Abstract
This paper presents multi-modal image data of different fibre reinforced polymer samples acquired with a desktop Talbot-Lau grating interferometer (TLGI) X-ray computed tomography (XCT) system and compare the results with images acquired using conventional absorption-based XCT. Two different fibre reinforced polymer samples are investigated: (i) a carbon fibre reinforced polymer (CFRP) featuring a copper mesh embedded near the surface for lightning conduction and (ii) a short glass fibre reinforced polymer (GFRP) sample. The primary goal is the non-destructive detection of internal defects such as pores and the quantification of porosity. TLGI provides three imaging modalities including attenuation contrast (AC) due to absorption, differential phase contrast (DPC) due to refraction and dark-field contrast (DFC) due to scattering. In the case of the CFRP sample, DPC is less prone to metal streak artefacts improving the detection of pores that are located close to metal components. In addition, results of a metal artefact reduction (MAR) method, based on sinogram inpainting and an image fusion concept for AC, DPC and DPC, are presented. In the case of the GFRP sample, DPC between glass fibres and matrix is lower compared to AC while DPC shows an increased contrast between pores and its matrix. Porosity for the CFRP sample is determined by applying an appropriate global thresholding technique while an additional background removal is necessary for the GFRP sample.
Highlights
X-ray computed tomography (XCT) based on absorption contrast (AC) is an essential imaging technique in order to Journal of Nondestructive Evaluation (2019) 38:1 small pores, gaps or cracks in the sub-voxel region that can be even smaller than the spatial resolution of the XCT system [11, 12]
We demonstrate that differential phase contrast (DPC) images show significantly decreased beam-hardening artefacts in a multi-material system with copper mesh and an increased contrast-to-noise ratio, facilitating pore segmentation
Each imaging modality offers specific insights into the material system, since AC, DPC and dark-field contrast (DFC) are sensitive to different material phases, properties and inhomogeneities due to different interaction mechanisms of X-rays with matter
Summary
X-ray computed tomography (XCT) based on absorption contrast (AC) is an essential imaging technique in order to Journal of Nondestructive Evaluation (2019) 38:1 small pores, gaps or cracks in the sub-voxel region that can be even smaller than the spatial resolution of the XCT system [11, 12]. DFC enables the extraction of information about microstructural anisotropy, since scattering information from the internal microstructure (e.g. differently orientated fibres [9] or fibre bundles [7]) is direction-dependent. DFC’s anisotropy in combination with the extraction of sub-voxel microstructure can be used to characterize anisotropic materials such as fibre reinforced polymers with a larger field of view as compared to AC imaging. This has been realised by different techniques such as X-ray vector radiography [14] or X-ray tensor tomography [15] based on combining an imaging setup with multiple sample orientations. DPC has proven its usefulness by improved diagnostic capabilities compared to conventional methods [17], but so far there is a rather low impact on materials science applications
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