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Tap testing methods are commonly used to check for disbonding or lack of adhesion in material systems. Methods vary from simple coin-tapping or hammer tapping to commercial bond testing equipment. Commercial equipment can use a variety of methods and is sometimes referred to as Acoustic impact testing.
To identify disbonding or lack of adhesive from the change in acoustic response
In the simplest application a coin or specialised hammer is tapped on the component. The operator will listen for changes in acoustic response which may be indicative of disbanding, lack of adhesive.
More sophisticated methods will use a tapometer system with the acoustic response monitored and recorded using an electronics box. The method used and the weight of the impact needs to be tailored to the specific application.
Tap-testing methods are widely used and well established. The methods are simple to apply. Reliability of interpretation for simple tapping methods is dependent on operator skill and hearing.
Tap testing was used in addition to core drilling to evaluate the bond quality following refurbishment of the M5 Quinton expressway in Birmingham in 1975, the first application in the UK of such refurbishing methods.
Core drilling showed adhesive was absent in some areas, including an important zone close to the end of a plate. Such areas had not been detected in any of the tapping surveys. These involve monitoring the sound emitted by the plate when tapped, a change in tone indicating a change in bond quality.
More detailed information on tap-testing and acoustic impact testing can be found on the MMS15 Interactive Knowledge Base IKB on NDE of composite materials which arose from the DTI funded MMS15 project. Links are: