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Brescia, Italy

Uus A.,City University London | Liatsis P.,City University London | Nardoni G.,I and T Nardoni Institute | Rahman E.,City University London
2015 22nd International Conference on Systems, Signals and Image Processing - Proceedings of IWSSIP 2015 | Year: 2015

Air-coupled ultrasound (ACU) is the novel emerging technique in non-destructive testing that allows removal of the coupling requirement, which significantly increases inspection speed. However, specifics of ACU caused by high impedance mismatch between air/solid interfaces set a number of limitations one of them being a requirement of two transducers in pitch-catch mode instead of a traditional single transducer in echo-mode. The goal of this paper is optimization of an ACU system geometry configuration in a specific task of single-side inspection of concrete/asphalt road pavements on the presence of subsurface delaminations. The findings provide the baseline for specification the general system setup guidelines for ACU system development under FP7 RPB HealTec project. 3D finite element modelling (FEM) is used for investigation of the impact of transducer positioning on the system's efficiency in detection of subsurface delaminations of varying depth and type. The simulation results indicated strong impact of transducer positioning on the measured response from test slabs with and without delaminations together with the significant impact of even small surface defects. Consequently, it was concluded that while ACU is sufficiently effective detection of various types of delaminations, it is highly sensitive to the surface condition and system setup. © 2015 IEEE.

Nardoni G.,I and T Nardoni Institute | Certo M.,I and T Nardoni Institute | Nardoni P.,I and T Nardoni Institute | Feroldi M.,I and T Nardoni Institute | And 4 more authors.
Insight: Non-Destructive Testing and Condition Monitoring | Year: 2012

The method described is able to produce a precise criteria by which defects can be classified as planar, volumetric or mixed (partially planar with rounded tips, although with some uncertainty depending on probe type and defect depth). Consequently, it could be of great interest to verify, by means of fracture mechanics criteria, if the transition value posed by the method is also coherent with the corresponding evaluations by fracture mechanics. This would show whether, for the defects classified as volumetric or planar by the method, the component condition can be evaluated using the relevant criteria for the respective type of defect.

Nardoni G.,I and T Nardoni Institute | Certo M.,I and T Nardoni Institute | Nardoni P.,I and T Nardoni Institute | Feroldi M.,I and T Nardoni Institute | And 4 more authors.
Materials Evaluation | Year: 2011

The paper deals with the detection and sizing of small transversal cracks in hydrocracking units. The minimum sensitivity code requirements for the tests were based on 4 × 4 × 0.3 mm planar discontinuities. This level of sensitivity was significantly higher than the normal requirements for sidedrilled holes from ASME Code Case 2235-9: Use of Ultrasonic Examination in Lieu of Radiography, Section V, Article 4; the difference was at least 12 to 18 dB (ASME, 2005). Special test blocks were prepared with electric discharge machining slits embedded in the weld thickness at different depths. Time of flight diffraction and phased array testing procedures were validated on these blocks. Height sizing was important in the testing as required by ASME Code Case 2235-9 (ASME, 2005). Both techniques optimized on the test blocks were able to detect and size small transversal cracks. Diffracted echoes were essential for sizing the height of cracks using the phased array technique.

Certo M.,I and T Nardoni Institute | Nardoni G.,I and T Nardoni Institute | Nardoni P.,I and T Nardoni Institute | Feroldi M.,I and T Nardoni Institute | Nardoni D.,I and T Nardoni Institute
Insight: Non-Destructive Testing and Condition Monitoring | Year: 2010

The application of phased array to the ultrasonic testing of components such as forged or plate products, with the longitudinal wave arranged in a sectorial scan centred at zero degrees, can be very attractive because of the possibility, due to the electronic sectorial scan of the ultrasonic beam, of producing a complete and documented volume inspection with a fewer number of scan lines than with using a standard probe. The problem is that, in this inspection technique, defect estimation is carried out, normally, by the use of a Distance Gain Size (DGS†) set of curves[1,4,5]. Such curves are easily available for standard probes of circular shape, but not for phased array probes whose active area is a function of the number of active elements chosen and which can be strongly rectangular. In order to avoid such difficulty, we have developed a computer model that is capable of generating the DGS curves from an input of the actual phased array parameters. This computer model has been assessed using some calibration blocks containing flat-bottomed holes. The results are very encouraging, showing good performance when defects are in the far field of the actual probe configuration, while in the near-field region the generated DGS curves lead to a defect overestimation.

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