1988-10-01

Computer Monitoring Permits Inclusion of Shot Peening Benefits in Design Allowables 881455

Reliability of aircraft components is greatly enhanced by the use of shot peening during manufacturing to prevent or retard metal failures from fatigue, fretting fatigue, stress corrosion cracking and corrosion fatigue. Because there exists in aircraft a potential for high overload stresses and surface damage, both of which reduce the reliability margins provided by the residual compressive stresses from shot peening, many parts, notably engine blades and discs, propellers and landing gear, are shot peened again at periodic overhaul.
As much as shot peening has been used in the past, there still is no non-destructive method of determining the quality of the peening on a given part. Because of this, the benefits of shot peening have not been included in the “Design Allowables”. Recently, the picture has changed dramatically with the introduction of “Computer Monitored Shot Peening”, (CM-SP) which, in fact, is the title of a new AMS specification being prepared by AMEC for the SAE. Use of CM-SP has already permitted the extention of the overhaul period of a recently introduced jet engine and the prospect of being able to take similar advantage in the design allowables for other engines, airframes, and landing gear, is creating considerable interest in the industry.
Paper discusses the practical advantages of computer monitored shot peening machines and the details of the programing and monitoring functions. A hard copy print-out can be generated for each part that is shot peened, providing full documentation of the process during execution.

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