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.

The Evaluation of Ductile Fracture Criteria (DFC) of 6061-T6 Aluminum Alloy

2010 ◽  
Vol 44-47 ◽  
pp. 2837-2841 ◽  
Author(s):  
Ying Tong
Keyword(s):  
Aluminum Alloy ◽  
Ductile Fracture ◽  
Metal Forming ◽  
True Strain ◽  
Mutual Support ◽  
Fracture Criteria ◽  
Forming Process ◽  
Forming Simulation ◽  
Ductile Fracture Criteria ◽  
Metal Forming Process

As one of the principal failures, ductile fracturing restricts metal forming process. Cockcroft-Latham fracture criterion is suited for tenacity fracture in bulk metal-forming simulation. An innovative approach involving physical compression experiments, numerical simulations and mathematic computations provides mutual support to evaluate ductile damage cumulating process and ductile fracture criteria (DFC). The results show that the maximum cumulated damage decreases with strain rate rising, and the incremental ratios, that is damage sensitive rate, vary uniformly during the upsetting processes at different strain rates. The damage sensitive rate decreases rapidly, then it becomes stability in a constant 0.11 after true strain -0.85. The true strain -0.85 was assumed as the fracture strain, and the DFC of 6061-T6 aluminum alloy is almost a constant 0.2. According to DFC, the exact fracture moment and position during various forming processes will be predicted conveniently.

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.

A Note on Ductile Fracture Criteria in Metal Forming

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
Sergei Alexandrov ◽  
Lihui Lang
Keyword(s):  
Ductile Fracture ◽  
Metal Forming ◽  
Fracture Criterion ◽  
Ductile Fracture Criterion ◽  
Hot Metal ◽  
Fracture Criteria ◽  
Material Models ◽  
Analysis And Design ◽  
Ductile Fracture Criteria ◽  
Forming Analysis

This paper deals with some general properties of a ductile fracture criterion, which generalizes two ductile fracture criteria conventionally adopted for metal forming analysis and design. The results are valid for a wide class of material models applicable to both cold and hot metal formings. It is expected that the theoretical features of the fracture criterion emphasized in the present paper can be useful for its experimental verification or for determining its parameters from the experiment.

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.

Finite Element Analysis of the Hydro-Mechanical Punching Process

2006 ◽  
Vol 505-507 ◽  
pp. 871-876
Author(s):  
Jong Hun Yoon ◽  
Hoon Huh ◽  
Yong Sin Lee ◽  
Seung Soo Kim ◽  
E.J. Kim ◽  
...  
Keyword(s):  
Hydrostatic Pressure ◽  
Ductile Fracture ◽  
Sheet Material ◽  
Middle Surface ◽  
Initial Crack ◽  
Fracture Criteria ◽  
Element Analysis ◽  
Final Fracture ◽  
Ductile Fracture Criteria ◽  
Punching Process

This paper investigates the characteristics of a hydro-mechanical punching process. The hydro-mechanical punching process is divided into two stages: the first stage is the mechanical half piercing in which an upper punch goes down before the initial crack is occurred; the second stage is the hydro punching in which a lower punch goes up until the final fracture is occurred. Ductile fracture criteria such as the Cockcroft et al., Brozzo et al. and Oyane et al. are adopted to predict the fracture of a sheet material. The index value of ductile fracture criteria is calculated with a user material subroutine, VUMAT in the ABAQUS Explicit. The hydrostatic pressure retards the initiation of a crack in the upper region of the blank and induces another crack in the lower region of the blank during the punching process. The final fracture zone is placed at the middle surface of the blank to the thickness direction. The result demonstrates that the hydro-mechanical punching process makes a finer shearing surface than the conventional one as hydrostatic pressure increases.

Damage evaluation in tube spinnability test with ductile fracture criteria

2015 ◽  
Vol 100 ◽  
pp. 99-111 ◽  
Author(s):  
Hao Ma ◽  
Wenchen Xu ◽  
Bo Cheng Jin ◽  
Debin Shan ◽  
Steven R. Nutt
Keyword(s):  
Ductile Fracture ◽  
Damage Evaluation ◽  
Fracture Criteria ◽  
Ductile Fracture Criteria

Behavior of Lode Dependent Plasticity at Plane Strain Condition and its Implication to Ductile Fracture

2016 ◽  
Vol 258 ◽  
pp. 213-216 ◽  
Author(s):  
František Šebek ◽  
Jindrich Petruška ◽  
Petr Kubík
Keyword(s):  
Ductile Fracture ◽  
Plane Strain ◽  
Uniaxial Stress ◽  
Complex Materials ◽  
Fracture Criteria ◽  
Dependent Plasticity ◽  
Ductile Fracture Criteria ◽  
Stress States ◽  
Aluminum Alloy 2024 ◽  
Von Mises

Variety of metals are complex materials exhibiting various behavior under different loading. Many metallic materials exhibit Tresca-like behavior rather than von Mises. It means different behavior in tension under plane strain and uniaxial stress conditions. This might be described by Lode dependent plasticity which should result in better prediction in force or torque responses of material tests. Good agreement between computation and experiment is also very important when calibrating the ductile fracture criteria. Several tests under plane strain and uniaxial stress states were carried out on aluminum alloy 2024-T351 where the Lode dependency was significant. The Lode dependent plasticity was implemented along with von Mises and Tresca-like yield criteria, which resulted in improvement of force–displacement responses of plane strain tests simulations. But it also caused significant change in the stress state of tensile flat and grooved plates which wrongly approached uniaxial tension condition. This inconvenience prevents plane strain experiments from using for calibration of ductile fracture criteria under these circumstances.

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