Residual Compressive Stress Benefits on Core Aerospace Materials Using Ultrasonic Shot Peening

Author:  McClurg K., Chateau F., Wagner L.
Source:  ICSP-13
Doc ID:  2017107
Year of Publication:  2017
Abstract:  
Introduction: Ultrasonic Shot Peening (USP) emerged within the past few decades as a promising alternative to Conventional Shot Peening (CSP) methods. SONATS is a leading designer and manufacturer of USP tooling and equipment. Previous shot peening studies investigated the benefits of CSP on the fatigue life of commonly used aerospace materials, such as the Army Research Lab (ARL) study, “Shot Peening Sensitivity of Aerospace Materials”(1). Following the same technical approach used in ARL’s study, Avion Solutions and SONATS conducted a qualification study to compare the effects of USP to the commonly used CSP(2). Avion compared these materials through saturation curves,coverage charts, surface roughness measurements, residual stress profiles, and fatigue testing to qualify this system for repair use on Critical Safety Items (CSI) for the U.S. Army. In order to expand the qualification data on USP, Avion, Clausthal University of Technology (TUC),and SONATS teamed together to complete additional testing on 6061 aluminum, non-carburized 9310 steel, and carburized 9310 steel. Testing was designed to mimic previous qualification testing of USP to be a continuation of the original study. This study aims to display the similarities between shot peening the same materials at the same intensities while using different media activation methods. Fatigue life and compressive residual stresses are used to determine the equivalence between peening processes based on activation with either air pressure (CSP) or ultrasonic vibrations (USP). USP is a non-conventional method used to induce compressive residual stresses in the surface layers of metals. This system utilizes a titanium sonotrode head vibrating at an ultrasonic frequency, 20 kHz, to supply kinetic energy to the media for shot peening; whereas conventional methods derive this kinetic energy from air pressure or centrifugal force. Since this process relies on the contact of the media to this ultrasonically vibrating sonotrode, a chamber is created to contain the media to a given area during peening. This closed chamber continuously re-energizes high quality media during each peening process. Since the chamber created establishes a sealed peening environment between the surface of the component to peen and the vibrating sonotrode head, this system mitigates the risk of Foreign Object Debris (FOD). This sealed peening chamber allows for peening on-aircraft, subassemblies, or on the shop floor with minimal set-up and tear down time.USP is computer controlled and adheres to many AMS Specifications including AMS 2580 and 2585,which corresponds to Ultrasonically Activated Shot Peening and USP Media, respectively.