Reducibility of Stress-Based Workability Diagram to Strain-Based Workability Diagram

2016 ◽  
Vol 08 (02) ◽  
pp. 1650022 ◽  
Author(s):  
Dragisa Vilotic ◽  
Sergei Alexandrov ◽  
Aljosa Ivanisevic ◽  
Mladomir Milutinovic
Keyword(s):  
Free Surface ◽  
Ductile Fracture ◽  
Metal Forming ◽  
Strain Path ◽  
Surface Fracture ◽  
Workability Diagram ◽  
Standard Tests ◽  
Principal Strains

The strain-based and stress-based workability diagrams are often used to predict the initiation of ductile fracture in metal forming. The strain-based workability diagram is restricted to free surface fracture and postulates that the initiation of fracture is independent of the strain path. It is shown in the present paper that under these conditions the strain-based workability diagram is identical to the stress-based workability diagram. Using an available stress-based workability diagram the strain-based workability diagram is found in a much larger domain in the space of two in-surface principal strains as compared to the typical domain covered by standard tests used to determine strain-based workability diagrams. Two feasible tests are designed to determine the complete strain-based workability diagram.

A theoretical—experimental method for the identification of the modified Cockroft—Latham ductile fracture criterion

2008 ◽  
Vol 222 (9) ◽  
pp. 1869-1872 ◽  
Author(s):  
S Alexandrov ◽  
D Vilotic
Keyword(s):  
Experimental Data ◽  
Free Surface ◽  
Ductile Fracture ◽  
Experimental Method ◽  
Fracture Criterion ◽  
Input Parameter ◽  
Primary Objective ◽  
Ductile Fracture Criterion ◽  
Surface Fracture ◽  
Principal Strains

The primary objective of the present study is to show that in many practical cases of free surface fracture, the modified Cockroft—Latham ductile fracture criterion is reduced to a relation between two in-surface principal strains. This finding can be combined with an appropriate set of experimental data to determine the input parameter of the criterion and/or verify it. An illustrative example is provided.

Ductile Fracture in Metal Forming: A Review of Selected Issues

2012 ◽  
Vol 528 ◽  
pp. 1-11 ◽  
Author(s):  
Sergei Alexandrov ◽  
Elena Lyamina
Keyword(s):  
Free Surface ◽  
Ductile Fracture ◽  
Experimental Method ◽  
Metal Forming ◽  
Experimental Methods ◽  
Fracture Criteria ◽  
Surface Fracture ◽  
Maximum Friction ◽  
Ductile Fracture Criteria ◽  
Friction Surfaces

The paper reviews several theoretical and experimental methods for the assessment of ductile fracture criteria and for their application to the fracture prediction in metal forming processes. In particular, distinguished features of two widely used ductile fracture criteria are demonstrated in the case of free surface fracture. Conventional empirical ductile fracture criteria are not compatible with behaviour of plastic solutions in the vicinity of maximum friction surfaces. An approach to overcome this difficulty is discussed. Finally, a theoretical/experimental method to reveal a possible effect of geometric singularities on the applicability of ductile fracture criteria is reviewed.

Forming Limit Analysis of Molybdenum Reinforced Carbon Steels

2018 ◽  
Vol 777 ◽  
pp. 306-310 ◽  
Author(s):  
Ananthanarayanan Rajeshkannan ◽  
Sumesh Narayan
Keyword(s):  
Plastic Deformation ◽  
Free Surface ◽  
Powder Metallurgy ◽  
Ductile Fracture ◽  
Limit Analysis ◽  
Metal Forming ◽  
Carbon Steels ◽  
Die Design ◽  
Cold Forging ◽  
Forming Limit

The occurrence of ductile fracture during the plastic deformation of powder metallurgy materials is adverse and damaging and the prediction of fracture is very important in the early stages as early modifications will prevent failure. This will tend to save a lot of money and forming limit studies in many metal forming processes is up most important. Forming limit analysis on the cold forged molybdenum reinforced carbon steels were carried out in this work. In this study two key strain hardening parameters are used to study the formability characteristics. This analysis is effectively used for design of powder metallurgy parts and most importantly the die design as repressing needs to be employed before pores appear as cracks on the free surface. The cold forging was carried out on Fe-0.8%C, Fe-0.8%C-1%Mo, Fe-0.8%C-1.5%Mo and Fe-0.8%C-2.0%Mo and the formability behavior of the same is presented.

Eulerian FEA With Volume of Solid (VOS) Application in Metal Forming

2010 ◽  
Author(s):  
K. S. Al-Athel ◽  
M. S. Gadala
Keyword(s):  
Finite Element ◽  
Free Surface ◽  
Process Improvement ◽  
Metal Forming ◽  
Material Flow ◽  
Solid Mechanics ◽  
Uniform Mesh ◽  
Element Formulation ◽  
Volume Of Fluid Method ◽  
Whole Process

The adaptation of the volume of fluid method (VOF) to solid mechanics (VOS) is presented in this work with the focus on metal forming applications. The method is discussed for a general non-uniform mesh with Eulerian finite element formulation. The implementation of the VOS method in metal forming applications is presented by focusing on topics such as the contact between the tool and the workpiece, tracking of the free surface of the material flow and the connectivity of the free surface during the whole process. Improvement on the connectivity of the free surface and the representation of curves is achieved by considering the mechanics of different metal forming processes. Different applications are simulated and discussed to highlight the capability of the VOS method.

Strain path dependency in incremental sheet-bulk metal forming

2020 ◽  
Author(s):  
S. Wernicke ◽  
M. Hahn ◽  
G. Gerstein ◽  
F. Nürnberger ◽  
A. E. Tekkaya
Keyword(s):  
Metal Forming ◽  
Strain Path ◽  
Path Dependency ◽  
Bulk Metal ◽  
Bulk Metal Forming

Stress-Based Forming Limits in Sheet-Metal Forming

2000 ◽  
Vol 123 (4) ◽  
pp. 417-422 ◽  
Author(s):  
Thomas B. Stoughton
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Strain Path ◽  
Forming Limit ◽  
Stress Strain ◽  
Strain Relation ◽  
Stress Strain Relation ◽  
The Stability ◽  
Definition Of

A strain-based forming limit criterion is widely used throughout the sheet-metal forming industry to gauge the stability of the deformed material with respect to the development of a localized neck prior to fracture. This criterion is strictly valid only when the strain path is linear throughout the deformation process. There is significant data that shows a strong and complex dependence of the limit criterion on the strain path. Unfortunately, the strain path is never linear in secondary forming and hydro-forming processes. Furthermore, the path is often found to be nonlinear in localized critical areas in the first draw die. Therefore, the conventional practice of using a path-independent strain-based forming limit criterion often leads to erroneous assessments of forming severity. Recently it has been reported that a stress-based forming limit criterion appears to exhibit no strain-path dependencies. Subsequently, it has been suggested that this effect is not real, but is due to the saturation of the stress-strain relation. This paper will review and compare the strain-based and stress-based forming limit criteria, looking at a number of factors that are involved in the definition of the stress-based forming limit, including the role of the stress-strain relation.

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