Image technique takes the strain in fault-finding

Researchers at the City University are experimenting with a new method of testing for faults in buildings, bridges, aircraft and electronics.

Shearography is an optical technique which uses a naturally generated laser-speckle pattern to detect deformations in materials, inventor and visiting research professor Dr Michael Hung Yau-yan said.

An electronic shearing camera captures images of the tested object before and after applying strain.

A special computer program analyses the data and displays easy-to-interpret images of deformations.

'Shearography permits full-field observation of surface deformities in a test object and reveals flaws by identifying flaw-induced deformation anomalies,' Professor Hung said.

He is also professor at the Department of Mechanical Engineering and associate director of the Centre for Robotics and Advanced Automation at Oakland University, Michigan.

Shearography is said to be more than 1,000 times faster than point-by-point ultrasonic inspection. And it does not require the rigid laboratory-controlled environment of holography.

The United States Federal Aviation Administration has adopted the technique to inspect tyres and aircraft.

City University researchers had previously used some of Professor Hung's applications to test micro-ceramic capacitors, dean of the Faculty of Science and Technology, Professor Chung Po-sheun, said.

'Professor Hung is a leading scientist in non-destructive inspection and we are pleased to have him with us to set up shearography in Hong Kong,' he said.

Professor Hung, who has six patents to his name, has also developed the world's first shearography courses at Oakland University.

Professor Chung said he could be asked to set up courses in Hong Kong.

Shearography could be used to inspect underground railways, buildings, bridges, pressure vessels, pipelines and packaging.

'Non-destructive testing of ageing civil structures is probably the most urgent application for Hong Kong,' Professor Hung said.