Plastic Deformation Influence on Material Properties of Autofrettaged Tubes Used in Diesel Engines Injection System

According to the DIN2391 standard, the DIN1.0406 steel is used to manufacture high-pressure injection tubes of diesel engines. The parts are autofrettaged during the manufacturing process to increase operating pressure and fatigue life. The autofrettage process is affected by loading–unloading cycle. In Bauschinger effect (BE) phenomenon, plastic deformation causes a loss in unloading yield strength. The ratio of unloading yield strength to the loading yield strength is called Bauschinger effect factor, BEF. In this paper, plastic deformation influence on the loading and unloading behaviors of DIN1.0406 steel is studied considering the BE. Uniaxial tension–compression experimental data are used to figure out a suitable model to study the BE. To carry out these experiments, a servohydraulic Instron machine is used. The sample tubes having inside diameter of 2.4 mm and outside diameter of 6 mm were made based on the standard ASTM E8M-97a. The tests were carried out using the total strain of 4.31%. Another important purpose of this paper is to investigate the effect of the amount of plastic strain on loading–unloading Young's modulus. Finally, the behavior of DIN1.0406 steel is compared with the steels such as DIN1.6959, HY 180, and PH 13-8Mo used in tubes.