Bad vibrations

Cars and aircraft could be made safer and quieter using a holographic analysis technique to detect metal fatigue, developed in a BMW-led European research project.

Metal fatigue, caused by vibrations in the body panels, can lead car and aircraft parts to deteriorate, potentially resulting in dangerous accidents. These vibrations also cause irritating rattles when driving, and increase the overall level of noise produced by the vehicle.

The existing method designers use to measure vibration involves attaching sensors to a test body panel. But this only measures vibration at the point where the sensor is attached, and using a large number of sensors changes the way the panel moves, altering the results.

Holographic analysis – developed by the BMW-led group including researchers at Belgian noise and vibration specialist LMS International and the Free University of Brussels – involves illuminating the panel with a laser beam, said Dr Herman Van Der Auweraer, project leader at LMS. ‘The technique is based on laser illumination of the object, from which measurements are taken of its vibration and deformation.’

By measuring the light reflected by the panel the system can produce a high-resolution 3D image of the whole surface as it vibrates.

The technique will help car makers to design safer and more durable body panels, while reducing the cost of vibration and noise-control research. The device could also be used in the aerospace industry to increase the safety of aircraft, said Van Der Auweraer. ‘In the aerospace sector it is critical that sheet panels can withstand heavy loads and do not deteriorate over time. We have had a lot of interest from the aerospace sector.’

BMW provided the team with car and testing facilities, and assisted in the trials, he said. ‘The company also participated in the project and steered the research towards meeting industry’s needs.’

The computer models produced using the measurement data will predict the effect of any changes, allowing engineers to try out different designs before building them. ‘We want to reduce the noise made by cars by identifying the parts that vibrate most. Car body and roof panels cause a lot of noise both inside and outside the vehicle.’

The technology can also be used to help design safer, quieter and more durable domestic appliances and office equipment.