-New equipment Computer-aided aircraft wheel inspection uses eddy current technique

Faults in aircraft wheels caused by metal fatigue, stress corrosion and/or heat damage can be detected by WheelScan," developed by Hocking NDT. The inspection machine is capable of finding cracks, and heat induced changes in metallurgical strength by using the largest eddy current technology controlled by a computer aided programming and operation system.

The automatic scanning program for a particular wheel is either recalled from memory or, for a new type of wheel, the profile and inspection area is 'learned' by moving the probe over the desired inspection area. The inspection sequence and scanning speed are controlled by the computer to minimize the inspection time without compromising quality or safety.

The eddy current test parameters and calibration settings are automatically stored and recalled from internal memory, although there is an option to use a lower cost manually calibrated eddy current unit.

The standard instrument automatically scans the wheel flange, rim, bead seat and barrel to detect cracks as small as 0.5 mm deep and 1 mm long in wheels up to 700 mm diameter. Optional facilities include a rotating probe drive unit for inspecting the internal surface of the bolt holes and an electrical conductivity module to detect heat damage in the body of the wheel.

Inspection results are displayed on a colour monitor and a hard copy thermal chart recorder. An optional dot matrix printer is available for screen dumps.

Hocking NDT Ltd, 129-135 Camp Road, St Albans, AL 1 5HP, UK

Aircraft wheel undergoing eddy current inspection with the WheelScan from Hocking

Radiographic digitizer and image processor

An advanced film scanner that converts analogue film density information into digital form and stores it has been developed by Du Pont. According to the company it can reveal more about the original subject that any other system. The operator can retrieve all or part of the information at will and enhance the image in a number of ways to evaluate it in minute detail.

Known as NDT Scan, it allows defects down to 38 mm to be recorded, far beyond the present requirements of today's NDT

inspection regulations.

NDT Scan IV is the top-of-the range equipment with a microprocessor controlled film digitizer, a workstation with image processor containing three TV monitors and 115 Mbyte hard disc storage, and a 2 gigabyte optical disc storage unit.

Exposed radiographs with optical density ranging from 0 to 4.8, and measuring up to 356 x 432 mm are the source material required, and the film is loaded into the flat-bed scanner/digitizer. The

N DT International October 1989 323

-New equipment radiograph is passed slowly between a linear array of fibre optic l ight sources and a 5000 element detector array. An inbuilt microprocessor optimizes the characteristics for viewing, and the data is stored onto a 115 Mbyte hard disc.

The scanning, digit izing and storage process takes some 30 s for 356 x 432 mm radiographs scanned to 70 #m resolution, or 50 s for 178 x 432 mm originals to 35 #m resolution.

Stored information is retrieved and manipulated by the image processor through an on-screen menu which gives the radiographer precise control over the process with three TV monitors on line simultaneously. One screen shows the full digitized radiograph, the second shows an enlarged portion of the image magnified by up to ten times, and the third screen shows the enlarged image with colour enhancements that often clarify an otherwise doubtful image area.

Image processing functions available under the control menu include varying brightness and contrast, a variety of edge enhancement techniques, zooming in on areas of specific interest, colour enhancement, unsharp masking, and convolut ion of image.

The illustration shows a radiograph of a bundle of Du Pont J12 fibres taped against a l ight box. Top left is the original radiograph; top right is an enlarged and digitized image of part of it. By adjusting the brightness (apparent density) and contrast as shown at bottom left the fibres stand out better against the background. By applying the unsharp mask routine the large dull edges of the background fibres and the small sharp tracer fibres are enhanced (bottom right).

Du Pont (UK) Limited, Imaging Systems Department, Wedgewood Way, Stevenage, Hertfordshire SG 1 4QN, UK

Digital processing of radiographs with the viewing and evaluation system from Du Pont

Real-time computer enhancement of X-rays

Stress fractures in aircraft components and corrosion beneath paint finishes on oil rigs are two potentially hazardous faults which can be detected faster and more precisely using a computer-based X-ray enhancement system from Draeger. Image enhancement software developed by NASA is used in the 'Damon Detect', which digitizes standard X-ray films and performs the necessary calculations quickly enough (0.03 s) so that the enhanced picture may be viewed on the screen in real time.

Instead of v iewing the film on a conventional l ight box, it is placed on the table of the instrument where it is scanned to produce a digitized version with high resolution (525 x 480 pixels). Computer manipulation of the data begins immediately, producing on the screen an

enhanced view on which defects show up more clearly than on the unprocessed original.

Increase in contrast detail is up to 500%,,,with a dynamic range of over 2000 grey levels and a resolution of 100 #m. An additional feature is the ability to simulate 3D imaging for contour enhancement. To assist inspection, the image may be viewed as a positive or negative, contrast may be varied, and a zoom function magnifies any area by up to 10 times.

As the picture is in a digitized form, it is easy to transmit the enhanced or unenhanced versions over standard telephone lines for a remote second opinion.

Draeger Limited, Medical Division, The Willows, Mark Road, Hemel Hempstead, Herts HP2 7BW, UK

324 N D T International October 1989