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- 검색키워드
- 저자 : A.H. Gorji (검색결과 3 건)
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A. Rajabloo,H. Gorji,M. Bakhshi‑Jooybari 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.7
A new method based on the EMF ring expansion test has been suggested for determining the dynamic characteristics ofannealed and as-received aluminum 1050 H18 sheet. The proposed method does not need any expensive hardware or datacollector. After performing quasi-static (QS) tensile tests, two coils and three sets of rings were prepared. The rings wereexpanded by coils at different voltages, and the strains induced were measured using 2D scanners. An inverse modelingalgorithm was used as a tool to determine the strain rate hardening coefficient by minimizing the difference between experimentallymeasured strain and that calculated from FEM simulation. The obtained strain-rate hardening coefficient of thematerial shows that annealed aluminum 1050 sheet is sensitive to strain rate, whereas the as-received is not. The obtainedresults showed that the as-received aluminum 1050 sheet depicts brittle failure behavior in both QS tensile test and high strainrate ring expansion test, but the annealed one withstands strains above 0.25 at both mentioned strain rates. The proposedmethod is successful in determining the flow curve of the material in sheet forming at high strain rates.
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A Comparison between Three Numerical Criteria for Prediction the Forming Limit Diagram of St14 Steel
M. Moslemi,S.J. Hosseinipour,M.E. Hosseini,A.H. Gorji 한국소성가공학회 2011 기타자료 Vol.2011 No.8
In this paper, the forming limit diagram (FLD) of a low carbon steel St14 (DIN 1623) is investigated experimentally and numerically. The objective of this study is to find a numerical criterion which enables a simple and reliable determination of the FLD. For this purpose, Out-of-plane stretching test method with hemispherical punch was simulated by using commercial finite element software, ABAQUSE 6.9. One-quarter of the geometry was used due to symmetry. The material was modeled as elastoplastic and the anisotropic properties were described by the Hill quadratic yield criterion. The model was assumed to be rate independent. Coulomb friction law was defined for all contact surfaces. The simulation process was performed in two steps. In the first step the blank-holder moves down and deforms the blank into the draw-bead. Then the punch moves up at 20 increments and deforms the specimen to a specified displacement. Three numerical criteria including maximum second thickness strain derivative (CRIT1), equivalent plastic strain increment ratio (CRIT2), and total equivalent plastic strain ratio (CRIT3) were evaluated and the forming limit curve (FLC) were obtained. The predicted FLC were compared with experimental data. Unlike the CRIT2, the CRIT1 and CRIT3 were in good agreements with were experimental data. The CRIT1 criterion predicted the lower bound of the experimental results. While by using the CRIT3 criterion both the lower and upper bounds of the experimental results were predicted.
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F. Zhalehfar,S.J. Hosseinipour,S. Nourouzi,A.H. Gorji 한국소성가공학회 2011 기타자료 Vol.2011 No.8
In this paper, numerical simulations are carried out to determine the forming limit diagram (FLD) of 5083 aluminum alloy. The aim is to predict the effect of strain path change on the forming limit curve (FLC) of this alloy. For this purpose, out-of-plane formability test method with hemispherical punch was simulated by using commercial finite element software, ABAQUSE 6.9. In the first stage, square blanks were modeled and then some of them were pre-strained uniaxially by tension test and some others were pre-strained biaxially by stretching over the hemispherical punch. In the second stage, the formability test specimens’ models were prepared by trimming the pre-strained blanks with the longitudinal axis parallel and perpendicular to the rolling direction. For trimming, a program was written in MATLAB 7.6 which could determine the new elements and introduce their properties to the FEM model. Ductile fracture criteria were used to predict failure. Furthermore, forming limit stress diagram (FLSD) was determined. The numerical results were compared with the experimental findings. Uniaxial pre-straining increased and shifted the FLC to the left hand side of the diagram for both parallel and perpendicular to the rolling direction. Biaxial pre-straining shifted the FLC to the right hand side of the diagram for both directions, and also decreased the FLC for the specimens parallel to the rolling direction.
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