A Theoretical Study of the Effect of the Double Strain Path Change on the Forming Limits of Metal Sheet

2013 ◽  
Vol 554-557 ◽  
pp. 127-138 ◽  
Author(s):  
Marilena Butuc ◽  
Frédéric Barlat ◽  
José Grácio ◽  
Gabriela Vincze
Keyword(s):  
Sheet Metal ◽  
Strain Path ◽  
Theoretical Study ◽  
Alloy Sheet ◽  
Initial Shape ◽  
Forming Limits ◽  
Remarkable Effect ◽  
Strain Paths ◽  
Strain Path Change ◽  
Strain Path Changes

The present paper aims at a theoretical study of the forming limits of a sheet metal subjected to double strain path changes by using as reference material the AA6016-T4 aluminum alloy sheet. The simulation of plastic instability is carried out through the Marciniak-Kuczynski analysis. The initial shape of the yield locus is given by the Yld2000-2d plane stress yield function. The strain hardening of the material is described by the Voce type saturation law. Linear and several complex strain paths involving single and double strain path changes are taken into account. The validity of the model is assessed by comparing the predicted and experimental forming limits under linear and selected one strain path change. A good accuracy of the developed software on predicting the forming limits is found. A sensitive analysis of the influence of the type and value of the double prestain in the occurrence of the plastic flow localization is performed. A remarkable effect of the double strain path change on the sheet metal forming limits is observed.

scholarly journals Mechanical Anisotropy Induced by Strain Path Change for AZ31 Mg Alloy Sheet

Metals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1049
Author(s):  
Chong Yang ◽  
Yibing Mei ◽  
Dan Meng ◽  
Guoguo Zhu ◽  
Shengwei Liu ◽  
...  
Keyword(s):  
Yield Strength ◽  
Strain Path ◽  
Texture Evolution ◽  
Rolling Direction ◽  
Mechanical Anisotropy ◽  
Heterogeneous Distribution ◽  
Az31 Sheet ◽  
Strain Paths ◽  
Strain Path Change ◽  
Strain Path Changes

The variation of strain paths induces anisotropy during practical sheet forming processes, which is very important for the subsequent processing technology of anisotropic Mg alloys. In this study, two-step loading tests (tension-tension) were performed to clarify the effect of strain path changes on the evolution of anisotropy on rolled AZ31 sheet. Specimens were preloaded with tension along the rolling direction (RD) with 9% of prestrain. Then, second tension was conducted along 0°, 30°, 45°, 60° and 90° from the RD. It was found that yield strength during the second loading increased along the same direction compared to uniaxial tension without prestraining. For the second loading, the yield strength and flow stress decreased with the increase of the angle from the RD. It was found that the strain path change resulted in stronger anisotropy than that induced by texture. Moreover, it was found that the main deformation modes were basal and prismatic slips during the second loading based on visco-plastic self-consistent (VPSC) modeling. The relative activities of basal and prismatic slips were affected by the second loading direction due to texture evolution. The mechanical anisotropy induced by strain path changes was ascribed to the coupling of the heterogeneous distribution of dislocations and texture evolution induced by prestraining.

Orientation and Path Dependence of Formability in the Stress- and the Extended Stress-Based Forming Limit Curves

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
C. Hari Manoj Simha ◽  
Kaan Inal ◽  
Michael J. Worswick
Keyword(s):  
Strain Path ◽  
Path Dependence ◽  
Forming Limit ◽  
Stress Space ◽  
Forming Limit Diagrams ◽  
Metall Trans ◽  
Strain Paths ◽  
Strain Path Changes ◽  
Path Dependent ◽  
Forming Limit Curves

This article analyzes the formability data sets for aluminum killed steel (Laukonis, J. V., and Ghosh, A. K., 1978, “Effects of Strain Path Changes on the Formability of Sheet Metals,” Metall. Trans. A., 9, pp. 1849–1856), for Al 2008-T4 (Graf, A., and Hosford, W., 1993, “Effect of Changing Strain Paths on Forming Limit Diagrams of Al 2008-T4,” Metall. Trans. A, 24A, pp. 2503–2512) and for Al 6111-T4 (Graf, A., and Hosford, W., 1994, “The Influence of Strain-Path Changes on Forming Limit Diagrams of Al 6111 T4,” Int. J. Mech. Sci., 36, pp. 897–910). These articles present strain-based forming limit curves (ϵFLCs) for both as-received and prestrained sheets. Using phenomenological yield functions, and assuming isotropic hardening, the ϵFLCs are transformed into principal stress space to obtain stress-based forming limit curves (σFLCs) and the principal stresses are transformed into effective stress and mean stress space to obtain the extended stress-based forming limit curves (XSFLCs). A definition of path dependence for the σFLC and XSFLC is proposed and used to classify the obtained limit curves as path dependent or independent. The path dependence of forming limit stresses is observed for some of the prestrain paths. Based on the results, a novel criterion that, with a knowledge of the forming limit stresses of the as-received material, can be used to predict whether the limit stresses are path dependent or independent for a given prestrain path is proposed. The results also suggest that kinematic hardening and transient hardening effects may explain the path dependence observed in some of the prestrain paths.

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.

Dislocation Microstructure in Copper Multicrystals Deformed under the Sequences: Rolling - Tension and Tension - Rolling

2006 ◽  
Vol 514-516 ◽  
pp. 589-593 ◽  
Author(s):  
Nataliya A. Sakharova ◽  
José Valdemar Fernandes
Keyword(s):  
Electron Microscopy ◽  
Strain Path ◽  
Deformation Mode ◽  
Slip Activity ◽  
Transmission Electron ◽  
Different Types ◽  
Strain Paths ◽  
Strain Path Change ◽  
Complex Strain ◽  
Types Of Change

The microstructure evolution of copper multicrystalline sheets, undergoing plastic deformation in the sequences of strain paths rolling – tension and tension – rolling, was studied in the present work. For both sequences, two different types of change of strain path were studied: the tensile and rolling directions were parallel and normal to each other. Samples submitted to these four complex strain paths were investigated by transmission electron microscopy (TEM). TEM observations have shown the typical dislocations microstructures for the prestrain paths in tension and rolling. The dislocation microstructures observed during the second path were analysed and discussed as a function of the sequence and of the type of strain path change (parallel and normal sequential paths). Special microbands features were observed during the second path, for both sequences, rolling – tension and tension – rolling. The appearance of such microstructural features is discussed in terms of the sequence and type of strain path change and it is linked with the slip activity during the second deformation mode.

Plastic Behavior of Polycrystalline Aluminum during Biaxial Compression with Strain Path Change

2007 ◽  
Vol 340-341 ◽  
pp. 883-888 ◽  
Author(s):  
Ichiro Shimizu ◽  
Naoya Tada
Keyword(s):  
Strain Path ◽  
Transient Increase ◽  
Biaxial Compression ◽  
Normal Stresses ◽  
Compression Tests ◽  
Polycrystalline Aluminum ◽  
Plastic Deformation Behavior ◽  
Stress Changes ◽  
Strain Paths ◽  
Strain Path Change

Biaxial compression tests with an abrupt strain path change have been performed on polycrystalline aluminum to investigate the plastic deformation behavior under complex strain histories. Attentions are paid especially to the rapid change in the normal stresses due to the abrupt strain path change. The influences of the prestrain amplitude and the angular relation of sequential strain paths on the stress changes were also studied. The results showed that the transient increase of the normal stresses related to the latent hardening phenomenon with strain path change as well as the plastic anisotropy increase with the pre-straining amplitude. The transient increase in the stress was also affected by the strain histories in the sequential compression tests with the strain path change. The transient stress increment became large to the maximum then decreases with the angle between the sequential paths.

Forming Limits Prediction of FCC Sheet Metal Adopting Crystal Plasticity

2007 ◽  
Vol 340-341 ◽  
pp. 179-186
Author(s):  
Wing Bun Lee ◽  
Yi Ping Chen ◽  
Sandy To
Keyword(s):  
Sheet Metal ◽  
Crystal Plasticity ◽  
Initial Imperfection ◽  
Rate Sensitivity ◽  
Alloy Sheet ◽  
Forming Limits ◽  
Factors Affecting ◽  
Rate Dependent ◽  
Initial Texture ◽  
Process Factors

A rate-dependent crystal plasticity constitutive model together with Marciniak- Kuczynski(M-K) approach is employed to perform numerical simulations of forming limits diagrams(FLDs). An initial imperfection in terms of a narrow band is adopted to initialize the sheet necking. Homogeneous deformations inside and outside the band are assumed and the enforcement of compatibility and equilibrium conditions is required only on the band interface. Constitutive computations are carried out on two aggregates of FCC crystal grains, with each representing one of the two zones, respectively. Taylor homogenization assumption is employed to establish the link of stress between single crystal and polycrystal, and to derive an average response of the aggregates. The same initial texture is imparted to the two aggregates and their evolutions will be traced in the necking process. Factors affecting the FLDs prediction, such as imperfection intensity, initial texture, strain rate sensitivity and crystal elasticity will be taken into account. The above procedure will be applied to an annealed aluminium alloy sheet metal

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.

Sheet Metal Forming Limits Under Complex Strain Paths Using Void Growth and Coalescence Model

1986 ◽  
Vol 108 (3) ◽  
pp. 240-244 ◽  
Author(s):  
U. S. Rao ◽  
R. C. Chaturvedi
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Void Growth ◽  
Metal Forming ◽  
Strain Ratio ◽  
Forming Limits ◽  
Coalescence Model ◽  
Strain Paths ◽  
Complex Strain ◽  
Void Growth And Coalescence

It is well established that ductile fracture occurs by nucleation, growth and coalescence of voids. Several models have been developed to predict limits under constant strain ratio paths considering void inhomogeneity and void growth. In this paper the void growth and coalescence model developed by Rao and Chaturvedi for predicting forming limits under constant strain ratio paths, has been extended for predicting forming limits under two stage strain paths. The predicted results have been compared with experimental results of Ishigaki and analyzed.

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