scholarly journals Experimental and Numerical Investigations into the Failure Mechanisms of TRIP700 Steel Sheets

Metals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 1073 ◽  
Author(s):  
Niloufar Habibi ◽  
Veera Sundararaghavan ◽  
Ulrich Prahl ◽  
Ali Ramazani
Keyword(s):  
Forming Limit Diagram ◽  
Forming Limit ◽  
Failure Behavior ◽  
Damage Initiation ◽  
Localized Necking ◽  
Steel Sheets ◽  
Numerical Studies ◽  
Necking Criterion ◽  
Stress States ◽  
Damage Criteria

The formability and failure behavior of transformation-induced plasticity (TRIP) steel blanks were investigated through various stress states. The forming limit diagram (FLD) at fracture was constructed both experimentally and numerically. Numerical studies were performed to evaluate the applicability of different damage criteria in predicting the FLD as well as complex cross-die deep drawing process. The fracture surface and numerical results reveal that the material failed in a different mode for different strain path. Therefore, the Tresca model, which is based on shear stress, accurately predicted the conditions where shear had a profound effect on the damage initiation, whereas Situ localized necking criterion could calculate the conditions in which localization was dominant.

scholarly journals Experimental and Numerical Investigations into the Failure Mechanisms of TRIP700 Steel Sheets

2018 ◽  
Author(s):  
Niloufar Habibi ◽  
Veera Sundararaghavan ◽  
Ulrich Prahl ◽  
Ali Ramazani
Keyword(s):  
Forming Limit Diagram ◽  
Forming Limit ◽  
Failure Behavior ◽  
Damage Initiation ◽  
Localized Necking ◽  
Steel Sheets ◽  
Numerical Studies ◽  
Necking Criterion ◽  
Stress States ◽  
Damage Criteria

The formability and failure behavior of TRIP steel blanks were investigated through various stress states. The forming limit diagram (FLD) at fracture is constructed both experimentally and numerically. Numerical studies are performed to evaluate the applicability of different damage criteria in predicting the FLD as well as complex cross-die deep drawing process.  The fracture surface and numerical results revealed that the material failed in a different mode for different strain path. Therefore, Tresca model which is based on shear stress accurately predicted the conditions where shear had the profound effect on the damage initiation, whereas Situ localized necking criterion was able to calculate the conditions which localization was dominant.

Influence of Pre-Forming on the Forming Limit Diagram of Aluminum and Steel Sheets

2007 ◽  
Vol 344 ◽  
pp. 113-118 ◽  
Author(s):  
Massimo Tolazzi ◽  
Marion Merklein
Keyword(s):  
Dual Phase Steel ◽  
Process Analysis ◽  
Forming Limit Diagram ◽  
Forming Limit ◽  
Linear Strain ◽  
Forming Limit Diagrams ◽  
Steel Sheets ◽  
Biaxial Stretching ◽  
Strain Paths

This paper presents a method for the experimental determination of forming limit diagrams under non linear strain paths. The method consists in pre-forming the sheets under two different strain conditions: uniaxial and biaxial, and then stretching the samples, cut out of the preformed sheets, using a Nakajima testing setup. The optical deformation measurement system used for the process analysis (ARAMIS, Company GOM) allows to record and to analyze the strain distribution very precisely with respect to both time and space. As a reference also the FLDs of the investigated grades (the deep drawing steel DC04, the dual phase steel DP450 and the aluminum alloy AA5754) in as-received conditions were determined. The results show as expected an influence of the pre-forming conditions on the forming limit of the materials, with an increased formability in the case of biaxial stretching after uniaxial pre-forming and a reduced formability for uniaxial load after biaxial stretching if compared to the case of linear strain paths. These effects can be observed for all the investigated materials and can be also described in terms of a shifting of the FLD, which is related to the art and magnitude of the pre-deformation.

Damage-coupled FLD of Sheet Metals for Warm Forming and Nonproportional Loading

2011 ◽  
Vol 20 (8) ◽  
pp. 1243-1262 ◽  
Author(s):  
M. Jie ◽  
C. L. Chow ◽  
X. Wu
Keyword(s):  
Evolution Equation ◽  
Damage Evolution ◽  
Strain Softening ◽  
Forming Limit ◽  
Sheet Metals ◽  
Nonproportional Loading ◽  
Damage Evolution Equation ◽  
Localized Necking ◽  
Loading Paths ◽  
Necking Criterion

A method of forming limit prediction for sheet metals at high temperatures and under nonproportional loading is presented. The method takes into account the strain-softening behaviors of the material at elevated temperatures. A localized necking criterion based on an isotropic damage-coupled acoustic tensor is developed and employed to determine the forming limits of strain-softening materials. The damage evolution equation is developed within the thermo-mechanical framework. A closed-form expression of the forming limit strains is derived by coupling the damage evolution equation into the localized necking criterion. A computer program, incorporating the incremental theory of plasticity, the damage evolution equation and the localized necking criterion, is developed to compute the forming limit strains under several nonproportional loading paths. A series of the uniaxial tensile tests is performed to measure the relevant mechanical properties of AA6061 at the elevated temperature of 450°C. The material damage variables are determined from the measured elastic modulii from a series of loading and unloading paths. The damage evolution equation of AA6061 at 450°C is formulated based on the test data. The computed limit strains are compared with the test results under various loading paths and a good agreement is observed. It is found that the critical damage value is independent on the stress states and loading paths. It may be concluded that the application of the material damage as a reliable criterion of localized necking including the nonproportional loading cases.

A New Approach to the Evaluation of Forming Limits in Sheet Metal Forming

2015 ◽  
Vol 639 ◽  
pp. 333-338 ◽  
Author(s):  
Marion Merklein ◽  
Andreas Maier ◽  
Daniel Kinnstätter ◽  
Christian Jaremenko ◽  
Emanuela Affronti
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Forming Limit Diagram ◽  
Forming Limit ◽  
Strain History ◽  
Failure Behavior ◽  
Forming Limits ◽  
Optical Strain Measurement ◽  
Optical Strain

The forming limit diagram (FLD) is at the moment the most important method for the prediction of failure within sheet metal forming operations. Key idea is the detection of the onset of necking in dependency of different sample geometry. Whereas the standardized evaluation methods provides very robust and reliable results for conventional materials like deep drawing steels, the determined forming limits for modern light materials are often too conservative due to the different failure behavior. Therefore, within this contribution a new and innovative approach for the identification of the onset of necking will be presented. By using a pattern recognition-based approach in combination with an optical strain measurement system the complete strain history during the test can be evaluated. The principal procedure as well as the first promising results are presented and discussed.

Analysis of Forming Limits Using the Hill 1993 Yield Criterion

1998 ◽  
Vol 120 (3) ◽  
pp. 236-241 ◽  
Author(s):  
Siguang Xu ◽  
Klaus J. Weinmann ◽  
Abhijit Chandra
Keyword(s):  
Bifurcation Analysis ◽  
Yield Criterion ◽  
Forming Limit Diagram ◽  
Anomalous Behavior ◽  
Forming Limit ◽  
Forming Limits ◽  
Material Parameters ◽  
Localized Necking ◽  
Wide Range ◽  
The Hill

Forming limits of thin sheets are investigated using a yield criterion recently proposed by Hill (1993). This criterion utilizes five independent material parameters, which can be determined from uniaxial and balanced biaxial experiments, to describe a wide range of material properties of sheet metals, including the anomalous behavior of aluminum. In the present work, a bifurcation analysis is pursued to predict the onset of localized necking in strain rate insensitive sheet materials. A detailed parametric study is then conducted to evaluate the effect of various material parameters on the positive minor strain side of the forming limit diagram. It is observed that limit strains are strongly dependent on the shape of the yield locus. Forming limits predicted using Hill’s 1993 yield criterion are compared with those predicted using Hill’s 1948 and 1979 criteria. Results from the bifurcation analysis are also compared with experimental observations, as well as the limit strain predicitons based on the M-K analysis.

A Unified Damage Approach for Predicting Forming Limit Diagrams

1997 ◽  
Vol 119 (4) ◽  
pp. 346-353 ◽  
Author(s):  
C. L. Chow ◽  
L. G. Yu ◽  
M. Y. Demeri
Keyword(s):  
Plastic Deformation ◽  
Sheet Metal ◽  
Damage Model ◽  
Forming Limit Diagram ◽  
Forming Limit ◽  
Unified Approach ◽  
Nonuniform Deformation ◽  
Localized Necking ◽  
Micro Cracks ◽  
Three Phases

Plastic deformation in sheet metal consists of four distinct phases, namely, uniform deformation, diffuse necking, localized necking, and final rupture. The last three phases are commonly known as nonuniform deformation. A proper forming limit diagram (FLD) should include all three phases of the nonuniform deformation. This paper presents the development of a unified approach to the prediction of FLD to include all three phases of nonuniform deformation. The conventional method for predicting FLD is based on localized necking and adopts two fundamentally different approaches. Under biaxial loading, the Hill’s plasticity method is often chosen when α(=ε2/ε1) <0. On the other hand, the M-K method is typically used for the prediction of localized necking when α > 0 or when the biaxial stretching of sheet metal is significant. The M-K method, however, suffers from the arbitrary selection of the imperfection size, thus resulting in inconsistent predictions. The unified approach takes into account the effects of micro-cracks/voids on the FLD. All real-life materials contain varying sizes and degrees of micro-cracks/voids which can be characterized by the theory of damage mechanics. The theory is extended to include orthotropic damage, which is often observed in extensive plastic deformation during sheet metal forming. The orthotropic FLD model is based on an anisotropic damage model proposed recently by Chow and Wang (1993). Coupling the incremental theory of plasticity with damage, the new model can be used to predict not only the forming limit diagram but also the fracture limit diagram under proportional or nonproportional loading. In view of the two distinct physical phenomena governing the cases when α(=ε2/ε1) < or α > 0, a set of instability criteria is proposed to characterize all three phases of nonuniform deformation. The orthotropic damage model has been employed to predict the FLD of VDIF steel (Chow et al, 1996) and excellent agreement between the predicted and measured results has been achieved as shown in Fig. 1. The damage model is extended in this paper to examine its applicability and validity for another important engineering material, namely aluminum alloy 6111-T4.

Prediction of Forming Limit Diagram Based on Damage Coupled Kinematic-Isotropic Hardening Model Under Nonproportional Loading

2002 ◽  
Vol 124 (2) ◽  
pp. 259-265 ◽  
Author(s):  
C. L. Chow ◽  
X. J. Yang ◽  
E. Chu
Keyword(s):  
Damage Mechanics ◽  
Kinematic Hardening ◽  
Forming Limit Diagram ◽  
Forming Limit ◽  
Isotropic Hardening ◽  
Strain History ◽  
Sheet Metals ◽  
Nonproportional Loading ◽  
Localized Necking ◽  
Theory Of Damage

Based on the theory of damage mechanics, an anisotropic damage coupled mixed isotropic-kinematic hardening plastic model for the prediction of forming limit diagram (FLD) is developed. The model includes the formulation of nonlinear anisotropic kinematic hardening. For the prediction of limit strains under nonproportional loading, a damage criterion for localized necking of sheet metals subjected to complex strain history is proposed. The model is employed to predict the FLDs of AL6111-T4 alloy. The predicted results agree well with those determined experimentally.

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