Maintaining the standards

Citation

(2003), "Maintaining the standards", Aircraft Engineering and Aerospace Technology, Vol. 75 No. 5. https://doi.org/10.1108/aeat.2003.12775eac.002

Maintaining the standards

Maintaining the standards

Keywords: Standards, Materials, Aerospace

An opportunity to view the latest technologies and keep up to date with developments in NDT was available at Materials Testing 2003 held recently in London. Although covering a wide range of applications, specific procedures were illustrated or demonstrated that were concerned with aerospace.

To ensure the integrity of turbine blades a high level of radiography is necessary and this is available in the VENLO system of X-Tek Industrial. The system uses micro and mini-focal X-ray sources but replaces X-ray fi91 m with an amorphous silicon detector. An early user of the VENLO system is Eldim of the Netherlands where it is employed during the manufacture of precision turbine components. The real-time X-ray imaging produces an image within 2 min.

X-ray inspection is essential, for example, for checking the cooling holes in turbine blades and by using the VENLO system the information is rapidly available. This X-Tek procedure can be supplied with a choice of three penetration levels; l60, 225, and 320 kV, the last of these is claimed to be the highest powered system of its type anywhere in the world. The X-ray source, detector and components load tray are enclosed in a cabinet and once the component has been loaded on to the tray, it is then processed and viewed as a radiograph and archived on to CD-R or DVD-R disks.

Ultrasonics and transistors

From Sonatest arose various digital ultrasonic flaw detectors, Sitescan 140, Sitescan 240, and Masterscan 340. The first of these is broadband and the 240 is narrowband, both of them utilising all the time-saving and storage functions associated with digital technology but retaining the analogue feel. A high brightness TFT display is incorporated with a choice of colours or alternatively, a monochrome transflective LCD display for use in bright sunlight. Accessories for the 140 and 240 include a compact monocular eyepiece. The LCD screen provides instant data response with real-time sharp images. There is a small DFD keyboard which plugs into the front socket of the flaw detector, enabling faster input of notes in standard QWERTY format into the documentation, instead of scrolling through alphanumeric text.

Sonatest data management software (SDMS) is a Windows-based data management tool which allows the user to interface with a PC. The software provides a frame to upload and download panel settings and A-scans. These can also be copied and pasted in Word for customised reporting. Thickness readings can be dumped directly into Excel with the ability to produce charts for B and C scans, colour 3D mapping, etc. These instruments can be used for routine applications such as weld inspections, thickness/corrosion testing, and small castings and wrought products.

The Masterscan 340 is a high performance flaw detector for the more demanding ultrasonic applications, such as high frequency, thin walled materials needing exceptional near surface resolution or low frequency, long range, long range attenuative materials requiring high penetrative power. Typical applications include aerospace materials (e.g. composites), and aircraft maintenance. A minimum range 0-1 mm is achieved by the rectifier design. With the contour reduced to the minimum zero setting and using a suitable high frequency delay line transducer it is possible to measure down to 0.15 mm.

Sonatest also showed their extensive range of transducers, with specific types suitable for aerospace. These include single and twin compression instruments, single and twin angle shear wave, and immersion transducers. Another type is time-of-flight diffraction (TOFD). One of its major applications is the ultrasonic examination of weld after final heat treatment and/or hydraulic testing, to verify the absence of cracks not detectable by radiography and to prove conformity with prior ultrasonic manual examination undertaken during construction.

This company also showed its ultrasonic couplants, the range including gels which are non-flammable at higher temperatures. Also available is another instrument for automated remote ultrasonic corrosion mapping.

Dakota Ultrasonics produces a series of precision thickness gauges to meet specific applications. The PX range measures from 0.006 to 1.00 inch (0.15 to 25.4 mm) with a resolution of 0.0001 inch (0.001 mm). Four readings per second for single point measurement or eight per second for Scan Mode will capture the minimum thickness. In the Echo-to-Echo Mode there is the ability to measure the thickness of materials without removing the paint ore covering. Another series, the MX range, measures from 0.025 inch and enables four readings per seconds to be taken for single point readings and 16 per second for Scan Mode.

The MMX series has been developed that possesses the durability of the MX range and adds the ability to measure through paint or coatings. It features a multi-mode control between pit and flaw detection (Pulse Echo Mode) and through paint and coatings (Echo-Echo Mode) through a press button. The display is multi-function 4.5 digit LCD with 0.5 inch numerals, and can be backlit for use in poor lighting conditions. Measurements are displayed in inches, inches/ microsecond, millimetres and metres/second.

Laser-based composites inspection

Information and demonstrations were featured by Laser Technology (UK) and a range of equipment was shown. The LTI-500 Digital Shearography System is a modular, all-mode system that has complete remote control of camera pan, tilt, focus, iris zoom and shear vector as well as laser beam steer and zoom. It consists of the SC-5100 Digital Shearography camera with built-in or external laser, remote control console, and the IP-5100 Image Processing Computer, as s interconnecting cables and various optional equipment. It enables real-time imaging of disbands, delaminations and impact damage in composites many times faster than ultrasonic C-scan.

Laser shearography provides a method that investigates the integrity of a composite structure with regard to its reaction to an applied stress. In this technique the equipment monitors the surface for any change to the surface strain field. When stressed in the appropriate method, the subsurface anomalies are shown on the surface of the structure. It is of particular use for the inspection of composite repairs, once the extent of a disbond has been determined and an effective repair designed.

Examination by the laser shearography technique is based on the comparison of two stress states in the structure. One method with the LTI-5100 is to introduce thermal energy to the surface by the application of hot air. A set of infrared lamps can be used to generate a similar response in the structure. The two stages of stressing captured by the camera can be immediately after the application of heat and a short while later when the thermal energy has been conducted into the structure and affected the material deep within it. In the foreground are the remote controls for the camera and laser. The image processor computer is portable and use of the system enables the operator to control all the parameters of the system from one point. Often after initial inspection, it is necessary to ascertain effectiveness with a more comprehensive examination. Inspection of a repair and post analysis of the data obtained can reveal profile information in the form of a horizontal or vertical slice. The sampling line can indicate whether the repair matches the original material in strength with little or no variation across its extent.

Another method of stressing for composite inspection uses localised vacuum stressing, as with this company's LTI 4200 system. Here, by reducing the ambient air pressure, either at the localised surface or surrounding the complete structure, the generated stresses within the structure act to highlight weaknesses. Thus, the out-of-plane stress directly plays upon the weakest vector of the material under examination. Disbonds and delaminations show themselves as changes in the strain map of the surface. A uniform, well- bonded structure will produce a uniform strain map under uniform stressing. A weakness will be evident as a strain concentration which will present a typically distinctive double bulls-eye fringe set.

Flaw detectors

Among the many instruments shown by GE Panametrics NDT was the Epoch III which is lightweight and easy to operate even in the most cramped conditions, since its hangs free from a chest harness. The LCD display has optimum viewing of the waveform trace in a wide variety of light conditions, with electroluminescence providing a fast update rate. The Epoch III B-Scan is claimed to be the first affordable encoded instrument of this kind and redefines ultrasonic corrosion inspection by mapping cross-sectional images of thickness measurements with full encoder compatibility. It has multiple scanning modes with software support for scanning speeds of up to 6 inch/s. An automatic audible alarm sounds if the scan speed exceeds the limit.

Epoch III has unequalled documentation possibilities allowing the user to view and track all setups. The alphanumeric datalogger stores and retrieves up to 130 A-scans with calibration setups or 3,000 thickness readings. An expandable memory (23MDB) allows storage of up to 260 A-scans with calibration setups, 6,000 thickness readings, or 200 B-scans with locations. There is a customised report template option which allows inspectors to use templates for consistent and time-saving reports. These are created in the Interface Program and down loaded to the Epoch III. Instructional memos are automatically recalled on the Epoch III display to inform the inspector of special test conditions at predetermined locations in the database. A successor, Epoch 4B recently introduced, offers many more measurement features and software options than its predecessor including greater memory capacity and thickness measurements taken from raw data and resolution not tied to screen range. The Epoch 4B can be customised with a variety of software options.

Digital radiography

Computerised Information Technology produces an extensive range of NDE Digital Information Storage Solutions including film radiograph digitisation, flexible re-useable film digital radiographic and film-less flat panel X-ray sensor radiographic systems. The company also enables digital data archiving to be undertaken as well as visual imaging data and has a digital copy/print service.

A typical system is the CIT/DR 1000 Med Compact Digital Radiography FPS which replaces conventional film radiography with flexible re-useable digital imaging plates, digital storage of images and retrieval of digital radiography images. The system provides a fast set-up which generates results within minutes and eliminates any chemicals, films and film wrappers and storage requirements. It uses an existing radiographic set-up but with reduced radiation strength value and reduced exposure time to generate the digital radiography image.

Other products feature a range of portable digital radiography systems that include the CIT/DR 4500 which enables inspection using 100 micron resolution amorphous silicon flat plate detector technology. The radiographic images of products under inspection are displayed within 6s capture cycle. This is to enable them to interpret radiographs, generate reports and plan the production, construction and maintenance scheduling workflow. The immediate benefits can be applied to condition monitoring, corrosion assessment and material loss.

Details available from:X-Tek Industrial Ltd. Tel: +44 (0)1493 600677; Fax: +44 (0)1493 6093347.Sonatest PLC. Tel: +44 (0)1908 316345; Fax: +44 (0)1908 321323.Dakota Ultrasonics. Tel: +1 831 465 8585; Fax: +1 931 465 8558.Laser Technology (UK). Tel/Fax: +44 (0)1780 722135.GE Panametrics NDT Ltd. Tel: +444 (0)1709 836115; Fax +44 (0)1709 835177.Computerised Information Technology Ltd. Tel: +44 (0)1908 260082; Fax: 01908 260084.