Michael K. Kalms

Laser-based systems for the structural diagnostic of artwork: an application to XVII-century Byzantine icons

Laser diagnostic systems based on shearography, vibrometry, and holography principles were employed to investigate the potential implementation of laser techniques in art conservation structural diagnostic field. The employed techniques offered the required measuring variability to allow a first discrimination on complex diagnostic uncertainties encountered often in art conservation. The systems were tested and used to assess the structural condition of well-documented Byzantine icons with known structural problems. Defects and mechanical deformations were identified in various distances from the artworks by alternative employment of techniques. In this way simultaneous eligibility classification of the used systems was also obtained. Results of the on-field application on the XVII century Byzantine icons are herein presented with discussion on the prospects of the techniques in the diagnostic field of art conservation.

Shearography system for the testing of large-scale aircraft components taking into account noncooperative surfaces

ABSTRACT Shearography is an approved and powerfiu! tool for the nondestructive inspection of industrial components with respect tomaterial faults and technical imperfections. An application field of high interest is the in-service inspection of aircraftcomponents. However, the non-cooperative character of the surface of various aircraft components to be inspected has tobe taken into account carefully. This paper describes a complete test facility consisting of a shearographic sensor, adaptedloading equipment for thermal and mechanical stressing and a new evaluation software ensuring a high sensitivity forfault detection. Furtheron a survey ofthe performance ofthe system is given on example of different aircraft componentsthat shows the advantages of shearography in comparison with other inspection techniques, such as ultrasonics andthermography. Keywords: shearography, system lay-out, non-destructive testing, non-cooperative surfaces, loading devices, fault recognition 1. INfRODUCTION

NDT on wide scale aircraft structures with digital speckle shearography

Carbon fiber technology and other lightweight constructions are used more and more for airplane parts. Modern airliners are already equipped with such components as e.g. in the vertical and horizontal stabilizer, rudder, airbrakes and spoiler. The application of the new materials is accompanied by new requirements for an optimal dimensioning. In this case, the investigation with respect to material and construction imperfections is of high interest. In order to receive a high safety of operation possible damages must be recognized prematurely within control examinations to prevent the total breakdown of the device. For this reason, adapted examination designs and especially developed testing methods are necessary. An appropriate testing method must meet the following requirements: (1) nondestructive evaluation, (2) inspection of large aircraft structures, (3) working with non- cooperative surfaces, (4) non-ambiguous flaw interpretation, (5) flexible and simple in operation. A testing method which can manage such examination designs is the shearography. It is a robust interferometric technique to determine locations with maximum stress on various material structures under an appropriate load. The procedure is also suitable for inspection where only one side of the aircraft-structure to be tested is accessible. This paper describes a complete procedure including loading and image processing facilities for structural testing and flaw recognition on non-cooperative aircraft surfaces.

Laser ultrasound: a flexible tool for the inspection of complex CFK components and welded seams

Modern production processes use more and more components made of new materials like carbon fiber reinforced plastics (CFRP). These components have different sizes, functionalities, high assembly complexity and high security requirements. In addition optimized joining processes, especially during welding are implemented in manufacturing processes. The increasing requirements during the manufacturing of complex products like cars and aircrafts demand new solutions for the quality assurance. The main focus is to find a measurement strategy that is cost effective, flexible and adaptive. The extension of the conventional ultrasound technique for non destructive testing with the laser ultrasound method brings new possibilities into the production processes for example for the inspection of small complex CFRP-parts like clips and the online observation during seam welding. In this paper we describe the principle of laser ultrasound, especially the adaptation of a laser ultrasound system to the requirements of non destructive testing of CFRP-components. An important point is the generation of the ultrasound wave in the surface of the component under investigation. We will show experimental results of different components with complex shape and different defects under the surface. In addition we will present our results for the detection of defects in metals. Because the online inspection of welded seams is of high interest experiments for the investigation of welded seams are demonstrated.

Applications of laser ultrasound NDT methods on composite structures in aerospace industry

Composite materials are used more and more in aircraft production. Main composite types are Carbon Fiber Reinforced Plastics (CFRP), Glass Fiber Reinforced Plastics (GFRP) and metal-aluminium laminates (e. g. Glass Fiber Aluminium Reinforced GLARE©). Typical parts made of CFRP material are flaps, vertical and horizontal tail planes, center wing boxes, rear pressure bulkheads, ribs and stringers. These composite parts require adequate nondestructive testing (NDT) methods. Flaws to be detected are delaminations and debondings, porosity and foreign body inclusion. Manual ultrasonic testing with single element transducers is still the most applied method for composite parts with small and medium size. The extension of the conventional ultrasound technique for nondestructive testing with the laser ultrasound method brings new possibilities into the production processes for example the inspection of complex CFRP-components and the possibilities of online observation under remote control. In this paper we describe the principle of laser ultrasound with respect to the demands of nondestructive testing especially of small complex CFRP and C/PPS parts. We report applications of laser-based ultrasound options with generated types of guided and bulk waves on modern aircraft materials.

Advanced shearographic system for nondestructive testing of industrial and artwork components

Modern optical methods such as speckle shearography have attracted interest not only for laboratory investigations but also for applications on the factory floor because they can be sensitive, accurate, non-tactile and non-destructive. Optical inspection and measurement systems are more and more used in the entire manufacturing process. In this paper a complete measurement system on the basis of digital speckle-shearography is described. It consists of a shearographic sensor, an adapted loading equipment for thermal and mechanical stressing and a new evaluation software ensuring a high sensitivity for fault detection. To improve the performance of the shearographic technique with respect to industrial environments new components and procedures were implemented and tested recently. To them belong a CMOS-camera to increase the dynamic range of the image sensor. The system was successfully tested for the inspection of aircraft components and artworks with respect to material faults and production defects.

Progress with the implementation of a shearography system for the testing of technical components

Shearography is an approved and powerful tool for the non-destructive inspection of industrial components with respect to material faults and technical imperfections. An application field of high interest is the in-service inspection of aircraft and automotive components. However, the non-cooperative character of the surface of various technical components has to be taken into account carefully. This paper describes a complete test facility consisting of a shearographic sensor, adapted loading equipment for thermal and mechanical stressing and a new evaluation software ensuring a high sensitivity for fault detection. To increase the performance of the system with respect to industrial applications new components and procedures were implemented and tested recently. To them belong a CMOS-camera to increase the dynamic range of the image sensor, a multiband light source to test the coherence requirements of a shearography system and tunable thermal loading equipment to improve the identification of material faults within components having a bigger wall thickness.

Improved shearography for use on optical non cooperating surfaces under daylight conditions

Recent developments will be presented that make the Phase Stepping Shearography Method fit for use in aircraft maintenance conditions. Outgoing from current commercially available systems we introduced a program to improve the capability of the shearography testing method to deal with metallic (highly reflective) surfaces, completely black parts (e.g. CFRP) as well as with surfaces where surface conditions vary in the inspection area. Another demand was the inspections must be carried out under daylight (with no cover) and in rough maintenance conditions (hangar, working on mobile platforms…) but the non contact character of the method should not be influenced. Several approaches have been investigated; from laser illumination to receiving optics, sensor and fringe processing software nearly nothing was left unchanged. The resulting system is highly portable, fast in use (nearly real-time) and produces clear and easy to read documents. The operating software is portable between almost all usual software p...

Active industrial surface inspection with the inverse projected-fringe technique

A technique is introduced for the industrial surface inspection of workpieces in production lines. This procedure is based on an active technology in optical shape measurement, the so called inverse projected-fringe-technique. After a precise reconstruction of the object shape with respect to the known weak points in the projected fringe technique, a new fringe pattern can be computed and projected using a free-programmable fringe modulator. The objective is to compensate the shape dependent distortions of the fringes. Such an inverse projection can be used for the comparison between a sample and its master piece in quality control. Having a test object that completely fits in shape with the master piece the inverse projection delivers an equidistant and non-distorted fringe pattern under the same observation direction. However, every faulty object area of the sample causes distortions relatively to this known model and can be consequently detected very fast by means of suitable correlation techniques. Especially the simplicity of the master pattern (straight and uniform fringes) offers the possibility of very simple optical filters and the rapid evaluation using an OASLM with an optical correlator (analog) or by applying the spatial heterodyne-technique (digital).

Integrated quality assurance for assembly and testing of complex structures

Modern production processes are directed by properties of the components to be manufactured. These components have different sizes, functionalities, high assembly complexity and high security requirements. The increasing requirements during the manufacturing of complex products like cars and aircrafts demand new solutions for the quality assurance - especially for the production at different places. The main focus is to find a measurement strategy that is cost effective, flexible and adaptive. That means a clear definition of the measurement problem, the measurement with adapted resolution, the data preparation and evaluation and support during measurement and utilisation of the results directly in the production. In this paper we describe flexible measurement devices on example of three different techniques: fringe projection, fringe reflection and shearography. These techniques allow the detection of surface and subsurface defects like bumps, dents and delaminations with high resolution. The defects can be optically mapped onto the objects surface. Results are demonstrated with big components taken from automotive and aircraft production. We will point out the most important adaptations of the systems to realize miniaturized, robust and mobile devices for the quality assurance in an industrial environment. Additionally the implementation into a Mobile Maintenance and Control structure is demonstrated.