Tensile creep measurements of ordinary ceramic refractories at service related loads including setup, creep law, testing and evaluation procedures

The performance of refractories under operating conditions is often influenced by tensile creep. This paper proposes a high-temperature tensile testing device which allows for long term creep measurements at operating loads. The chosen specimen geometry is more adequate for the testing of ordinary ceramic refractories which may be heterogeneous with respect to grain size (maximum grain size e.g. 5 mm) and chemical composition. For this application the innovative design exhibits not only improved specimen and loading alignments, but also reliable specimen holding and cooling systems. Specific procedures were followed to avoid uneven stress distribution along the specimen gauge length. The testing procedure was optimized by simulating experimental creep conditions with a finite element (FE) model built with the software Abaqus. Measurements were performed on magnesia-chromite material at different temperatures and applied stresses. Under these testing conditions, three creep stages emerged. The Norton-Bailey creep rate equation was employed to describe the creep behavior for the three stages. An evaluation using the Generalized Reduced Gradient (GRG) algorithm was then performed in order to identify the three creep stages and inversely estimate the Norton-Bailey creep parameters n, a and K for each stage.