High intensity acoustic testing of flight structures

Abstract

High intensity acoustic testing has been an important part of Air Force technology for nearly thirty years. With the advent of jet aircraft in the 1950s, acoustic fatigue of aircraft structures became a significant problem. In the 1960s the Wright Laboratory constructed the first large acoustic fatigue test facilities in the United States, and the laboratory has been a dominant factor in high-intensity acoustic testing since that time. In addition to fatigue of jet aircraft structures, other severe acoustic environments have been identified. Of particular importance are the acoustic environments of missiles in captive carry on fighter aircraft, and the high-temperature acoustic environments of blown flaps, hypersonic structures, and engine exhaust structures of stealthy aircraft. This paper describes the causes of these intense dynamic environments and some of the new facilities designed for testing structures subjected to these dynamic loads. The Wright Laboratory facilities now include three new chambers: (1) a sub-element acoustic chamber for testing structural panels up to 12"/spl times/18" [0.30/spl times/0.46 m], (2) a combined environment acoustic chamber for panels up to 4'/spl times/4' [1.23/spl times/1.23 m], both at acoustic levels of 175-180 dB and heat fluxes of 50 to several hundred Btu per square foot per second [5000 W/m/sup 2/], and (3) a random fatigue chamber for vibration testing of structural coupons up to 3"/spl times/7" [0.8-0.0.2 m] at temperatures from -250/spl deg/F to +2700/spl deg/F [120/spl deg/C-1470/spl deg/C] at atmospheric or lower pressures in the present of hydrogen and helium gases.