An Approach to Predicting Evolution of Material Properties Near Surfaces With High Friction in Metal Forming

2005 ◽  
Author(s):  
S. Alexandrov
Keyword(s):  
Strain Rate ◽  
Material Properties ◽  
Evolution Equations ◽  
Plastic Material ◽  
Equivalent Strain ◽  
Maximum Friction ◽  
Perfectly Plastic ◽  
Equivalent Strain Rate ◽  
Strain Rate Intensity ◽  
Friction Surfaces

In the case of rigid/perfectly plastic material, the velocity fields in the vicinity of maximum friction surfaces must be describable by nondifferentiable functions. In particular, the equivalent strain rate follows an inverse square root rule near such surfaces and, therefore, approaches infinity at the surface. Because the equivalent strain rate is involved in many evolution equations for material properties, its behavior near the maximum friction surfaces should lead to high gradients in the material properties near the surface, which is confirmed by experiment. To quantitatively describe the evolution of material properties in the vicinity of surfaces with high friction, the concept of strain rate intensity factor can be adopted.

Effect of Plastic Anisotropy on the Strain Rate Intensity Factor: A Simple Analytic Solution

2014 ◽  
Vol 626 ◽  
pp. 240-245
Author(s):  
Sergei Alexandrov ◽  
Elena Lyamina ◽  
Hguyen Minh Tuan ◽  
Natalia Kalenova
Keyword(s):  
Intensity Factor ◽  
Strain Rate ◽  
Analytic Solution ◽  
Equivalent Strain ◽  
Maximum Friction ◽  
Equivalent Strain Rate ◽  
Strain Rate Intensity Factor ◽  
Rate Intensity ◽  
Strain Rate Intensity ◽  
Friction Surfaces

Solutions for many rigid/plastic models are singular in the vicinity of maximum friction surfaces. In particular, the magnitude of the equivalent strain rate near such surfaces is controlled by the strain rate intensity factor. This factor is the coefficient of the leading singular term is a series expansion of the equivalent strain rate in the vicinity of maximum friction surfaces. Since the equivalent strain rate has a great effect of material properties, it is of important to reveal the dependence of the strain rate intensity factor on parameters characterizing material models. In the present paper, quite a general model of anisotropic plasticity under plane strain conditions is adopted. Then, using an analytic solution for instantaneous compression of a layer of plastic material between two parallel plates the effect of the shape of the yield locus on the asymptotic behavior of the equivalent strain rate in the vicinity of the friction surface is demonstrated.

An Effect of Plastic Anisotropy on the Strain Rate Intensity Factor

2010 ◽  
Author(s):  
Sergei Alexandrov
Keyword(s):  
Intensity Factor ◽  
Strain Rate ◽  
Plastic Anisotropy ◽  
Rigid Plastic ◽  
Maximum Friction ◽  
Perfectly Plastic ◽  
Strain Rate Intensity Factor ◽  
Rate Intensity ◽  
Strain Rate Intensity ◽  
Friction Surfaces

The strain rate intensity factor in the theory of rigid perfectly plastic isotropic materials is the coefficient of the principal singular term in a series expansion of the equivalent strain rate in the vicinity of maximum friction surfaces. This coefficient can be used to predict the evolution of material properties in a narrow layer in the vicinity of surfaces where the friction stress is high. Usually, conventional evolution equations are not compatible with the plasticity equations near maximum friction surfaces. It is therefore of interest to extend the theories based on the strain rate intensity factor to more general models than the rigid perfectly plastic isotropic solids. The present paper deals with plane strain deformation of rigid plastic anisotropic material. It is shown by means of a simple analytic solution that the velocity field is singular in the vicinity of maximum friction surfaces. Thus the strain rate intensity factor can be introduced for such materials. An effect of plastic anisotropy on its value is demonstrated. In addition, it is shown that rigid plastic solutions for anisotropic materials can exhibit various types of singularity in the vicinity of maximum friction surfaces, in contrast to isotropic materials where one type only is possible. Nevertheless, in most cases the type of singularity is same for isotropic and anisotropic materials.

Modelling of Damage Evolution in the Vicinity of Frictional Interfaces in Metal Forming

2012 ◽  
Vol 579 ◽  
pp. 124-133
Author(s):  
Elena Lyamina ◽  
Sergei Alexandrov ◽  
Yeau Ren Jeng ◽  
Yeong-Maw Hwang
Keyword(s):  
Strain Rate ◽  
Ductile Fracture ◽  
Fracture Criterion ◽  
Equivalent Strain ◽  
Ductile Fracture Criterion ◽  
Equivalent Strain Rate ◽  
Strain Rate Intensity Factor ◽  
Rate Intensity ◽  
Strain Rate Intensity ◽  
Friction Surfaces

Conventional ductile fracture criteria are not applicable in the vicinity of maximum friction surfaces for several rigid plastic material models because the equivalent strain rate (second invariant of the strain rate tensor) approaches infinity near such surfaces. In the present paper, a non-local ductile fracture criterion generalizing the modified Cockroft-Latham ductile fracture criterion is proposed to overcome this difficulty with the use of conventional local ductile fracture criteria. The final form of the new ductile fracture criterion involves the strain rate intensity factor which is the coefficient of the principal singular term in a series expansion of the equivalent strain rate in the vicinity of maximum friction surfaces. When the velocity field is not singular, the new ductile fracture criterion reduces to the modified Cockroft-Latham criterion. The strain rate intensity factor cannot be found by means of commercial finite element packages since the corresponding velocity field is singular. In the present paper, the new fracture criterion is illustrated with the use of an approximate semi-analytical solution for plane strain drawing. It is shown that the prediction is in qualitative agreement with physical expectations.

The Strain Rate Intensity Factor and its Applications: A Review

2009 ◽  
Vol 623 ◽  
pp. 1-20 ◽  
Author(s):  
Sergei Alexandrov
Keyword(s):  
Intensity Factor ◽  
Strain Rate ◽  
Material Properties ◽  
Velocity Fields ◽  
Rigid Plastic ◽  
Maximum Friction ◽  
Strain Rate Intensity Factor ◽  
Rate Intensity ◽  
Strain Rate Intensity ◽  
Friction Surfaces

The present paper concerns with the concept of the strain rate intensity factor in rigid plastic solids. The strain rate intensity factor is the coefficient of the principal singular term in the expansion of the equivalent strain rate in a series in the vicinity of maximum friction surfaces. Such singular velocity fields appear in solutions based on several rigid plastic models. Because of this singularity in the velocity field, many conventional evolution equations for material properties are not compatible with such rigid plastic solutions. On the other hand, qualitative behaviour of the singular rigid plastic solutions in the vicinity of maximum friction surfaces is in agreement with a number of experimental results. Therefore, the primary objective of research in this direction is to develop an approach to relate parameters of the singular velocity fields and parameters characterizing material properties. The approaches proposed in previous works are based on the strain rate intensity factor. In the case of analytical and semi-analytical solutions the strain rate intensity factor can be found by means of an asymptotic analysis of the solutions. A number of such solutions obtained by inverse methods are reviewed in the present paper and the strain rate intensity factor is found. An effect of process parameters on its magnitude is shown and discussed.

Velocity Gradients and the Evolution of Material Properties in a Narrow Layer near Surfaces of High Friction in Metal Forming Processes

2012 ◽  
Vol 504-506 ◽  
pp. 549-554 ◽  
Author(s):  
Sergei Alexandrov ◽  
Yeau Ren Jeng
Keyword(s):  
Grain Size ◽  
Strain Rate ◽  
Material Properties ◽  
Metal Forming ◽  
Equivalent Strain ◽  
Experimental Results ◽  
Material Layer ◽  
Narrow Layer ◽  
Velocity Gradients ◽  
Equivalent Strain Rate

Theoretical solutions for several rigid plastic models used to describe plastic flow in metal forming processes are singular in the vicinity of maximum friction surfaces. In particular, velocity gradients and the equivalent strain rate approach infinity near such surfaces. Such singular behavior can be excluded from consideration by choosing another friction law or material model. However, a different approach is proposed in the present paper. The starting point of this approach is that many experiments show that velocity gradients are very high in the vicinity of surfaces of high friction and that a narrow material layer is formed near such surfaces whose properties are very different from the properties in the bulk. Taking into account that the equivalent strain rate has a significant effect on the evolution of material properties, this experimental fact suggests that a theory based on the singular plastic solutions can be developed to describe the formation of the aforementioned material layer. In the present paper such a theory is proposed to describe the evolution of grain size. It is assumed that, in addition to the equivalent strain rate, the material spin has an effect of the evolution of grain size. It is then shown that the solutions for the material spin are singular as well. The interrelation between the present theory and strain gradient theories of plasticity is discussed. It is shown that it is necessary to account for the strain rate gradient to propose a more adequate theory to deal with the material flow near surfaces of high friction. Some experimental results on the formation of the narrow layer of ultra-fine grains in the vicinity of the fraction surface in extrusion are presented. An illustrative example to relate these experimental results and the new theory is given.

scholarly journals Coefficients of Restitution Based on a Fractal Surface Model

2003 ◽  
Vol 70 (3) ◽  
pp. 339-345 ◽  
Author(s):  
Chung-Jen Lu ◽  
Ming-Chang Kuo
Keyword(s):  
Surface Topography ◽  
Material Properties ◽  
Plastic Material ◽  
Coefficient Of Restitution ◽  
Surface Model ◽  
Fractal Surface ◽  
Normal Contact ◽  
Perfectly Plastic ◽  
Fractal Models ◽  
Elastic Perfectly Plastic

Equations of rigid-body mechanics provide a means to predict the post-collision behavior without recourse to highly complex, detailed analysis of deformations during contact. Before the prediction can be completed, the coefficient of restitution, which relates the rebound velocity to the incident velocity, must be estimated properly. The coefficient of restitution depends on the surface topography in addition to the material properties and incident velocity. Recent investigations showed that surface topography can be characterized properly by fractal models. This paper proposes a normal contact model for a fractal surface in contact with a rigid smooth half-space. The fractal surface is constructed based on the Cantor set and composed of elastic-perfectly plastic material. Asymptotic continuous expressions for the load-displacement relations during loading and unloading are derived. Based on these results, we study the effects of surface roughness, material properties and incident velocity on the coefficient of restitution.

scholarly journals An An Analysis of Strain Rate Distribution Using Streamline Model and A Quick Stop Device in Metal Cutting

2019 ◽  
Vol 22 (2) ◽  
pp. 136-142
Author(s):  
Osama Ali Kadhim ◽  
Fathi A. Alshamma
Keyword(s):  
Strain Rate ◽  
Chip Formation ◽  
Metal Cutting ◽  
Equivalent Strain ◽  
Element Analysis ◽  
Rate Distribution ◽  
Equivalent Strain Rate ◽  
Cumulative Plastic Strain ◽  
Cutting Speeds ◽  
Strain Rate Distribution

In this paper, a quick stop device technique and the streamline model were employed to study the chip formation in metal cutting. The behavior of chip deformation at the primary shear zone was described by this model. Orthogonal test of turning process over a workpiece of the 6061-T6 aluminum alloy at different cutting speeds was carried out. The results of the equivalent strain rate and cumulative plastic strain were used to describe the complexity of chip formation. Finite element analysis by ABAQUS/explicit package was also employed to verify the streamline model. Some behavior of formation and strain rate distribution differs from the experimental results, but the overall trend and maximum results are approximately close. In addition, the quick stop device technique is described in detail. Which could be used in other kinds of studies, such as the metallurgical observation.

The Research and Optimization of a 6061 Aluminum Rectangular Tube Extrusion Using Porthole Dies According to the Parameter of Split Ratio

2012 ◽  
Vol 268-270 ◽  
pp. 391-395
Author(s):  
Shu Mei Lou ◽  
Guo Liang Xing ◽  
Sheng Xue Qin ◽  
Lin Jing Xiao
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Strain Rate ◽  
Equivalent Strain ◽  
Tube Extrusion ◽  
Split Ratio ◽  
Die Structure ◽  
Rectangular Tube ◽  
Equivalent Strain Rate ◽  
Deform 3D

Extrusions of a 6061 aluminum rectangular tube using porthole dies with three assigned different split ratios were simulated by the software DEFORM-3D based on Finite element method. The distributions of stress, equivalent strain rate, temperature, velocity of the deformation materials and the mold stress during the three extrusion processes were obtained, respectively. By analyzing the distributions of those fields, the most reasonable split ratio is selected and then the die structure is modified.

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