Forming limit prediction for two-stage aluminum alloy sheet forming process considering the effect of normal stress

2016 ◽  
Vol 33 (4) ◽  
pp. 1192-1204
Author(s):  
Feifei Zhang ◽  
Jieshi Chen ◽  
Jun Chen
Keyword(s):  
Aluminum Alloy ◽  
Normal Stress ◽  
Forming Limit ◽  
Stress Effect ◽  
Linear Strain ◽  
Content Type ◽  
Second Stage ◽  
Non Linear ◽  
Strain Paths ◽  
Normal Stress Effect

Purpose – The purpose of this paper is to analyze theoretically the influence of normal stress on the formability of aluminum alloy sheets in non-linear strain paths. Design/methodology/approach – Four loading modes of non-linear strain paths are investigated in detail to consider the effect of normal stress on formability of aluminum alloy sheets. Findings – Results show that the influence of normal stress in the first stage can be ignored. However, the normal stress in the second stage enhances the formability of aluminum alloy sheets obviously. Besides, the normal stress in the second stage is found to have larger effect on forming limit stress than that in the first stage. Research limitations/implications – Maybe more experiment data should be obtained to support the theoretical findings. Originality/value – This current study provides a better understanding of normal stress effect on the formability of aluminum alloy sheets in non-linear strain paths. Since the reacting stage of normal stress play important roles in normal stress effect on the formability of aluminum alloy sheets, the insight obtained in this paper will help to judge the instability of aluminum alloy sheets in complex forming processes with normal stress reacting on the sheet or tube.

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

Response of harmonic sources in couple stress thermoelastic medium with state space approach

2014 ◽  
Vol 10 (3) ◽  
pp. 449-471
Author(s):  
Rajneesh Kumar ◽  
Krishan Kumar ◽  
Ravindra Chandra Nautiyal
Keyword(s):  
Normal Stress ◽  
Tangential Stress ◽  
Couple Stress ◽  
Wave Number ◽  
Stress Effect ◽  
State Space Approach ◽  
Content Type ◽  
Stress Components ◽  
Circular Frequency ◽  
Space Approach

Purpose – The purpose of this paper is to investigate the two-dimensional problem in couple stress thermoelastic medium for a half space is established and state space approach has been applied to solve the problem. Design/methodology/approach – Normal mode analysis is used to obtain the exact expressions for normal stress, tangential stress and couple stress. Numerical calculation is prepared for these quantities and depicted graphically for a special model. Findings – The expressions for normal stress, tangential stress and couple stress are obtained numerically and depicted graphically to see the couple stress effect. Originality/value – It is found that couple stress effect decrease the value of normal stress components for circular frequency equal to 0.5 for small values of the wave number and then increases whereas the values of normal stress components decrease first and then increase monotonically for circular frequency equal to 0.1 when the force is applied in normal direction and the values of tangential stress components and couple stress components decrease for all values of wave number. But the values for normal stress components, tangential stress components and couple stress components increase when the force is applied in tangential direction.

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