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Models of Calculating the Properties of Laminates and Spatially Reinforced Composites

Fibre-reinforced composite materials have heterogeneous properties. The properties of fibre-reinforced composite materials depend on the properties of the matrix, properties of reinforcement as well as properties on the interface, The properties also depend on form, size and position of the reinforcement. The heterogeneous characteristic of properties of composites results from various properties of reinforcement in the direction of the fibres compared to the properties perpendicular to this direction. In order to use the properties of the reinforcement, the interface between them and the matrix has to transfer the load from the matrix to the reinforcement. The properties of the fibre-reinforced composites are determined by the weakest link in the matrix-interface-reinforcement chain. As long as the share of the matrix in the material prevails, it will determine the properties of the composite. By increasing the share of the reinforcement the influence of the interface is becoming stronger until it is equal to the influence of the matrix. After that the dominant influence on the properties is taken over by the interface which transfers an adequate part of the stress from the matrix to the reinforcements. The starting model for studying the fibre-reinforced composites is the material reinforced by parallel fibres “ Unidirectional lamina” (1 D) [1] and [2]. The properties of a composite reinforced by parallel fibres in the direction of the fibres are better than the properties perpendicular to that direction. In studying the tensile strength in line rotated at an angle of 45° a tendency has been observed of the sample rotating in the test tools. This phenomenon has been described in literature [1]. This has led to the idea of setting parallel fibrous reinforcement in one more direction perpendicular to the first line and obtaining a composite reinforced in two directions (2D) “ laminate” . The properties of a composite reinforced by parallel set fibres in two mutually perpendicular lines are more homogeneous than the properties of composites reinforced in one direction (1D) (Figure 1a). Further improvement can be achieved by setting one more group of parallel set fibres in the third orientation (Figure 1b). The properties in line perpendicular to the reinforcing directions i.e. to the plane defined by the reinforcing lines are poorer than the properties in that plane. In studying the tensile strength the plane-reinforced composite material in line rotated at an angle of 45° compared to the reinforcing surface is again observed the tendency of the sample to rotate in the testing tools. This has led to the idea of setting additional parallel fibrous reinforcement in line perpendicular to the reinforcing plane and production of composites reinforced in three directions (3D). The properties of composites reinforced by parallel fibres set at three mutually perpendicular lines is less anisotropic than the properties of composite materials reinforced in one direction (1D) and in two directions (2D). The best tensile strength of these materials lies in the direction of reinforcement, in lines rotated at an angle of 45° the tensile strength is lower whereas for a line rotated by an angle of 45° and inclined at an angle of 45° the tensile strength is the lowest (Figure 2a). In studying the tensile strength spatially in three directions (3D) of the reinforced composite material in line inclined at an angle of 45° compared to the reinforcing surface, no tendency has been noticed of the sample rotation in the testing tools. Further improvement can be achieved by setting one more group of parallel set fibres in the fourth direction (Figure 2b) (4D) [3]. References [1] Hull, Derek and T.W. Clyne, An introduction to composite materials, Cambridge solid state science series, Cambridge University Press, 1996, Cambridge, UK. [2] Matthews, F.L., Rawlings R.D., Composite materials: engineering and science, Woodhead Publishing Ltd, 2000, Cambridge, UK. [3] Tarnopol'skii, Yu. M., Zhigun, I.G., Polyakov, V.A., Spatially Reinforced Composites, Tehnomic Publishing Co. Inc, 1992, Lancaster, Pennsylvania USA.

strength; laminate; spatially reinforced composite.

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