Dynamic fatigue behaviour of a steatite ceramic

Abstract

Dynamic fatigue of a low dielectric loss steatite was investigated. To this end, the values of n and B, the so-called subcritical crack growth (SCG) parameters were experimentally determined. The steatite exhibited the expected dynamic fatigue behaviour, so that the stress corrosion susceptibility parameter, n, of 24 was obtained. In addition, the material/environment parameter B, which is a constant for a given test environment, was also attained. These parameters are instrumental in predicting the lifetime of components under stress. When the applied load is such that the resulting strength equals half of the inert strength (σ i ), defined as the strength of a sample tested in an inert environment or at a fast stress rate, i.e. where no subcritical crack growth occurs, the time to failure (t f ) of the material was found to bẽ 140 h. Measurement of the fracture toughness of steatite is also of upmost importance and so it was determined using three test methods. A value of K Ic = 1.91 ± 0.29 MPa m 1/2 was attained by the indentation fracture method through measurement of the cracks emanating from the Vickers indentation. This value is in good agreement with those determined using the K Isc (surface crack in flexure) test method (2.21 ± 0.07 MPa m 1/2 ) and fractography analysis test method (2.00 ± 0.44 MPa m 1/2 ). Differences in test procedure and analysis causing the values from each test method to be different are discussed. Keywords: Steatite / fracture toughness / dynamic fatigue / slow crack growth / flexural strength Schlüsselwörter: Steatit / Bruchzähigkeit / dynamische Ermüdung / langsames Risswachstum / Biegefestigkeit