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2008 Contents


USING DIGITAL SHEAROGRAPHY TO VISUALIZE AND QUANTIFY DEFECTS IN COMPOSITE AEROSPACE COMPONENTS (2008)

ABSTRACT

A fairly rapid evolution in design and assembly processes is taking place in the Aerospace industry where materials of composite nature are increasingly being utilized due to the benefits of reduced weight, the ease of formability and good mechanical properties that they offer. Closely tied to these above mentioned properties is the possible accumulation of flaws and defects which will adversely impact on the life of the composite. Digital Shearography reveals defects beneath the surface of an object by identifying anomalies in the field of surface displacement gradients.

The authors focus on an example of the protocol followed using Digital Shearography to identify and quantify man made defects on composite material sourced from a helicopter main rotor blade. The NDT problem of dealing with structures made from composite material is unlikely to yield a closed form solution. The experimental work and the results obtained as presented in this paper can however be used as a basis for designing a testing procedure (turn key solution) for a particular composite material component or structure.

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EVALUATING LOW COST PORTABLE SHEAROGRAPHY ON AIRCRAFT COMPONENTS (2008)

ABSTRACT

Non destructive testing is an important application in the production of safety critical components and the maintenance thereof. Digital Shearography is an emerging NDT technique, particularly suited for the detection of defects within composite structures as found for example in the aircraft and aerospace industries. This paper presents the initial results of a project aimed at developing a low cost portable NDT prototype based on the principles of digital Shearography. As part of the cost saving measures the system is designed to operate off a laptop using a FireWire interface.

The final system is used to inspect a helicopter rotor blade section and a UAV wing section for man made defects. The results are presented and discussed and clearly indicate that the prototype detects all the defects and is able to present the results in various forms including a 3D displacement gradient map. The paper is concluded with an analysis of the performance of the prototype.

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NDT DETECTION AND QUANTIFICATION OF INDUCED DEFECTS ON COMPOSITE HELICOPTER ROTOR BLADE AND UAV WING SECTIONS (2008)

ABSTRACT

Digital Shearography and Infrared Thermography (IRT) techniques were employed to test non-destructively samples from aircraft structures of composite material nature. Background information on the techniques is presented and it is noted that much of the inspection work reviewed in the literature has focused on qualitative evaluation of the defects rather than quantitative. There is however, need to quantify the defects if the threshold rejection criterion of whether the component inspected is fit for service has to be established. In this paper an attempt to quantify induced defects on a helicopter main rotor blade and Unmanned Aerospace Vehicle (UAV) composite material is presented.

The fringe patterns exhibited by Digital Shearography were used to quantify the defects by relating the number of fringes created to the depth of the defect or flaw. Qualitative evaluation of defects with IRT was achieved through a hot spot temperature indication above the flaw on the surface of the material. The results of the work indicate that the Shearographic technique proved to be more sensitive than the IRT technique. It should be mentioned that there is "no set standard procedure" tailored for testing of composites.

Each composite material tested is more likely to respond differently to defect detection and this depends generally on the component geometry and a suitable selection of the loading system to suit a particular test. The experimental procedure that is reported in this paper can be used as a basis for designing a testing or calibration procedure for defects detection on any particular composite material component or structure.

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ESPI OF AEROSPACE COMPOSITES USING DIGITAL SHEAROGRAPHY (2008)

ABSTRACT

It is demonstrated that a portable digital shearography system is capable of obtaining measurements, in addition to the gradients' field of normal surface displacements, the actual field of normal to the surface displacements, commonly identified as displacement interferograms obtained usually through digital holographic set-ups, labeled ESPI (Electronic Speckle Pattern Interferometry).

This has been accomplished as reported here, by increasing excessively the shear or the distance separating the two images in a shearography system, which employs the modified Michelson interferometer as the shearing device, and allowing a portion of a "reference" surface to reflect on the beam splitter of the digital shearography's head. The technique is demonstrated by the results obtained when testing manufactured defects on composite specimens from an Oryx helicopter main rotor blade.

Complete Paper ((296kB)