Theoretical and experimental results of the elastic—plastic response of a circular rod subjected to non-proportional combined torque and tension loadings

Experimental and theoretical results concerning the elastoplastic response of a circular steel rod subjected to non-proportional biaxial loadings are reported. The following loading paths were studied: elastoplastic torsion followed by tension, keeping the initial angle of twist constant, and elastoplastic tension followed by torsion, holding the initial axial displacement constant. Experimental results show that when the rod is initially subjected to a torque and then, keeping the corresponding angle of twist constant, to a gradually increasing axial load, the rod behaves as if its torque-carrying ability has been drastically reduced without in any way affecting its axial load-carrying ability. Similarly, when the rod is initially subjected to an axial load and then, keeping the corresponding axial displacement constant, to a gradually increasing torque, the rod behaves as if its load-carrying ability has been considerably reduced without in any way affecting its torque-carrying ability. The mechanisms of such reduction are discussed in relation to the theoretical predictions based on Gaydon's [1] analytical model. Numerical solution has also been obtained along the lines of the above-mentioned model. The findings of this work have a direct bearing on the relaxation of tightening torques or axial loads as experienced by critical engineering components, such as couplings, bolted joints and rotating shafts, that are subjected to similar types of biaxial loading.