Simulation of ultrasonic phased array technique for imaging and sizing of defects using longitudinal waves

Many shell structures used in modern technology consist of regular shell parts joined together along their common boundaries. We review different theoretical, numerical, and experimental approaches to modelling, analyses and design of the compound shell structures with junctions. Several alternative forms of boundary, continuity and jump conditions at the singular midsurface curves modelling the shell junction are reviewed. We also analyse the results obtained for special shell structures containing the cylinder–cylinder intersections, cone– , sphere– , and plate–cylinder junctions, tubular joints as well as other special types of junctions appearing in complex multi-shell structures.

https://www.imp.gda.pl/files/wp/wppub/2012/Praca10.pdf

Junctions in shell structures: A review

Using ultrasonic arrays to detect and characterise surface breaking cracks is important in the non-destructive evaluation (NDE) field. It can provide early warning of failure and useful information for component integrity assessment. Typically, cracks are approximated by machined slots and used to examine and assess defect detection and characterisation methods. In this paper, real surface breaking cracks are fabricated in 3-point bending specimens following ASTM standard E1820 and used to examine the performance of two array defect characterisation methods: image-based and scattering matrix sizing. In both cases, an array is used to record the full matrix capture (FMC). In image-based sizing, the total focusing method (TFM) is used to form an image from which the defect size is measured directly. This approach is shown to work well for cracks greater than two wavelengths in size. The FMC is also used to extract the defect scattering matrix which is then compared to a pre-computed smooth-crack scattering matrix database. The best match between experiment and this database is found by cross-correlation and used to characterise the defect. This approach is shown to work well for defects in the range of 0.78–1.84 wavelengths. Within these ranges of applicability, both methods show excellent agreement between the known crack length and that measured ultrasonically, with errors less than 19% in all cases.

https://research-information.bris.ac.uk/files/165662689/PDF.pdf

The sizing of small surface-breaking fatigue cracks using ultrasonic arrays

New techniques developed using the array transducer, to image and size the bottom-surface and near-through-wall crack-like defects in thick carbon steel components are discussed. Three studies are reported here including (a) Optimal beam steering angle for focused and unfocused inspection using phased array method for bottom-surface crack sizing. (b) A front wall correction algorithm for sizing of near-through-wall crack-like defects. (c) A small aperture technique for sizing of near-through-wall crack-like defects. A Finite Difference Time Domain (FDTD) based simulation was used to study and verify the experimental observations. The application of time domain scheme relative arrival time technique (RATT), to measure the size of the near-through wall crack-like defects for the leak before break (LBB) criterion, was also investigated and found to be insufficient. A conventional SAFT algorithm was used for improving the sizing using the small aperture technique.

Sizing Cracks in Power Plant Components Using Array Based Ultrasonic Techniques

Ultrasonic arrays have been widely used and developed for defect detection and characterisation over the last 10 years. In this paper, the question of how to inspect and characterise near-surface defects that are small with respect to wavelength is addressed. The challenge is to overcome the effect of the proximity of these scattered signals to high-amplitude signals reflected from structural features, such as planar surfaces. Here, a method is proposed to extract the scattered signals from a near-surface defect which overlap with signals from a structural feature in both the time and frequency domains. The extracted signals are then used to generate a scattering coefficient matrix, from which it is possible to characterise the defect. In the proposed method, the location of the defect is first approximately identified from an image. The arrival time difference between the signals from the defect and the nearby planar surfaces for each combination of transmitter and receiver array elements is then...

/pdf/measurement-of-the-ultrasonic-scattering-matrices-of-near-bfypur6ilg.pdf

Measurement of the ultrasonic scattering matrices of near-surface defects using ultrasonic arrays

This paper reports experimental sizing of fatigue crack profiles that are initiated from artificially made circumferential starter notches in stainless steel pipes of 169 mm outer diameter and 14.33 mm thickness, which were subjected to cyclic bending loads in a four point bending load arrangement using two nondestractive evaluation (NDE) methods: (a) phased array ultrasonic technique and (b) alternating current potential drop technique. The crack growth estimated using the two NDE techniques were compared with the beach marks that were present in the fracture surface. A simulation study using the ray tracing method was carried out to model the ultrasonic wave propagation in the test specimen, and the results were compared with the experimental results.

Phased Array Ultrasonic Measurement of Fatigue Crack Growth Profiles in Stainless Steel Pipes

Steam generators are important components of a nuclear reactor. They are subjected to system pressure and force controlled bending moments. Leak before break (LBB) criteria based on a fracture mechanics approach is used to ensure the reliability of the primary heat transport system of nuclear reactors. Experimental studies were recently completed for justifying LBB for the cold end of the shell–nozzle junction of the steam generator of the 500 MWe Fast breeder reactor (FBR) under construction at Kalpakkam. The internal diameter of the main tube is 1120 mm and that of the nozzle is 386.4 mm. The thickness of the main tube is 24 mm while that of the nozzle is 18 mm. Fatigue tests were conducted on two carbon steel and two modified 9Cr1Mo steel shell–nozzle junction specimens at room temperature under constant internal pressure and cyclic in-plane bending moment. Fracture tests were conducted on these components until collapse after the fatigue test. FEM analysis was also performed to identify critical locations and factor of safety for fatigue loading and collapse. The objective of the studies was to obtain the factor of safety for crack initiation, through-wall and critical crack size, and collapse. The studies demonstrated adequate factor of safety for all the above LBB criteria.

D. M. Pukazhendhi

Papers

Phased Array Ultrasonic Measurement of Fatigue Crack Growth Profiles in Stainless Steel Pipes

Investigations on shell–nozzle junction of steam generator for LBB justification