Experimental analysis for defining forming limit diagram for thick sheets

In this paper a combined procedure to determine the forming limit diagram (Keeler-Goodwin diagram) for thick sheets is proposed. It is defined for cold rolled steel sheet Č0147 (RSt 13 DIN 17006) with thickness of 5 mm using two different criteria: maximum uniform elongation and the criteria of tearing. For the area of one positive and one negative strain (the left part of the diagram) the curves of limit strain are determined using the method of inline stretch of test tubes with circular lateral clips of sheet with thickness of 5 mm. The curves of limit strain are gained by drawing using rough hemispherical punch of sheet strips with different widths for the same quality of the material, but with thickness of 1 mm. For the area of two positive strains (the right part), the curves of limit strain for sheet with thickness of 5 mm are determined so that, in continuation to the right end side of the limit curves, gained with stretching of the test tubes with circular lateral clips, the for material with thickness of 1 mm are drawn, retaining the same form in the process. Key words: strain, limit deformability, diagram of limit deformability, curves of limit strain