Influence of humidity on the flexural strength of alumina

The influence of humidity on the flexural strength of alumina was investigated. The strengths tested at relatively high relative humidities (>45%) were smaller than those tested at relatively low relative humidities (<45%) as much as ∼10%. It was demonstrated by a round robin test that the influence of the humidity could produce a problem in the reproducibility of the strength data. It was discussed, that the problem in the reproducibility can be avoided by testing and using the inert strength in the comparison of strength data. It was recommended that, to test the inert strength, the strength measurement be made after the specimens had been coated with oil to protect them from contact with environmental moisture.