Critical analysis of the evaluation of plastic material properties obtained from standard round tensile specimens

Since the well-known papers of Bridgman (1) and Davidenkov-Spiridonova (2) have been published in the fifties, researchers applied their simple formulae to determine the yield stress for hardening plastic materials. In the years 1970-1980 several attempts based on computer simulation have been done to verify the assumptions of the approximation formulae, to recognize the possible error or even to improve the formulae (3-7). It was stated that the error connected with application of the simple formulae can be estimated as 10% in comparison with the numerical simulations, which was considered as an acceptable accuracy. Recently, researchers have applied the same simple formulae to analyze such complicated effects arising from damage and fracture of the material in the last stage of plastic deformation (8, 9) and for notched specimens (8). This arises in these new circumstances once again the questions for accuracy of the simple formulae and for their justification for notched specimens. Moreover, new generation of powerful computers and software enables us to believe in success. In this paper, the finite element method is applied for the high accurate simulation of the tensile tests. The obtained results are discussed in the context of the approximation formulae and previously known results.