Papers by Keyword: Anisotropy

Abstract: The continuous development of packaging steels for thickness reduction processes requires an advanced process design. This process is increasingly supported by finite element analysis to simplify tool construction and material selection purposes. Therefore, the fundamental basis is always the precise material characterization of packaging steel commonly based on tensile tests to determine flow curve and Lankford coefficients. However, due to strong temper rolling and the occurrence of slip bands, most packaging steels just show little elongation in tensile test. Therefore, a method of Paul et al. to determine the flow curve with digital image correlation (DIC) methods in the necking zone was applied in this work to meet the requirements of packaging steel. For the use of anisotropic yield functions, it is necessary to determine Lankford coefficients. Thus, a new method is proposed to measure Lankford coefficients locally with a DIC system in tensile test, also in case that no homogenous forming condition is reached. With the presented approaches the packaging steel TH415 was characterized. In order to validate the developed methods, a demonstrator was simulated with anisotropic yield function Yld2000-2d . The comparison between simulation and experiment showed clear improvements in simulation accuracy when using the newly presented methods for packaging steel.

Abstract: Numerical process design leads to cost and time savings in sheet metal forming processes. Therefore, a modeling of the material behavior is required to map the flow properties of sheet metal. For the identification of current yield criteria, the yield strength and the hardening behavior as well as the Lankford coefficients are taken into account. By considering the anisotropy as a function of rolling direction and stress state, the prediction quality of anisotropic materials is improved by a more accurate modeling of the yield locus curve. According to the current state of the art, the layer compression test is used to determine the corresponding Lankford coefficient for the biaxial tensile stress state. However, the test setup and the test procedure is quite challenging compared to other tests for the material characterization. Due to this, the test is only of limited suitability if only the Lankford coefficient has to be determined. In this contribution, a simplified test is presented. It is a reduction of the layer compression test to one single sheet layer. So the Lankford coefficient for the biaxial tensile stress state can be analyzed with a significantly lower test effort. The results prove the applicability of the proposed test for an easy and time efficient characterization of the biaxial Lankford coefficient.

Abstract: In the present study, two different yield criteria were investigated to model and compare the yield thresholds functions for the plastic behavior of rolled sheets. These two different yield criteria as described via Hill48 yield quadratic and F. Barlat Yld2000-2d non-quadratic criterion. For this purpose, an experimental device of simple tensile test and the studied material are described. The experimental results in terms of Yield stress and Anisotropic coefficient are estimated from the Associated Flow Rule (AFR) and Non-Associated Flow Rule (NAFR). However, it is found that the criterion of Yld2000-2d is the most appropriate model in comparison with the experimental results.

Abstract: It is known that metallic materials are characterized by anisotropy of their mechanical properties, with this being attributed to the conditions during the manufacturing process. For sheet metals, this anisotropy occurs symmetrically to the three orthogonal axes of the rolling, transverse and normal direction. This characteristic is referred to as orthotropic behaviour and manifests itself, for example, in earing during cupping tests. Therefore, orthotropic yield criteria are highly relevant for the numerical simulation of sheet metal forming processes. The Lankford coefficient, also known as the r-value, is a good experimental measure for characterizing orthotropic ductile behaviour of sheets, and can easily aid in parameter identification for yield criteria such as the Hill approaches. In the present investigations, Lankford coefficients were determined as a function of local strain in uniaxial tensile tests through high-resolution digital image correlation. The sample direction was varied between 0°, 45° and 90° to the rolling direction and the test temperature varied from RT to 350 °C at three different strain rates (0.01-1 s^-1). By means of a novel backward analysis, the measuring range for the Lankford coefficients was positioned exactly in the necking area. An increase in temperatures showed a decrease in the initial Lankford coefficient. The results showed non-constant Lankford coefficients and commence the course of a natural exponential function depending on the local strain. Regardless of strain rate, the results revealed that the Lankford coefficients (r-values) at 150 °C, 250 °C and 350 °C approaches a steady-state of r = 1.14 with strains greater than 50 %.

Abstract: Cold spraying is being developed as effective and promising additive manufacturing process. However, how to create a deposit by cold spraying with comparable properties to bulk material is still challenge. It is well known that post-spray annealing is an effective process to enhance the deposit properties. In this paper, copper deposits are cold-sprayed at three different sets of spray conditions corresponding to three mean particle velocities of 578, 745, and 807 m/s. The tensile strength, thermal conductivity and electrical conductivity are measured at three different directions to clarify the anisotropy of deposit properties, which are parallel to gun moving direction and other two perpendicular directions. Furthermore, the influence of post-spray annealing on the anisotropy effect is also investigated by examining the effect of spray conditions and annealing conditions on the deposit properties at three different directions. The results clearly demonstrate the anisotropy of as-deposited Cu. Although it can be found that post-spray annealing significantly improves the properties of the as-sprayed deposits and reduces anisotropy of Cu deposit properties, the microstructure of the as-sprayed initial Cu deposit presents a significant effect on final annealed deposit. Therefore, an optimized cold-sprayed deposit will benefit manufacturing of a deposit with comparable properties with bulk by cold-spraying combined with post-spray annealing.

Abstract: It is established that when physical modifications to the blown film of LDPE in extrusion installation for large values of the ratio of the longitudinal drawing of the melt, K_m from 7.2 to 12.4, there is the technological anisotropy K_at in the range of 2.8 to 3.7. It is 1.8 times higher than the anisotropy of strength of K_aσ films. At uniaxial tension of such films in polarized light, the appearance of isochromes associated with the value of K_at is observed.

Abstract: Based on the hypocycloid theory, a highspeed orthogonal cutting simulation model was established. The cutting parameters (cutting speed, feed rate) and plane forming angle of the workpiece of aeronautical aluminium alloy 7050-T7451 pre-stretched rolled sheet were simulated and validated. The mapping relationship between cutting parameters, anisotropy and cutting performance was analyzed. The results show that the degree of anisotropy and the difficulty of material cutting are proportional to the forming angle, and the anisotropy decreases with the increase of cutting speed and the decrease of feed speed. Finally, the optimal cutting process range of aluminum alloy 7050-T7451 was obtained, which provides data support for highspeed cutting of anisotropic materials.

Abstract: The paper devotes a new general experimental method for studying the anisotropy of conducting materials of various functional purposes. The difference between the presented method and the previously known one is in the high rate of anisotropy assessment, ensuring the possibility of anisotropy assessment of the properties of materials by the volume of the sample or product under investigation during their manufacture or operation. The procedure for measuring the anisotropy of electrophysical properties and the results of the study of some samples are presented.

Abstract: This work concerns the numerical modeling of stationary conduction heat transfer in a 3D three-dimensional anisotropic material subjected to an internal heat source, based on the finite element method MEF and using the Galerkin method. The field of study is a cube representing the seven crystalline systems subjected to an internal heat source and convective boundaries. The obtained equation system is solved by the LU method. The automatic mesh is managed for all the domain nodes via the program which we have written in FORTRAN language. This program allowed temperature field calculation and was applied for different crystalline systems: monoclinic, triclinic, orthorhombic, trigonal, cubic that are identified by their thermal conductivity tensors [kij]. The obtained temperature profiles obtained are in accordance with heat transfer theory and clearly illustrate the crystalline structure symmetry; this calculation permits to predict the possible thermal deformations in an anisotropic solid.

Abstract: The structural, elastic and anisotropic properties for rare earth manganites compound YMnO3 in ferromagnetic state with hexagonal structure, have been investigated using the ab initio calculations based on the density functional theory, this calculations were based on the full potential linearized augmented plane wave (FP-LAPW) method with the generalized gradient approximation (GGA). The agreement of the DFT (FP-LAPW) calculations including internal atomic relaxations, with the experimental data is very good. Other relevant quantities such as elastic constants, shear modulus, Young’s modulus, Poisson’s ratio, anisotropy factors, sound velocity, and Debye temperature have been calculated and discussed.