Background
On 26 October 2001 Lockheed Martin won the $US 200+ Billion contract to develop F-35 Joint Strike Fighter (JSF) which was officially named Lightning II on 6 July 2006. Australia is one of nine partnering nations participating to the System Development and Demonstration phase of the F-35.
GKN Aerospace Engineering Services (GKNAES) opened in Australia on 1st August, 2001 and is the Australian branch of GKN. The headquarters are located in Melbourne with two engineering offices in Sydney and Brisbane. GKN AES is a leader in Knowledge Based Engineering which provides software tools and techniques for capturing knowledge on how to design, analyse and manufacture new products. In 2003, GKN AES won a multi-million dollar contract for the design, analysis and manufacture of metal and composite components for the Joint Strike Fighter fuselage.
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Figure 1: Joint Strike Fighter F-35 |
Manufactured parts made of composite materials are required to be 100% inspected for defects and/or abnormalities before being fitted in an aircraft. Non-destructive imaging techniques, such as ultrasound are used to visualise the internal structure of parts, some of which can be metres across. Ultrasonic waves propagate through the part and are reflected at the boundaries between the materials in the composite, which have different acoustic impedances. Impact damage, defects, inclusions, etc will change this impedance locally and affect the sound wave propagating through the part. One type of measurement, referred as a c-scan, provides a 2D image representing the thickness of the scanned object. It is then straightforward to pinpoint the location of any defect that might be present.
The Challenge
This new project investigates the possibility of using image processing techniques to convert ultrasound c-scan data into a three dimensional representation of the part that can be then compared to the original Computer Aided Design (CAD) geometry. This exploratory project is investigating new development of tools to aid in the non-destructive testing of aerospace parts and in particular those required by the JSF program.The Method
It was not possible to obtain c-scans and CAD of parts used in the JSF program because these data are subject to International Traffic in Arms Regulations (ITAR) and require an export license. CCI Pope in Sydney provided a sample c-scan for this project (see Fig. 2). Although no CAD model was available, the scanning shows the top half of a metallic pipe with internal corrosion or impact damage. The pipe was 0.85 m long with a radius of 0.1 m.
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Figure 2: Ultrasound c-scan image of a damaged
half-pipe. |
Brett Petersen (UQ & GKN) developed an algorithm in Matlab that maps the image to the surface of the part (assumed to be a perfect half-cylinder). Since colour in the c-scan represents depth, it is possible to find the internal surface of the part. The solid section of the part defined by the surface points and the internal points is then discretised into voxels. The end-product is a voxel representation of the c-scan data, with each voxel containing depth information. He then used a technique known as texture rendering to visualize the 3D part as seen in Fig. 3 below. The part can be inspected interactively. The full conversion process takes about 18 minutes on a Pentium M 2.0 GHz machine, so high performance computing is required for more complex parts.
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Figure 3: Inner surface of the model showing the impact damage. |
Benefits
Engineering product design – time, quality…
Where is the technology headed?
The test image was small and the conversion from c-scan to 3D object took about 18 minutes on a Pentium M 2.0 GHz machine. The code needs to be improved and ported to supercomputers to handle larger data. The geometry used in this project was simple: the methodology needs to be tested on parts with increasing complexity. However this test project shows that it is possible to develop such tools.Acknowledgements
Ken Brown at CCI Pope provided the c-scan for this project.Contact
Dr Adrian Smith, GKNAESReferences
Joint Strike
Fighter Program Office. Updated 2006.
(Accessed 26 July 2006).
GKN.
Updated 2006. (Accessed 26 July 2006).