EXPERIMENTAL INVESTIGATION OF MICROSTRUCTURAL EFFECT ON SHORT FATIGUE CRACK BEHAVIOUR OF NOTCHED α+β TITANIUM ALLOY SPECIMENS

摘要

This paper is aimed to evaluate the influence of microstructure on the fatigue microcrack behaviour of the Ti- 6Al- 4V alloy. Pulsating four point bending tests were carried out on prismatic specimens carrying a central hole. The conditions of initiation and first propagation of fatigue cracks were investigated. To this purpose a specific device based on the "in situ" detection of cracks by photomicroscopy was developed. Results were analyzed quantitatively considering cracks as mechanically small fatigue cracks. Furthermore the information on fatigue crack initiation and propagation was discussed on the basis of careful microstructural and fractographical analysis of the specimens. The importance of the biphasic microstructure on the material damage was highlighted and correlated to the observed oscillations in the crack growth rate.