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Keywords: multiphase flow, Lagrangian particle tracking, superellipsoid, collision, friction
Published in DKUM: 28.03.2024; Views: 171; Downloads: 9
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Abstract: This paper presents the stress-dilatancy behavior of sand incorporating particle breakage. A series of the drained triaxial tests were conducted on the Silica sand No.5 and the pre-crushed sands that were produced by several drained triaxial tests on Silica sand No.5 under 3MPa confining pressure in simulating the high-pressure shear process to result in particle breakage, to investigate the stress-dilatancy behavior of sand incorporating particle breakage. For a given initial void ratio, particle breakage was found to result in deterioration of the stress-dilatancy behavior in the impairment of the dilatancy of sand to become more contractive with a reduction in the maximum dilatancy angle and the excess friction angle (the difference between the peak-state friction angle and the critical-state friction angle). By introducing the concept of the skeleton void ratio in considering particle breakage, a linear stress-dilatancy relationship between the maximum dilatancy angle-over-the excess friction angle and peak-state skeleton void ratio was proposed in semi-logarithmic plane and popularized to the mobilized stress-stain state as a stress-dilatancy equation pertaining to particle breakage, which would be useful in assessing the evolution of the stress-dilatancy behavior of sand during particle breakage.
Keywords: dilatancy angle, friction angle, particle breakage, sand, triaxial tests
Published in DKUM: 18.06.2018; Views: 1706; Downloads: 122
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Abstract: A series of cyclic triaxial tests was performed on snail-soil samples with different porosities. The cyclic loading was performed with a Wykeham Farrance cyclic triaxial system. The investigation was based on a series of tests in which the following conditions were varied: the initial effective pressures (50, 100, and 150 kPa), the void ratio after consolidation (2.0–1.2) and the cyclic loading expressed by the cyclic stress ratio CSR (0.1–1.0). Measurements were made of the stress, the deformation and the pore-water pressure. The results of the tests show that interdependency exists between the geomechanical characteristics and the porosity. These relationships can be expressed as functions of the density, the porosity or the water content. It is evident from the results that the changes in the coefficient of permeability, the coefficient of consolidation, and the coefficient of volume compressibility are non-linear with respect to the changes in the porosity. However, the changes at high porosity are much greater than the changes at low porosity, and the changes of the mechanical parameters, such as the Young’s modulus, Poisson’s ratio, and the friction angle, are indistinct and almost linear at lower changes of porosity, and after that become non-linear. The initial void ratio e is extremely high and the snail soil is liquid after consolidation; a volume strain of εvol > 16 % is needed for the plastic limit state. The chemical and mineral composition, the particle size distribution and the remains of micro-organisms in the snail soil are constants. In addition, the specific surface is independent of the porosity and the density or unit weight, the porosity and the volume strain are in the well-known correlation. The performed cyclic triaxial tests show the dynamic characteristics of the snail soil and the influence of the porosity on the cyclic loading strength. The snail soil was recognized as a highly sensitive material. A large strain appears after the initial cycles. The pore pressure, increases already during the first cycle, to the hydrostatic part of the cyclic loading, or more (depending on CSR). The damping ratio increases exponentially with strain, after some cycles it reach its maximum value, and after that it decreases to the asymptotic value. The reason for such behaviour is the large deformation. The maximum and asymptotic values of the damping ratio are a changed minimum with a void ratio. There is obviously no influence of the porosity on the damping ratio. The shear modulus is described in relation to shear strain. The increasing of the pore pressure is independent of the porosity until it reaches some value of the pore-pressure ratio (>0.7). Similarly, the increasing of the shear strain becomes dependent on the void ratio until it reaches some particular value of the shear strain (>3%). The deformation and failure lines for the different porosities are determined from the relationship between the shear stress and the effective stress at some shear strain, after 10 cycles. The relationships between the shear stress and the effective stress at some value of the pore-pressure ratio are expressed in a similar way. Two kinds of criteria were used to determine the triggering of liquefaction during the cyclic triaxial tests: first, when the pore pressure becomes equal to the effective confining pressure, and, second, when the axial strain reaches 5% of the double amplitude.
Keywords: snail soil, cyclic triaxial test, porosity, permeability, consolidation, Young’s modulus, shear modulus, damping ratio, Poisson’s ratio, friction angle
Published in DKUM: 18.05.2018; Views: 1700; Downloads: 98
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Abstract: In this paper, the influence of rotation speed and welding speed on the impact strength, microstructure and cross section micro hardness of FSW welded joints of Al-Zn-Mg-Cu high strength aluminium alloy is studied. Rotation speed was varied from 750 min−1 to 850 min−1 and welding speed from 60 mm/min to 80 mm/min. It was found that the energy of crack propagation is up to three times higher than the energy of crack initiation. This ratio was found by testing the Charpy notched specimens taken from left and right from the weld centre, 4 mm from the notch in a direction opposite to a direction of welding. Micro hardness distribution in the nugget does not show large dissipation of value regardless if the measuring point is in the upper or lower section of the nugget. Weld microstructure characteristics and zones are clearly defined at the basis of grain size and material flow.
Keywords: dynamic recrystallization, friction stir welding, impact strength, micro hardness distribution
Published in DKUM: 12.07.2017; Views: 1551; Downloads: 397
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