Issue 49

C. Bellini et alii, Frattura ed Integrità Strutturale, 49 (2019) 791-799; DOI: 10.3221/IGF-ESIS.49.70 797 The FEM results of Fig. 8 highlight how the distance measured from the centre of the specimen to the point in which FLP = 1 varies for different values of the friction coefficient. Fig. 9 shows the strain values measured in fracture conditions of the sheet tested using the polytetrafluoroethylene sheet as a lubricant. Figure 8 : Distance evaluated by FEM between the FLP = 1 point and the specimen centre at the friction coefficient varying. Figure 9 : S train s at break measured in experimental tests compared to the FLC of the necking condition (FLP = 1). C ONCLUSIONS n this work, a FEM-based two-dimensional model is chosen to analyse the friction influence on the stamping process of circular sheet metal. The sheet is modelled with the mechanical characteristics of the AA6060 aluminium alloy. In addition to the constitutive equation of the material (obtained from the tensile test), the limit formability curve (FLC) for the condition of material necking is considered. This curve depends on the hardening index of the tested material. The numerical and experimental results highlight the dependence of some characteristic parameters (such as the punch stroke, the distance between the specimen centre and the necking point) on the friction coefficient value assumed in numerical simulations. I