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

Departure from linearity of fibre Bragg grating temperature coefficients

We have measured the Bragg wavelength shift of three gratings from -30degreesC to +80degreesC. The observed deviation from linearity is a quadratic function of temperature, arising from the non-linear thermo-optic coefficient of silica glass

Application of Hilbert transforms to high resolution strain and temperature characterisation of fibre Bragg grating sensors

We report measurements of the strain and temperature coefficients of optical fibre Bragg gratings with similar to 1pm wavelength resolution using Fourier transform spectroscopy and Hilbert transform signal processing

Bend measurement using Bragg gratings in multicore fibre

We describe the measurements of curvature made using Bragg gratings written in separate cores of a multicore optical fibre. The gratings act as independent, but isothermal, strain gauges. Thus the difference in Bragg wavelength between the gratings provides a measurement of local curvature

Transverse loading of multicore fibre gratings

We report experimental measurements of the reflection spectra of Bragg gratings inscribed in 4-core fibres under transverse loading. Broadening and splitting of the Bragg peaks from each core are observed as a function of load and fibre orientation