Influence of artificial and casting defects on fatigue strength of moulded components in Ti‐6Al‐4V alloy

Abstract

The influence of defects on the fatigue strength of a cast Ti‐6Al‐4V alloy has been investigated. An experimental programme has been defined with different castings. On a first stage, a flat fatigue specimen has been developed to be representative of the real aircraft component. Then, reference fatigue properties have been determined and reduction of the fatigue strength has been quantified for artificial and natural defects. It is shown that an artificial defect with a chemically milled surface is representative of an in‐service component surface machining: surface pinholes have similar influence on the fatigue behaviour. Furthermore, the experimental results have shown that the geometrical morphology is not the major parameter that governs the fatigue life reduction: the defect type has a major influence. It is also shown that the initiation stage is not negligible in the total fatigue life about 105 cycles. Kitagawa diagrams were built to determine critical defect sizes.

Very-high-cycle fatigue behavior of a structural steel with and without induced surface defects

“…Morel et al [38] investigated the competition between microstructure and defect by using FE simulations, and summarized that local stress field is highly scattered and differs significantly from the macroscopic response of the polycrystalline aggregate. The research of Leopold et al [39] on Ti-6Al-4V alloy obtained a similar result. They stated that fatigue life, from 10 5 to 10 7 cycles, is controlled by crack initiation even for the initiation from defects.…”

A comparison of fatigue strength sensitivity to defects for materials manufactured by AM or traditional processes

“…5 and 6. We also note that the defects reported by Giglio et al [85] and Léopold et al [80] are artificial and are created using electro discharge machining. Artificial defects were also adopted by Gong et al [67], who built defects directly during the 3D printing of the AM specimen.…”

“…Considering the results related to traditional processes, Léopold et al [80] reported the fatigue limit of cast Ti6Al4V before and after machining. The influence that different microstructures have on the dynamic properties is investigated in [44,81].…”

Faceted crack initiation characteristics for high-cycle and very-high-cycle fatigue of a titanium alloy under different stress ratios

“…Notch effects and size effects are also important topics in the investigation of HCF and VHCF of titanium alloys [42,43]. For specimens with notches, the failure type of no faceted crack initiation will be dominant for the surface notches decrease the threshold value of no faceted crack initiation, which will restrain the other two failure types of faceted crack initiation.…”