Optimization Of Shot Peening To Improve The Fatigue Strength Of Ti-6a1-4v

Author:  Franz, H.E. and Olbricht, A.
Source:  Conf Proc: ICSP-3, (p.439-446)
Doc ID:  1987061
Year of Publication:  1987
Abstract:  
Reducing airframe weight is an extremely important consideration in the engineering of both military and commercial aircraft. Apart from static strength, the primary concern in aircraft engineering is fatigue strength, which, if improved, can mean significant savings in airframe weight. The fatigue strength of components can be improved in specific instances by shot peening. The chief aim of this study was to optimize the shot peening process to improve the fatigue strength of the titanium alloy Ti-6A1-4V. According to the literature, the peening of titanium alloys is a particularly sensitive process and has also been known to result in reduced fatigue strength. A further important goal was to learn the mechanism effecting the change in fatigue strength. Practice has shown that fatigue strength is dependent upon the type of cyclical loading, component form, material and certain secondary factors. One of these factors is the surface, which has been subjected to various treatments and processes and provided with protective coatings. Shot peening changes the properties of near-surface layers, depending upon the condition of the material. The extent of the change can be determined in terms of certain characteristic values or parameters, and is also related to the original values for these parameters. The three most important parameters are: residual stresses, work-hardening and surface topography or morphology. Also to be taken into consideration are phase transformations and the implantation of shot-peening media. According to Wohlfahrt, changes in parameters, whether positive or negative, are in part responsible for the change in fatigue strength, depending upon the material's prior condition and the type of stress applied. The influence of microstructure on fatigue strength is well-known. By cutting all the specimens from a plate in essentially the same way, it was ensured that the microstructure was approximately the same in all the specimens and would manifest itself solely in the statistical distribution of fatigue strength values.