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Abstract
Determining the mechanical properties of short fibre reinforced CMC using standard sized coupons has always been a challenge due to a high statistical scattering of the measured values. Although the random orientation of short fibres results in a quasi-isotropic material behavior of 2D-structures with a sufficiently large volume, the small volume typical for test coupons usually results in a non-isotropic fibre orientation in the tested volume. This paper describes a method for manufacturing unidirectional oriented short fibre reinforced CMC materials and presents material properties of UD-C/C-SiC. After verifying the fibre orientation of the CMC using micro-computed tomography, coupons were extracted to determine the orthotropic material properties. These orthotropic material properties were then used to predict the properties of C/C-SiC with randomly distributed short fibres. To validate the method, micro-computed tomography is used to quantitatively determine the fibre orientation within coupons extracted from randomly distributed short fibre C/C-SiC. After mechanical three-point-bending tests, the measured stiffness and bending strength is compared with the predicted properties. Finally, the data are used to devise a method suited for reducing the inherent large spread of material properties associated with the measurement of CMC materials with randomly distributed short fibres.
Highlights
Material testing of randomly distributed short fibre reinforced composites has always been challenging due to the large spread of material properties
4.1 Computed tomography Analysis of Unidirectional Material The computed tomography data show a good alignment of the fibre bundles
The method presented in this paper for aligning fibre bundles in short fibre reinforced C/C-SiC allows the manufacturing of material with unidirectionally oriented fibre bundles
Summary
Material testing of randomly distributed short fibre reinforced composites has always been challenging due to the large spread of material properties. Due to the small coupon size, the mechanical properties are influenced from the locally inhomogeneous fibre distribution. This necessiates a large number of specimens to ensure that the material properties are statistically determined, resulting in high costs and a high scattering of the data obtained. A solution commonly used in polymer reinforced materials involves the manufacturing of coupons with all short fibres oriented in one direction using techniques such as injection moulding [1]. Due to the flow processes involved, the short fibres within the polymer orient themselves in one direction, resulting in an orthotropic material suited for determining orthotropic material properties. The obtained orthotropic data is used as a basis to calculate the material properties of the composite with random fibre distribution [2]
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