Experimental prediction of sheet metal formability of AW-5754 for non-linear strain paths by using a cruciform specimen and a blank holder with adjustable draw beads on a sheet metal testing machine

2016 ◽  
Vol 10 (4) ◽  
pp. 597-605 ◽  
Author(s):  
David Jocham ◽  
Christian Gaber ◽  
Ole Böttcher ◽  
Patrik Wiedemann ◽  
Wolfram Volk
Keyword(s):  
Sheet Metal ◽  
Testing Machine ◽  
Linear Strain ◽  
Blank Holder ◽  
Cruciform Specimen ◽  
Experimental Prediction ◽  
Non Linear ◽  
Strain Paths

scholarly journals Identification of forming limits at fracture of DP600 sheet metal under linear and unloaded non-linear strain paths

2017 ◽  
Vol 207 ◽  
pp. 562-567 ◽  
Author(s):  
Xiao Song ◽  
Lionel Leotoing ◽  
Dominique Guines ◽  
Eric Ragneau
Keyword(s):  
Sheet Metal ◽  
Linear Strain ◽  
Forming Limits ◽  
Non Linear ◽  
Strain Paths

Prediction on Localized Necking in Sheet Metal Forming: Finite Element Simulation and Plastic Instability in Complex Industrial Strain Paths

2007 ◽  
Vol 344 ◽  
pp. 825-832 ◽  
Author(s):  
Augusto Barata da Rocha ◽  
Abel D. Santos ◽  
Pedro Teixeira
Keyword(s):  
Finite Element ◽  
Finite Element Simulation ◽  
Sheet Metal ◽  
Numerical Models ◽  
Plastic Instability ◽  
Linear Strain ◽  
Localized Necking ◽  
Element Simulation ◽  
Non Linear ◽  
Strain Paths

The use of Finite Element Simulation allows accurate predictions of stress and strain distributions in complex stamped parts. The onset of necking is strongly dependent on the strain paths imposed to the parts and therefore the prediction of localized necking can be a difficult task. Numerical models of plastic instability have been used to predict such behavior and recent and more accurate constitutive models have been applied in these calculations. In many manufacturing areas such as automotive, aerospace, building, packaging and electronic industries, the optimization of sheet metal processes, through the use of numerical simulations, has become a key factor to a continuously increasing requirement for time and cost efficiency, for quality improvement and materials saving. This paper makes an analysis of the evolution of strain gradients in stamped parts. The combination of Finite Element Analysis with a Plastic Instability Model, developed to predict localized necking under complex strain paths, shows that it is possible to predict failure with precision. Several constitutive laws are used and comparisons are made with experiments in stamped benchmark parts. Considering non linear strain paths, as detected in stamped parts, more accurate failure predictions are achieved. The work described in this paper shows the need to include a post processor analysis of failure, capable of predicting the behavior of the material under non linear strain paths. Taking this phenomenon into account, it is shown that it is possible to increase the accuracy of the onset of localized necking prediction.

Influence of Different Pre-Stretching Modes on the Forming Limit Diagram of AA6014

2012 ◽  
Vol 504-506 ◽  
pp. 71-76 ◽  
Author(s):  
Alexandra Werber ◽  
Mathias Liewald ◽  
Winfried Nester ◽  
Martin Grünbaum ◽  
Klaus Wiegand ◽  
...  
Keyword(s):  
Plane Strain ◽  
Biaxial Loading ◽  
Forming Limit Diagram ◽  
Forming Limit ◽  
Linear Strain ◽  
Forming Limits ◽  
Systematic Analysis ◽  
Measurement Systems ◽  
Non Linear ◽  
Strain Paths

In order to evaluate the formability of sheet materials forming limit diagrams (FLD) are recorded which represent the values of major and minor strain when necking occurs. FLDs are recorded based on the assumption that exclusively linear strain paths occur. In real forming parts, however, particularly in those with complex shapes, predominantly non-linear strain paths occur which reduce the accuracy of the failure prediction according to a conventional FLD. For this reason forming limits after loading with non-linear strain paths have to be investigated. In this contribution a systematic analysis of the forming limits of a conventional AA6014 alloy after loading with non-linear strain paths is presented. This material is pre-stretched in uniaxial, plane strain and biaxial direction up to several levels before performing Nakajima experiments in order to determine FLDs. During the pre-stretching process as well as during the Nakajima experiment the strain distribution can be measured online very precisely with the optical deformation measurement systems GOM Aramis or VIALUX. The gained curves are compared to the FLD of the as-received material. The results prove a significant influence of the pre-stretching condition on the forming limits of the used aluminum alloy. For a low pre-stretching in uniaxial as well as in biaxial direction the FLDs show a slightly reduced formability while after higher pre-stretching levels the forming limit can be improved such as for biaxial loading after uniaxial pre-stretching. The formability after pre-stretching in plane strain direction was changed. Also, a shift of the FLD depending on the direction of pre-stretching can be observed.

Evaluation of non-linear strain paths using Generalized Forming Limit Concept and a modification of the Time Dependent Evaluation Method

2016 ◽  
Vol 10 (3) ◽  
pp. 345-351 ◽  
Author(s):  
Christian Gaber ◽  
David Jocham ◽  
Hannes Alois Weiss ◽  
Ole Böttcher ◽  
Wolfram Volk
Keyword(s):  
Evaluation Method ◽  
Time Dependent ◽  
Forming Limit ◽  
Linear Strain ◽  
Limit Concept ◽  
Non Linear ◽  
Strain Paths

Formability Evaluation Using Modified Cockcroft Criterion with Strain Paths for Sheet Metal Forming

2014 ◽  
Vol 626 ◽  
pp. 495-501 ◽  
Author(s):  
Rong Shean Lee ◽  
Ta Wei Chien
Keyword(s):  
Tensile Test ◽  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Strain Path ◽  
Dome Height ◽  
Bulge Test ◽  
Cruciform Specimen ◽  
Strain Paths ◽  
Good Agreement

In most situations, original Cockcroft criterion underestimates material formability in the first quadrant of FLD. So far, some modified Cockcroft criteria have been reported for different applications. This presentation will focus on the modified Cockcroft criterion which takes strain-path effect into consideration. This paper demonstrates the accuracy of this criterion through limiting dome height test, free bulge test, and the biaxial tensile test using cruciform specimen respectively. The results showed that the modified Cockcroft criterion with strain path effect has good agreement with experimental results.

Optimisation of Cruciform Test Specimen for Biaxial Tensile Testing of Sheet Metal

2011 ◽  
Vol 264-265 ◽  
pp. 114-122
Author(s):  
Peter Tiernan ◽  
Alan Hannon
Keyword(s):  
Sheet Metal ◽  
Tensile Testing ◽  
Testing Machine ◽  
Low Carbon Steel ◽  
Low Carbon ◽  
Tensile Testing Machine ◽  
Cruciform Specimen ◽  
Biaxial Tensile ◽  
Optimum Specimen ◽  
Biaxial Tensile Testing

One of the most restricting aspects of the biaxial tensile test for sheet metal is the design of the cruciform specimen. Although specimens of the cruciform type have previoussly been investigated quite extensively, no standard geometry for the cruciform specimen exists. Using a specifically designed pantograph apparatus for operation in a standard tensile testing machine, various cruciform specimens were analysed experimentally. Finite element modelling of the specimens was also conducted to establish optimum specimen geometry. Through a process of optimisation, a standard cruciform specimen was designed which can be used to accurately predict the mechanical behaviour of cold rolled low-carbon steel when formed in multiple directions simultaneously.

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