scholarly journals Effect of Dilatancy on Instability, Pre-Instability Strain Softening of Sand Along Proportional Strain Paths

2007 ◽  
Vol 47 (4) ◽  
pp. 757-770 ◽  
Author(s):  
Peijun Guo ◽  
Xubin Su
Keyword(s):  
Strain Softening ◽  
Instability Strain ◽  
Strain Paths

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.

Deformation Modes and Lip Fracture During Hole Flanging of Circular Plates of Anisotropic Materials

1977 ◽  
Vol 99 (3) ◽  
pp. 738-748 ◽  
Author(s):  
W. Johnson ◽  
N. R. Chitkara ◽  
H. V. Minh
Keyword(s):  
Plastic Anisotropy ◽  
Orthotropic Materials ◽  
Circular Plates ◽  
Anisotropic Behavior ◽  
Plastic Properties ◽  
Different Depths ◽  
Instability Strain ◽  
Strain Paths ◽  
Hole Flanging ◽  
Deformation Modes

An experimental investigation was carried out to determine the deformation leading to failure of the hole periphery in the hole flanging process using a conical punch. Circular plates of various hole sizes and of different materials were tested to different depths of punch penetration and the lip strain paths as well as the variation of thickness around the periphery of the lip were studied. In all cases, failure of the plate was due to lip fracture and the onset of lip instability was determined from the examination of the secondary surface texture of the lip of the plate during various stages of lip deformation. The instability strain in the hole flanging process was then calculated and it was found to be influenced by the process geometry and the plastic properties of the material. Hill’s model of plastic anisotropy for orthotropic materials was applied to a plane stress case to predict the variation of thickness around the periphery of the lip and the results were compared with experimental data. The influence of the anisotropic behavior of the material on the direction of lip fracture was also investigated.

Rate Dependent Constitutive Equations of Cyclic Softening

1985 ◽  
Vol 40 (7) ◽  
pp. 653-665
Author(s):  
J. S. Mshana ◽  
A. S. Krausz
Keyword(s):  
Stress Relaxation ◽  
Low Temperature ◽  
Constitutive Equations ◽  
Strain Softening ◽  
Structural Characteristics ◽  
High Stress ◽  
Cyclic Strain ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Stress Softening

Constitutive equations of cyclic strain and stress softening for materials with low internal stress levels are derived from the rate theory. The study shows that over the high stress and low temperature range where the description of plastic flow in cyclic softening can be approximated with activation over a single energy barrier, cyclic strain softening is well related to stress relaxation process while cyclic stress softening is related to creep process. The material structural characteristics for cyclic strain softening, cyclic stress softening and stress relaxation are identical. Subsequently, it is shown that cyclic stress and strain softening within the high stress and low temperature range can be evaluated from the constitutive equations using the material structural characteristics measured from a simple stress relaxation test.

Numerical solutions for strain-softening surrounding rock under three-dimensional principal stress condition

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Sheng Yu-ming ◽  
Li Chao ◽  
Xia Ming-yao ◽  
Zou Jin-feng
Keyword(s):  
Finite Element ◽  
Principal Stress ◽  
Stress Condition ◽  
Strain Softening ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Strength Criterion ◽  
Surrounding Rock ◽  
Flow Rule ◽  
Finite Element Software

Abstract In this study, elastoplastic model for the surrounding rock of axisymmetric circular tunnel is investigated under three-dimensional (3D) principal stress states. Novel numerical solutions for strain-softening surrounding rock were first proposed based on the modified 3D Hoek–Brown criterion and the associated flow rule. Under a 3D axisymmetric coordinate system, the distributions for stresses and displacement can be effectively determined on the basis of the redeveloped stress increment approach. The modified 3D Hoek–Brown strength criterion is also embedded into finite element software to characterize the yielding state of surrounding rock based on the modified yield surface and stress renewal algorithm. The Euler implicit constitutive integral algorithm and the consistent tangent stiffness matrix are reconstructed in terms of the 3D Hoek–Brown strength criterion. Therefore, the numerical solutions and finite element method (FEM) models for the deep buried tunnel under 3D principal stress condition are presented, so that the stability analysis of surrounding rock can be conducted in a direct and convenient way. The reliability of the proposed solutions was verified by comparison of the principal stresses obtained by the developed numerical approach and FEM model. From a practical point of view, the proposed approach can also be applied for the determination of ground response curve of the tunnel, which shows a satisfying accuracy compared with the measuring data.

scholarly journals Kinematic and tectonic significance of microstructures and crystallographic fabrics within quartz mylonites from the Assynt and Eriboll regions of the Moine thrust zone, NW Scotland

1986 ◽  
Vol 77 (2) ◽  
pp. 99-125 ◽  
Author(s):  
R. D. Law ◽  
M. Casey ◽  
R. J. Knipe
Keyword(s):  
Strain Path ◽  
Extensional Flow ◽  
Crystallographic Preferred Orientation ◽  
X Ray ◽  
Tectonic Significance ◽  
Thrust Zone ◽  
Thrust Sheets ◽  
Strain Paths ◽  
Tectonic Loading ◽  
Microstructural Studies

ABSTRACTUsing a combination of optical microscopy and X-ray texture goniometry, an integrated microstructural and crystallographic fabric study has been made of quartz mylonites from thrust sheets located beneath, but immediately adjacent to, the Moine thrust in the Assynt and Eriboll regions of NW Scotland. A correlation is established between shape fabric symmetry and pattern of crystallographic preferred orientation, a particularly clear relationship being observed between shape fabric variation and quartza-axis fabrics.Coaxial strain paths dominate the internal parts of the thrust sheets and are indicated by quartzc- anda-axis fabrics which are symmetrical with respect to foliation and lineation. Non-coaxial strain paths are indicated within the more intensely deformed quartzites located near the boundaries of the sheets by asymmetricalc- anda-axis fabrics. These kinematic interpretations are supported by microstructural studies. At the Stack of Glencoul in the northern part of the Assynt region, the transition zone between these kinematic (strain path) domains is located at approximately 20 cm beneath the Moine thrust and is marked by a progression from symmetrical cross-girdlec-axis fabrics (30cm beneath the thrust), through asymmetrical cross-girdlec-axis fabrics to asymmetrical single girdlec-axis fabrics (0·5 cm beneath the thrust).Tectonic models (incorporating processes such as extensional flow, gravity spreading and tectonic loading) which may account for the presence of strain path domains within the thrust sheets are considered, and their compatibility with local thrust sheet geometries assessed.

Sign in / Sign up

Export Citation Format

Share Document