Analysis of hybrid composite properties by grating interferometry method
* Eulalia Klata, * Izabella Krucińska, ** Małgorzata Kujawińska, *** Grzegorz Dymny * Politechnika Łódzka, Katedra Metrologii Włókienniczej, ul. Żeromskiego 116, 90-543 Łódź ** Politechnika Warszawska, Instytut Mikromechaniki i Fotoniki, ul. Chodkiewicza 8, 02-525 Warszawa *** Fundacja Wdrażania, Wspierania i Rozwoju Technik Optycznych, ul. Chodkiewicza 8, 02-525 Warszawa
Annals 2 No. 4, 2002 pages 143-148
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abstract In this research work the application of grating interferometry method to determination of hybrid composite properties has been presented. The thermoplastic composites have been manufactured from hybrid glass/PA6 yarns used in the form of the knitted fabrics. The hybrid yarns were obtained using four various spinning processes. Each of the manufacturing techniques of hybrid yarns gives a yarn of different appearance and structure: - friction spinned (DREF) yarn - a core yarn, a braid from staple thermoplastic multifilaments and a core from glass multifilament (Fig. 1), - twisted yarn - one glass multifilament twisted uniform with two polyamide multifilaments (Fig. 2), - air interlaced yarn - yarn with point joints by fibres shifting againts one another under the influence of compressed air (Fig. 3), - textured yarn - connectedin the length by shifting of filament fibres of both components and forming loop structure on the yarn surface (Fig. 4). The mechanical properties of produced hybrid yarns are presented in Table 1. Each of these spinning methods give the different mechanical properties of yarn, the different blending of fibres in yarn and different adhesion conditions between polyamide 6 and glass surfaces. The thermal pressing of the layer arrangement of knitted fabrics was performed on a hydraulic press in optimal conditions. The tensile, shear and bending tests for these composites were carried out by means of an Instron tester. The mechanical properties of composites are dependent on using yarn. By grating (moire) interferometry system we can determine the functions u(x, y) and v(x, y) describing the in-plane displacement in x and y direction respectively for composites in tensile test. Grating interferometry requires specimen preparation by replication on its surface a high-frequency diffraction grating (25x25 mm). The setup of grating interferometry system is shown in Figures 5. The maxima of fringes are formed when u(x, y) = Nd/2, where N = 0, 1, 2, ... is the fringe number, d is grating period. It means that the interferogram is the displacement map with basic sensitivity equal to half of the specimen grating period. In this work is applied grating with frequency 1200 lines/mm, which gives basic sensitivity 417 nm per fringe. Figures 6 and 9 show the u and v displacement maps and Figures 7 and 10 show the strains ε x and ε y within the 4 x 6 mm obtained for the tensile force 50 N. For the composite manufactured from the air-interlaced yarn the strains are uniform on all measurement field. This yarn has the highest degree of fibre blending. The highest values of strains are for the composite manufactured from the textured yarn. The mean value of the strains (with the exception of composite manufactured from air-interlaced yarn) in the tensile direction of specimen is higher than perpendicular to the tensile direction of specimen.