We do repairing and overhauling of load compressors at our facility. The impellers of these machines (which are made of Ti-6Al-4V) sometimes require repairs or rework. Afterwards they are shot peened. I have two questions regarding this:
1) I know there has been research regarding coverage and intensity vs. fatigue life of Ti-6Al-4V parts. But this seems to be applicable only to new parts. What criteria should we use for R&O parts? How many times can one repair a part, shot peen it, place it back into the field, get it back after a number of operating hours and repeat this procedure? Or to put it more concretely: how many times can we shot peen a part before the shot peening itself becomes detrimental to the part, taking into account that the part experience operating conditions between each session? Is there any literature available on this topic?
2) As said these parts have a number of operating hours between each R&O shop visit. During operating conditions these parts experience centrifugal and thermal loads. Is there any literature available regarding the influence of operating loads on the shot peen layer? Will the compressive stress slowly decrease? If so, what is the effect of this on the number of times such part can be shot peened?
