PRINCIPLES OF SHEAROGRAPHY AND ITS APPLICATION IN NON-DESTRUCTIVE TESTING

This article outlines the procedure of shearography and its use in monitoring the development of cracking in tyres in use. Previous non-destructive testing involved holography. Shearography requires a lens but no film and represents real-time data. It measures out-of-plane displacement derivatives and digital processing makes automatic and quantitative evaluation possible. The object studied is illuminated by an expanded laser beam with a shearing device in front of the lens which produces a random interference pattern to show displacement information. It is noted that in the USA drivers are employing high speeds and often run on under-inflated tyres. A study featured passenger car tyres being temperature tested and shearographed. Shearography used at intervals during testing can allow tyre engineers to monitor the initiation and location of cracks in different conditions and provides a cause and failure relationship to crack initiation and propagation.