چكيده به لاتين
Today according to the importance of the amount of the waste materials, Energy and time costs, much attention has been focused to the forming limit, number of the required steps to result the required forming, etc. so studying the effects of new methods of forming such as high rate forming on FLDs which are a criterion of metal forming limit Has become important as well.
In this research strain rate effect was studied on FLDs for Al 6061 sheets in two thicknesses of 1 and 3mm. since in tension forming processes strain rate has a direct connection with the change in press speed, strain rate effects with press speed effect was modelled and the results were studied.
The press speed for 1 mm sheets was adjusted at speeds of 20 and 100 mm/min and for 3 mm sheets it was adjusted at 20, 100 and 200 mm/min. In this research, out of 2D tensile process simulation has been done to determine Aluminum sheet FLD and ABAQUS 6.9 Is used to model the simulations.
In order to validate the experimental results, two criterion of tearing location and FLDs obtained from simulation were compared with experimental results. Tearing location in experimental samples and modellings are compared and the tearing zone is approximately the same in both of them and the diagrams obtained, were close in their test speeds with acceptable error. According to these points experimental data verity can be trusted.
The experiments showed that by increasing strain rate, FLD also increases in both thicknesses but the amount of improvement is different. In a way that by increasing the press speed from 20 mm/min to 100 mm/min in 1mm thickness sheets, FLD increases for 3.8 percentage but in 3mm thickness this increase is 5.2 percentage, also by increasing press speed from 20 mm/min to 200 mm/min in 3mm sheets, FLD increases for 9.3 percentage. According to the similar researches and relations, this difference in amount of improvement is related to the thickness effect and inertia force effect which causes deformation in the work piece and more deforming stability against necking growth.
