The Effect of Boring After Autofrettage of Pressure Cylinders

In this work, the effect of boring on residual stress distribution in thick walled pressure cylinders after autofrettage is studied by numerical simulation using finite element method. Autofrettage is performed using mandrelling technique. The simulations are validated by experiment. In this regard, some cylinders are autofrettaged through mandrelling technique and residual stress is measured using central hole drilling method. The simulation of boring is performed by removing elements of cylindrical layers of small thickness after the loading and unloading processes (autofrettage) are completed. The diametral interferences of 0.4 mm and 0.6 mm between the mandrel and the cylinder are considered for the simulations. The results indicate that boring increases the through thickness residual Von-Mises and compressive hoop stresses from the inner surface up to a certain radius thereafter the trend changes and the stresses begin to reduce. Boring has reducing effect on radial stress distribution across the wall of the cylinder. Since residual stress measurement on the inner surface of the cylinder is difficult, the measurements are made only on the outer surface of the vessel. A good agreement between the trend of numerical predictions and experimental results are observed for boring. On the whole, boring can increase the residual stress at the inner surface and reduce it at the outer surface of pressure cylinder.