Effect of mechanical and thermo-mechanical treatments on fatigue behaviour of V-shaped notched round bars

In the present paper, the fatigue behaviour of a metallic round bar with a V-shaped circumferential notch and a surface crack at the notch root is examined. The bar is subjected to pulsating tension, and different crack shapes are considered: almond, sickle, straight-front crack. Residual stresses due to the cold-drawing process are herein considered and, since they are detrimental to fatigue life, two treatments are devised in order to decrease them, more precisely: (1) a further drawing with a very small area reduction (about 1%); (2) a procedure based on a combination of heating and stretching of the bar. The strong dependence of the fatigue crack propagation on the residual stress field is quantified in terms of evolution of both surface crack shape and crack growth rate.