Torsion creep of circular and noncircular tubes

Abstract

A torsio n creep theory for nonc ircula r tubes was developed by applying a multiaxial creep theory to a derived ge neraHzation of Bredt's equations.A review of the literature revealed no torsion creep data on noncircular tubes. Hence, to evalu ate the theory , a tes t program was carried out on twelve specimens of aluminum alloy st ructural tubing, of four confi guration s, at 400 O F.Observed discrepancies betwee n the torsion creep th eory and experiment are smaller than variation s in the meas ured c reep properties of th e specim en material from one tube configuration to another and are not appreciably greater than di scre pan cies bet wee n elastic torsion theory and experiment. Most of the observed discrepan cies are consistent with meas ured anisotropy in the tubes, while other di sc repancies are ascribed to nonhomogeneity in creep properties and a hyd rostati c stress effect in multiaxj a l c reep.For the calc ulation of torsion stresses in ci rcu lar tubes the thin-wall approximation is adequate for thick ness-to-radiu s ratios up to one-tenth. F or strai ght -s id ed tubes equ ivalen t accuracy is obtained for effective ratios up to only one-twentieth. These c rite ria apply to creep conditions as well as to elasti c co ndition s.