Studies on Testing and Modelling of Formability in Aluminium Alloy Sheet Forming

Abstract

In this paper, the influence of tensile and formability parameters on the forming limit diagram is reported and a model is created to predict the forming limit strains of various grades of aluminium sheet metals. Aluminium alloys of grades AA5052, AA6061 and AA8011 with a thickness 0.8 mm, 1.0 mm and 1.2 mm have been selected for the study. Experiments are conducted to construct the forming limit diagram (FLD) for the above mentioned sheet metals. Tensile tests were conducted to evaluate strain hardening index, strength coefficient, ductility, yield strength, ultimate tensile strength, normal anisotropy, planar anisotropy and strain rate sensitivity. The fractured surfaces of the specimens were viewed with a scanning electron microscope. Using Design of Experiments (DOE), regression modelling was done by taking the tensile properties and formability parameters as input variables and the forming limit strain as response. Regression equations were created to predict the limiting strain values at the tension-tension, plane strain and tension-compression strain states. The experimentally evaluated strain values were compared with the predicted strain values and the comparison shows good agreement of the values. The Taguchi method of optimization was used to find the optimum values for the input variables and using these optimum values, the optimum forming limit strains were found. It is found that the so created regression model predicts the FLD of various grades of sheet metals by which the tedious job of experimental determination of the FLD can be avoided.Studies on Testing and Modelling of P. Chinnaiyan, S.N. Chinnaiyan Formability in Aluminium Alloy Sheets Forming (K), normal anisotropy (r) and strain rate sensitivity (m) can be determined by using the tensile test. The forming limit diagram was introduced by Keelar [10], an extensive work was done by Goodwin [11] and the evaluation of the FLD was made simple by Hecker [12]. Strano and Colosimo [13] emphasised an approach to determine the forming limit curve based on experimental results. Their work focused on the separation of safe strains and failure strains.In spite of such efforts to improve the experimental accuracy of determining the forming limits, it is essential to conduct a complete experimental investigation. Tigran Abovan et al. [4] created a finite element based criterion for predicting the FLD under isothermal conditions for the AA5000 series. Their findings indicate that the developed criterion predicted the forming limit for each strain path. Elangovan et al.[9] developed a model to predict the forming limit strain of perforated AA8011 alloy sheets of varying geometrical feature by using the artificial neural network. Ravikumar [14] made an attempt to correlate the crystallographic texture with the formability parameters. Korhonen [15] conducted experiments to determine the FLD along the rolling and transverse direction. They found that the measured limit strain in the case of the uniaxial tension is well predicted by the Rice-Tracey theory. ...

Prediction of forming limit diagrams for steel sheets with an artificial neural network and comparison with empirical and theoretical models

“…However, these experimental and theoretical studies guide the researchers by giving information about the factors affecting the FLC. Subramani et al [18] experimentally determined FLCs for three different thicknesses of three other aluminium alloys and modelled them with the Taguchi experimental design. They determined the mechanical properties, such as yield strength and hardening exponent, using tensile tests.…”

Prediction of forming limit diagrams for steel sheets with an artificial neural network and comparison with empirical and theoretical models

“…However, these experimental and theoretical studies guide the researchers by giving information about the factors affecting the FLC. Subramani et al [18] experimentally determined FLCs for three different thicknesses of three other aluminium alloys and modelled them with the Taguchi experimental design. They determined the mechanical properties, such as yield strength and hardening exponent, using tensile tests.…”