USING FUZZY-SETS IN THE PREDICTION OF FLEXURAL STRENGTH AND DENSITY OF SILICON-NITRIDE CERAMICS

In this work we use fuzzy sets theory to evaluate and predict flexural strength and density of NASA 6Y silicon nitride ceramic. Processing v ariables of milling time, sintering time, and sintering nitrogen press ure are used as an input to the fuzzy system. Flexural strength and de nsity are the output parameters of the system. Data from 273 silicon n itride modulus of rupture bars tested at room temperature and 135 bars tested at 1,370-degrees-C (2,500-degrees-F) are used in this study, G eneralized mean operator and Hamming distance are used to construct th e fuzzy predictive model. The maximum test error for density does not exceed 3.3 percent, and for flexural strength 7.1 percent. These resul ts demonstrate that fuzzy sets theory can be incorporated into the pro cess of designing materials such as ceramics, especially for assessing more complex relationships between the processing variables and param eters like strength, which are governed by randomness of manufacturing processes.