Assuring quality in lightweight construction

1 min read

Boats, aircraft and spacecraft are getting lighter and lighter – lightweight structures help reduce fuel and carbon dioxide (CO2) emissions.

“To ensure that police and marine emergency services can rely on their lifeboats, even in high seas, the lightweight components undergo comprehensive quality assurance before being put to actual use,” affirms Joachim Montnacher, Head of Department for Testing Systems at the Fraunhofer Institute for Manufacturing Engineering and Automation IPA in Stuttgart, Germany.

Together with Dr Tina Wilhelm, Group Manager for Measurement and Testing Technology, and colleague Wolfgang Schmidt, the Fraunhofer researchers are hard at work on quality assurance systems for lightweight construction. At the COMPOSITES EUROPE trade show, they will present a combination of two testing systems: shearography and thermography.

“Shearography is a laser optical procedure that allows measurement of material deformations in the triple-digit nanometer range," explains Wilhelm. "Thermography allows one to measure temperature differences on the surface of materials with accuracy of just a few Millikelvins. If an air pocket is enclosed on the adhesive side of a component, then the thermographic camera will measure different heat values than those of the properly seamed locations. With shearography, the material expands differently at the site where a defect occurs.”

For both procedures, the material must be stimulated mechanically, thermally or electrically, using force, ultrasound or light. The researchers measure twice – once before and once after the stimulus. The measurement values clearly indicate where delaminations have occurred with the materials during processing.

“Depending on the procedure, various physical effects are used for the testing," says Montnacher. "What’s important is that you can reliably detect defects with the two technologies – and specifically both on the surface and in the interior of the component. Since it is necessary to apply a stimulus to the materials being tested in any case, the combination allows you to eliminate one processing step, while simultaneously improving quality control.”

Montnacher summarises the functional process of measurement and the advantage of the combination. At the trade show, the Frauhofer researchers will demonstrate the two testing technologies on a clutch disk.

In the laboratory, a focal point of the working group is to ascertain for which materials shearography is best suited in order to find hidden delaminations, and when it is better to utilise thermography.

“There is still a considerable amount of research needed,” Wilhelm concludes.

Fraunhofer will exhibit in Hall 4 on booth D04 at COMPOSITES EUROPE 2009 in Stuttgart, Germany, on 27-29 October.