Papers by Keyword: Effective Stress

Abstract: The article is devoted to studying the rheological properties of metals and alloys in a cold state based on the results of tensile tests of cylindrical specimens. The aim of this study is to apply the method for optical measuring the neck profile for determining the hardening curve and to evaluate the accuracy of the data obtained using reverse simulation of the test process. For the study, the specimen of aluminum was used, which is characterized by increased plasticity and a continuous stage of deformation concentrated in the neck. The experimental data were processed using the Bridgman, Davidenkov-Spiridonova, and Ostsemin models. The results of the reverse simulation that performed using the hardening curve based on the Ostsemin model have the greatest convergence with the laboratory experiment in terms of tensile force and convergence at the level of other models in terms of neck shape change.

Abstract: This study uses the dies of the dray fasteners processing graphics provided by the fastener’s industry to establish 3D dies and components solid models based on the embedded drawing function tools provided by the component model (Standard.ipt) of Autodesk Inventor CAD software. After finishing the dies and components drawing, the integrated assembly drawing of dies can be obtained through the assembly model (Standard.iam) firstly. Three stages forming processes can be conducted and carried out the FEM simulation to check the forming acceptance. The effective stress, the effective strain, the velocity field, and the forging force can be obtained by the FEM simulation. Moreover, the realistic experiment can be performed to verify the acceptance of FEM simulation. The dimensions of final product can be measured to get the errors between FEM and experiment. It is noted that the errors show a good agreement with the experiment.

Abstract: The paper presents the simulated 3D Finite Element Model (FEM) while grinding the Ti6Al4V alloy using a single abrasive wheel. Grinding simulation was carried out using a Lagrangian finite element based machining model to predict the tangential cutting force, temperature distribution at grinding zone and the effective stress and strain. All simulations were performed according to the cutting conditions designed, using the plane up-grinding. The work piece was considered as typical materials to machine difficulty. As the cutting speed is increased from 15 m/min to 33 m/min at higher feed rate, a maximum value of 750 MPa stress and higher temperature localization to an extent of 900°C at grinding zone were observed.

Abstract: A u-p formulation based on the mixture theory is presented for describing the dynamic flow and deformation behaviour of unsaturated soils. In the formulation proposed, the solid displacement, pore water pressure, and pore gas pressure are considered as primary variables. The spatial discretization of the governing equations is achieved using finite element method, whereas the time integration is conducted using the Newmark technique. The coupling between solid and fluid phases is enforced according to the effective stress principle taking suction dependency of the effective stress parameter into account. Numerical examples and comparisons with known analytical solutions are presented, demonstrating the performance of the proposed approach.

Abstract: Based on the principle of disc slitting process, a 3D model of the disc slitting process for galvanized sheet was established by using DEFORM-3D software, and the deformation, fracture and material effective stress of galvanized sheet were analyzed. The surface morphology of numerical simulation is in good agreement with the actual result. The curve of shearing force was obtained and well matched with the change rule of slitting process. Compared with the theoretical calculation result, the simulation result is reliable and can provide a reference for the calculation of shearing force.

Abstract: Under cyclic load, the major shortcoming–ratcheting is produced in Wolffersdorff hypoplastic constitutive model. For eliminating ratcheting, Wolffersdorff hypoplastic model is ameliorated based on intergranular strain tensor. The added parameters in ameliorated model are determined by optimization method. Under cyclic load of triaxial consolidation undrained condition, the mechanics features of sand are described by the ameliorated Wolffersdorff hypoplastic constitutive model. Preliminary result shows that with increasing times of cyclic load excess pore water pressure is increased gradually and effective stress is reduced gradually. When effective is reduced to zero, the liquefaction happens. So in many projects, excess pore water pressure must dissipate by means of some measures. The sand liquefaction under the dynamic load is avoided.

Abstract: At present, there are still some disputes on the influence of pressure on the relative permeability of oil and water phase in low permeable reservoirs. This text carried out the displacement experiments to study the influences of effective stress and displacement pressure on the relative permeability. The results indicate that: with the decreasing of displacement pressure, the relative permeability of oil and water and the displacement efficiency become poor; the lower the permeability is, the worse the effective permeability and displacement efficiency are; low permeable reservoirs have strong stress sensitivity, the relationship between permeability and effective stress follows power function; when the reservoir energy drops, the effective stress of rock increases, which causes the physical property worse, and meanwhile the flooding pressure decreases, which ultimately reduce the displacement efficiency, so high energy preserving level is the guarantee of improving the flooding efficiency. The results also indicate that the displacement pressure gradient should consider the actual producing pressure gradient after meeting the requirement of π number, otherwise, the testing displacement efficiency may be larger than the actual. The studying results provide theoretical references for high efficiency development of low permeable oilfields.

Abstract: The efficient conservation, restoration and protection of stone historical buildings could not be dissociated from the researches of mechanism of stone decays. While various mechanisms of stone degradations are considered and studied in previous studies, in this paper is focused on the cumulative damage modeling of wall stones due to the fatigue induced from quotidian fluctuations of thermal and hydric conditions. The thermoporomechanics theory of partially saturated media is used to describe the behavior of stone wall and its interaction with climatic conditions. Further, the effective stress concept firstly introduced by Terzaghi is extended for partially saturated media providing a quite powerful tool for design and analysis [. The behavior of a typical stone wall from Chambord castle (Center region of France) is then simulated, taking into account the heterogeneity of the stone-mortar contacts. The climatic conditions are introduced in the model as boundary conditions. The records of temperature and humidity from meteorological stations close to castle are used to establish time-variation of condition with a time resolution of 6 hours. From performed numerical analyses, it is shown that variation of temperature and relative humidity leads to the variation and fluctuation of effective stress in the stone, more intensively on the outdoor. The contact of stone with mortar is a natural stress concentration center, but even there the stress is much lower than tensile strength of the white tuffeau stone. The fatigue of the stone due to the stress fluctuation induced by the variations of meteorological conditions seems to be a major factor of stone degradation. A model is used to assess the cumulative damage of the stone wall as a function of the time.

Abstract: The cyclic deformation behavior and fatigue characteristics of a new austenitic manganese steel with composition FeMn18Cr7C0.8N0.2 (wt%) have been explored and analyzed based on the partition of hysteresis loops linked with microstructure by low cycle testing in the total strain amplitudes 0.3% - 1.0%. The new N+C austenitic manganese steel exhibited immediate cyclic softening for small strain amplitude and initial hardening at the onset of fatigue life followed by softening for medium and high strain amplitudes. For low and high strain amplitudes the evolution of internal stress and effective stress partitioned from the hysteresis loop with the prolonged cycles both corresponded to the change in the total stress amplitudes. With the exception of 316LN0.2 austenitic stainless steel, the effective stress and internal stress made a contribution to the cyclic deformation behavior with similar effect. The markedly improved contribution of effective stress in the new N+C austenitic manganese steel was attributed to the enhanced short range order caused by N+C alloying whereas the decreasing of effective stress with the number of cycles was because of this broken short range interaction. TEM observations showed that the significantly increased planar dislocation structures due to the presence of N+C were responsible for the strong tendency to cyclic softening, in association with the decrease of effective stress and internal stress simultaneously. Moreover the fatigue short crack could be observed on the fractured sample surface at high strain amplitude.

Abstract: In order to optimize select the best experimental conditions on testing tight sandstone starting pressure gradient in the laboratory, the advanced equipment of ASF300^TM Used to do experiments of constant pressure injection and constant flow injection under the conditions of two modes: constant confining pressure and constant net confining pressure, the data obtained was analysed in the form of linear regression fitting, obtained four different starting pressure gradient values under the different conditions. The experimental results and test methods were careful analysed and comprehensive evaluated according to each different experimental conditions and combined with the existing theory. The experimental results indicate that constant flow experiment is not suitable for large-scale use in the laboratory because of its longer time consuming under the condition of constant confining pressure mode, and the starting pressure gradient values are often larger, net confining pressure can be controlled more than 11 MPa to reduce experimental error. Under the condition of constant net confining pressure mode, the result is reliable, but it takes time longer too. On the contrary, the experiment of constant pressure injection takes time shorter, and the results are accurate under the mode of constant net confining pressure. But under the mode of constant confining pressure the value is on the high side. Based on the above, the best condition of testing starting pressure gradient for tight sandstone is net confining pressure mode and the fluid injected in the form of constant pressure.