A simple novel technique for evaluation of viscoelastic properties of ceramic composites

Abstract

Relatively large residual and processing stresses may be developed during the manufacturing of ceramic composites. Such stresses can be responsible for generating microcracks during the cooldown cycle of hot pressing, or can remain in the body and contribute to the formation of cracks during the service life of the components. These stresses can be effectively modeled by the finite element method (FEM), in conjunction with a viscoelastic constitutive material model. The FEM, however requires parameters, such as the elastic and viscoelastic properties, that are not readily available. Although there are techniques available for measuring the elastic properties as a function of porosity and temperature, limited measurement values are available at elevated temperatures. Moreover, measurement of the viscoelastic parameters is very complicated. In this paper we discuss a simple yet elegant approach for evaluating the viscoelastic properties of ceramic composites. The method uses readily available data (i.e. hot pressing pressure and ram displacement, both time dependent quantities). The method therefore produces ‘in-processing’ viscosity data. The properties obtained using the method was used to conduct transient nonlinear viscoelastic finite element analysis (FEA). The FEA results were in close agreement with those measured experimentally, thereby validating the integrity of the proposed method.