Sub-Critical Crack Growth in Alumina - a Comparison of Different Measurement and Evaluation Methods

摘要

Every brittle failure of a ceramic component is preceded by a certain amount of sub-critical crack growth (SCCG). In Order to incorporate lifetime predictions into de-sign considerations, material data on this phenomenon have to be known. Such material data are only available for a few materials. This is primarily due to the fact that the necessary experiments are time consuming and the evalu-ation of the data may be complicated. In this work two common measurement methods, static bend tests and constant stress-rate tests were used to de-termine the parameters for sub-critical crack growth, n and B of a commercial alumina ceramic. Several evaluation procedures were applied to the constant stress-rate data. The data evaluation turned out to be straightforward be-cause a clear Separation of the inert strength plateau from the SCCG influenced strength could be observed. A large range of stress-rates spanning five Orders of magnitude could be used for the evaluation.All evaluation procedures lead to comparable values for n and B, constant stress-rate tests provide more accurate values for the SCCG parameters than the evaluation of the lifetime distribution. While n could be determined with rea-sonable scatter, the variety in B was much bigger.