A new method for modelling the support effect under rotating bending fatigue: application to Ti‐6Al‐4V alloy, with and without shot peening

Abstract

The subject of this paper is to investigate the capability of the relative stress gradient to properly represent the beneficial effect of residual stress states on the fatigue life of Ti‐6Al‐4V specimens, with notches of different severity. The research was developed considering notched and un‐notched specimens with different geometries and different shot‐peening treatments. The results were determined by running fatigue experimentation under rotating bending and by developing a novel predictive model based on the relationship between the local fatigue limit and a generalized form of the relative stress gradient, accounting for the peening‐induced residual stresses. The proposed tool for fatigue limit estimation was completed by a stochastic analysis, which considered the variability of the involved parameters, in particular the residual stress entity. This made it possible to finally determine the component failure probability in a general, efficient and accurate way.

Enhanced fatigue behavior of powder metallurgy Ti–6Al–4V alloy by applying ultrasonic impact treatment

“…Compared with the fatigue strength of the pristine material ( $ 212 MPa) approx. 60% increase ( $330 MPa) is observed after UIT on the base of 10 7 cycles, and this increase appears to be even higher ( $ 70% -see dashed line in Fig.6a) when all the obtained points would be interpolated to account for the stochastic character of fatigue strength/life [43]. The largest effect of UIT on lifetime is observed at s a ¼300 MPa and s a ¼400 MPa, where fatigue lives are increased by roughly two orders of magnitude (Fig.…”

“…When the surface roughness is essentially minimized the microstructural evolution goes to the forefront and starts to play more essential role in fatigue performance [42,43,47,59]. Thus, in the pristine material chaotic arrangements of dislocations are effective obstacles for mobile dislocations at cyclic loads, and these mobile dislocations can aggregate in slip planes provoking strain localization.…”

Effects of stress ratio on high-cycle and very-high-cycle fatigue behavior of a Ti–6Al–4V alloy

“…They proposed a model based on a twodimensional Poisson defect distribution to describe the competition of failure modes. It is known that many factors, such as stress ratio [10][11][12], environment [13] and surface treatment [14][15][16], may affect fatigue crack initiation and propagation behavior of metallic alloys. As an important topic, the effects of stress ratio on fatigue crack initiation and propagation of titanium alloys were investigated in previous papers [17,18].…”

Effect of shot peening on metastable austenitic stainless steels

“…Among a great variety of surface treatments, shot peening is one of the most widely used techniques to increase the resistance of metal parts to fatigue in a large range of industries, such as automotive, aerospace and petrochemical [7,8,9]. It consists of blasting high velocity small beads on the metal component to generate surface hardening and compressive residual stresses which oppose to the nucleation of cracks and also exert a closure effect on those cracks already nucleated, avoiding their propagation [10,11]. Shot peening usually produces detrimental surface effects too, such as increasing roughness, nevertheless it has been shown that the average effect of both beneficial phenomena is more important than those induced by superficial detrimental effects [12,13].…”