Determination of material properties for short fiber reinforced ceramic matrix composite under bending load

Kurzfassung

For continuous fiber reinforced ceramic matrix composites (CMC), there is an extensive knowledge of the influence of coupon geometry on the failure mode and the determined resistance in bending tests. In contrast, there are few studies on this topic for short fiber reinforced CMC and no geometry standard for bending tests for such materials exists. In this work, the influence of different sample numbers, coupon geometry and test conditions on the calculated mean and variance of flexural strength has been investigated. Two different short fiber CMCs were examined under four point bending mode. It is shown that a number of five coupons is sufficient for getting reliable data. Furthermore it is shown that below a certain specimen cross-section a decrease of the determined strength was observed. The standard deviation and the distribution of rupture stress strongly depended on the specimen geometry size, the fiber length and the loading span width. The correlation of the fiber orientation in the loaded area, of the region of failure initiation and of the measured flexural strength were investigated by high resolution X-ray computer tomography and SEM in order to obtain further insight into the causes of strength scatter in these materials. The presented results will be proposed to a future standard for the bending test of short fiber reinforced CMC materials.