Vahid Norouzifard; Aghil Yousefikoma
Abstract
The built up layer thickness in secondary deformation zone is one of the important parameters in metal cutting process. The built up layer (BUL) is formed in second deformation zone near the tool-chip interface in the back of the chip. This parameter influences the tool life and machined surface quality. ...
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The built up layer thickness in secondary deformation zone is one of the important parameters in metal cutting process. The built up layer (BUL) is formed in second deformation zone near the tool-chip interface in the back of the chip. This parameter influences the tool life and machined surface quality. This BUL should not be confused with the built up edge (BUE). The deformation of the BUL in the secondary shear zone is a stable and continues process; leading to an uniform thickness of the BUL along the chip's back but the deformation of the BUE is an unstable process in front of the tool edge. Numerical simulation is a suitable method for determination of temperature, stress and strain distribution in metal cutting since it dose not suffer the analytical methods limitations and experimental methods cost. In this paper a new method is presented to calculate the built up layer thickness in secondary deformation zone using finite element simulation of orthogonal metal cutting process. There are two main concepts about chip separation mechanisms from work piece, i. e. crack propagation and pour deformation without crack. In the present work chip formation process is assumed as a pour plastic deformation, considering second chip separation mechanism. There is no separation criterion in the simulations based on pour deformation, but Adaptive remeshing is performed during simulation to avoid the difficulties associated with deformation-induced element distortion. An updated Lagrangian finite element model of two-dimensional orthogonal cutting process is developed. This model is meshed using 4-node plain strain elements. Thermo-mechanical coupled analysis, with adaptive remeshing is performed by LS-DYNA finite element code. Johnson-Cook material model is used for determination of the work piece material flow stress and the cutting tool is assumed as a rigid body. An updated coulomb friction law is used to describe friction condition in tool-chip interface. The temperature and equivalent strain distribution diagrams in cutting zone are shown at various cutting speeds. The built up layer thickness in various cutting speed are also calculated by equivalent strain gradient in second deformation zone. The numerical calculated tool average temperatures and the built up layer thicknesses in various cutting speeds are compared with the experimental data given in literature and good agreement is observed between them.
Kiumars Mazaheri; Ali Tarokh
Abstract
In this work the effect of the accuracy of a FAE detonation modeling on the generated blast wave is investigated. First, a one-dimensional numerical simulation with a reduced chemical kinetics of C2H2-O2-Ar, involving 25 elementary reactions, is used as the base model. The properties of the blast calculated ...
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In this work the effect of the accuracy of a FAE detonation modeling on the generated blast wave is investigated. First, a one-dimensional numerical simulation with a reduced chemical kinetics of C2H2-O2-Ar, involving 25 elementary reactions, is used as the base model. The properties of the blast calculated with this model is compared with those of simpler models, the similarity solution of Taylor, the constant volume (CV) explosion model, and the CJ-burn model. It is found that the result of Taylor's similarity model is in very good agreement with the result of the base model. The blast properties that calculated with the CJ-burn model are also in close agreement with those of the base and Taylor's models. However, the CV model prediction shows considerable difference with the base model. Considering the computational cost and the accuracy, the Taylor's model is recommended as the favorite model for the calculation of the FAE blast properties.
Ali Asghar Mirghasemi; Helia Rahmani
Abstract
In some natural events such as soil failure the deformations are localized in narrow restrictions, which are called shear bands. This event which is a fundamental phenomenon in granular material, has been widely investigated during recent decades within expensive experimental tests and also some numerical ...
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In some natural events such as soil failure the deformations are localized in narrow restrictions, which are called shear bands. This event which is a fundamental phenomenon in granular material, has been widely investigated during recent decades within expensive experimental tests and also some numerical simulations. Most of previously used numerical methods are based on continuum theories describing shear bands as interfaces along which solid masses move like rigid blocks. In this interpretation many physical events such as changes of the soil structure around failure line are neglected. In this paper the discrete element method is used to simulate the shear bands. Since in this method some of the problems of experiments and simulations are solved,
It would be an ideal method to obtain the stresses and strains, and also to investigate the behavior of shear bands in a granular media, while exposing to external forces. In this research by the use of DEM and conducting series of biaxial tests on assemblies of two-dimensional ellipse shaped particles, the effect of different factors such as average grain size, particle shape and confining pressure on the shear bands are studied and the results show that some investigated factors like average grain size and confining pressure have considerable effect on the shear bands characteristics.
The main results can be summarized as follows:
• The amount of rotation is a very sensitive characteristic and it changes considerably by all of the factors measured in this research.
• The most affecting factors on the displacement of the particles across the shear bands are the loading rate and confining pressure. Moreover by increasing the particle size the displacements increase with a great amount but if these values are divided by the particle radius, no significant changes in the particle displacement will be observed. Other factors do not seem to have any effects on this issue.
• 6-13d50 seems to be the best estimation for the shear band thickness, and other controlled factors affect this value within this restriction. The width of the shear bands seems to increase by the loading rate and confining pressure increase.
• The inclination of this localization is mostly affected by confining pressure (which increase leads to angle decrease), porosity (which increase leads to angle decrease), grading (its uniformity causes smaller shear band angles), and size (greater sizes of grains would result in failure with lower angles of sear band). Among these factors grain size has the least effect.
