Vibrostrengthening

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Vibrostrengthening is a fatigue enhancement process originally developed for the Russian aviation industry, which has not been applied outside of Russia.  This process provides an alternative to shot peening, a standard surface treatment for fatigue enhancement in the aerospace industry.  Further, vibrostrengthening offers potential application benefits over shot peening, such as shorter processing time for treatment of components that are geometrically complex or that contain thin webs.   Vibrostrengthening is a modification of a typical vibratory finishing process, in which a workpiece and abrasive granular media are vibrated together in a processing tub causing the particles to mechanically ‘work’ the surface of the workpiece.  In vibrostrengthening, the workpiece is fixed to the tub, increasing the relative velocities between the particles in the medium and the workpiece, thus resulting in (surface/subsurface) plastic deformation of the material as a consequence of media impacting and abrasively processing the workpiece.  

In this study, vibrostrengthening is applied to aluminum components for fatigue life enhancement.  The effects of various process parameters on the fatigue strength of a specimen are studied, in order to provide proper process characterization.    A visualization approach is taken to understand the flow of the granular media within the vibrostrengthening process and obtain the impact velocity, interaction with the workpiece, and process mechanisms.  The visualization was obtained by constructing a viewable replica of the tub with a transparent window for observation and viewing the flow with a high speed camera and tracking software, which recorded the media’s motion with respect to time.  A computational model is developed to predict the fatigue enhancement of the vibrostrengthening process by means of a crack growth simulation.  A preliminary study suggested that the intermediate variables of the process, the surface topography and residual stress profile, could be predicted by a finite element simulation.

The benefits of the vibrostrengtheningprocess result from the combination of an induced compressive residual stress field and an enhanced surface finish.  The results indicate that the vibrostrengthening process produced an average of three times longer fatigue life compared to the baseline (as machined) sample, mainly due to a significant imposition of compressive subsurface residual stresses.  Further, the results of this process are shown to perform as well, if not better than shot peening in the fatigue testing. The measured values of residual stress in the vibrostrengthening samples were approximately 35% lower than the values measured in shot peening, while the Ra measure of the surface roughness was on average three times smaller in vibrostrengthening than shot peening.  The experimental results demonstrate that vibrostrengthening offers an effective alternative to shot peening for the fatigue life enhancement of aluminum components.

 

Project Sponsors: The Boeing Company

Collaborators: Placid M. Ferreira (University of Illinois, Urbana-Champaign) and James A. Stori (SFM Technology, Inc.)

References:

Sangid MD, Stori JA, Ferreira PM, “Process characterization of vibrostrengthening and application to fatigue enhancement of aluminum aerospace components – Part II.  Process visualization and modeling,” The International Journal of Advanced Manufacturing Technology 53 561-575 (2011).

Sangid MD, Stori JA, Ferreira PM, “Process characterization of vibrostrengthening and application to fatigue enhancement of aluminum aerospace components – Part I.  Experimental study of process parameters,” The International Journal of Advanced Manufacturing Technology 53 545-560 (2011).


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