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 loadcarrying 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.

This paper suggests the use of a modified elliptic shape which gives less stress concentration when compared to semicircular notch and groove. The ratio of minor and major half axes of the ellipse should be between 0.3 and 0.4. The introduction of shoulder with elliptic notch and groove even reduces the stress concentration. The results obtained from FEM analysis propose optimal values of geometrical design parameters. The study represents not only a precise view of stress distribution, but also to develop charts that can be used by designer for practical purposes.Keywords: Notch and groove, stress concentration factor, elliptic notch, finite element, Von-Mises stress. NOMENCLATURE Greek symbols