Analysis of Central Bursting Defects in Extrusion and Wire Drawing

1968 ◽  
Vol 90 (1) ◽  
pp. 79-90 ◽  
Author(s):  
B. Avitzur
Keyword(s):  
Strain Rate ◽  
Fracture Criterion ◽  
Yield Criterion ◽  
Cone Angle ◽  
Flow Characteristics ◽  
Wire Drawing ◽  
Ductile Material ◽  
Stress Deviator ◽  
Major Conclusion ◽  
Metal Properties

The central burst defect, also called chevroning, in the extruded or drawn product is analyzed. A criterion for the unique conditions that promote this defect has been derived. Measures to prevent the occurrence of central burst are indicated. A major conclusion of the study is that, for a range of combinations of cone angle, reduction, and friction, central bursting is expected in any metal that can be called “Mises’ material.”1 Under such a combination (reduction, cone angle, and friction), even the most ductile material can burst centrally. The flow characteristics, described by Mises’ stress deviator-strain rate relations associated with Mises’ yield criterion, are the only metal properties needed to predict central bursting. No additional fracture criterion is associated with this failure.

scholarly journals Calculation of flow characteristics of liquid fuel supplied through pressure jet atomizers of small-sized gas turbine engines

2021 ◽  
Vol 20 (2) ◽  
pp. 19-35
Author(s):  
N. I. Gurakov ◽  
I. A. Zubrilin ◽  
M. Hernandez Morales ◽  
D. V. Yakushkin ◽  
A. A. Didenko ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Liquid Fuel ◽  
Cone Angle ◽  
Flow Characteristics ◽  
Design Parameters ◽  
Turbine Engines ◽  
Gas Turbine Engines ◽  
Spray Cone Angle ◽  
Spray Cone ◽  
Semi Empirical

The paper presents the results of studying the flow characteristics of liquid fuel in pressure jet atomizers of small-sized gas turbine engines with nozzle diameters of 0.4-0.6 mm for various operating and design parameters. The study was carried out using experimental measurements, semi-empirical correlations and CFD (computational fluid dynamics) methods. The Euler approach, the volume- of- fluid (VOF) method, was used to model multiphase flows in CFD simulations. Good agreement was obtained between experimental and predicted data on the fuel coefficient and the primary spray cone angle at the nozzle outlet. Besides, the assessment of the applicability of semi-empirical techniques for the nozzle configurations under consideration is given. In the future, the flow characteristics in question (the nozzle flow rate, the fuel film thickness, and the primary spray cone angle) can be used to determine the mean diameter of the droplets (SMD) required to fully determine the boundary conditions of fuel injection when modeling combustion processes in combustion chambers of small-sized gas turbine engines.

Comparison of Two Complete Solutions in an Axisymmetric Extrusion With Experiment

1969 ◽  
Vol 91 (3) ◽  
pp. 543-548 ◽  
Author(s):  
A. H. Shabaik ◽  
E. G. Thomsen
Keyword(s):  
Strain Rate ◽  
Effective Strain ◽  
Cone Angle ◽  
Low Friction ◽  
First Approximation ◽  
Strain And Strain Rate ◽  
Conical Die ◽  
Stream Lines ◽  
Half Cone ◽  
Half Cone Angle

An upper-bound and a potential solution to a forward extrusion problem were compared with experimental results obtained by the visioplasticity method. The process consisted of extruding a 2-in-dia billet of preforged lead through a conical die having a half-cone angle of 45 deg under the condition of relatively low friction. The comparison was made for steady state stream lines, velocities, strain rate components, effective strain and strain rate, grid distortion, and stress distribution. It was found that the curves were generally of similar shape and that some differences existed in magnitude only. It is suggested that the theoretical solutions can be used to advantage to a first approximation in predicting all important variables.

A Theory of the Yield Point and the Transition Temperature of Mild Steel

1956 ◽  
Vol 23 (2) ◽  
pp. 219-224
Author(s):  
F. Forscher
Keyword(s):  
Transition Temperature ◽  
Mild Steel ◽  
Strain Rate ◽  
Yield Point ◽  
Structural Model ◽  
Yield Criterion ◽  
State Of Stress ◽  
Yield Point Phenomenon ◽  
Stress And Strain Rate ◽  
Temperature Strain

Abstract Experimental results indicate the dependence of the yield-point phenomenon of mild steel on temperature, strain rate, duration of stress, and stress state. This paper proposes a yield criterion which can account for these variables. The theory is developed on the basis of a “structural” model, by which the behavior of microscopic and submicroscopic elements is idealized. The theory postulates as yield criterion a critical number of relaxation centers (active Frank-Read sources) or, equivalently, a critical size of relaxation centers. The transition-temperature phenomenon is considered to be the result of an inhibition of yielding (upper yield point) by means of geometry, temperature and/or strain rate. A relation is given which expresses its dependence on the state of stress and strain rate.

The Creep of Thick Tubes Under Internal Pressure

1957 ◽  
Vol 24 (3) ◽  
pp. 464-466
Author(s):  
C. D. Weir
Keyword(s):  
Internal Pressure ◽  
Strain Rate ◽  
Shear Strain ◽  
Rate Equation ◽  
Strain Energy ◽  
Strain Energy Function ◽  
Stress Deviator ◽  
Constant Density ◽  
Creep Stress ◽  
Shear Strain Energy

Abstract Using the usually accepted assumption that the strain rate of a material undergoing creep is given by the product of the stress deviator and a function of the shear-strain energy, and assuming constant density, equations are derived for the creep stresses in a thick-walled tube under internal pressure for a generalized form of the shear strain-energy function. It is shown that these reduce to previously published equations on the substitution of a power law stress-strain rate equation. The nonisothermal case is considered also and creep-stress equations are obtained in a similarly generalized form.

scholarly journals The theory of plane plastic strain for anisotropic metals

1949 ◽  
Vol 198 (1054) ◽  
pp. 428-437 ◽  
Keyword(s):  
Plastic Strain ◽  
Strain Rate ◽  
Shear Strain ◽  
Plane Strain ◽  
Yield Criterion ◽  
Elliptic Functions ◽  
Shear Strain Rate ◽  
Maximum Shear Strain ◽  
Geometrical Properties ◽  
Plane Plastic

A yield criterion and plastic stress-strain relations are formulated for anisotropic metals deformed under conditions of plane strain. The equations are shown to be hyperbolic, the characteristics coinciding with the directions of maximum shear strain-rate. When the anisotropy is uniformly distributed, the variation of the stresses along the characteristics is expressed in terms of elliptic functions, and geometrical properties of the field of characteristics are established. The theory is applied to the problem of indentation by a flat die.

A Proposed Generalized Model for Forming Limit Diagram

2015 ◽  
Author(s):  
Aly El Domiaty ◽  
Abdel-Hamid I. Mourad ◽  
Abdel-Hakim Bouzid
Keyword(s):  
Constitutive Equation ◽  
Strain Rate ◽  
Strain Hardening ◽  
Power Law ◽  
Yield Criterion ◽  
Rate Of Change ◽  
Forming Limit ◽  
Strain Hardening Exponent ◽  
Sensitivity Factor ◽  
Generalized Model

One of the most significant approaches for predicting formability is the use of forming limit diagrams (FLDs). The development of the generalized model integrates other models. The first model is based on Von-Misses yield criterion (traditionally used for isotropic material) and power law constitutive equation considering the strain hardening exponent. The second model is also based on Von-Misses yield criterion but uses a power law constitutive equation that considers the effect of strain rate sensitivity factor. The third model is based on the modified Hill’s yield criterion (for anisotropic materials) and a power law constitutive equation that considers the strain hardening exponent. The current developed model is a generalized model which is formulated on the basis of the modified Hill yield criterion and a power law constitutive equation considering the effect of strain rate. A new controlling parameter (γ) for the limit strains was exploited. This parameter presents the rate of change of strain rate with respect to strain. As γ increases the level of the FLD raises indicating a better formability of the material.

A Yield Criterion for Porous Ductile Media at High Strain Rate

1997 ◽  
Vol 64 (3) ◽  
pp. 503-509 ◽  
Author(s):  
Ze-Ping Wang ◽  
Qing Jiang
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
Yield Surface ◽  
High Strain ◽  
Yield Criterion ◽  
Matrix Material ◽  
Yield Function ◽  
Inertial Effects ◽  
The Matrix ◽  
Dynamic Yield

An approximate yield criterion for porous ductile media at high strain rate is developed adopting energy principles. A new concept that the macroscopic stresses are composed of two parts, representing dynamic and quasi-static components, is proposed. It is found that the dynamic part of the macroscopic stresses controls the movement of the dynamic yield surface in stress space, while the quasi-static part determines the shape of the dynamic yield surface. The matrix material is idealized as rigid-perfectly plastic and obeying the von Mises yield. An approximate velocity field for the matrix is employed to derive the dynamic yield function. Numerical results show that the dynamic yield function is dependent not only on the rate of deformation but also on the distribution of initial micro-damage, which are different from that of the quasi-static condition. It is indicated that inertial effects play a very important role in the dynamic behavior of the yield function. However, it is also shown that when the rate of deformation is low (≤103/sec), inertial effects become vanishingly small, and the dynamic yield function in this case reduces to the Gurson model.

Dynamic fracture under impact and high-strain-rate loading

1995 ◽  
Vol 73 (5-6) ◽  
pp. 315-323 ◽  
Author(s):  
M. J. Worswick ◽  
J. A. Clarke ◽  
R. J. Pick
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
Ductile Fracture ◽  
Damage Evolution ◽  
High Strain ◽  
Yield Criterion ◽  
Damage And Fracture ◽  
Split Hopkinson ◽  
Strain Rate Loading ◽  
Dynamic Loading Conditions

A constitutive model based on a pressure-dependent yield criterion is used to predict damage evolution and ductile fracture under dynamic loading conditions. The model predicts the influence of porosity on plastic flow in metals and the nucleation, growth, and coalescence of internal microvoids to cause ductile fracture. The constitutive equations have been implemented in the DYNA2D finite-element code and have been used to simulate three high-strain-rate experiments: (i) the symmetric Taylor cylinder impact, (ii) the plate impact, and (iii) the tensile split Hopkinson bar experiments. In each case, the model is shown to capture qualitatively the damage and fracture within the experiments modelled. Comparison with recent symmetric Taylor impact experiments on leaded brass suggests that the model over-predicts the rate of damage evolution under the high-strain rate, high-triaxiality conditions associated with impact.

Analysis of Wire Drawing and Extrusion Through Conical Dies of Large Cone Angle

1964 ◽  
Vol 86 (4) ◽  
pp. 305-314 ◽  
Author(s):  
Betzalel Avitzur
Keyword(s):  
Cone Angle ◽  
Wire Drawing ◽  
Wire Radius ◽  
Yield Limit ◽  
Process Variables ◽  
Absolute Value ◽  
Direct Extension ◽  
Yield Value ◽  
Half Angle ◽  
Large Cone Angle

This work is a direct extension of reference [3]. There the problem was treated with the assumption that the cone angle was small. Here this limitation exists no more. The operations of wire drawing and extrusion through conical dies are treated on the assumption that “Mises” material is formed. An upper-bound solution is obtained for the drawing stress in wire drawing and for the pushing stress in extrusion. The effect of each of the process variables on these forces is presented graphically. The process variables are: the cone half-angle (α), initial (Ri) and final (Rf) wire radius, material yield limit (σ0) under uniaxial load, back pull (σxb) and front pull (σxf), coefficient of friction (μ) or shear factor (m), die land (L), exit velocity (vf), and entrance velocity (vi). On the assumption that the maximum front tension cannot exceed the yield limit of the material under uniaxial tension, a solution is obtained for maximum possible reduction in wire drawing. An analogous assumption, i.e., that the absolute value of the pushing stress also cannot exceed the yield value, gives a criterion for maximum possible reduction in extrusion.

A Study of the Influences on Stress and Temperature Caused by Different Wire Drawing Parameters by Numerical Simulation

2013 ◽  
Vol 803 ◽  
pp. 489-495
Author(s):  
Peng Jie Sun ◽  
Fen Lou Zhai ◽  
Dong Xu Liu ◽  
Jia Li Yan ◽  
Jing Ning
Keyword(s):  
Numerical Simulation ◽  
Working Conditions ◽  
Cone Angle ◽  
Wire Drawing ◽  
Experimental Results ◽  
Drawing Die ◽  
Drawing Speed ◽  
Temperature Experiment ◽  
Steel Cords ◽  
Hole Structure

This paper analysed the first-step of dry drawing of steel cords by numerical simulation. In different working conditions,a couple of simulations were made to analyses the influences on stress and temperature,different work cone angle,drawing speed,high of die bearing . Afer measuring the actual data of temperature experiment, the experimental results were in good great agreement with numerical simulartion.In this paper,some measures were concluded to reduce the drawing stress and temperature,which have guiding significance for the production of steel cord.Key words:Wire drawing die;Hole structure;Temperature;Decoupling

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