FINITE-ELEMENT MODELING OF LOW-TEMPERATURE AUTOFRETTAGE OF THICK-WALLED TUBES OF THE AUSTENITIC STAINLESS-STEEL AISI-304-L - PART-I - SMOOTH THICK-WALLED TUBES

The stresses and strains introduced by low-temperature autofrettage of smooth thick-walled tubes made of the austenitic stainless steel AISI 304 L were modelled by the finite-element (FE) method. The objective was to show that low-temperature autofrettage is much more efficient t han autofrettage at room temperature in enhancing the fatigue resistan ce by introducing a higher beneficial tangential (hoop) residual compr essive stress at the inner part of the tube. Attention was paid to the influences of the autofrettage temperature and pressure, the work har dening and the reverse yielding on the residual stress components and on the total strain components of the tube. The FE calculations confir med that more beneficial residual stress patterns can be attained by a utofrettage at low rather than at room temperature. From the quantitat ive calculations, the optimal autofrettage temperature and pressure of the tube were concluded to be about -90 degrees C and 4000 bar, respe ctively. The results of the calculations were shown to be in good agre ement with recently measured data.