FINITE-ELEMENT MODELING OF LOW-TEMPERATURE AUTOFRETTAGE OF THICK-WALLED TUBES OF THE AUSTENITIC STAINLESS-STEEL AISI-304-L - PART-II - THICK-WALLED TUBE WITH CROSS-BORE

In part I, the autofrettage of a smooth thick-walled tube of the auste nitic stainless steel AISI 304 L was studied by finite-element (FE) mo delling. It was shown that low-temperature autofrettage is more effici ent than autofrettage at room temperature, since it produces a larger beneficial compressive residual tangential (hoop) stress at the inner bore of the tube and hence permits a more significant enhancement of t he the fatigue resistance against pulsating internal pressure. The obj ective of the present study (part II) was to investigate the technical ly more relevant case of a thick-walled tube with a cross-bore made of the same steel. For this purpose, three-dimensional FE calculations w ere performed in order to characterize the influences of the autofrett age pressure and temperature on the stress and strain changes, in part icular at the site of the cross-bore, also taking into account the eff ects of work hardening and reverse yielding. The results indicate that low-temperature autofrettage cah also be applied advantageously in th e case of thick-walled tubes with a cross-bore by virtue of the signif icantly larger residual compressive stresses, compared to room tempera ture autofrettage. From the quantitative FE calculations, the optimal combination of autofrettage temperature and pressure were concluded to lie in the range of -90 degrees C/3500 bar to -110 degrees C/3250 bar , respectively. The calculated results were found to be in fair agreem ent with the measured values.