Papers by Keyword: Large Strain

Abstract: A first-order hexahedral (H8)-element-based smoothed finite element method (S-FEM) with a volumetric-deviatoric split for nearly incompressible materials was developed for highly accurate deformation analysis of large-strain problems. In the proposed method, the isovolumetric part of the deformation gradient at the integration point is derived from F based on the beta finite element method (i.e., an S-FEM), whereas the volumetric part of the deformation gradient is derived from F on the basis of the standard FEM with reduced integration elements. This method targets H8 elements that are automatically generated from tetrahedral elements, which makes it quite practical. This is because the FE mesh can be created automatically even if the targeted object has a complex shape. This method eliminates the phenomena of volumetric and shear locking, and reduces pressure oscillations. The proposed method was implemented in the commercial FE software Abaqus and applied to the large-deformation contact problem to verify its effectiveness.

Abstract: Physical simulation of the stress-strain state and microstructure evolution, which are similar to that occurring during asymmetric rolling with a large strain, is very important for design of technologies of producing ultra fine grained metallic materials. This paper presents the results of optimization of specimen geometry and a special multi-cycle shear-compression technique for the physical simulation of asymmetric rolling with a large strain up to e ~ 4. The specimen consisted of a parallelepiped having an inclined gauge section created by two diametrically opposed semi-circular slots which were machined at 45°. The specimen was compressed between two flat dies during shear-compression testing in accordance to the special multi-cycle scheme. Each cycle of the shear-compression testing consisted of two steps. The first step included height reduction of specimen, after that specimen was rotated by 90º. The second step included length reduction of the specimen for getting the quasi original shape of a parallelepiped. The specimen provided simultaneous pure and simple shear in an inclined gauge-section. The level of effective strain was controlled through adjustment of the specimen geometry, height reduction, load application direction and number of cycles of shear-compression. Gauge thickness, width and radius of the specimen were optimized by FEM with using of software DEFORM 3D. Numerical simulation and comparison of the stress-strain state during shear-compression testing and asymmetric rolling of low-carbon steel AISI 1010 were performed. Results of FEM analysis of the applicability of the multi-cycle shear-compression testing to the modeling of asymmetric rolling were discussed.

Abstract: This paper is concerned with the characterization of the OFHC copper flow stress at strain rates ranging from 10⁻³ s⁻¹ to 10⁶ s⁻¹ considering the large strain and high temperature effects. Several uniaxial material tests with OFHC copper are performed at a wide range of strain rates from 10⁻³ s⁻¹ to 10³ s⁻¹ by using a INSTRON 5583, a High Speed Material Testing Machine (HSMTM), and a tension split Hopkinson pressure bar. In order to consider the thermal softening effect, tensile tests at 25°C and 200°C are performed at strain rates of 10⁻³ s⁻¹,10¹ s⁻¹, and 10² s⁻¹. A modified thermal softening model is considered for the accurate application of the thermal softening effect at high strain rates. The large strain behavior is challenged by using the swift power law model. The high strain rates behavior is fitted with the Lim–Huh model. The hardening curves are evaluated by comparing the final shape of the projectile from numerical simulation results with the Taylor impact tests.

Abstract: The effect of various factors on the kinetics of microstructure evolution in commercial-purity titanium and two-phase Ti-6Al-4V alloy during deformation was studied. The kinetics of microstructure refinement can be raised via intensification of deformation twinning. In two-phase titanium alloys the kinetics of spheroidization can be increased considerably by decrease in the thickness of initial α lamellae. The influence of interphase boundaries energy on deformation behavior was discussed with respect to Ti-6Al-4V and Ti/TiB alloys.

Abstract: Some features ofstructure, way of production and mechanical properties of titanium andtwo-phase titanium alloys with ultrafine-grained (UFG) microstructure werediscussed. Various methods of UFG structure formation was considered andoptimal conditions for attaining of a homogeneous microstructure with thesmallest grain size were determined. The kinetics of microstructure evolutionin titanium and two-phase titanium alloys during large (severe) plasticdeformation in a wide temperature interval and the mechanisms of ultrafinegrain formation were analyzed. The influence of grain size on static mechanicalproperties was determined. Significantly reduced temperatures of superplasticforming of the UFG conditions were shown. Some examples of practical applicationsof the UFG two-phase titanium alloys were discussed.

Abstract: Differential settlement may occur in structure foundations for the differences between vertical loads in different parts of the superstructures, or the differences between deformation features of the foundation soils. Then it is of great significance to develop new methods for controlling foundation differential settlement by using special materials, of which the deformation features can be controlled. Through the compression tests, settlement controllable materials can be selected by comparing the bearing capacity and deformation features of different materials experimented in the tests. According to the results of the compression tests in short term and long term, this article analyzed the bearing capacity and deformation features of different materials through the stress-strain curves. The research shows that XPS (Extruded Polystyrene) boards are of high bearing capacity, large strain property and long-term property stability, and are well suited to be used in civil engineering by controlling the differential settlement of the structure foundation.

Abstract: The coefficient of compressibility a_v and the coefficient of permeability k_v of clays decrease during the one dimention consolidation process, especially when the strain of clays in the process are large. This paper studies the effects of large strain, decreasing compressibility and decreasing permeability during the one dimention large strain consolidation process by analyzing results obtained from the nonlinear finite element method and comparing with results from the conventional consolidation theory. The research results of this paper shows that the compression index C_c and the permeability change index C_k are two important clay parameters which influence one dimention large strain consolidation process.When the instantaneous load increment remains unchanged, the larger the value of the C_{c ,} the larger the value of the final settlement and the slower the settlement development; the larger the value of the C_k, the faster the dissipation of excess pore water pressure in one dimention large strain consolidation process.

Abstract: Shear tests of rectangular sample are widely used by the scientific community for characterizing the material behavior due to large strains obtained. However, for some hard metals, such as the dual-phase steel DP 980, premature rupture occurs in the vicinity of the grips. Due to this fact, the shape of the shear specimen is optimized in this work with the aim of maximizing the deformation achieved in the central part of the specimen without the occurrence of rupture near the grips. As the rupture occurs at the corners of the shear specimen only the boundaries are subjected to shape optimization. A representation with cubic splines is adopted for the definition of the boundaries geometry. The material is defined by Hill’s 1948 yield criterion combined with an isotropic hardening law. Two macroscopic rupture criteria are considered and an objective function approach based on the maximization of the shear strain average value is defined. For this study, a direct search optimization method is used for minimizing the objective function. The optimized geometries obtained for the different rupture criteria and different set of design variables are compared. The use of a larger number of design variables allows to obtain optimized geometries with higher average shear strain. The best specimen geometry shape allows increasing the maximum deformation of DP 980 steel to 1.05 without occurrence of rupture. In addition, the final specimen geometries show a concave shape for the boundaries which means that this kind of shape is the best one to delay the rupture in shear specimens.

Abstract: An Al-1%Si alloy cold rolled to a von Misses stain of 4.5 was isothermally annealed at 210°C. A random recrystallization texture was obtained, which was attributed to the effects of particles of different sizes on the nucleation and growth of grains during recrystallization.

Abstract: The hyperelastic-viscoelastic model was applied on HTPB propellant to simulate the large strain problem during tensile test. The feasibility of using micro bow-shaped transducer to measure the large strain of HTPB propellant was discussed. The ABAQUS package was used to simulate the HTPB propellant tensile test with different sizes of micro bow-shaped transducer. The effect of micro bow-shaped transducer size on large strain measuring was concluded, and the foundation of determining bow-shaped transducer size was given. The strain transfer relational expression for a given size was obtained. It will be reference for solving the large strain measuring of HTPB propellant in complex working condition.