Xiaozhou Xia
Keyword(s):  
Reinforced Concrete ◽  
Consistency Condition ◽  
Three Dimensional ◽  
Yield Function ◽  
Constitutive Relationship ◽  
Flow Rule ◽  
Failure Behavior ◽  
Behavior Simulation ◽  
Elasticity Problems ◽  
Three Dimensional Elasticity

ABSTRACTA non-local, ordinary state-based, peridynamic elastoplastic model is formulated to numerically simulate the fracture of reinforced concrete materials. Several basic definitions are first discussed to avoid confusion; and then, a detailed derivation of the force vector state is presented, leading to a unified expression of force state for one-, two- and three-dimensional elasticity problems. Furthermore, an ordinary state-based peridynamic (OSB PD) elastoplastic analysis approach is developed for both plastic compressible and incompressible materials, including the constitutive relationship, the yield function, the consistency condition and the plasticity flow rule. The peridynamic predictions of a quasi-static deformation of the steel rods are in good agreement with the analytical solution. Moreover, the OSB PD plasticity is verified by analyzing a square plate with or without a central hole suffering different loading-unloading paths. Finally, a two dimensional reinforced concrete clamped beam subjected to impact loading is simulated with the proposed OSB PD elastoplasticity, demonstrating its capability in capturing the damage characteristics and structural failure behavior. Simulation results show good accuracy of the peridynamics in simulating elastoplastic problems.

Three-dimensional elastoplastic damage concrete model by dissipation-based arc-length method

2016 ◽  
Vol 19 (12) ◽  
pp. 1949-1962
Author(s):  
Cheng Ma ◽  
Wei-zhen Chen
Keyword(s):  
Damage Model ◽  
Three Dimensional ◽  
Iterative Solution ◽  
Yield Function ◽  
Flow Rule ◽  
Arc Length ◽  
Mapping Algorithm ◽  
Return Mapping ◽  
Operator Split ◽  
Elastoplastic Damage

This article presents a three-dimensional isotropic elastoplastic damage model for concrete structures. The plasticity of concrete is described by a nonassociated flow rule, using a three-parameter yield function as well as a modified Drucker–Prager-type potential. The damage of concrete is seen as a contribution work of tensile and compressive damage, with the evolution histories driven by the internal tensile and compressive variables, respectively. The iterative solution of plasticity and damage is carried out according to the concept of operator split, where a return-mapping algorithm as well as a substepping strategy is used. The consistent tangent stiffness considering the recursive relationship among substeps is derived. For the solution of global iteration, a dissipation-based arc-length method is employed. Good agreements are found in comparisons between numerical results and experimental data on both elementary and structural levels. Furthermore, the sensitivities of parameters that control strain softening are investigated.

Experimental study of one-dimensional compression creep in crushed dry coral sand

2020 ◽  
Vol 57 (12) ◽  
pp. 1854-1869
Author(s):  
Jiabo Wang ◽  
Pengxian Fan ◽  
Mingyang Wang ◽  
Lu Dong ◽  
Linjian Ma ◽  
...  
Keyword(s):  
Relative Density ◽  
Deformation Behaviour ◽  
Particle Breakage ◽  
Time Dependent ◽  
Silica Sand ◽  
Lateral Strain ◽  
Test Results ◽  
Compression Tests ◽  
One Dimensional ◽  
Coral Sand

Understanding the time-dependent deformation behaviour of backfill coral sand is important to the long-term stability of engineering facilities built on reefs and reclaimed land. A series of one-dimensional compression tests (with no lateral strain) were carried out on crushed coral sand with a variety of grading and relative densities (50%, 70%, and 90%) sampled from the South China Sea. Axial pressure was applied in stepped loading form: 100, 200, 400, 800, and 1600 kPa. Each level loading was applied for 3 days and then completely unloaded until the deformation was stable, after which the next loading level was applied. The test results indicate: (i) the deformation of coral sand is much larger than silica sand and involves a larger proportion of time-dependent and plastic deformation; (ii) the total deformation of coral sand and proportion of irreversible deformation decreases as the relative density increases; (iii) coral sands of better grading tend to deform less in total and have larger proportions of elastic and time-dependent deformation; and (iv) the grading of coral sand changes during the deformation process due to particle breakage. Based on the test results, the relationships between particle breakage and pressure, relative density, and grading, as well as the grain-scale mechanism of the deformation, are discussed.

Criteria for defining the required duration of a creep test

2015 ◽  
Vol 52 (7) ◽  
pp. 883-889
Author(s):  
Z. Tomanovic ◽  
B. Miladinovic ◽  
S. Zivaljevic
Keyword(s):  
Creep Test ◽  
Time Dependent ◽  
Rock Properties ◽  
Theoretical Issue ◽  
Plastic State ◽  
Practical Issue ◽  
Compression Tests ◽  
Creep Tests ◽  
Material Parameters ◽  
Rock Creep

Time-dependent behaviour of some types of rocks is of the “creep” type, in particular in underground works, mining works, and in measuring procedures of rock properties. Tests used for defining material parameters or parameters relevant to defining a failure or behaviour of a material in the plastic state are usually of significantly shorter duration than the creep test. The duration of creep tests may vary from several hours to several years depending on the material being tested and the phenomenon that is the subject of the research. The required duration of the creep test, which provides reliable definition of the time-dependent material parameters of the rheological model, is a theoretical but also practical issue. The theoretical issue relates to establishing criteria for defining the required duration of the creep test. The practical issue relates to minimizing the duration of the creep test from which the necessary material parameters of the rock mass are obtained for correct numerical calculations. This paper proposes criteria for defining the required duration of a rock creep test, based on analysis of the results of unconfined uniaxial compression tests performed on marly rock samples.

Experimental Observation of Correlation Between Creep and Uniaxial Ratchetting of Sn∕37Pb and Sn∕3Ag∕0.5Cu Solder Alloys

2006 ◽  
Vol 129 (1) ◽  
pp. 82-89 ◽  
Author(s):  
Katsuhiko Sasaki ◽  
Takuji Kobayashi ◽  
Ken-ichi Ohguchi
Keyword(s):  
Creep Deformation ◽  
Empirical Method ◽  
Time Dependent ◽  
Lead Free ◽  
Compression Tests ◽  
Solder Alloys ◽  
Creep Tests ◽  
Cyclic Tension ◽  
Reliability Of Solder Joints ◽  
Free Solder

Time-dependent deformations such as creep and ratchetting of solder alloys are significant deformation phenomena that need to be understood to ensure the safety and reliability of solder joints in electronic packaging. There is much research on creep deformation of solder alloys, but ratchetting deformation, especially the correlation between creep and ratchetting deformation of solder alloys has not been investigated. This paper discusses the correlation between creep and uniaxial ratchetting deformation to establish the differences in the time-dependent deformation of lead-free and lead-containing solder alloys. Uniaxial ratchetting tests were conducted by cyclic tension–compression tests or cyclic tension–unloading tests at several ratios of the maximum to minimum stresses. Additional creep tests following the uniaxial ratchetting were also conducted to observe the effect of the uniaxial ratchetting on creep deformation. An empirical method to select an optimal lead-free solder alloy is discussed by defining a uniaxial ratchetting strain rate. The additional creep tests also show that the uniaxial ratchetting deformation has a strong correlation to the creep deformation and that the correlation is different for lead-free and lead-containing solder alloys.

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