Identification strategy influence of elastoplastic behavior law parameters on Gurson–Tvergaard–Needleman damage parameters: Application to DP980 steel

This work adopts elastic–plastic/damage coupling in order to describe tensile behavior with validation on the deep-drawing test of a DP980 Dual Phase steel sheet. The damage model used is the Gurson–Tvergaard–Needleman (GTN model). The hardening laws used are those of Swift (non-saturating law), Voce (saturating law), Hockett-Sherby (saturating law) and the two combined laws Swift/Hockett-Sherby and Swift/Voce. An identifying method for elastic–plastic parameters and GTN damage model parameters is presented using the software modeFRONTIER. This method based on the inverse analysis is also proposed for the identification of weighting coefficient α of the Swift/Hockett-Sherby combined hardening law. Finally, a parametric study was carried out to show that the plastic modulus can be considered as another criterion for the choice of a hardening law. Dependence of the damage model parameters to the hardening law is clearly established. The different behavior laws are introduced via a VUHARD type subroutine in the calculation code Abaqus.

Evaluation of Uniaxial Tensile Behavior under Pulsed Current for Electrically Assisted Warm Forming of Light Weight Alloys

In this study, the electric current effects in the deformation of light weight alloys are investigated to improve the formability. To begin with, a test system is built up to carry out the tensile test with heavy electric current flowing through the specimen. The evolutions of the flow stresses and failure elongations were obtained using this test system. The thermal and athermal effect such as electro-plastic effect of metallic materials induced by high density current make significant reduction of the flow stress, which is beneficial to the forming process of less formable metal. From the uniaxial test results, pulse current-assisted deep drawing test were conducted. The experimental results demonstrate that electrically assisted warm forming provides lower energy consumption and higher efficiency.

Avaliação das condições tribológicas em estampagem de chapas através do ensaio de dobramento sob tensão

RESUMO A lubrificação em estampagem de peças tem um papel importante no processo de produção, auxiliando na redução do enrugamento, fratura prematura e afinamentos muito localizados da espessura da chapa. Para tal, o lubrificante deve ser capaz de reduzir o atrito a níveis baixos mas não tão baixos a ponto de promover outros tipos de defeitos como o enrugamento da chapa. Uma boa lubrificação também reduz o desgaste prematuro das ferramentas de estampagem que são utilizadas para produção de peças, assim como é essencial para se ter sucesso no processo desenvolvimento de novas peças. Neste trabalho, 4 condições de lubrificações foram avaliadas (3 lubrificantes líquidos e a ausência de lubrificantes) através do ensaio DST (Dobramento Sob Tensão) e ensaio Swift (deep drawing test). A atuação benéfica (redução do atrito) ao processo de estampagem, dos lubrificantes, foi testada através da medição da força máxima de embutimento no ensaio Swift, da força em cada lado da chapa, torque e força vertical no pino do ensaio DST. O material de estudo foi o alumínio comercialmente puro AA1100. As conclusões indicam que o lubrificante que minimiza o atrito sempre fica evidente, não importando o tipo do ensaio a que a chapa foi submetida, porém a medição do torque facilita a identificação do mesmo. É observado também que a medição da força vertical gerada no pino é menor quanto mais ineficiente for o lubrificante.

Improvement in Material Flow During Nonisothermal Warm Deep Drawing of Nonheat Treatable Aluminum Alloy Sheets

Automotive industries are very much interested in implementing warm forming technology for fabrication of light weight auto-body panels using aluminum alloys without localized thinning or splitting. A nonheat treatable and low formable AA5754-H22 aluminum alloy sheet was selected in the present work, and a laboratory scale warm deep drawing test set-up and process sequences were designed to improve material flow through independent heating of punch and dies. Significant enhancement in cup depth was observed when the temperature of punch and dies were set to 30 °C and 200 °C, respectively. Thermo-mechanical finite-element (FE) model of the nonisothermal deep drawing test was developed successfully to study the improvement in material flow incorporating Barlat-89 yield theory using temperature dependent anisotropy coefficients and Cowper–Symonds hardening model. It was found that a nonisothermal temperature gradient of approximately 93 °C was established within the blank from the center to flange at the start of deformation, and subsequent evolution of temperature gradient helped in improving material flow into the die cavity. The effect of temperature gradient on forming behavior in terms of cup height, ear profile, and thinning development across flange, cup wall, and blank center were predicted and validated with experimental results.

Measurement of Coefficient of Friction in Hot Stamping by Hot Deep Drawing Test

Hot stamping process has been developed to produce the steel automobile parts with an ultra-high-strength of 1500 MPa. The effect of scale thickness on the formability in hot stamping was investigated by a hot deep drawing test in our previous research. The draw-in lengths of flange increased with decreasing the scale thickness. It is supposed that thin scale thickness resulted in low coefficient of friction at the flange area. The other reason is the temperature of wall zone would become low according to decreasing the scale thickness or increasing of the thermal transfer coefficient and it slightly inhibits local deformation at the wall area. It is difficult to separate these phenomena. To quantify the effect of scale thickness on the friction at the flange area during hot deep drawing, the coefficient of friction was directly measured. The coefficient of friction decreases with decreasing scale thickness.

Improvement in Material Flow During Non-Isothermal Warm Deep Drawing of Non-Heat Treatable Aluminum Alloy Sheets

Automotive industries are very much interested in implementing warm forming technology for fabrication of light weight auto-body panels using aluminum alloys without localized thinning or splitting. A non-heat treatable and low formable AA5754-H22 aluminum alloy sheet was selected in the present work, and a laboratory scale warm deep drawing test set-up and process sequences were designed to improve material flow through independent heating of punch and dies. Significant enhancement in cup depth was observed when the temperature of punch and dies were set to 30°C and 200°C respectively. Thermo-mechanical finite element model of the non-isothermal deep drawing test was developed successfully to study the improvement in material flow incorporating Barlat-89 yield theory using temperature dependent anisotropy coefficients and Cowper-Symonds hardening model of AA5754-H22 material. It was found that a non-isothermal temperature gradient of approximately 93°C was established within the blank from the center to flange at the start of deformation, and subsequent evolution of temperature gradient helped in improving material flow into the die cavity. The effect of temperature gradient on forming behavior in terms of cup height, ear profile and thinning development across flange, cup wall, and blank center were predicted and validated with experimental results.

Formability Analysis of AA6061 Sheet in T6 Condition

Formability of a material is defined as its ability to deform into desired shape without being fracture. There will always be a need for formability tests, a larger number of tests have been used in an effort to measure the formability of sheet materials. Aluminium Alloy 6061 is a magnesium and silicon alloy of aluminium. It is also called as marine material as it has high corrosion resistance to seawater. In this paper Formability test of AA6061 sheet is done by Forming Limit Diagram (FLD) Analysis. FLD or Forming Limit Curve (FLC) for the forming processes of AA6061 sheets is obtained by Experimental method and FEM. Experimental method involves Deep drawing test of the sheet and ANSYS software is used for FEM.

A Same Area Method Used to Calculate the Strain in Forming for an Axisymmetric Workpiece

An experimental study is conducted to explore a new method to calculate the strain in axisymmetric workpiece forming. When designing deep drawing die for an axisymmetric workpiece, the principal strain during the forming is needed to estimate formability and to decide whether the forming is finished in one pass. Strain calculation is a difficult task, so an ideal same area method used to calculate the strain for an axisymmetric workpiece along with a correction same area method considered thickness reduction rate is proposed here. The deep drawing test for an axisymmetric workpiece is used to obtain the strain along circumference and generatrix direction. The strain along the two directions calculated by the ideal same area method and correction same area method is compared with experimental results. The results show that ideal same area method can be used to calculate the strain during the forming process for an axisymmetric workpiece and the result from correction same area method is close to the experiment.

Mechanical Property of Roll Cast Al-11%Si Alloy

Al-11%Si (-0.44%Fe-0.16%Cu-0.14%Mg) was cast into the strip using a vertical type high speed twin roll caster at speed of 60m/min. Cooling rate of the strip was ranging from 2000OC/s at surface to 1000OC/s at center of thickness. The eutectic Si was smaller than 2μm. The homogenization, cold rolling down to 1mm, and annealing were carried out before the tension test, 180 degrees bending test and deep drawing test. Tensile stress was 192MPa, 0.2%proof stress was 84MPa, and elongation was 23.8%. Roll cast Al-11%Si had excellent elongation. The specimen was not broken by the 180 degree bending. LDR (Limiting Drawing Ratio) of the deep drawing test was 1.8. The ductility was drastically improved by the high speed twin roll caster. These results show that roll cast Al-11%Si has ability to be used for sheet forming. Moreover, Fe was increased up to 1.0% as the model of recycled alloy. The elongation was 15.9% and LDR was 1.7 in the condition that Fe content was 1.0%. Al-Si-Fe intermetallic became fine by the effect of rapid solidification. As the result, deterioration of the ductility was improved.