Effect of Intensive Plastic Deformation Near Frictional Interfaces on Ductile Fracture

2012 ◽  
Vol 586 ◽  
pp. 306-309
Author(s):  
Sergei Alexandrov ◽  
Dragisa Vilotic ◽  
Elena Lyamina ◽  
Yeau Ren Jeng
Keyword(s):  
Plastic Deformation ◽  
Ductile Fracture ◽  
Metal Forming ◽  
Fracture Criterion ◽  
Fracture Initiation ◽  
Experimental Results ◽  
Ductile Fracture Criterion ◽  
Special Design ◽  
Upsetting Test ◽  
Ductile Fracture Initiation

A layer of intensive plastic deformation often appears in the vicinity of frictional interfaces in metal forming processes. The paper presents a study to reveal a possible effect of intensive plastic deformation in such a layer on ductile fracture. To this end, an upsetting test of special design is used to move the site of ductile fracture initiation to the friction surface independently of the effect of intensive plastic deformation on the occurrence of ductile fracture. Experimental results obtained are compared to the theoretical prediction based on a conventional empirical ductile fracture criterion. It is shown that there is some deviation of the fracture conditions predicted theoretically from the experimental results.

Failure Prediction in Drawing Processes of Mg Alloy Sheet by the FEM and Ductile Fracture Criterion

2011 ◽  
Vol 264-265 ◽  
pp. 813-818 ◽  
Author(s):  
Sang Woo Kim ◽  
Young Seon Lee ◽  
Beom Soo Kang
Keyword(s):  
Ductile Fracture ◽  
Fracture Criterion ◽  
Elevated Temperatures ◽  
Failure Prediction ◽  
Fracture Initiation ◽  
Tensile Tests ◽  
Alloy Sheet ◽  
Fe Analysis ◽  
Uniaxial Tensile ◽  
Ductile Fracture Criterion

In this work, in order to predict the forming failure of AZ31 magnesium alloy sheet in drawing process at elevated temperatures, a series of square cup tests at various temperatures and FE analyses were carried out. The critical damage values and the mechanical properties dependent on strain rates and temperatures were evaluated from uniaxial tensile tests and those were utilized to the forming failure prediction using FE analysis. Based on the plastic deformation history obtained from FE analysis and Cockcroft and Latham’s ductile fracture criterion, the fracture initiation time and location were predicted and verified with the experimental results.

Evaluation of prediction error resulting from using average state variables in the calibration of ductile fracture criterion

2017 ◽  
Vol 27 (8) ◽  
pp. 1231-1251 ◽  
Author(s):  
Xincun Zhuang ◽  
Yehui Meng ◽  
Zhen Zhao
Keyword(s):  
Ductile Fracture ◽  
Prediction Error ◽  
Fracture Criterion ◽  
Stress Triaxiality ◽  
Fracture Initiation ◽  
Equivalent Strain ◽  
State Variables ◽  
Ductile Fracture Criterion ◽  
Series Of Experiments ◽  
Relationship Of

In order to evaluate the prediction error resulting from using average state variables in the calibration procedure of the ductile fracture criterion, a series of experiments and corresponding simulations were performed to extract the evolution of fracture-related state variables such as stress triaxiality (η), Lode parameter, and equivalent strain to fracture at the fracture initiation points. The average stress triaxiality, average Lode parameter, and equivalent strain to fracture were used to calibrate the Lou-Huh (L-H) ductile fracture criterion. The average induced prediction error was evaluated by comparing the accumulated damage value, which was computed with the calibrated L-H ductile fracture criterion at the fracture initiation point, with the critical threshold value. Comparisons based on a series of experiments covering a wide range of values for stress triaxiality indicated the existence of an average induced prediction error for the compression tests, and demonstrated that different values of embedded-constants C1 and C2 of L-H ductile fracture criterion resulted in entirely different average induced prediction errors. Thus, a parameter study was performed to investigate the influences of C1, C2, the relationship of η and equivalent plastic strain ([Formula: see text]), and the internal function of the integral formula on the average induced relative error. The influence of the relationship of [Formula: see text] could be represented by the influence of the exponent a, the intercept for the stress triaxiality, and the allocation of equivalent strain for the segmented function. Among these influence factors, the value of C2, the value of the exponent a, and the value of the negative intercept for stress triaxiality contributed significantly to an increase in relative error.

Prediction and analysis of ductile fracture in sheet metal forming—Part I: A modified Ayada criterion

2014 ◽  
Vol 23 (8) ◽  
pp. 1189-1210 ◽  
Author(s):  
HS Liu ◽  
MW Fu
Keyword(s):  
Finite Element ◽  
Plastic Strain ◽  
Ductile Fracture ◽  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Fracture Criterion ◽  
Ductile Fracture Criterion ◽  
Wide Range ◽  
Stress States

A modified ductile fracture criterion is proposed based on the traditional Ayada criterion and coded into the finite element simulation platform of VUMAT/ABAQUS for prediction and analysis of ductile fracture in metal plastic strain processes. In this modified ductile fracture criterion, stress triaxiality is taken into account, and more importantly, the exponential effect of the equivalent plastic strain on the damage behavior, which is generally ignored in other ductile fracture criteria, is also considered. The material related constants in the modified ductile fracture criterion are determined by tensile tests together with finite element simulations. The applicability and reliability of the ductile fracture criterion in ductile fracture prediction in two types of classic stress states, viz. shear stress, tensile stress in sheet metal forming, are investigated based on the deformation behavior and fracture occurrence in two case studies with two typical types of materials, i.e. Al 6061 and T10A. The materials have a wide range of plasticity. The simulation and experimental results verify the applicability and reliability of the developed ductile fracture criterion in prediction of the ductile fracture with and without necking in different stress states of plastic strain.

Prediction of ductile fracture for Al6016-T4 with a ductile fracture criterion: Experiment and simulation

2019 ◽  
Vol 29 (8) ◽  
pp. 1199-1221 ◽  
Author(s):  
Saijun Zhang ◽  
Yanchun Lu ◽  
Zhaohui Shen ◽  
Chi Zhou ◽  
Yanshan Lou
Keyword(s):  
Ductile Fracture ◽  
Metal Forming ◽  
Fracture Criterion ◽  
Stress Triaxiality ◽  
Yield Function ◽  
Isotropic Hardening ◽  
Ductile Fracture Criterion ◽  
Fracture Locus ◽  
Hardening Law ◽  
Tension Tests

The key point in this paper is the prediction of the onset of ductile fracture with a newly proposed ductile fracture criterion in various stress state ranging from shear to uniaxial tension. A series of tension tests with different material orientations are carried out up to fracture. The anisotropic Drucker yield function with an isotropic hardening law is identified to describe the elastic–plastic behaviors of Al6016-T4 aluminum alloy. The uncoupled ductile fracture criterion is calibrated and then utilized to construct the fracture locus of Al6016-T4, which is implemented into the ABAQUS/Explicit to validate the prediction of ductile fracture criterion by comparing experimental results to numerical ones. The validation demonstrates that the ductile fracture criterion can accurately predict the onset of ductile fracture for Al6016-T4 in medium stress triaxiality ranging from 0.1 to 0.44 where most ductile fracture occurs in sheet metal forming.

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.

Incorporation of a Fracture Criterion in Ideal Flow Design

2016 ◽  
Vol 713 ◽  
pp. 143-146 ◽  
Author(s):  
Elena Lyamina ◽  
Sergei Alexandrov
Keyword(s):  
Ductile Fracture ◽  
Metal Forming ◽  
Fracture Criterion ◽  
Design Method ◽  
Stress And Strain ◽  
Preliminary Design ◽  
Ductile Fracture Criterion ◽  
Ideal Flow ◽  
Ideal Plastic ◽  
The Ideal

The theory of sheet and bulk ideal plastic flows is used for the preliminary design of metal forming processes. The present paper develops an approach to incorporate the Cockroft and Latham ductile fracture criterion in this design method for stationary bulk flows. In particular, it is demonstrated that the initiation of ductile fracture can be predicted without having the ideal flow solution for stress and strain in the plastic zone (it is only necessary to know that the solution exists). Using the approach proposed the initiation of ductile fracture in axisymmetric drawing is predicted.

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