Effect of 3-D distance textile reinforcement on mechanical properties of composites
Hubert Schmidt, Małgorzata Cieślak, Irena Kamińska Instytut Inżynierii Materiałów Włókienniczych, ul. Gdańska 118, 90-520 Łódź
Annals 2 No. 5, 2002 pages 309-312
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abstract Composites consisting of reinforced fibres and a matrix, usually of thermoplastic or chemosetting resin, since a long time are used as construction materials. Recently more and more often woven and knitted spatial textile structures of continuous filament or two-dimensional textiles arranged in layers are used as reinforcement. The aim of present study was to prepare light composites designed for structural elements satisfying requirements such as good heat insulation and low weight, e.g. boat bodies, heat transporting ducts, motor-car bodies, light roofs and the like. This goal can be reached by composite, being at least three-component, which in addition to polymeric matrix and reinforcement contains many free air spaces. Taking this assumption into consideration, light weight structural composites have been made up of matrices consisting of chemosetting polyester and epoxy resins, reinforced with three-dimensional distance (3-DD) textiles (Fig. 1). Polyester and polyamide 3-DD textiles were used as reinforcement. The composites have weight by volume of 200 to 480 kg/m3 and contain 60 to 85% of empty spaces (Tab. 1). Resin content doesn’t exceed 350 kg/m3. Mechanical properties such as compression strength and bending strength of the composites, and their modulus of elasticity have been assessed (Tab. 2). Series of composites were prepared with 3-DD reinforcement and various content of polyester and epoxy resin matrices. Figures 2 and 3 show the relationships between bending strength Rz of such composites (c in Fig. 1), and their ratios of strength to weight by volume, and resin content (% by mass of reinforcement). They are approximately rectilinear. Out of straight line lie only the values for high resin content. The compression strength Rs and ratio of strength to weight by volume in relation to resin content are shown in Figure 4. The strength of composites with epoxy resin matrices as well as the strength of composites with polyester matrices is very similar. Good mechanical properties were obtained with 3-DD knitted fabric made of voluminous polyester or polyamide yarn connected with polyester monofilament (composites a and b in Fig. 1). 3-DD woven fabric reinforced composites (composites d in Fig. 1) have very low mass by volume and high strengths to weight ratios but it was difficult to obtain good impregnation with resin of such reinforcement because of its to small elastic recovery. The performed study made it possible to obtain very light composites with a high elasticity, good compression and bending strengths as well as a high ratio of strength to the weight by volume. Thick and voluminous yarn of joining elements in 3-DD knitted reinforcement provides good compression strength in thick composites, but increases their weight. Fine, smooth yarn reinforcement give light composites with sufficient bending strength.