The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
David C. Dunand - One of the best experts on this subject based on the ideXlab platform.
-
Transformation superplasticity in Zircadyne 705
Journal of Materials Engineering and Performance, 2004Co-Authors: Hipolito J. Gonzalez, David C. DunandAbstract:The zirconium alloy Zircadyne 705 (main alloying addition: 2.5 wt.% Nb) was thermally cycled from 900 °C (100% β-phase) to 710 °C (80% α-phase and 20% β-phase), resulting in Strain Increments after each cycle that are linearly proportional to stress up to 2 MPa. Tensile elongations in excess of 240% were achieved without fracture. The Newtonian flow behavior and high ductility indicate that transformation superplasticity is the dominant deformation mechanism. The superplastic Strain Increment decreases as the cycling amplitude and period decrease, in general agreement with existing transformation superplasticity models.
-
Transformation Superplasticity of Zirconium
Metallurgical and Materials Transactions A, 1998Co-Authors: Peter Zwigl, David C. DunandAbstract:A tensile Strain of 270 pct was achieved for coarse-grained zirconium subjected to transformation superplasticity conditions, where Strain Increments are accumulated upon repeated thermal cycling around the allotropic transformation temperature under the biasing effect of a uniaxial tensile stress. The Strain Increment per cycle was found to consist of two equal contributions from transformations on heating and cooling and to increase linearly with the applied stress. The measured Strain Increments are in good quantitative agreement with predictions based on the average internal stress during the transformation, which was determined independently from experimental transformation times. As the cycling frequency is raised, the average Strain rate increases (a maximum value of 1.3·10−4 s−1 was measured), but the Strain Increment per cycle decreases above a critical cycling frequency, for which the sample gage section undergoes only a partial phase transformation. The resulting reduction in internal mismatch and increase in internal stress are modeled using the experimental observation that β-Zr deforms by a mixture of diffusional and dislocation creep in the stress range of interest.
Poul V Lade - One of the best experts on this subject based on the ideXlab platform.
-
non coaxiality of Strain Increment and stress directions in cross anisotropic sand
International Journal of Solids and Structures, 2014Co-Authors: Nina M Rodriguez, Poul V LadeAbstract:Abstract An experimental program was carried out in a recently developed torsion shear apparatus to study the non-coaxiality of Strain Increment and stress directions in cross-anisotropic deposits of Fine Nevada sand. Forty-four drained torsion shear tests were performed at constant mean confining stress, σ m , constant intermediate principal stress ratios, as indicated by b = ( σ 2 − σ 3 )/( σ 1 − σ 3 ), and constant principal stress directions, α . The experiments were performed on large hollow cylinder specimens deposited by dry pluviation and tested in an automated torsion shear apparatus. The specimens had height of 40 cm, and average diameter of 20 cm, and wall thickness of 2 cm. The stress–Strain behavior of Fine Nevada sand is presented for discrete combinations of constant principal stress direction, α , and intermediate principal stress. The effects of these two variables on the non-coaxiality are presented. The experiments show that the directions of the Strain Increments do not in general coincide with the directions of stresses, and there is a switch from one to the other side between the two quantities.
-
CHARACTERIZATION OF CROSS-ANISOTROPIC SOIL DEPOSITS FROM ISOTROPIC COMPRESSION TESTS
Soils and Foundations, 2005Co-Authors: Poul V Lade, Andrei V. AbelevAbstract:Isotropic compression tests have been performed on two fine sands. Specimens of Nevada sand were prepared by air pluviation and by funnel deposition followed by tapping to relative densities of 30, 50, 70, and 90%. Specimens of Santa Monica Beach sand were prepared by air pluviation to a relative density of 90%. All specimens exhibited cross-anisotropic behavior, both in terms of total Strains and in terms of unloading Strains. Small pressure cycles performed during loading and unloading were used to study elastic behavior. The inclination angles of the total and plastic Strain Increment vectors relative to the hydrostatic axis in the principal stress space were used to express and to study the evolution of cross-anisotropy in the sand deposits. In the context of elasto-plastic constitutive modeling, the variation of the inclination of the plastic Strain Increment vector was further characterized by a rotation of the plastic potential surface as a means to capture the inherent cross-anisotropic behavior observed in such sand deposits.
Dieter Stolle - One of the best experts on this subject based on the ideXlab platform.
-
micromechanical analysis of non coaxiality between stress and Strain Increment in granular materials
Acta Geotechnica, 2020Co-Authors: Dieter StolleAbstract:It is known that non-coaxiality between the directions of the principal stresses and the principal plastic Strain Increments in granular material is physically resulted from the material and mechanical anisotropy as well as their evolutions. A novel study was conducted to verify the contributions of the material and mechanical anisotropies to the magnitude of non-coaxiality during the rotation of the principal stress orientation. Micromechanical analysis indicates that the non-coaxial behavior can occur in a granular assembly with mostly non-sliding contacts acting. Moreover, the magnitude of non-coaxiality is a function of the stress level, the ratio of contact stiffness, the material and mechanical anisotropy as well as their evolutions. This has been confirmed by numerical simulation. The numerical results indicate that the non-sliding interparticle connectivity is one of the dominant sources of non-coaxiality. The interparticle sliding has been found to reduce the magnitude of the non-coaxiality.
Marte Gutierrez - One of the best experts on this subject based on the ideXlab platform.
-
Influence of the intermediate principal stress and principal stress direction on the mechanical behavior of cohesionless soils using the discrete element method
Computers and Geotechnics, 2017Co-Authors: Liangliang Chen, Marte GutierrezAbstract:Abstract In this paper, the Discrete Element Method (DEM) is employed to numerically explore the response of hollow cylinder specimens of granular soils under complex stress paths. Two series of numerical tests are conducted to clarify the effects of the principal stress direction α and the intermediate principal stress through the b-value on the mechanical response of granular materials. The effects of α and b-value on the non-coaxiality of the principal stress and the principal plastic Strain Increment directions are investigated. It is observed that b-value and α significantly affect the non-coaxial behavior of granular materials. Finally, the results are discussed and compared with those obtained from physical laboratory tests.
-
non coaxiality and energy dissipation in granular materials
Soils and Foundations, 2000Co-Authors: Marte Gutierrez, Kenji IshiharaAbstract:ABSTRACT The paper presents a theoretical and experimental study of the effects of non-coaxiality or non-coincidence of the principal stress and the principal plastic Strain Increment directions on the behaviour of granular materials. Experimental results from hollow cylindrical tests on sand involving principal stress rotation which support previously published results on non-coaxiality are presented. These results imply that constitutive relations cannot be sufficiently formulated in the principal stress space unless the deviations between the principal stress and plastic Strain Increment directions are taken into consideration. It is shown that plasticity formulations with plastic potentials that are scalar functions of the stress invariants alone implicitly assume coaxiality and cannot be used for loading involving principal stress rotation. The paper presents a comprehensive analysis of the effects of non-coaxiality on the energy dissipation of sand. The paper shows that energy dissipation calculated from the principal stresses and the principal plastic Strain Increments or from the stress and plastic Strain Increment invariants, would be erroneous and would over-estimate the amount of dissipated energy during loading in the case of non-coaxial flow. A non-coaxiality factor is introduced in order to account for the effects of non-coaxiality on the energy dissipation equation and in a stress-dilatancy relation for granular materials. Explicit expressions of the non-coaxiality factor for two-and three-dimensional loading conditions are given at the end of the paper. Experimental results are presented to show the validity of the proposed energy dissipation and stress-dilatancy equations.
-
FLOW THEORY FOR SAND DURING ROTATION OF PRINCIPAL STRESS DIRECTION
Soils and Foundations, 1991Co-Authors: Marte Gutierrez, Kenji Ishihara, Ikuo TowhataAbstract:The paper presents the results of a series of tests using the hollow cylindrical apparatus on the flow of sand during loadings involving rotation of principal stress direction. The results establish an important feature of the flow of sand during principal stress rotation, namely, nonuniqueness of flow or the dependency of the plastic Strain Increment direction on the stress Increment direction. This feature contradicts the usual assumption in plasticity theory of a unique flow during loadings causing plastic deformations in a material. Guided by the results of the experiments, a plastic potential theory capable of representing the dependency of the flow of sand on the stress Increment direction is proposed. Comparisons with the experimental results and the outcome of stress probe experiments show the validity of the proposed theory.
Ali Nayebi - One of the best experts on this subject based on the ideXlab platform.
-
Cyclic uniaxial and multiaxial loading with yield surface distortion consideration on prediction of ratcheting
Mechanics of Materials, 2012Co-Authors: H. Rokhgireh, Ali NayebiAbstract:Abstract In this study, the yield surface distortion was incorporated in the cyclic plasticity modeling as well as its center movement. The combination of Chaboche’s model and the yield surface distortion model of Baltov was used in a set of uniaxial and multiaxial loadings. The variation of the stress amplitude and the mean stress and different multiaxial loadings such as tension-torsion tests were studied. It was shown that the consideration of the distortion of the yield surface via the distortion parameter and its sign in modeling has an important effect on the plastic Strain Increment determination and so on the ratcheting rate. The combined model was applied to the experimental results. It was shown that the combination of the nonlinear kinematic hardening model of Chaboche and the yield surface distortion leads to a good estimation of the ratcheting Strain Increment in different uniaxial and multiaxial tests.
