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The relationship between the structural anisotropy of the PFA polymer/compressed expanded graphite-matrix composites and acoustic emission characteristics

Berdowska Sylwia, Berdowski Janusz, Aubry Frederic

Bulletin of the Polish Academy of Sciences. Technical Sciences

2021

Vol. 69, nr 5

art. no. e138235

The main aim of the study was to search for the relationship between the anisotropy of the structure of polyfurfuryl alcohol (PFA) – polymer/compressed expanded graphite (CEG)-matrix composites at subsequent stages of the technological process and characteristics of the acoustic emission (AE) descriptors. These composites, obtained after successive technological procedures of impregnation, polymerization, and carbonization, possess different structure, densities, porosity, and other physicochemical properties. In the structures of composites prepared on the basis of CEG, two basic directions can be distinguished: parallel to the bedding plane of graphite sheets and perpendicular to it. The measurements were carried out for the stress acting in these two main directions. The investigation has shown that the AE method enables the detection of anisotropy in the structure of materials. The results of the research show that all four of the acoustic emission descriptors studied in this work are sensitive to the technological stages of these materials on the one hand and their structure anisotropy on the other. Fourier analysis of the recorded spectra provides interesting conclusions about the structural properties of composites as well as a lot of information about the bonding forces between the carbon atoms of which the CEG matrix is composed and the PFA polymer or turbostratic carbon.

Digital identification of the yarn take-up gradient in anisotropic warp knitted fabrics

Mikołajczyk Z.

Zeszyty Naukowe. Włókiennictwo / Politechnika Łódzka

2000

z. 58

209-218

The anisotropic multiple-guide-bar fabrics are an important product group among the warp knitted fabrics. Their characteristic feature is variation of the take-up, in the courses Wr and wales Wk, of threads in the structural elements of the fabric. Analysis of the parameters of various anisotropic warp knitted fabrics (Jacuard, inlaid, tucking, etc.) reveals that differences in the amount of thread take-up are between a few and a few hundred percent [1]. These large differences in take-up of the warp threads between different structural elements of the stitch or pattem repeat create a problem with selection of the correct yarn feeding method and, consequently, with the programming of the feeding of varied lengths of warp needed for the formation of the successive elements of the fabric.