Observation of microstructure and damage in materials by phase sensitive radiography and tomography

Abstract

The novel possibilities of phase feature detection in radiography at a third generation synchrotron radiation source are used to image, both in projection and in computed tomography, a cracked silicon single crystal and metal matrix composites strained in tension. Through an instrumentally very simple technique, based on Fresnel diffraction, phase jumps related to the interface between the matrix and the reinforcing phases of the composites are detected even when these phases show very similar x-ray attenuation. Strain-induced cracks with openings below the micrometer range are also visible through the phase modulation they introduce, illustrating the potential of the technique for assessing damage in materials with improved resolution and sensitivity.

A comparison of multi-scale 3D X-ray tomographic inspection techniques for assessing carbon fibre composite impact damage

“…2(b) and (c) demonstrate the benefits of phase-enhanced edge contrast and increased resolution: details of individual fibres and resin rich regions are clearly visible, with damage micromechanisms clearly delineated. SRCT and SRCL yield qualitatively similar damage visualisation employing the edge-enhancing phase contrast [26,28], with the benefit of SRCL being the intact coupon geometry. However in the case of SRCL, artefacts resulting from incomplete Fourier-space sampling can arise: an exact inversion of the modulation transfer function (MTF) is not possible.…”

“…Key benefits of synchrotron imaging include fast acquisition speed with high signal-to-noise, convenient exploitation of phase contrast effects particularly propagation methods for enhanced edge detection [26], and submicrometer resolutions, when compared to conventional micro-focus sources [27].…”

Phase contrast imaging simulation and measurements using polychromatic sources with small source-object distances

“…[1][2][3][4][5][6][7][8][9] In a typical setup for this type of experiment, the radiation produced by a relatively small x-ray source acquires partial coherence during propagation in free space, crosses an object placed at relatively large distance from the source, and produces an image on an observation plane ͑screen͒. The amplitude of the interference fringes produced on the screen is particularly large around the border of structures inside the object having a refractive index different from the surrounding material.…”

“…In many cases phase contrast can reveal structures that are hardly visible through absorption imaging. [4][5][6] The Van-Cittert-Zernike theorem 10 gives a relationship between the spatial coherence function of an electromagnetic wave and the intensity distribution of the source. In particular, the radiation produced by a quasimonochromatic and totally incoherent source becomes partially coherent at a large distance compared to the linear size of the source.…”

Boundary-enhanced region-of-interest image reconstruction in propagation-based x-ray phase-contrast tomography

“…We refer to this variant of PCT as boundary-enhanced PCT, 7,[13][14][15] which is conceptually similar to Lambda tomography methods that have been developed for conventional CT. 16 Because the need for phase-retrieval is avoided, image reconstruction algorithms for boundary-enhanced PCT 12,17 do not possess Fourier space singularities and can be relatively robust to experimental errors and even the effects of wavefield polychromaticity. 15 Data truncation is another important experimental factor that is not accommodated by most conventional tomographic image reconstruction algorithms.…”