Experimental assessment of the response of sands under shear–volume coupled deformation

2008 ◽  
Vol 45 (9) ◽  
pp. 1310-1323 ◽  
Author(s):  
S. Sivathayalan ◽  
P. Logeswaran
Keyword(s):  
Shear Strength ◽  
Boundary Conditions ◽  
Pore Pressure ◽  
Effective Stress ◽  
Strain Path ◽  
Stress Ratio ◽  
Volumetric Strain ◽  
Strain Paths ◽  
Pressure Boundary Conditions ◽  
Effective Stress Ratio

An experimental study of the behaviour of an alluvial sand under different strain increment paths representing shear–volume coupled deformation is presented. Both pore pressure and pore volume change simultaneously in these tests. Linear strain paths with different levels of limiting volumetric strain and nonlinear strain paths that simulate different pore pressure boundary conditions were applied to the soil specimen in the laboratory. The strain paths imposed included both expansive and contractive volumetric deformation. Nonuniform excess pore pressures generated during earthquakes (on account of the heterogeneity in natural soils) often lead to such deformation in situ following the end of strong shaking. The shear strength of the soil could decrease significantly when the pore pressure boundary conditions result in volume inflow that leads to a considerable reduction of the effective confining stress. The rate of volume inflow plays a significant role on the resulting stress–strain and pore pressure responses. Both the peak and the minimum shear strength mobilized during the test were significantly dependent on the strain path. The effective stress ratio at the instant of peak pore pressure is independent of the strain path followed, and it is equal to the effective stress ratio noted at the instant of phase transformation in undrained tests.

Numerical and Experimental Investigations of Key Assumptions of Analytical Failure Models in Sheet Metal Forming

2012 ◽  
Author(s):  
Raed Hasan ◽  
Tugce Kasikci ◽  
Igor Tsukrov ◽  
Brad L. Kinsey
Keyword(s):  
Effective Stress ◽  
Stress Ratio ◽  
Numerical Data ◽  
Strain Ratio ◽  
Material Behavior ◽  
Analytical Models ◽  
Experimental Investigations ◽  
Shell Elements ◽  
Strain Paths ◽  
Effective Stress Ratio

In this paper, the key assumptions in the M-K and effective stress ratio models are investigated for AISI 1018 steel specimens with a thickness of 0.78 mm using experimental and numerical data from Marciniak tests. The experimental procedure included Digital Imaging Correlation (DIC) to measure the major and minor in-plane strains. Strain components were obtained at points inside (i.e., the defect region) and adjacent (i.e., the safe regions) to the high strain concentrations for four different strain paths. In the numerical analysis, FEA simulations with Marc Mentat were performed with shell elements to investigate the four specimen geometries. The key assumptions of interest are the incremental major strain ratio from M-K model and the critical stress concentration factor from effective stress ratio model. Thus, the mechanics- and material-based failure phenomena in these two analytical models are examined in this paper to provide insight into the material behavior at failure.

Numerical and Experimental Investigations of Key Assumptions in Analytical Failure Models for Sheet Metal Forming

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Raed Hasan ◽  
Tugce Kasikci ◽  
Igor Tsukrov ◽  
Brad L. Kinsey
Keyword(s):  
Effective Stress ◽  
Stress Ratio ◽  
Numerical Data ◽  
Strain Ratio ◽  
Material Behavior ◽  
Analytical Models ◽  
Experimental Investigations ◽  
Shell Elements ◽  
Strain Paths ◽  
Effective Stress Ratio

In this paper, the key assumptions in the M-K and effective stress ratio models are investigated for AISI 1018 steel specimens with a thickness of 0.78 mm using experimental and numerical data from Marciniak tests. The experimental procedure included Digital Imaging Correlation (DIC) to measure the major and minor in-plane strains. Strain components were obtained at points inside (i.e., the defect region) and adjacent (i.e., the safe regions) to the high strain concentrations for four different strain paths. In the numerical analysis, FEA simulations with Marc Mentat were performed with shell elements to investigate the four specimen geometries. The key assumptions of interest are the incremental major strain ratio from M-K model and the critical stress concentration factor from effective stress ratio model. Thus, the mechanics- and material-based failure phenomena in these two analytical models are examined in this paper to provide insight into the material behavior at failure. Also, data are presented that shows clearly the localization (both size and strain value) for the various strain paths.

Effective Stress Ratio of Triangular Pattern Perforated Plates

2008 ◽  
Author(s):  
Naoto Kasahara ◽  
Hideki Takasho ◽  
Nobuchika Kawasaki ◽  
Masanori Ando
Keyword(s):  
Effective Stress ◽  
Material Properties ◽  
Constitutive Equations ◽  
Stress Ratio ◽  
Equivalent Material ◽  
Solid Materials ◽  
Perforated Plates ◽  
Non Linear ◽  
Effective Stress Ratio ◽  
Equivalent Material Properties

Tubesheet structures utilized in heat exchangers have complex perforated portions. For realistic design analysis, axisymmetric models with equivalent solid materials of perforated plate are conventionally adopted to simplify perforated area (figure1). Sec.III Appendix A-8000 (ASME 2004) provides elastic equivalent solid materials for flat tubesheets. Plastic properties were studied by Porowski et al. (1974), Gorden et al. (2002) and so on. Elevated temperature design of tubesheets requires plastic and creep properties in addition. The purpose of this study is to develop a general determination method of non-linear equivalent material properties for perforated plates and to confirm their applicability to both flat and spherical tubesheets. Main loadings of tubesheets in fast reactor heat exchanges are inner pressure and thermal stress at transient operations. Under above conditions, average stress of perforated area becomes approximately equi-biaxial. Therefore, average inelastic behaviors of various perforated plates subjected to equi-biaxial field were investigated by inelastic finite element method. Though above investigations, Authors clarified that perforated plates have their own effective stress ratio (ESR). ESR is a function of geometry and is independent from their materials. ESR can determine non-linear equivalent material properties of perforated plates for any kind of constitutive equations of base metals. For simplified inelastic analysis of perforated plates, the brief equations were proposed to determine equivalent plastic and creep material properties for perforated plates. It is considered that physical meaning of ESR is an effective stress ratio between perforated plates and equivalent solid plates. ESR is a function of geometry and is independent from constitutive equations. ESR can determine non-linear equivalent material properties for perforated plates from any kind of constitutive equations of base materials. Assumptions in ESR are von Mises’s equivalent stress-strain relationship and equi-biaxial loadings. Applicability of ESR was investigated through finite element analyses of various flat and spherical tubesheets.

scholarly journals Analysis of models for porosity evolution in reservoir during steam injection

2019 ◽  
pp. 91-105
Author(s):  
A A Kostina ◽  
M S Zhelnin ◽  
O A Plekhov
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Balance Equation ◽  
Volumetric Strain ◽  
Gravity Drainage ◽  
Oil Viscosity ◽  
Fluid Filtration ◽  
Water Steam ◽  
Porosity Evolution ◽  
Steam Assisted Gravity Drainage

Depletion of traditional hydrocarbon reserves leads to the development of extracting methods for heavy crude oil and bitumen characterized by extremely high viscosity. The most effective technology is the steam-assisted gravity drainage. The aim of this method is to decrease oil viscosity by injection of hot steam into the reservoir. Increase of temperature, pore pressure and change of stress-strain state during this process significantly affect porosity which is the key storage parameter of the reservoir. This work is devoted to the analysis of models for porosity evolution during the steam-assisted gravity drainage process. The authors have developed an original model to describe steam-assisted gravity drainage which includes the mass balance equation for a three-phase flow, the energy balance equation involving latent heat due to vaporization/condensation of water/steam and Darcy’s law for fluid filtration. Numerical implementation of the proposed equations was based on the pressure-saturation algorithm. The results have shown a substantial qualitative and quantitative disagreement between the considered models. Coupling of porosity with volumetric strain leads to the rise of its magnitude. Models relating porosity to pore pressure show simultaneous existence of high-porous (near the injection well) and low-porous (near the production well) areas. In case when porosity is dependent on effective stress a circular area of a compacted soil is formed. Therefore, to obtain a correct estimation of the oil production rate in an arbitrary reservoir it is necessary to define the prevailing mechanism of porosity evolution (volumetric strain, pore pressure or effective stress).

The Law of Effective Stress for Rocks in Light of Results of Laboratory Experiments / Prawo Naprężeń Efektywnych Dla Skał W Świetle Wyników Badań Laboratoryjnych

2012 ◽  
Vol 57 (4) ◽  
pp. 1027-1044 ◽  
Author(s):  
Andrzej Nowakowski
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Compression Test ◽  
Triaxial Compression ◽  
Volumetric Strain ◽  
Pore Fluid ◽  
Effective Pressure ◽  
Test Results ◽  
Strength Limit ◽  
The Law

Abstract This paper presents the results of laboratory tests carried out in order to formulate effective stress law. The law was sought for two different cases: first - when rock was treated as a porous Biot medium (Biot, 1941; Nur & Byerlee, 1971) and second - when the law was formulated according to definition of Robin (1973) developed by Gustkiewicz (1990) and Nowakowski (2007). In the first case coefficents (4) and (5) of the Biot equation (3) were were determined on the basis of compressibility test, in the second one effective pressure equation (9) and effective pressure value (11) were found on the basis of results of so called individual triaxial compression test (see Kovari et al., 1983) according to the methodology given by Nowakowski (2007). On the basis of Biot coefficients set of values was found that volumetric strain of the pore space described by a coefficient (5) was not dependent on the type of pore fluid and the pore pressure of only, while in case of volumetric strain of total rock described by coefficient (4) both the structure and texture of rock were important. The individual triaxial compression test results showed that for tested rock an effective pressure equation was a linear function of pore pressure as (15). The so called Rebinder effect (Rehbinder & Lichtman, 1957) might cause, that the α coefficient in equation (15) could assume values greater than one. This happened particularly in the case when the porous fluid was non-inert carbon dioxide. In case of inert pore fluid like kerosene the test results suggested that the a coefficient in equation (15) decreased while the differential strength limit was increasing. This might be caused by, so called, dillatancy strengthening (see Zoback & Byerlee, 1975). Another considered important parameter of the equation (15) was the value of the effective press p'. The results showed that the value of this parameter was practically independend on the pore fluid type. This conclusion was contrary to previous research (see, for example, Gustkiewicz et al., 2003 and Gustkiewicz, 1990) so these results should be treated with caution. There are no doubts, however, over p' increasing simultaneously with increase in Rσ1-σ3. Basically, the differential strength limit of the specimen is greater the greater is confining pressure applied to it. Thus, higher Rσ1-σ3 values are accompanied by higher p'.

Behaviour of sands under generalized drainage boundary conditions

2007 ◽  
Vol 44 (2) ◽  
pp. 138-150 ◽  
Author(s):  
Siva Sivathayalan ◽  
Paramaguru Logeswaran
Keyword(s):  
Boundary Conditions ◽  
Pore Pressure ◽  
Strain Softening ◽  
Soil Mechanics ◽  
Excess Pore Pressure ◽  
Systematic Change ◽  
Direct Evaluation ◽  
Liquefaction Susceptibility ◽  
Volumetric Deformation ◽  
Strain Paths

An experimental study of the behaviour of sands under generalized drainage boundary conditions is presented. The influence of partially drained conditions, which generally is a reflection of the loading rate and the permeability of the soil, has been studied by limiting the volumetric deformation between drained and undrained states. The effect of potential pore-pressure variations in situ has been assessed by simulating various levels of volumetric deformation during shear. Conventional drained and undrained tests were also carried out on the same sands to enable a direct evaluation of the effect of drainage. A triaxial device with the ability to control strain-paths was used to carry out the tests, and all tests were performed under compression loading with no change in total lateral stress. A systematic change in the stress–strain response was noted as the drainage conditions gradually change from drained to undrained. The maximum excess pore pressure generated owing to inhibition of drainage is almost linearly related to the amount of drainage blocked. These results support the contention that the undrained state may not represent the most damaging scenario under field loading conditions. Much smaller minimum shear strength values compared with the undrained strength were measured when pore-pressure boundary conditions caused expansive volume changes. The domain of strain-softening response, and hence liquefaction susceptibility, increased owing to such loading.Key words: partial drainage, liquefaction, strain softening, laboratory testing, soil mechanics.

Cyclic fatigue crack growth from indentation flaw in silicon nitride: Influence of effective stress ratio

1994 ◽  
Vol 42 (11) ◽  
pp. 3837-3842 ◽  
Author(s):  
Guen Choi ◽  
Susumu Horibe ◽  
Yoshikuni Kawabe
Keyword(s):  
Fatigue Crack ◽  
Silicon Nitride ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Effective Stress ◽  
Stress Ratio ◽  
Cyclic Fatigue ◽  
Effective Stress Ratio

scholarly journals Effective stress response of clay to undrained cyclic loading

1994 ◽  
Vol 31 (5) ◽  
pp. 714-727 ◽  
Author(s):  
M. Zergoun ◽  
Y.P. Vaid
Keyword(s):  
Stress Response ◽  
Cyclic Loading ◽  
Effective Stress ◽  
Stress Ratio ◽  
Cyclic Stress ◽  
Initial Direction ◽  
Marine Clay ◽  
Test Characteristic ◽  
Characteristic Behaviour ◽  
Effective Stress Ratio

The effective stress response of a natural marine clay to slow undrained symmetrical cyclic reversal in shear stress is presented. The effects of cyclic principal stress difference amplitude, cyclic principal effective stress ratio amplitude, initial direction of loading, and step increase in cyclic stress level on the clay stress–strain response are studied under stress conditions of the triaxial test. Characteristic behaviour patterns are identified in terms of effective stresses. Key words : clay, cyclic loading, effective stress, hysteretic work, loading direction, step loading.

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