Nano-scale Near-Field Ptychography of aerospace-grade Carbon Fibre Composites

Near-Field Ptychography (NFP) is a coherent diffraction imaging technique employed at high-brilliance x-ray sources like third- or fourth-generation synchrotrons or free electron lasers. In this study, NFP is used to image carbon fibre reinforced polymers (CFRP) at high resolution and with high image quality. CFRPs are lightweight materials with high strength and stiffness, their versatility makes them one of the most employed composite materials on the market. Two samples were involved in the experiments, both loaded in tension with a special rig in order to stress the material to its limits. Four post-mortem ptycho-tomographies were acquired at the beamline ID16A, located at the European Synchrotron Radiation Facility (ESRF). Two different pixel sizes were used: $40 ~ nm$ and $150 ~ nm$. The results obtained from the data analysis concern mainly the defects present in the materials, and the damage undergone during the tensile test. The latter is primarily subdivided into three types: fibre cracks, matrix cracks and debonding, which is the detachment of the polymeric matrix from the carbon fibres. These features are described in detail thanks to the high resolution that has been possible to obtain at the beamline ID16A and to the careful 3D segmentation done during the data analysis. The defects of CFRPs include the presence of voids, or porosity, in the matrix, and the misalignment of fibres, but also their distribution across the material cross-section and their diameters. The misalignment of fibres, or even their clustering in some regions of the sample, severely reduces the strength of the material, which derives its properties from the uniform distribution of the loads across the cross-section. Segmentation helped in the analysis of voids, while the other features have been analysed with other techniques developed in this study and described thoroughly in the thesis. The second part of the study is dedicated to the application of Speckles Based Imaging (SBI) to some images of a test Siemens Star at $10 ~ nm$ pixel size. By adding a diffuser to the imaging setup at ID16A the goal was to understand the limits of SBI and NFP, bridging the gap between them. Reconstructing these data using the Unified Modulated Pattern Analysis (UMPA), a software dedicated to SBI, revealed the limits of this technique. It does not perform well in the case of a long propagation between the sample and the detector. Moreover, the same data acquired with a typical SBI experimental setup are reconstructed using PtyPy, a software dedicated to NFP. In this case the results reveal how the quality of the images is deteriorated by the additional diffusing element.