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2004 Contents


A COMPARISON OF THE CAPABILITIES OF PORTABLE SHEAROGRAPHY AND PORTABLE ELECTRONIC SPECKLE PATTERN INTERFEROMETRY (2004)

ABSTRACT

Optical interference techniques such as electronic speckle pattern interferometry (ESPI) and Digital Shearography have been shown to be of great value for the Non-destructive Evaluation of composite materials. The recent signing of a contract to purchase numerous Airbus aircraft for commercial use in South Africa as well as the purchase of the Grippen military aircraft has resulted in the capabilities of optical interference techniques for NDE purposes receiving increased attention.

The NDT Laboratory in the Department of Mechanical Engineering at the University of Cape Town has for a number of years been involved with the research, development, and applications of the optical NDE techniques of ESPI and Digital Shearography. This has led to the development of a portable inspection unit, based on Digital Shearography and the latest addition of a portable ESPI prototype.

In order to compare the capabilities of the developed prototypes, industry acceptable test specimens of composite aircraft components are subjected to tests using both systems. The results are presented and comparisons are drawn highlighting the advantages and disadvantages of these two optical NDE techniques.

Complete Paper (1301kB)


PLANT INSPECTION USING PORTABLE SHEAROGRAPHY AND ELECTRONIC SPECKLE PATTERN INTERFEROMETRY (2004)

ABSTRACT

Non-destructive Testing and Evaluation techniques are valuable tools used to determine the integrity of manufactured materials and components, either before commissioning or during regular maintenance inspection intervals. Optical interference techniques such as electronic speckle pattern interferometry (ESPI) and Digital Shearography are two such techniques, which have been shown to be of great value for the Non-destructive Evaluation of a range of materials, including ferrous and non-ferrous metals and composites..

For the last 20 years, the NDT Laboratory in the Department of Mechanical Engineering at the University of Cape Town has been involved with the research, development, and applications of the optical NDE techniques. Originally all applications were based on the use of Holographic Interferometry. However, with the introduction of computer based image processors, the focus shifted from the film based holographic techniques to the digital equivalents, namely ESPI and Digital Shearography. Until recently, all research was conducted under laboratory conditions on a purpose make vibration isolation table. However, with the award of an Armscor research contract, all emphasis was focused on developing portable equivalents of the laboratory based NDE techniques. This has led to the development of two portable inspection prototypes, the first based on Digital Shearography and the second based on ESPI.

This paper reports on the development of the two prototypes. The units and their respective underlying optical interference techniques are described in detail. Selected samples with man-made defects are then subjected to inspections using both systems. The results are presented and comparisons are drawn highlighting the advantages and disadvantages of these two optical NDE techniques.

Complete Paper ((1378kB) 1186


PORTABLE SHEAROGRAPHY AND PORTABLE ELECTRONIC SPECKLE PATTERN INTERFEROMETRY: A PRESENTATION OF THEIR CAPABILITIES (2005)

ABSTRACT

Optical interference techniques such as electronic speckle pattern interferometry (ESPI) and Digital Shearography have been shown to be of great value for the Non-destructive Evaluation of many new age materials. The use of composites in motor vehicles, sea craft and aircrafts including the possible use of ‘Glare’ in the new A380 Airbus has resulted in the capabilities of optical interference techniques for NDE purposes receiving increased attention.

The NDT Laboratory in the Department of Mechanical Engineering at the University of Cape Town has for a number of years now been involved with the research, development, and applications of optical NDE techniques such as Holographic interferometry, ESPI and Digital Shearography. This first led to the development of a portable inspection unit based on Digital Shearography and recently a portable prototype based on the principles of ESPI.

This paper reports on the development of the portable ESPI unit and compares the performance of this unit with that of the portable shearography unit. This is accomplished through the inspection of selected acceptable test specimens of composite aircraft components using both systems. The results are presented and comparisons are drawn highlighting the advantages and disadvantages of these two optical NDE techniques.

Complete Paper ((1723kB)


RESIDUAL STRESS DETERMINATION AND DEFECT DETECTION USING ELECTRONIC SPECKLE PATTERN INTERFEROMETRY (2004)

ABSTRACT

The paper deals with the methodology of determining residual stresses using Electronic Speckle Pattern Interferometry (ESPI). ESPI can be used as a truly non-destructive testing technique in that it is a laser based, optical, full field, non contacting method which reveals surface displacements to an accuracy of approximately 300 nanometres when a Helium Neon laser is used. In a simple experiment, a fixed-ends rectangular aluminium plate was subjected to uniform loading and the out of plane surface displacement field was obtained through ESPI.

Subsequently a comparison of these measurements was made with measurements obtained after the plate was subjected to shot peening. The above method aimed to identify the extent of residual stresses that were imposed on the rectangular plate after the shot peening process which is known to induce such stress.

Bearing in mind that ESPI produces a full field surface displacement map through a characteristic interference fringe pattern, any anomaly displayed on the fringe pattern could be interpreted as a flaw or defect on or beneath the surface under observation. The authors have included in this paper typical examples where the ESPI applied in a prototype device constructed by the authors, has identified defects in various engineering components made from a variety of materials.

Complete Paper ((659kB)


NEUTRON RADIOGRAPHY AND OTHER NDE TESTS OF MAIN ROTOR HELICOPTER BLADES (2004)

ABSTRACT

A few nondestructive examination (NDE) techniques are extensively being used worldwide to investigate aircraft structures for all types of defects. The detection of corrosion and delaminations, which are believed to be the major initiators of defects leading to aircraft structural failures, are addressed by various NDE techniques. In a combined investigation by means of visual inspection, X-ray radiography and shearography on helicopter main rotor blades, neutron radiography (NRad) at SAFARI-1 research reactor operated by Necsa, was performed to introduce this form of NDE testing to the South African aviation industry to be evaluated for applicability. The results of the shearography, visual inspection and NRad techniques are compared in this paper. The main features and advantages of neutron radiography, within the framework of these investigations, will be highlighted.

Complete Paper ((650kB)