Investigation of fundamental ultrasonic propagation characteristics in NDT of electron beam melting additive manufactured samples

New approaches for efficient NDT inspection of modern additively manufactured metallic components are required urgently to qualify and validate the next generation of metallic parts across a range of industries. Ultrasonic testing is a fundamental component of NDT for such additive manufacturing processes. This work studies the ultrasonic propagation characteristics of EBM manufactured sample coupons in Alloy 718 material. Fundamental longitudinal and shear wave velocity measurements are experimentally measured in 3 orthogonal build directions of the sample coupons. Results show a dependency of the ultrasonic velocities and the build direction. The measured velocities are further verified in a phased array measurement showing successful results that highlights the potential of continued studies with synthetic apertures techniques

In-process calibration of a non-destructive testing system used for in-process inspection of multi-pass welding

In multi-pass welding, there is increasing motivation to move towards in-process defect detection to enable real-time repair; thus avoiding deposition of more layers over a defective weld pass. All defect detection techniques require a consistent and repeatable approach to calibration to ensure that measured defect sizing is accurate. Conventional approaches to calibration employ fixed test blocks with known defect sizes, however, this methodology can lead to incorrect sizing when considering complex geometries, materials with challenging microstructure, and the significant thermal gradients present in materials during the inter-pass inspection period. To circumvent these challenges, the authors present a novel approach to calibration and introduce the concept of in-process calibration applied to ultrasonic Non-Destructive Testing (NDT). The new concept is centred around the manufacturing of a second duplication sample, containing intentionally-embedded tungsten inclusions, with identical process parameters as the main sample. Both samples are then inspected using a high-temperature robotic NDT process to allow direct comparative measurements to be established between the real part and the calibration sample. It is demonstrated that in-process weld defect detection using the in-process calibration technique can more reliably identify defects in samples which would otherwise pass the acceptance test using a traditional calibration

Analysis of pigments in polychromes by use of laser induced breakdown spectroscopy and Raman microscopy

Two laser-based analytical techniques, Laser Induced Breakdown Spectroscopy (LIBS) and Raman microscopy, have been used for the identification of pigments on a polychrome from the Rococo period. Detailed spectral data are presented from analyses performed on a fragment of a gilded altarpiece from the church of Escatrón, Zaragoza, Spain. LIBS measurements yielded elemental analytical data which suggest the presence of certain pigments and, in addition, provide information on the stratigraphy of the paint layers. Identification of most pigments and of the materials used in the preparation layer was performed by Raman microscopy.This work has been supported by the Ultraviolet Laser Facility operating at FO.R.T.H. under the Large Installations Plan of the EU, by DGICYT (PB96-0844-C02-01), Spain and by the U.L.I.R.S. (London)

Analysis of pigments in polychromes by use of laser induced breakdown spectroscopy and Raman microscopy

Two laser-based analytical techniques, Laser Induced Breakdown Spectroscopy (LIBS) and Raman microscopy, have been used for the identification of pigments on a polychrome from the Rococo period. Detailed spectral data are presented from analyses performed on a fragment of a gilded altarpiece from the church of Escatrón, Zaragoza, Spain. LIBS measurements yielded elemental analytical data which suggest the presence of certain pigments and, in addition, provide information on the stratigraphy of the paint layers. Identification of most pigments and of the materials used in the preparation layer was performed by Raman microscopy.This work has been supported by the Ultraviolet Laser Facility operating at FO.R.T.H. under the Large Installations Plan of the EU, by DGICYT (PB96-0844-C02-01), Spain and by the U.L.I.R.S. (London)

Laser-induced breakdown spectroscopy and Raman microscopy for analysis of pigments in polychromes

A polychrome from the Rococo period was analysed by use of two laser-based analytical techniques, laser-induced breakdown spectroscopy (LIBS) and Raman microscopy. The analysis, performed on a fragment of a gilded altarpiece from the church of Escatrón, Zaragoza, Spain, provided detailed spectral data that have been used for the identification of pigments. LIBS measurements yielded elemental analytical data that suggest the presence of certain pigments and, in addition, provide information on the stratigraphy of the paint layers. Identification of most pigments and of the materials used in the preparation layer was performed by Raman microscopy.This work has been supported by the Ultraviolet Laser Facility operating at FO.R.T.H. under the Large Installations Plan of the EU, by DGICYT (PB96-0844-C02-01), Spain and by the U.L.I.R.S. (London)

Control of broadband optically generated ultrasound pulses using binary amplitude holograms

In this work, the use of binary amplitude holography is investigated as a mechanism to focus broadband acoustic pulses generated by high peak-power pulsed lasers. Two algorithms are described for the calculation of the binary holograms; one using ray-tracing, and one using an optimization based on direct binary search. It is shown using numerical simulations that when a binary amplitude hologram is excited by a train of laser pulses at its design frequency, the acoustic field can be focused at a pre-determined distribution of points, including single and multiple focal points, and line and square foci. The numerical results are validated by acoustic field measurements from binary amplitude holograms, excited by a high peak-power laser