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.

Stress–strain pattern–based criterion to assess cyclic shear resistance of soil from laboratory element tests

2016 ◽  
Vol 53 (9) ◽  
pp. 1460-1473 ◽  
Author(s):  
Dharma Wijewickreme ◽  
Achala Soysa
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Shear Stiffness ◽  
Large Strains ◽  
Fundamental Parameter ◽  
Stress Strain ◽  
Cyclic Shear ◽  
Excess Pore Water Pressure ◽  
Excess Pore

The cyclic shear response of soils is commonly examined using undrained (or constant-volume) laboratory element tests conducted using triaxial and direct simple shear (DSS) devices. The cyclic resistance ratio (CRR) from these tests is expressed in terms of the number of cycles of loading to reach unacceptable performance that is defined in terms of the attainment of a certain excess pore-water pressure and (or) strain level. While strain accumulation is generally commensurate with excess pore-water pressure, the definition of unacceptable performance in laboratory tests based purely on cyclic strain criteria is not robust. The shear stiffness is a more fundamental parameter in describing engineering performance than the excess pore-water pressure alone or shear strain alone; so far, no criterion has considered shear stiffness to determine CRR. Data from cyclic DSS tests indicate consistent differences inherent in the patterns between the stress–strain loops at initial and later stages of cyclic loading; instead of relatively “smooth” stress–strain loops in the initial parts of loading, nonsmooth changes in incremental stiffness showing “kinks” are notable in the stress–strain loops at large strains. The point of pattern change in a stress–strain loop provides a meaningful basis to determine the CRR (based on unacceptable performance) in cyclic shear tests.

Post-Peak Behaviour of Sensitive Clays in Undrained Shear

1968 ◽  
Vol 5 (2) ◽  
pp. 59-68 ◽  
Author(s):  
B Ladanyi ◽  
J P Morin ◽  
C Pelchat
Keyword(s):  
Shear Strength ◽  
Indirect Method ◽  
Peak Stress ◽  
Large Strains ◽  
Peak Strain ◽  
Stress Strain ◽  
Strain Behaviour ◽  
Structural Breakdown ◽  
Undrained Shear

The post-peak stress-strain behaviour in undrained shear of three different clays has been investigated by using an indirect method. This method, which is in principle similar to that used by Kallstenius (1963), consists in first compressing a clay specimen to a given post-peak strain between two parallel platens and subsequently determining its current remoulded strength by the laboratory vane method. By a repeated compression procedure, axial strains of up to 200 per cent have been attained. As the three clays tested differed widely in sensitivity, a comparison of their post-peak behaviour made clearly apparent the effect of structural breakdown on the reserve shear strength at large strains.

Stress-Based Forming Limits in Sheet-Metal Forming

2000 ◽  
Vol 123 (4) ◽  
pp. 417-422 ◽  
Author(s):  
Thomas B. Stoughton
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Strain Path ◽  
Forming Limit ◽  
Stress Strain ◽  
Strain Relation ◽  
Stress Strain Relation ◽  
The Stability ◽  
Definition Of

A strain-based forming limit criterion is widely used throughout the sheet-metal forming industry to gauge the stability of the deformed material with respect to the development of a localized neck prior to fracture. This criterion is strictly valid only when the strain path is linear throughout the deformation process. There is significant data that shows a strong and complex dependence of the limit criterion on the strain path. Unfortunately, the strain path is never linear in secondary forming and hydro-forming processes. Furthermore, the path is often found to be nonlinear in localized critical areas in the first draw die. Therefore, the conventional practice of using a path-independent strain-based forming limit criterion often leads to erroneous assessments of forming severity. Recently it has been reported that a stress-based forming limit criterion appears to exhibit no strain-path dependencies. Subsequently, it has been suggested that this effect is not real, but is due to the saturation of the stress-strain relation. This paper will review and compare the strain-based and stress-based forming limit criteria, looking at a number of factors that are involved in the definition of the stress-based forming limit, including the role of the stress-strain relation.

scholarly journals Monte Carlo Study of Rubber Elasticity on the Basis of Finsler Geometry Modeling

Symmetry ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 1124 ◽  
Author(s):  
Hiroshi Koibuchi ◽  
Chrystelle Bernard ◽  
Jean-Marc Chenal ◽  
Gildas Diguet ◽  
Gael Sebald ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Finsler Geometry ◽  
Standard Technique ◽  
Rubber Elasticity ◽  
Large Strains ◽  
Surface Model ◽  
Stress Strain ◽  
Geometry Model ◽  
Strain Induced Crystallization ◽  
Induced Crystallization

Configurations of the polymer state in rubbers, such as so-called isotropic (random) and anisotropic (almost aligned) states, are symmetric/asymmetric under space rotations. In this paper, we present numerical data obtained by Monte Carlo simulations of a model for rubber formulations to compare these predictions with the reported experimental stress–strain curves. The model is defined by extending the two-dimensional surface model of Helfrich–Polyakov based on the Finsler geometry description. In the Finsler geometry model, the directional degree of freedom σ → of the polymers and the polymer position r are assumed to be the dynamical variables, and these two variables play an important role in the modeling of rubber elasticity. We find that the simulated stresses τ sim are in good agreement with the reported experimental stresses τ exp for large strains of up to 1200 % . It should be emphasized that the stress–strain curves are directly calculated from the Finsler geometry model Hamiltonian and its partition function, and this technique is in sharp contrast to the standard technique in which affine deformation is assumed. It is also shown that the obtained results are qualitatively consistent with the experimental data as influenced by strain-induced crystallization and the presence of fillers, though the real strain-induced crystallization is a time-dependent phenomenon in general.

Forensic Analyses of Stress-Strain Diagrams to Evaluate Contributions from Microstructure

2018 ◽  
Vol 941 ◽  
pp. 2270-2277 ◽  
Author(s):  
Shigeo Saimoto ◽  
Michael R. Langille ◽  
Marek Niewczas
Keyword(s):  
Work Hardening ◽  
Shape Change ◽  
Constitutive Relations ◽  
Pure Aluminum ◽  
Ductile Failure ◽  
Large Strains ◽  
Strain Diagram ◽  
Annihilation Process ◽  
Stress Strain ◽  
Strength Factor

The conventional characterization of work-hardening is to approximate the stress-strain diagram using the empirical curve-fitting of Hollomon or Voce. The new method uses the Taylor slip analyses to derive a functional form which is optimally fitted to the data. This constitutive relations analysis (CRA) duplicates the data using at least two fit loci. The fit parameters relate to the slip motion within the microstructure and hence its interpretation reveals the possible dynamic shape-change reactions. The fit-process defines a new yield stress which separates the yielding from the deformation mechanisms at large strains that breaks up into two regions separated by intersection parameters. The applications of CRA to nanovoid formation and growth leading to ductile failure, plane stress yield locus prediction using tensile tests and decoding the stress-strain diagram for age-hardened aluminum alloys have been successful. Using super-pure aluminum, this study confirms that CRA is based on crystal plasticity principles and that CRA can predict the correlation of the obstacle strength factor, α, with work-hardening, hence permitting conversion of flow stress at given strains to obstacle density. The derived results show that the inherent annihilation process and the changing strength factor are coordinated to result in a self-consistent constitutive relation.

Real time SAXS/stress–strain studies of thermoplastic polyurethanes at large strains

Polymer ◽  
2002 ◽  
Vol 43 (19) ◽  
pp. 5197-5207 ◽  
Author(s):  
D.J Blundell ◽  
G Eeckhaut ◽  
W Fuller ◽  
A Mahendrasingam ◽  
C Martin
Keyword(s):  
Real Time ◽  
Large Strains ◽  
Stress Strain ◽  
Thermoplastic Polyurethanes

A numerical solution of cavity expansion problem in sand based directly on experimental stress-strain curves

1998 ◽  
Vol 35 (4) ◽  
pp. 541-559 ◽  
Author(s):  
Branko Ladanyi ◽  
Adolfo Foriero
Keyword(s):  
Numerical Solution ◽  
Strain Path ◽  
Shear Resistance ◽  
Cavity Expansion ◽  
Large Strains ◽  
Volume Changes ◽  
Stress Strain ◽  
Stress Variation ◽  
Cylindrical Cavity Expansion ◽  
State Of Stress

A numerical solution of a spherical and cylindrical cavity expansion problem in sand is presented herein. The underlying theory is unbiased in that it is based directly on experimentally determined stress-strain curves. The solution makes it possible to follow the continuous variation of strains, stresses, and volume changes produced by cavity expansion. It essentially uses the "strain path" approach to determine the state of stress around the cavity, taking into account large strains and the effect of spherical stress variation on the mobilized shear resistance and the associated volume strains. A limited comparison with experimental data shows a reasonable agreement between theory and measurements.Key words: cavities, expansion, sand, stress-strain curves, numerical solution.

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