PSI - Issue 41

552 A.M. Ignatova et al. / Procedia Structural Integrity 41 (2022) 550–556 Ignatova A.M., Balakhnin A.N., Bannikov M.V., Kuper K.E., Nikitiuk A.S., Naimark O.B./ Structural Integrity Procedia 00 (2019) 000–000 3 The purpose of the study was to develop a method for obtaining the integral characteristic of a structure of a loaded composite material on the basis of a microtomographic study exemplified by porosity evaluation. Research methods. The research used 2×2×2 mm cylindrical cutouts from CCCM samples before loading and after 17 kN tensile loading. 800х15х8.5 mm samples from which cutouts were made had a hole, which acted as a stress raiser. The specified loading value did not result in the destruction of samples, but, according to the authors’ experience, these conditions lead to structural changes caused by deformation. Fig. 1 shows a scheme of a sample cutout. Thus, the study's objects were a cutout from the unloaded sample and two cutouts from the loaded sample, one of which was located in the stress raiser zone, and the other along the loading axis.

Fig. 1. Scheme of the location of cutouts in the sample: (1) sample cutout without loading, (2) sample cutout after loading in the stress raiser zone, (3) sample cutout along the loading axis. Synchrotron radiation (SR) from the wiggler mounted on VEPP-3 charged particle accelerator (Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences) was used as an X-ray source. The value of angular dispersion of SR from VEPP-3 was in the region of 0.1 milliradian, and the total power of radiation was 0.1 kW in the X-ray range, which is several orders of magnitude greater than the power produced by X ray machines. Due to low divergence and high SR brightness, high spatial resolution was achieved at the level of 1 μm for the short-wave range (5-30 keV). The test arrangement is shown in Fig. 2. 4 μm thick thin-film scintillation screens were used in microtomographic imaging. A high-resolution CCD matrix (Hamamatsu ORCA-Flah2.8) with a 2048  2048 pixel matrix size was used as a detector. The size of one pixel, taking into account the lens magnification, was 0.6 μm. The sample, scintillation screen and detector were positioned relative to the X-ray beam with an accuracy of 1 µm in linear coordinates and 0.001  in angular coordinates. The SR beam was formed using a 1.5  1.5 mm X-ray collimator. The final result of the X-ray microtomography was a three-dimensional density matrix of the studied sample, the size of which was 800x800x601 voxels (voxel size 2.6x2.6x2.6 µm3).

Fig. 2. Microtomography research scheme.

To extract the integral characteristic of the structure porosity from the obtained data, we used an image analysis method based on threshold segmentation selecting the regions with a given range of gray shades. To decompose the general matrix into derivatives and for their subsequent analysis, the universal software ImageJ-FiJi was used.