The structure of deformation autosoliton fronts in rocks and geomedia

The paper describes numerical modeling of the generation and propagation of the fronts of moving deformation autosolitons in a loaded nonlinear strong medium. It presents solving a system of dynamic equations for solid mechanics, using an equation of state written in a relaxation form that takes into account both an overload of the solid medium and subsequent stress relaxation. The structure of a deformation autosoliton front is investigated in detail. It is shown that the front of a deformation autosoliton that is moving in an elastoplastic medium is a shear band (i.e. a narrow zone of intense shearing strain), which is oriented in the direction of maximum shear stress. Consecutive formation of such shear bands can be viewed as deformation autosoliton perturbations propagating along the axis of loading (compression or extension). A fine structure of a deformation autosoliton front is revealed. It is shown that slow autosoliton dynamics is an integral component of any deformation process, including the seismic process, in any solid medium. In contrast to fast autosoliton dynamics (when the velocities of stress waves are equal to the speed of sound), slow deformation autosoliton perturbations propagate at velocities 5–7 orders of magnitude lower than the velocities of sound. Considering the geomedium, it should be noted that slow dynamics plays a significant role in creating deformation patterns of the crust elements.

FINITE STRAIN MEASUREMENT USING IMAGE ANALYSIS UNDER REVERSE SHEAR AFTER FORWARD SHEAR

The purpose of this research is to investigate the progress of local deformation under finite deformation by using image analysis based on the Natural Strain theory. Since Natural Strain used in the image analysis can satisfy the addition law of strain on an identical line element and can remove the rigid body rotation from shearing strain component, it is an effective strain for representing stress and strain behavior under large deformation. Therefore, in this research, these features of Natural Strain theory will be incorporated into the method of image analysis. In the present study, using the test pieces made of high purity tough pitch copper, the local deformation occurring under large simple shear is investigated by comparing the strains in each element from the upper position to the middle position with the average strain in the gauge length. In order to investigate the progress of local deformation caused by differences of strain hardening in the material, the experiments are conducted under different deformation histories which are given by applying reverse shear after applying forward shear with different sizes. Consequently, it is revealed that if the value of plastic strain obtained by integrating over the whole deformation path is almost the same, the progress of local deformation is approximately the same even if the deformation path is different.

A Shearing Strain Model for Cylindrical Stress States

A shearing strain model for soil was developed that includes soil behavior under compressive normal and shear stresses great enough to attain maximum compaction. The model was developed for a clay and a clay loam from triaxial data with various stress loading paths. This model relates the ratio of maximum shear stress acting on the cylindrical sample (tmax) to major principal stress (s1), to the ratio of maximum natural shearing strain to natural volumetric strain occurring after shear stress is initiated. The model accurately describes the shearing distortion of triaxial soil samples under cylindrical stress loading prior to yielding by plastic flow. This model predicts soil shearing strain for input stress states that realistically represent field conditions. Keywords: Principal stress and strain, Shearing strain, Shear stress, Soil compaction, Soil parameters, Triaxial tests.

Dynamic Response of Bridge-Ship Collision Considering Pile-Soil Interaction

According to most countries’ norms, and to find the effect of the bridge collision the equivalent static method was designed for bridge-ship collision, ignoring the dynamic effects of shocks. It is sharply different from actual situation. So based on the theory of Winkler foundation, shearing strain theory of Timoshenko and potential energy variation functional principle of Hamilton, the simulation models of bridge piers was built considering the pile–soil interaction. Lateral transient vibration equation of bridge piers was concluded. Based on the theory of integral transform, the differential equation of the collision system and the boundary conditions were transformed with Laplace transformation; the analytical solution of the stress wave in frequency domain was concluded. And then the inversion of solution in frequency domain was carried out using Matlab based on the Crump inverse transformation. Finally the dynamic response law of displacement, normal stress and the shear stress of bridge piers were obtained.

Benefits of Using Diamond Dies for Cold Alternate Drawing of Magnesium Alloys

In recent years, due to its low density and high strength/weight ratio, magnesium alloy wires has been considered for application in many fields, such as welding, electronics, medical field (for production of stents). But for those purposes, we need to acquire wires with high strength and ductility. For that we purpose we proposed alternate drawing method, which is supposed to highly decrease the shearing strain near the surface of the wire after drawing, by changing the direction of the wire drawing with each pass and thus acquiring high ductility wires.We have done research on the cold alternate drawing of magnesium alloy wires, by conducting wire drawing of several magnesium wires and testing their strength, hardness, structure, surface and also finite element analysis, we have proven the increase of ductility at the expense of some strength.In this research we are looking to further improve the quality of the drawn wires by examining the benefits of using diamond dies over tungsten carbine dies. Using the alternate drawing method reduces the strength of the drawn wires and thus lowering their drawing limit. By using diamond dies we are aiming to decrease the drawing stress and further increase the drawing limit of the alternate drawn wires and also improve the quality of the finishing surface of the wires. With this in mind we are aiming to produce a good quality wire with low diameter, high ductility, high strength and fine wire surface.

IMAGE ANALYSIS BASED FINITE STRAIN MEASUREMENT OF LOCAL DEFORMATION UNDER UNIAXIAL LOAD USING NATURAL STRAIN

This paper describes the effectiveness of image analysis based on the Natural Strain theory for measuring the finite strain. Since the additive law of strain on an identical line element can be satisfied and the rigid body rotation can clearly be removed from the shearing strain components, the Natural Strain theory is significantly effective for representing the stress-strain behavior under large elasto-plastic deformation. In this study, the strain measurements under large deformation are conducted by making use of such merits into the image analysis. In our previous studies, in order to verify the effectiveness of this method, the results of strain measurement by image analysis have been compared with the results of conventional strain measurement based on the displacement meter. Consequently, since the results of both measurements almost coincide, the validity of this image analysis has been confirmed. However, these experiments were limited to uniform deformation fields, although in the range of finite deformation. Hence, as for the local deformation, the detailed measurements have not been carried out yet in our previous study. So, in this paper, the local deformations generated under uniaxial tension and simple shear are investigated as the fundamental research. Especially, the progress of local deformations is revealed by comparing the measured values of upper and middle positions in the specimen.

Shear strength of clayey soils from the vicinity of Gorlice and Ciężkowice

The work presents results of maximum and residual strength tests of six clayey soils from the landslide areas near Gorlice and Ciężkowice. The tests were carried out in a direct shear apparatus on samples of dimensions 60 × 60 mm that were sheared at least three times. A shearing strain rate was equal 0.1 mm·min–1, and the range of horizontal deformation of the samples was equal 20%. The results of the tests revealed that multiple shearing of the soil caused a significant decrease of its shear strength, resulting in significant changes in cohesion, and the smaller changes in the angle of internal friction. It was shown that the three-time shearing reduced the initial shear strength of about 50%, and further three series of shearing decreased it approximately 15% more. The study also showed that by using a Coulomb-Mohr shear strength linear equation, the analyzed soils had a little residual cohesion. Therefore, to describe the characteristics of the residual strength, there were used two non-linear equations proposed by Mesri and Shanien (2003) and Lade (2010), which led to the same results. It was also shown that the use of non-linear characteristics of the residual strength at low values of the normal stresses gave more unfavourable results of stability calculations in relation to the method based on the linear strength characteristic taking into consideration the presence of the residual cohesion.

Mechanical Behavior Analysis of Concrete Short Columns Pushed out from Over-Thick Steel Tube

An axial symmetry elasticity model of the concrete short column which is pushed out from over-thick steel tube is set up, and the equations of displacement method are derived. The experiment of push-out test of the short column was carried out. On the base of the test, the adhesive thin-layer between the concrete and the over-thick steel tube is introduced. The experimental results show that the shearing stress in the adhesive thin-layer is uniform along the height, which is coincide with the results obtained by the axial symmetry elasticity model of the concrete short column set up in this paper. Therefore, the adhesive shearing stress between steel tube and concrete can be precisely measured by the push-out test of the concrete short column and the relation of shearing stress-shearing strain of the adhesive thin-layer can be determined.

Joining Experiment of Aluminum Sheets Using High-Speed Shearing

A novel method for joining of sheet edges was investigated. It makes use of the sheared faces under high-speed. The temperature remarkably elevates and the material softens in the thin severely deformed layer. The cut faces are contacted each other with sliding motion immediately after shearing. Sheet materials are a pure aluminum A1050 and its alloy A5052. Two similar sets of circular shearing punch, die and sheet are concentrically stacked in the device for performing the simultaneous shearing. The upper sheared circular sheet slides into the hole of the lower one for joining shortly after the shearing. Strain-rate order was about 104/s in shearing, where the punches were driven by a drop-weight. Quasi-static test was also conducted for comparison. Joining was achieved only in the high-speed test. Joining boundary was not visible at the central portion in thickness, though the gap openings were seen near both sheet surfaces. Joining efficiency was evaluated as the relative strength to the tensile strength of the material. It was improved as the shearing clearance becomes smaller. The maximum efficiency was about 30 % for A1050 material. It is about 25 % for A5052. It was at most 10 % in the joining of A1050 and A5052.