Fractographic and Fracture Mechanical Investigations of Refractories under Different Loading Conditions

Crack initiation and propagation have been investigated under tensile and shear loading in ceramically and carbon bonded refractories.A wedge splitting test procedure and a modified shear test have been applied.Test results have been used for material characterization especially with respect to brittleness.Furthermore a microscopic fractographic test procedure was developed and applied on fractured test specimens.In order to explain brittleness dependence on structure properties correlation of fractographic and fracture mechanical results has been evaluated.Frequently brittleness reduction is achieved by a lower amount of transgranular crack propagation associated with a strength decrease while maintaining specific fracture energy unchanged.Deviations from pure linear fracture mechanics increase with decreasing brittleness and contribute to specific fracture energy.Shear specimens may show two generations of cracks,a first one initiated by tensile loads （stable propagation） and a second one by shear loads （unstable propagation）.

Advanced Measures to Characterize Mechanical Properties of Refractories

The thermomechanical modelling method is becoming an important tool nowadays for the refractory researchers, suppliers and end-users. On one hand, applications focus on the post-mortem thermomechanical analysis to interpret the occurred fitiluw phenomena of refractories in service. On the other hand, a priori investigation is very helpful for the design of refractory lining con- cepts before putting them into effect; as a result it will minimize the probability of refractory lining premature .failure and save costs for the refractory suppliers as well as for the end-users. For both investigation routines, suitable material constitutive models and testing approa- ches are of relevance. Existing material constitutive mod- els often used for refractories are the fictitious crack model acting for tensile failure, the Mohr - Coulomb or Drucker- Prager model describing shear failure, and the Norton - Bailey model representing creep. To charac- terize tbe tensile and shear fitilure of refractories at room temperatare and elevated temperatures, a wedge splitting test and a modified shear test can be applied, respectively. The creep behavior and corresponding creep parameters of refractories can be determined with an appropriate creep testing device at elevated loads. The proper appli- cation of material constitutive models and testing approa-ches allows for improving the thermo-mechanical modelling and the optimizatian of the lining design.