On the Material Modeling of the Autofrettaged Pressure Vessel Steels

Material modeling of high strength steels plays an important role in the accurate analysis of autofrettaged tubes. Although, the loading behavior of such materials is nearly elastic-perfectly plastic, their unloading behavior due to Bauschinger effect is very complicated. DIN1.6959 steel is frequently used for construction of autofrettaged tubes in some countries such as Germany and Switzerland. In spite of similarity between chemical compositions of this steel with that of A723 steel, due to different material processing, these two steels have an unlikely behavior. In this paper the material behavior of DIN1.6959 was accurately modeled by uniaxial tension-compression test results. Both 6 mm and 12.5 mm diameter specimens were used and compared. Also various relations for modeling of autofrettaged steels were investigated, and a new relation was introduced for accurate modeling. Moreover, two test methods, i.e., uniaxial tension-compression and torsion tests, used for modeling of autofrettage steels, were analyzed. Also, material models of three important autofrettage steels, i.e., A723, HB7, and DIN1.6959, were compared.