A review of miniaturised Non-Destructive Testing technologies for in-situ inspections

Non-destructive testing (NDT) techniques have become attractive trends of product manufacturing, installation and post-maintenance in the aerospace, automotive and manufacturing industry, because of its benefits such as cost saving, easy to use and high efficiency etc. With the industrial products becoming large-scale, high integration and complication, developing the NDT miniaturisation technique for in-situ inspections is highly demanded and becoming an inevitable trend. However, in-situ inspection using NDT have been limited by a number of factors, such as the heavy weight, large size or complex structure etc. This paper aims to systematically identify and analyse the current state-of-the-art of NDT miniaturisation techniques in research and innovation, and discuss the challenge and prospect of miniaturisation of the commonly used NDT techniques

A match coefficient approach for damage imaging in structural components by ultrasonic synthetic aperture focus

Ultrasonic Synthetic Aperture Focus (SAF) techniques are commonly used to image structural defects. In this paper, a variation of SAF based on ideas borrowed from Matched Field Processing (MFP) is evaluated to reduce artifacts and sidelobes of the resulting images. In particular, instead of considering the full RF ultrasonic waveforms for the SAF time backpropagation, only selected features from the waveforms are utilized to form a “data vector” and a “replica” (expected) vector of MFP. These vectors are adaptive for the pair of transmitter-receiver and the focus point. The image is created as a matched filter between these two vectors. Experimental results are shown for an isotropic and homogenous metallic plate with simulated defects, probed by six piezoelectric patches used as receivers or transmitters

Multiple wavemode scanning for near and far-side defect characterisation

The combination of ultrasonic inspections using different wavemodes can give more information than is available with single mode inspection. In this work, the response of shear and Rayleigh waves to surface-breaking defects propagating on the near-side and far-side of a sample is investigated. The directivity of shear waves generated by a racetrack coil electromagnetic acoustic transducer (EMAT) is identified and used to set an ideal separation for a pair of transmit-receive EMATs. Defects are indicated by a reduction in the transmitted Rayleigh wave amplitude, and by blocking of the shear wave. Used together, these can identify features in the bulk wave behaviour which are due to near-face surface-breaking defects, and give a full picture of both surfaces. By using a combination of the two wavemodes, the angle of propagation and length of any near-side defects can additionally be identified. A scanning method for samples is proposed

Non-Destructive Inspection of Impact Damage in Composite Aircraft Panels by Ultrasonic Guided Waves and Statistical Processing.

This paper discusses a non-destructive evaluation (NDE) technique for the detection of damage in composite aircraft structures following high energy wide area blunt impact (HEWABI) from ground service equipment (GSE), such as heavy cargo loaders and other heavy equipment. The test structures typically include skin, co-cured stringers, and C-frames that are bolt-connected onto the skin with shear ties. The inspection exploits the waveguide geometry of these structures by utilizing ultrasonic guided waves and a line scan approach. Both a contact prototype and a non-contact prototype were developed and tested on realistic test panels subjected to impact in the laboratory. The results are presented in terms of receiver operating characteristic curves that show excellent probability of detection with low false alarm rates for defects located in the panel skin and stringers

Deciphering acoustic emission signals in drought stressed branches: the missing link between source and sensor

When drought occurs in plants, acoustic emission (AE) signals can be detected, but the actual causes of these signals are still unknown. By analyzing the waveforms of the measured signals, it should, however, be possible to trace the characteristics of the AE source and get information about the underlying physiological processes. A problem encountered during this analysis is that the waveform changes significantly from source to sensor and lack of knowledge on wave propagation impedes research progress made in this field. We used finite element modeling and the well-known pencil lead break source to investigate wave propagation in a branch. A cylindrical rod of polyvinyl chloride was first used to identify the theoretical propagation modes. Two wave propagation modes could be distinguished and we used the finite element model to interpret their behavior in terms of source position for both the PVC rod and a wooden rod. Both wave propagation modes were also identified in drying-induced signals from woody branches, and we used the obtained insights to provide recommendations for further AE research in plant science

Ultrasonic Transducer And Method For Using Same

An improved ultrasonic transducer fabricated on a silicon base has a piezoelectric layer of polyvinylidene fluoride-trfluroethylene copolymer. The piezoelectric layer is sandwiched between two conductive electrodes, all of which are supported on a dielectric layer on top of the silicon base. At least one of the electrodes forms a Fresnel zone plate to focus the ultrasonic signals from the transducers. To improve the performance of the transducer, the silicon base behind the active area is removed, leaving the dielectric layer as a membrane to support the electrodes and the piezoelectric layer. The resulting void in the silicon base is filled with an acoustically matched backing, such as an epoxy, to enhance the wideband performance of the transducer. The transducer is especially suited for characterizing anatomical structures or features requiring very high resolution.Georgia Tech Research Corp.Medical College Of Georgia Research Institut

Nanomechanical morphology of amorphous, transition, and crystalline domains in phase change memory thin films

In the search for phase change materials (PCM) that may rival traditional random access memory, a complete understanding of the amorphous to crystalline phase transition is required. For the well-known Ge2Sb2Te5 (GST) and GeTe (GT) chalcogenides, which display nucleation and growth dominated crystallization kinetics, respectively, this work explores the nanomechanical morphology of amorphous and crystalline phases in 50 nm thin films. Subjecting these PCM specimens to a lateral thermal gradient spanning the crystallization temperature allows for a detailed morphological investigation. Surface and depth-dependent analyses of the resulting amorphous, transition and crystalline regions are achieved with shallow angle cross-sections, uniquely implemented with beam exit Ar ion polishing. To resolve the distinct phases, ultrasonic force microscopy (UFM) with simultaneous topography is implemented revealing a relative stiffness contrast between the amorphous and crystalline phases of 14% for the free film surface and 20% for the cross-sectioned surface. Nucleation is observed to occur preferentially at the PCM-substrate and free film interface for both GST and GT, while fine subsurface structures are found to be sputtering direction dependent. Combining surface and cross-section nanomechanical mapping in this manner allows 3D analysis of microstructure and defects with nanoscale lateral and depth resolution, applicable to a wide range of materials characterization studies where the detection of subtle variations in elastic modulus or stiffness are required

Instantaneous baseline damage localisation using sensor mapping

In this paper an instantaneously recorded baseline method is proposed using piezoelectric transducers for damage localisation under varying temperature. This method eliminates need for baselines required when operating at different temper- atures by mapping a baseline area onto the interrogation area. Instantaneously recorded baselines and current interrogation signals are calibrated based on the sensor mapping. This allows extraction of damage scatter signal which is used to localise damage. The proposed method is used to localise actual impact damage on a composite plate under varying temperatures. The method is also applied to a stiffened fuselage panel to accurately localise impact damage

Knowledge-based support in Non-Destructive Testing for health monitoring of aircraft structures

Maintenance manuals include general methods and procedures for industrial maintenance and they contain information about principles of maintenance methods. Particularly, Non-Destructive Testing (NDT) methods are important for the detection of aeronautical defects and they can be used for various kinds of material and in different environments. Conventional non-destructive evaluation inspections are done at periodic maintenance checks. Usually, the list of tools used in a maintenance program is simply located in the introduction of manuals, without any precision as regards to their characteristics, except for a short description of the manufacturer and tasks in which they are employed. Improving the identification concepts of the maintenance tools is needed to manage the set of equipments and establish a system of equivalence: it is necessary to have a consistent maintenance conceptualization, flexible enough to fit all current equipment, but also all those likely to be added/used in the future. Our contribution is related to the formal specification of the system of functional equivalences that can facilitate the maintenance activities with means to determine whether a tool can be substituted for another by observing their key parameters in the identified characteristics. Reasoning mechanisms of conceptual graphs constitute the baseline elements to measure the fit or unfit between an equipment model and a maintenance activity model. Graph operations are used for processing answers to a query and this graph-based approach to the search method is in-line with the logical view of information retrieval. The methodology described supports knowledge formalization and capitalization of experienced NDT practitioners. As a result, it enables the selection of a NDT technique and outlines its capabilities with acceptable alternatives