An acoustic impedance investigation of spray-on foam insulation to detect bonding condition

Date
2004-01-01
Authors
McKee, Matthew
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Altmetrics
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Abstract

Spray-on foam insulation (SOFI) is used by NASA to keep the external fuel tank on the space shuttle cool, while the launch vehicle in on the launch pad. Loss of SOFI was blamed by the Columbia Accident Investigation Board as the primary cause of the Columbia Incident. The cause of the SOFI loss is unknown but NASA desires a method to identify the bonding condition of the SOFI with the aluminum tank. Several methods are currently being tested to detect the bonding condition of the SOFI. In this thesis the approach taken was that the change in bonding condition changes the audible acoustic impedance of the surface of the foam. A method was developed for measuring acoustic impedance. Four conditions were tested; the impedance was measured in an anechoic chamber, in a reverberant room, in a reverberant room with a moving source and in an impedance tube. Consistent differences between the impedance over bonded and un-bonded areas of the foam sample were found in the anechoic chamber and in the reverberant room. These differences were used to create an indicator of the bonding condition.

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Aerospace engineering, Engineering mechanics
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