Orientation and formability of orthotropic sheet metals

1997 ◽  
Vol 32 (1) ◽  
pp. 61-81 ◽  
Author(s):  
D W A Ress ◽  
R K Power
Keyword(s):  
Plane Strain ◽  
Principal Stress ◽  
Stress Ratio ◽  
Rolling Direction ◽  
Forming Limit Diagram ◽  
Forming Limit ◽  
Sheet Metals ◽  
Principal Stresses ◽  
Thickness Strain ◽  
Automotive Sheet

This paper examines the formability of automotive sheet metals: CR steels and 6000 series aluminium-magnesium alloys. Necking strains are used to determine the forming limits; i.e. a diffuse instability condition is reached under in-plane biaxial stressing. The theory admits material anisotropy, work-hardening and sheet orientation under any ratio of applied principal stresses. It has been programmed to accept orientations between the principal stress axes and the sheets' rolling direction in 15° increments between 0° and 90°. The ratio between the principal stresses may vary between 0 and ± 1. The input data required are the width-thickness strain ratios ( r values) in directions 0°, 45° and 90° to the roll and the Hollomon hardening exponent ( n value). The output is presented in four diagrams: the critical subtangent-stress ratio and plots between three combinations of the limiting principal engineering strains: (a) two in-plane strains, (b) major in-plane strain versus thickness strain and (c) minor in-plane strain versus thickness strain. Each diagram shows the influence of rotating the principal stress axes in increments of 15° to the roll. The forming limit diagram of type (a) gives the traditional presentation of a forming limit diagram (FLD). This FLD may be established experimentally from the strain in a surface grid lying around splits. In practice, a few production panels may be gridded for die-tryout and to examine a change in material. The alternative FLDs, types (b) and (c), are proposed to provide quality control with the increasing use of ultrasonics to monitor thickness of pressed panels. An example of type (b) is determined experimentally for CR1 steel.

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.

Integrated Hydraulic Bulge and Forming Limit Testing Method and Apparatus for Sheet Metals

2014 ◽  
Vol 626 ◽  
pp. 171-177 ◽  
Author(s):  
Yan Yo Chen ◽  
Yu Chung Tsai ◽  
Ching Hua Huang
Keyword(s):  
Forming Limit Diagram ◽  
Close Correlation ◽  
Biaxial Stress ◽  
Forming Limit ◽  
Hydraulic Pressure ◽  
Sheet Metals ◽  
Stress Strain ◽  
Testing Method ◽  
Hydraulic Bulge ◽  
Strain Relationship

This paper proposes an integrated hydraulic bulge and forming limit testing method and apparatus for sheet metals. By placing a PU (Polyurethane) plate between molds and uniformly applying hydraulic pressure to sheet metals, a biaxial stress-strain relationship and forming limit diagram (FLD) displaying both left and right sides were acquired using the same apparatus. An uniaxial tension test and traditional drawing test were conducted to compare the results obtained from the proposed hydraulic bulge and forming limit testing methods, respectively. A close correlation between the results of the stress-strain relationship and FLD in both comparisons verified the feasibility and capability of this integrated hydraulic testing method and apparatus for use with sheet metals.

Rim and pole failures from elliptical bulging of oriented orthotropic sheet metal

2000 ◽  
Vol 35 (2) ◽  
pp. 109-120 ◽  
Author(s):  
D W A Rees
Keyword(s):  
Plane Strain ◽  
Sheet Metal ◽  
Rolling Direction ◽  
Alloy Sheet ◽  
Biaxial Stress ◽  
Forming Limit ◽  
Maximum Pressure ◽  
Rolled Sheet ◽  
Aspect Ratios ◽  
Stress Ratios

Two criteria of instability are required to predict the failure in rolled sheet metal when bulged by lateral pressure through elliptical dies. The attainment of a pressure maximum is observed when the ratio of the lengths of the ellipse axes approaches unity. In nearly circular bulges this marks the onset of failure by diffuse necking under a falling pressure in the polar region. Dies with sharper elliptical apertures produce plane strain failures under a rising pressure in the region of the rim. In stretching flat sheet a local instability occurs when the rim force attains its maximum. The influence of sheet curvature upon plane strain fracture alters the limiting strain. Predictions of the critical pressure are derived for each failure and applied to an automotive aluminium alloy sheet (Alusuisse AC 120). The theory confirms experiments that show plane strain failure as a cut-off point in the plot of pressure versus height. A maximum pressure marks the start of a failure by diffuse pole thinning. In contrast, edge failures occur with uniform thinning from pole to rim along the minor axis of the ellipsoid bulge. A generalized theoretical approach accounts for each failure with an r variation in the plane of the sheet and orientation of the ellipse axes to the rolling direction. The tests reported refer to alignments between the roll direction and both axes of five elliptical dies with different aspect ratios. Pole failures provide positive forming limit strains for biaxial stress ratios between 0.5 and 1. Rim failures supply the limiting plane strains.

Experimental Determination of Anisotropic Properties and Evaluation of FLD for Sheet Metal Operations

2021 ◽  
Vol 106 ◽  
pp. 39-45
Author(s):  
Araveeti C. Sekhara Reddy ◽  
B. Sandeep ◽  
J. Sandeep Kumar ◽  
B. Sanjanna
Keyword(s):  
Deep Drawing ◽  
Grain Orientation ◽  
Forming Limit Diagram ◽  
Experimental Tests ◽  
Rolling Process ◽  
Forming Limit ◽  
Drawing Process ◽  
Sheet Metals ◽  
Deformation Models

Most of the sheet metals in general exhibit high an-isotropic plasticity behavior due to the ordered grain orientation that occurred during the rolling process. This results in an uneven deformation yield property that tends to develop ears in case of deep-drawing operation. The deep drawing process is used for the production of cup-shaped articles having applications in automobiles, beverages, home appliances etc. It is essential to know the formability of sheet metals for minimisation of test runs and reducingthe defects. Forming Limit Diagram (FLD) is one of the methods for assessment of formability of sheetmetals. This paper describes various deformation models, yielding and an-isotropic properties and itsdetermination. Through experimental tests, FLD constructed for aluminium alloy AA6111 sheet metalhaving 0.9 mm thickness.

Investigations on Influence of Geometric Parameters in Drawing of Perforated Sheet Metals

2016 ◽  
Vol 852 ◽  
pp. 229-235 ◽  
Author(s):  
G. Venkatachalam ◽  
J. Nishanth ◽  
M. Mukesh ◽  
D.S. Pavan Kumar
Keyword(s):  
Sheet Metal ◽  
Software Package ◽  
Parametric Analysis ◽  
Forming Limit Diagram ◽  
Simulation Software ◽  
Geometric Parameters ◽  
Forming Limit ◽  
Sheet Metals ◽  
Open Area ◽  
Perforated Sheet

Forming Limit Diagram (FLD) is a resourceful tool to study the formability of sheet metals. Research on the formability of Perforated Sheet Metal is growing over the years as perforated sheet metal finds its applications in various fields. But finding FLD of perforated sheet metals is complex due to the presence of holes. Also, the hole size, shape and pattern, ligament ratio, thickness of the blank, percentage of open area influence the formability of a perforated sheet metal.In the present scenario, various simulation softwares have made the process of plotting FLD much easier, saving time and money. This paper is an attempt to predict the formability of mild steel perforated sheet metal through simulation software package LS Dyna. Also, Parametric analysis is performed to determine the influence of geometric parameters on the drawability of the perforated sheet metal.

Theoretical and Experimental Evaluation of the Formability of Anisotropic Zinc Sheets

2011 ◽  
Vol 473 ◽  
pp. 390-395 ◽  
Author(s):  
Yann Jansen ◽  
Roland E. Logé ◽  
Marc Milesi ◽  
S. Manov ◽  
Elisabeth Massoni
Keyword(s):  
Metal Forming ◽  
Mechanical Response ◽  
Damage Model ◽  
Rolling Direction ◽  
Forming Limit Diagram ◽  
Tensile Tests ◽  
Forming Limit ◽  
The Past ◽  
Force Criterion ◽  
Critical Strains

. Formability of metal sheet has been widely studied for the past 40 years. This study leads to the well known Forming Limit Diagram (FLD) proposed by Keeler and Backhofen [1]. Such a diagram needs typical drawing and stretching experiments to be achieved. Lots of different metals have been considered as steel, aluminium, titanium or magnesium alloys [2]. Despite of the large amount of papers about sheet metal forming, few deal with Zinc sheets. The material has an anisotropic mechanical response due to its hexagonal crystallographic lattice and its microstructural texture. In the presented work, Nakazima and tensile tests have been performed for different mechanical orientations (0°, 45° and 90° angle to the rolling direction) in order to characterise this typical response. A high anisotropic behaviour has been noticed for the hardening and for the critical strains. The FLD is therefore a function of the orientation. Moreover thickness sensitivity is observed and leads to some criticisms about the plane stress assumption usually used in the FLD predictive models [3, 4]. The Modified Maximum Force Criterion (MMFC) is evaluated, and discussed. Then, this model is compared to a damage model used in [5] within an FEM formulation.

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