The evaluation of large strains from industrial sheet metal stampings with a square grid

1986 ◽  
Vol 4 (2) ◽  
pp. 143-156 ◽  
Author(s):  
Erik Schedin ◽  
Arne Melander
Keyword(s):  
Sheet Metal ◽  
Large Strains ◽  
Square Grid

scholarly journals Characterization of Flow Induced Anisotropy in Sheet Metal at Large Strain

2021 ◽  
Author(s):  
F. Gutknecht ◽  
H. Traphöner ◽  
T. Clausmeyer ◽  
A. E. Tekkaya
Keyword(s):  
Strain Rate ◽  
Sheet Metal ◽  
Strain Path ◽  
Large Strain ◽  
High Strength ◽  
Bulge Test ◽  
Large Strains ◽  
Steel Grades ◽  
Strain Path Change ◽  
Cross Hardening

Abstract Background Many metals exhibit a stress overshoot, the so-called cross-hardening when subjected to a specific strain-path change. Existing tests for sheet metals are limited to an equivalent prestrain of 0.2 and show varying levels of cross-hardening for identical grades. Objective The aim is to determine cross-hardening at large strains, relevant for forming processes. Mild steel grades (DC04, DC06, DX56) and high strength steel grades (BS600, DP600, ZE800) are investigated to quantify the level of cross-hardening between different grades and reveal which grades exhibit cross-hardening at all. Method A novel test setup for large prestrain using hydraulic bulge test and torsion of curved sheets is developed to achieve an orthogonal strain-path change, i.e. the strain rate tensors for two subsequent loadings are orthogonal. The influence of strain rate differences between the tests and clamping of curved sheets on the determined cross-hardening are evaluated. The results are compared to experiments in literature. Results Cross-hardening for sheet metal at prestrains up to 0.6 true plastic strain are obtained for the first time. For DX56 grade the maximum cross-hardening for all prestrains have a constant level of approximately 6%, while the maximum cross-hardening for DC04 and DC06 grades increases, with levels between 7 and 11%. The high strength grades BS600 and ZE800 do not show cross-hardening behavior, while, differencing from previous publications, cross-hardening is observed for dual phase steel DP600. Conclusion Depending on the microstructure of the steel grade the cross-hardening increases with large prestrain or remains constant.

New Forming Processes for Sheet Metal with Large Plastic Deformation

2007 ◽  
Vol 344 ◽  
pp. 251-258 ◽  
Author(s):  
Peter Groche ◽  
Jens Ringler ◽  
Dragoslav Vucic
Keyword(s):  
Sheet Metal ◽  
Cross Sections ◽  
Lightweight Design ◽  
High Surface ◽  
Surface Hardness ◽  
Band Edge ◽  
Experimental Investigations ◽  
Large Strains ◽  
Linear Flow ◽  
Flow Splitting

Due to the high effort involved, bifurcated constructions in mass market products made from sheet metal remained largely unused. Extruded profiles with cross-sections containing bifurcations show the possibility to increase the stiffness and allow modern lightweight design using load optimized structures as well as in box strap, sandwich and stringer constructions or different profiles. The two new forming processes linear flow splitting and linear bend splitting developed at the PtU enable the production of bifurcated profiles in integral style made of sheet metal without joining, lamination of material or heating of the semi-finished product. These forming processes use obtuse angled splitting rolls and supporting rolls to transform the sheet metal at ambient temperature. Whereas the linear flow splitting process increase the surface of the band edge and forms the band into two flanges. At linear bend splitting a bended sheet metal as semi finished product is used. Thereby bifurcations at nearly any place of a sheet metal can be produced. Both processes induce high hydrostatic compressive stresses in the local forming zone during the process which leads to an increased formability of the material and thereby to the realization of large strains. Parts produced are characterized by increased stiffness, high surface hardness and low surface roughness. Experimental investigations have shown an increasing of the band edge surface at maximum splitting depth up to 1800%. By a following forming process new multi-chambered structures and integral stringer construction can be realized with thin walled cross-sections from steel of higher strength.

Measuring Stress Strain Curves to Large Strains on Sheet Metal

2007 ◽  
Vol 35 (2) ◽  
pp. 100082 ◽  
Author(s):  
A Bacha ◽  
M Feuerstein ◽  
C Desrayaud ◽  
H Klöcker
Keyword(s):  
Sheet Metal ◽  
Large Strains ◽  
Stress Strain

The Large Strain Flow Stress Behaviour of Aluminium Alloys as Measured by Channel-Die Compression (20-500°C)

2006 ◽  
Vol 519-521 ◽  
pp. 783-788 ◽  
Author(s):  
A. Bacha ◽  
Claire Maurice ◽  
Helmut Klocker ◽  
Julian H. Driver
Keyword(s):  
Flow Stress ◽  
Sheet Metal ◽  
Large Strain ◽  
Large Strains ◽  
Stress Strain ◽  
Sheet Plane ◽  
Die Set ◽  
Flow Stress Data ◽  
Set Up ◽  
Stress Behaviour

Two recent methods for obtaining flow stress-strain relations up to large strains of order 1.5 by channel-die compression are presented: i) for sheet metal formability tests, composite samples have been made of glued sheet layers and deformed at room temperature in a channel-die with the compression axis directed along one of the sheet metal edge directions, i.e. RD or TD. The sheet plane is parallel to the lateral compression die face. It is shown that, using a suitable lubricant, the sample deformation is homogeneous up to strains of 1.5. Tests carried out on 5xxx and 6xxx alloys to evaluate the stress-strain relations show that a generalized Voce law gives a good quantitative fit for the data. ii) for high temperature plate processing, quantitative flow stress data can be obtained up to 500°C with a rapid quench using a hot channel-die set-up. Some new results are presented here for high strain hot PSC tests on Al-Mn and Al-Mg alloys together with microstructure analyses.

An Interferometer Based Experimental Technique to Evaluate Large Strains and Springback on Sheet Metal

2013 ◽  
Author(s):  
Luis Rafael Sanchez ◽  
Shannon Peterson ◽  
Carl G. Simonsen ◽  
Abrar Satar
Keyword(s):  
Sheet Metal ◽  
Three Dimensional ◽  
Bending Moment ◽  
Large Strains ◽  
Two Dimensional ◽  
Strain Gages ◽  
Additional Information ◽  
Software Algorithms ◽  
Dimensional Measurements ◽  
Vertical Scanning Interferometry

A technique was successfully developed to measure large tensile, compressive strains, springback and strain reversal effects on sheet metal bent to small radii. Vertical Scanning Interferometry (VSI) was used to measure three dimensional data from surfaces with sides varying from 160 nm to 2 mm. Software algorithms were utilized to determine surface topography maps from three-dimensional curved locations and to represent them in a two dimensional plane. Fine reference marks were engraved on both sides of sample. The sample was bent /unbent to small radii under a pure bending moment. Outer strains were calculated from VSI two-dimensional measurements of the original and final lengths between the reference marks. Strain gages, applied at locations close to the reference marks, gave additional information at the elasto-plastic range. Experimental data collected included bending moment as a function of strain, 3-D curvature profiles, springback and reverse bending effects. The technique was proved useful for the experimental evaluation and theoretical validation of bending and springback properties of sheet metal. Experimental results for aluminum and steel alloys are presented.

A Generalized Finite Element Analysis of Sheet Metal Forming With an Elastic-Viscoplastic Material Model

1986 ◽  
Vol 108 (1) ◽  
pp. 9-15 ◽  
Author(s):  
A. Chandra
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Large Strain ◽  
Present Report ◽  
Material Behavior ◽  
Large Strains ◽  
Element Analysis

A finite element analysis for elastic-viscoplastic problems in the presence of large strains is presented in this paper. The formulation is capable of using any of a class of combined creep-plasticity constitutive models with state variables for the description of material behavior. The specific problem considered is plane strain sheet metal forming using the constitutive model originally proposed by Hart. Numerical results are presented for sample problems and the effects of variations in several process parameters, such as velocity, friction at punch, and die interfaces, are investigated. The present report includes membrane, bending, and shear effects as well as the coupling among them and no a priori assumption is made about the strain distribution across the thickness. Thus, it unifies the earlier approaches used in sheet metal forming analysis and helps in gaining crucial insights into the process of sheet metal forming. It can also be extended to other large strain design and manufacturing problems.

Intrinsic Errors on Sheet Strain Measurements Based on a Printed Square Grid

1998 ◽  
Vol 122 (4) ◽  
pp. 760-765
Author(s):  
Herman C. J. Bruneel
Keyword(s):  
Periodic Structure ◽  
Mechanical Deformation ◽  
Large Strains ◽  
Measuring Process ◽  
Strain Measurements ◽  
Square Grid

The paper studies the intrinsic errors on strain measurements induced by the application of an electrochemical etched square grid through serigraphy. Systematic periodic strains are observed when the etched grid is directly measured before any mechanical deformation. These apparent, non-zero strains are the errors induced by the imperfection of the applied grid. They determine the limiting precision of the measuring process. The errors are due to interference between the periodic square grid and an underlying periodic structure, the dot structure of the printer used for the original drawing of the grid or the periodic pitch of the serigraphic tissue and even both. Although they are small, they can suggest an unstable deformation, even at large strains. [S1087-1357(00)02004-9]

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