In order to investigate the optimum condition of the autofrettage process for the diesel engine fuel injection pipe, different values of autofrettage pressure, pressure rising time, pressure holding time, and repetition of autofrettage process were applied. Autofrettage was performed by applying the hydrostatic internal pressures of 604MPa, 535MPa, 500MPa on the fuel injection pipe, corresponding to theoretical 50%, 30%, and 20% overstrain levels, respectively. The autofrettage residual stresses in the injection pipe were experimentally determined by using X-ray diffractometer. As the overstrain level increased, the magnitude of compressive residual stress at the bore increased. It was found that the rising time to reach the autofrettage pressure, holding time at the autofrettage pressure, and repeated application of the autofrettage pressure on the pipe had no significant influence on the residual stress distributions.

• 고승기(군산대학교) | 고승기 Corresponding author