Diametral compression test: Analysing the H/D ratio influence on the mechanical resistance of UO2-green pellets

Abstract

[EN] Fired ceramic components and green compacted bodies from ceramic powder are both fragile structures. Their particles have weak mechanical links or are just agglomerated by a binder. Due to the compaction process failure can occur during unloading and ejection stages and also after a certain level of densification or powder cohesion has been achieved. Ceramic materials normally have worse standard deviation in the splitting tensile strength values when subjected to static or dynamic impact tests than metals. The height-to-diameter (H/D) ratio has been studied for several materials showing that by having different geometrical correlations the mechanical resistance of the tested specimens is highly affected. Cylindrical UO2-green pellet samples, having approximately the same density with three different diameters and four different heights, were pressed and experimentally studied by means of the diametral compression (Brazilian) test. By combining the diameters and the heights different H/D ratios could be tested. Results, which were analysed using Weibull statistics, showed that the cylinder size has a great influence on the Weibull module (m), whereas for the Weibull tensile strength no conclusive tendency could be observed except if we keep the height fixed and increase the pellet diameter. Pellets having the same height showed an increased tendency for the m value if their diameter is increased. The largest volume by each diameter has the highest Weibull module values.