Neutron diffraction, finite element and analytical investigation of residual strains of autofrettaged thick-walled pressure vessels

Residual strain distributions, positions of elastic-plastic juncture and 1st yielding etc. of autofrettaged thick-walled pressure vessels were revealed quantitatively using Neutron Diffraction (ND), Finite Element (FE) and Analytical solution. FE models were validated with ND results. Relationships between autofrettage pressures (Pmii, Pmao, Paopt) and load bearing capacity versus radius ratio K were respectively established via FE parametric study, by which optimal radius ratio K = 3 rather than K = 4 was identified for some existing vessels. Based on ND and FE results, new formula for calculating optimal juncture radius rjopt was deduced which narrowed the gap between analytical and FE results by 0.5 mm. Four coefficients Cj were proposed to modify conventional equations for calculating juncture radius rj, that facilitated a tool to address residual strains of autofrettaged pressure vessels. These results may be referred to for the design, manufacture, and proper application of the autofrettage technique onto pressure vessels and relevant engineering components.