Materials Science Forum Vols. 575-578

Abstract: Methods of modeling stress strain curves for nonlinear stress analysis are discussed in order to obtain comparable results between different finite element analysts and between different versions of designs. The most common method for modeling stress strain curves is to use Ramberg- Osgood equation. For materials with significant discontinuous yielding, Ramburg-Osgood approximation leads to some problems near discontinuous yielding point. Discontinuous yielding occurs when sudden onset of plastic deformation associated Luders band takes place in a uniform test sample. For engineering structures and machine components, the propagation of Luders band may not occur in deformation process because of non-uniform stress distribution caused by stress concentration, complicated loading condition etc. A modified Ramberg-Osgood method for modeling stress strain curve is proposed.

Abstract: The variety of metal forming processes can be arranged according to some essential features such as structure, properties and structure evolution of the metal being deformed, deformation temperature and dynamics of its changing during deformation, interrelation between flow stress, strain and strain rate, temperature and structural parameters etc. These features in the aggregate compose rheological behavior of the metal being deformed and the rheological equation’s database for simulation of metal forming processes in cold, warm, hot and superplastic state. Taking these ideas into account, the authors would like to present some basic elements of these rheological models database i.e. classification of metallic materials as objects of deformation, classification of deformation modes in dependence on temperature regimes, thermal-kinetic map of metal processing and, as a result of this analysis, a set of rheological models related to certain modes of metal forming processes, which can be used as basic elements of computer software systems for simulation of these processes.

Abstract: The aluminum tube with rectangle section can be produced by two-pass drawing process including non-plug and with-plug drawing. It is an effective method to study the deforming mechanisms by simulation, based on which the section varying of two-pass drawing got schemed and the relevant dies with reasonable dimensions got designed. The dynamics model and elasto-plastic FE model of the non-plug and with-plug drawing were established based on FEM software, then the simulation was performed. The sizing section of drawing die got optimized with angle β=178°, which eliminated instability. The influence of different semi-die angle 2 a on drawing load was researched, and a proper value of 2 a and 1 a was found. The touch boundary and touch-stress distribution of transitional drawing were achieved. Furthermore the residual stress and spring-back strain distribution after final drawing were achieved, which contributes to modifying the dimensions of rectangle sizing section.

Abstract: In this paper, we present a modified density-dependent Drucker-Prager Cap (DPC) model with a nonlinear elasticity law developed to describe the compaction behavior of pharmaceutical powders. The model is implemented in ABAQUS with a user subroutine. Using microcrystalline cellulose (MCC) Avicel PH101 as an example, the modified DPC model is calibrated and used for finite element simulations of uniaxial single-ended compaction in a cylindrical die. To validate the proposed model, finite element simulation results of powder compaction are compared with experimental results. It was found that finite element analyses gave a good prediction of both the loading-unloading curves during powder compaction and the compaction force required for making a tablet with a specified density. Further, the failure mechanisms of chipping, lamination and capping during tabletting are investigated by analysing the stress and density distributions of powders during the three different phases of the tabletting processes, i.e. compression, decompression and ejection. The results indicate that the model has excellent potential to describe the compaction process for generic pharmaceutical powders.

Abstract: According to the N-S equation in fluid mechanics, it is analyzed the rheological properties of strip cast-rolling deforment area with flow function method. The research problem can be simplified into 2-D when the wide of cast-rolling strip are greater than thickness. But, it still difficult to find solution for established two-dimensional partial differential equation directly. A mathematics model of velocity field in the cast-rolling area has been built by flow function method. The model not only satisfies the continues equation, the condition of no-compression and velocity boundary, but it also make the most possible to solute partial differential equation. So, in the future continue research, it has created possible conditions for saluting the mathematics model of average unit compression stress distribution in the cast-rolling deforment area.

Abstract: In order to understand and control the process of laser peen forming (LPF) of sheet metal, a developed FEM model was established and the process of LPF was simulated by FEM code ABAQUS. Special emphasis was posed on the part of the model devoted to the analysis of 3D residual stress distribution under laser shock wave loading. With the aid of simulation method, the influence of laser parameters, number of shots, peening tracks and the characteristics of sheet bending were investigated. The results indicate that the bending deformation of metal sheet is relative to laser peening numbers, peening coverage and the plate’s thickness, both upper and back layers of the deformed sheet exists residual compressive stresses.

Abstract: In-plane bending is an advanced plastic processing technology which controls the uneven compressing plastic deformation of strip metal harmoniously and forces the strip metal to produce in-plane bending and to form an open circle. In-plane bending is divided into incremental and continuous process according to the loading manner. While much attention has been paid to the continuous in-plane bending techniques and achievements have been made at home and abroad, only limited experimental investigation has so for been done on incremental in-plane bending by overseas scholars. In this paper, a 3D finite element simulation based on the rigid-plastic principle is performed for incremental in-plane bending of pure aluminum sheet with width of 25 ~ 27.5 mm, thickness of 1.5 ~ 3 mm. Influences of technical parameters such as punch inclined angle αp, punch indentation s, thickness of strip t0, width of strip w0 and strip pitch p on the strip bending radius Rin are studied. The achievement of this study enriches the uneven deformation theory. It lays a theoretical foundation for generalization and industrialization of incremental in-plane bending and offers a new idea to the research and development of the advanced plastic processing technologies.

Abstract: In temper rolling thickness reduction is small (0,5 – 2%) and the elastic deformation of the work roll should be taken into account. During finishing rolling, classical cold rolling theories fail to predict the roll flattening and thus the rolling force. Numerous different mathematical models have been developed for temper rolling process. However, often the non-circular theories are computationally expensive and the range of usability is questionable. In this study, elasto- plastic finite element analysis, laboratory rolling tests and inverse computing from skin pass mill process data has been carried out. The aim is to find the roll shape, contact length and the rolling force to create a simplified model for controlling of temper rolling. In addition, the ability of different skin pass rolling theories has been compared with measured process values.

Abstract: Sheet hydroforming has drawn much attention in the world because of its many advantages such as high drawing ratio, good surface quality and high dimensional accuracy, less springback etc. Based on the practical needs and the development of the hydroformed production, this paper presents the recent development of the sheet hydroforming and some innovative methods for the equipment, the processes and the numerical analysis methods have been introduced shortly.