DEVELOPMENT OF EXPRESS CALCULATION-EXPERIMENTAL TECHNIQUE TO ESTIMATE LIFE AND RELIABILITY OF CERAMIC PARTS AND COMPONENTS

摘要

The analysis of existing programs to develop advanced ceramic gas turbine engines indicates that the challenge to ensure a target life of ceramic components is of a paramount importance. The up-to-date express methodologies to define life have some principal limitations which necessitates to carry out labor-and time-consuming tests of bulky batches of ceramic samples and parts. The accuracy of the predicted results, at the same time, remains rather low which does not allow their practical application to design ceramic parts and components. An improvement of techniques of the life estimation could be attained considering that a crack growth takes place under load, this phenomenon occurring with the crack shear stress generation, this stress correlating with a threshold value of the stress intensity factor. It turns out here that along with the dynamic failure, the test duration is also a significant parameter, i.e. the parameter which is neglected by the current methodology to estimate the static failure and life. The developed methodology demonstrates not a bad correlation between the estimates and the experimental values, whereby reducing the scope of the initial data compared with the current methodology. Furthermore, using this approach one can predict results of proof tests which enables opting for an optimum proof duty. A result of the proof tests is essentially dependent on three test condition parameters, namely: 1. The value of a selected trial loading or a fraction of the parts rejected; 2. The exposition time under the trial loading; 3. The test temperature and the initial scatter of the strength properties. The sequence of the calculation carrying out is as follows: 1. A required Weibull modulus is identified using the static failure estimate technique for a target reliability of the ceramic element, stresses under the operation conditions, operation time, dynamic failure parameters. 2. The proof test conditions are identified using the Weibull modulus required.