Application of Different Hill’s Yield Criteria to Predict Limit Strains for Aerospace Titanium and Aluminum Sheet Alloys

More recently, Titanium and aluminum alloys are gaining more interests to be implemented in hydro-forming applications. It is necessary to predict forming limits for these sheet alloys. Forming limits play an important role in metal forming processes. Forming limit diagrams, present the limit strains for various linear strain paths. In other hand, forming limit curve (FLC), illustrates localized formability for sheet metals under proportional loadings and are known as a powerful tool for trouble-shooting in sheet metal forming processes. In this study, mechanical properties of Ti-6Al-4V titanium sheets, AA7075-T6 and AA2024-T3 aluminum sheets are investigated through the uni-axial tensile test. Anisotropy coefficients as well as work-hardening exponent resulted from tensile test were used to theoretically prediction and numerical simulations of limit strains. For the theoretical prediction of the forming limit curves, several constitutive models were implemented. Several Hill’s yield criteria combined with Swift equation and empirical equation proposed by NADDRG were accomplished to predict the FLDs. Results showed that calculated numerical results are in good agreement with the predicted theoretical data when Hill93-Swift is the instability criteria used.

[1]  Faramarz Djavanroodi,et al.  Experimental and numerical evaluation of forming limit diagram for Ti6Al4V titanium and Al6061-T6 aluminum alloys sheets , 2010 .

[2]  R. Hill,et al.  A user-friendly theory of orthotropic plasticity in sheet metals , 1993 .

[3]  Amit K. Ghosh,et al.  Effects of strain path changes on the formability of sheet metals , 1978 .

[4]  Gorton M. Goodwin,et al.  Application of Strain Analysis to Sheet Metal Forming Problems in the Press Shop , 1968 .

[5]  Z. Marciniak,et al.  Influence of the plastic properties of a material on the forming limit diagram for sheet metal in tension , 1973 .

[6]  J. Lian,et al.  Forming limit diagram of sheet metal in the negative minor strain region , 1987 .

[7]  Prediction of the forming limit diagrams in pulsatory straining , 1994 .

[8]  Z. Marciniak,et al.  Limit strains in the processes of stretch-forming sheet metal , 1967 .

[9]  D. Banabic.  Limit strains in the sheet metals by using the new Hill's yield criterion (1993) , 1999 .

[10]  R. Hill.  A theory of the yielding and plastic flow of anisotropic metals , 1948, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[11]  H. W. Swift.  Plastic instability under plane stress , 1952 .

[12]  A. Needleman,et al.  Sheet Necking—I. Validity of Plane Stress Assumptions of the Long-Wavelength Approximation , 1978 .

[13]  The effect of vibratory straining upon forming limit diagrams , 1992 .

[14]  R. Hill,et al.  On discontinuous plastic states, with special reference to localized necking in thin sheets , 1952 .