Plastic Instability in Simple Stretching of Sheet Metals

1968 ◽  
Vol 90 (2) ◽  
pp. 387-392 ◽  
Author(s):  
F. Negroni ◽  
S. Kobayashi ◽  
E. G. Thomsen
Keyword(s):  
Maximum Load ◽  
Plastic Instability ◽  
Sheet Metals ◽  
Principal Stresses ◽  
Flat Sheet ◽  
Limiting Equilibrium ◽  
Strain Paths ◽  
Dead Loading

The plastic instability was examined for stretching a plane flat sheet by in-plane tensile principal stresses. Limiting equilibrium or development of nonuniform strains defines the onset of plastic instability. Under dead loading the Swift theory gives the conditions for limiting equilibrium, while it results in the condition for the failure of uniqueness for given strain paths. When the initial nonuniformity of the properties and dimensions in the sheet is considered, the Dorn maximum load criterion is applicable for the condition of plastic instability. The optimum paths along which the maximum strains can be achieved before instability takes place were obtained and the limiting maximum strains was calculated along these paths for the Dorn criterion and for the Swift theory.

Influence of damage on the plastic instability of sheet metals under complex strain paths

1984 ◽  
Vol 19 (12) ◽  
pp. 4133-4137 ◽  
Author(s):  
F. Barlat ◽  
A. Barata Da Rocha ◽  
J. M. Jalinier
Keyword(s):  
Plastic Instability ◽  
Sheet Metals ◽  
Strain Paths ◽  
Complex Strain

Numerical Analysis for Process Parameter Effect in Electromagnetic Impact Welding of Aluminum Alloy Sheet

2014 ◽  
Vol 548-549 ◽  
pp. 297-300
Author(s):  
Dae Yong Kim ◽  
Hyeon Il Park ◽  
Ji Hoon Kim ◽  
Sang Woo Kim ◽  
Young Seon Lee
Keyword(s):  
Aluminum Alloy ◽  
Numerical Analysis ◽  
Deformation Behavior ◽  
Three Dimensional ◽  
Alloy Sheet ◽  
Aluminum Alloy Sheet ◽  
Sheet Metals ◽  
Charge Voltage ◽  
Flat Sheet ◽  
Impact Welding

Studies on electromagnetic impact welding between similar or dissimilar flat sheet metals using the flat one turn coil have been recently achieved. In this study, three dimensional electromagnetic-mechanical coupled numerical simulations are performed for the electromagnetic impact welding of aluminum alloy sheets with flat rectangular one turn coil. The deformation behavior during impact welding was examined. The effect of process parameters such as charge voltage, standoff distance and gap distance were investigated.

scholarly journals Plastic Instability in Complex Strain Paths Predicted by Advanced Constitutive Equations

2011 ◽  
Author(s):  
Marilena C. Butuc ◽  
Frédéric Barlat ◽  
José J. Gracio ◽  
Gabriela Vincze
Keyword(s):  
Constitutive Equations ◽  
Plastic Instability ◽  
Strain Paths ◽  
Complex Strain

Experimental Program for Investigating the Influence of Cladding Defects on Burst Pressure

2006 ◽  
Author(s):  
Shengjun (Sean) Yin ◽  
B. Richard Bass ◽  
Wallace J. McAfee ◽  
Paul T. Williams
Keyword(s):  
Finite Element ◽  
National Laboratory ◽  
Maximum Load ◽  
Plastic Instability ◽  
Experimental Program ◽  
Finite Element Models ◽  
Ductile Tearing ◽  
Oak Ridge ◽  
Clad Layer ◽  
Good Agreement

An experimental program was conducted by the Heavy-Section Steel Technology Program at the Oak Ridge National Laboratory (ORNL) to evaluate the structural significance of defects found in the unbacked cladding of the Davis-Besse vessel head. ORNL conducted total 13 clad burst tests with unflawed/flawed specimens. Failure pressure data from those tests indicated a high degree of repeatability for the tests performed in the clad burst program. Unflawed clad burst specimens failed around the full perimeter of the disk from plastic instability; an analytical model for plastic collapse was shown to adequately predict those results. The flawed specimens tested in the program failed by ductile tearing of the notch defect through the clad layer. Analytical interpretations that utilized 3-D finite element models of the clad burst specimens were performed for all tests. Fractographic studies were performed on failed defects in the flawed burst specimens to verify the ductile mode of failure. Comparisons of computed results from 3-D finite element models with measured gage displacement data (i.e., center-point deflection and CMOD) indicated reasonably good agreement up to the region of instability. For tests instrumented with the CMOD gage, good agreement between calculated and measured CMOD data up to the onset of instability implies that ductile tearing initiated near the maximum load and (with a small increase in load) rapidly progressed through the clad layer to produce failure of the specimen.

On the Plastic Tensile Instability Criteria

1969 ◽  
Vol 91 (3) ◽  
pp. 659-663 ◽  
Author(s):  
F. Negroni ◽  
E. G. Thomsen
Keyword(s):  
Strain Hardening ◽  
Sheet Material ◽  
Maximum Load ◽  
Experimental Results ◽  
Strain Rates ◽  
Prior Deformation ◽  
Biaxial Stretching ◽  
Flat Sheet ◽  
Tensile Instability ◽  
Hardening Parameter

The Dorn maximum load criterion and the Swift criterion for plastic tensile instability of a flat sheet stretched by in-plane forces are discussed. Both hypotheses are applicable when an initial nonuniformity of a sheet material is considered but that one is valid which is satisfied first. Experimental results in biaxial stretching of aluminum sheet specimens showed general agreement with both criteria; however, the Dorn maximum load criterion more accurately described the condition for necking when both principal strain rates on the plane of the sheet were positive. The significance and the calculation of the strain hardening parameter n = (ε/σ)(dσ/dε) are discussed, and the effect of prior deformation of the material on instability is analyzed.

Numerical Prediction of Damage Evolution in Sheet Metal Forming Processes with Nonlinear and Complex Strain Paths

2011 ◽  
Vol 473 ◽  
pp. 653-658
Author(s):  
Babak Jamshidi ◽  
Farhad Haji Aboutalebi ◽  
Mahmoud Farzin ◽  
Mohammad Reza Forouzan
Keyword(s):  
Sheet Metal ◽  
Plane Stress ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Damage Evolution ◽  
Finite Strain ◽  
Damage Model ◽  
Sheet Metals ◽  
Strain Paths ◽  
Complex Strain

Various thin-walled parts with fairly complex shapes are produced from sheet metals such as automotive panels and other structural parts. In these processes, damage and fracture may be observed on the work piece, and formability plays a fundamental role. Therefore, determination of forming limits and prediction of rupture modes in these operations is very important for process design engineers. In this paper, first, based on plane stress elasto-plasticity and finite strain theories a fully coupled elastic-plastic-damage model is used to predict damage evolution in one sheet metal forming process with nonlinear and complex strain paths. As the plane stress algorithm is valid for thin sheet metals and finite strain theory is recommended for large deformations or rotations, the model is able to quickly predict both deformation and damage behaviour of the parts with nonlinear and complex strain paths. The numerical simulations are compared with experimental tests. Comparison of the numerical and experimental results shows that the proposed damage model is accurate for various forming conditions. Hence, it is concluded that finite element method combined with continuum damage mechanics, can be used as a reliable and rapid tool to predict damage evolution in sheet metal forming processes with nonlinear and complex strain paths.

Experimental Characterisation of Structured Sheet Metal

2011 ◽  
Vol 473 ◽  
pp. 404-411 ◽  
Author(s):  
Sebastian Fritzsche ◽  
Ralf Ossenbrink ◽  
Vesselin Michailov
Keyword(s):  
Tensile Test ◽  
Deformation Behaviour ◽  
Local Strain ◽  
Specimen Geometry ◽  
Sheet Metals ◽  
Measuring Methods ◽  
Flat Sheet ◽  
Strain Behaviour ◽  
Strength And Deformation ◽  
Standardised Testing

Structured sheet metals with regular bumps offer higher bending stiffness compared to flat sheet metals. The application of structured sheet metals requires new investigations regarding their strength and deformation behaviour. Standardised testing methods like the tensile test considering defined specimen geometry and measuring methods exist. Those methods, however, have been developed for plain sheets and cannot be directly transferred to structured sheet metals. The assessment of the strength and deformation behaviour of structured sheet metals needs adapted specimen geometry and measuring methods. In this paper the adaption of the standardised tensile test in accordance with DIN EN ISO 6892-1 to the specific characteristics of structured sheet metals is introduced. In order to determine the appropriate specimen geometry their dimensions were methodically varied and the influence of the structure position on the strength and the deformation behaviour was identified. The analysis of the local strain behaviour was carried out by 3D displacement measurement with the ARAMIS-system. For the derivation of the material properties different analysing methods were developed. The test results were compared to those of flat sheet metals.

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