- Comparing Infrared Thermography and ESPI for NDE of Aircraft Composites
- Benchmarking Shearographic NDT for Composites
- Impact damage detection on composites using optical NDT techniques
Infrared Thermography is gaining acceptance by industry as a suitable non destructive testing and evaluation (NDT/E) technique. Likewise Electronic Speckle Pattern Interferometry (ESPI) has also been shown to be suited for similar purposes, particularly for the inspection of composite materials.
This paper presents the theory of the two inspection methods. Selected composite samples containing defects are subjected to identical inspection procedures using both techniques. The results are presented and compared with each other. From the results it is clear that both techniques are suited for the detection of the defects in the composite sample. The results also indicate that ESPI is a more sensitive inspection technique than IRT. Comparisons are drawn and the benefits of each technique discussed.
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This paper reviews Digital Shearography in its current state of development. The technique was originally proposed as a strain measurement method but has more recently found an equally important role in the field of non destructive testing. Digital Shearography, as is currently practiced in research laboratories and in industry, reveals defects beneath the surface of an object by identifying anomalies in the field of surface displacement gradients.
Shearography as a non destructive testing tool has found innumerable applications involving a wide range of materials and in particular has had notable success in identifying debonds and delaminations in composite material structures. In the face of distinct advantages over other NDT methods, such as full field view, non-contacting and real time evaluation, and proven in a vast number of applications in the laboratory/field/factory environment, surprisingly it does not yet have a standard, like for example an ISO International Standard.
The objective of this paper is a call for the standardization of Digital Shearography based on the involvement of interested parties calling for the start of the process, perhaps as is suggested here, by the technical committee TC 135 of the ISO.
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The paper presents the work that was carried out in the detection and, beyond of what is obviously visible to the naked eye, the extent of impact damage inflicted on composite panels designed and manufactured for structural applications in the aerospace industry. Using a drop-weight impact tester the composite specimens were subjected to controlled impact conditions i.e. relatively low velocity impact levels analogous to those expected from the drop of a heavy tool, collision with a bird etc.
The composite specimens consisted of Monex core sandwiched between thin carbon/glass fibre reinforced plastic skins, typically identical to those used in the fabrication of unmanned air vehicles and helicopter rotor blades. The investigation attempted to establish the probability of detecting such barely visible impact damage with optical non-destructive testing methods such as Digital Shearography, Electronic Speckle Pattern Interferometry and Infrared Thermography.
These NDT techniques were chosen to be employed in this study, because they are non-contacting, whole field, not limited to particular material types, provide fast and easy results in real-time and have been proven reliable in a large number of applications in the laboratory/factory/field environment.
Complete Paper ((1329kB)