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Reliability Problems in Methods of Residual Creep Life Assessment
Kloc, Luboš ; Sklenička, Václav
The service life of components designed to operate for long periods under loading at elevated temperatures is limited by the creep deformation and fracture phenomena. Possibility of a reliable prediction of the residual creep life is of major practical and economical relevance. A number of approaches has been used for the estimation of the creep damage and residual life; these approaches could be divided into two principal branches. The microscopic methods are based on the microstructural observations of accumulated damage in the samples of material after service, while macroscopic meth- ods use mechanical testing of the samples under some reference conditions. However, both approaches still do not provide enough reliable results for wide practical use, be- cause of result scatter and missing generally applicable models for the creep damage evolution. The most important factors which make the results unreliable are analyzed in the present paper. These are mainly: i) production scatter in the material's properties, ii) inhomogeneity of the material, iii) sampling problem in microscopic methods, iv) extrapolations involved in macroscopic methods. Some suggestions to overcome these problems are made and the need for a new approach and new experimental techniques is presented.
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Statistics in educational test development
Otřísal, Václav ; Pecáková, Iva (advisor) ; Sixta, Jaroslav (referee)
The paper deals with a justifiability of the application of statistics in the process of test development. It also aims to show possibilities of its application on the final test version. The first part of the thesis brings up the fundamentals of test development theory. The second part aims to describe general impact of statistics application on the test qualities. It further focuses on item analysis as one of the tool to evaluate test items qualities. Among others it includes information about reliability and validity analysis so as about the test equating methods. The analytical part contains analysis conducted on the OSP test. The analytical part also deals with predicted test validity and with the quality level of data gained from pre-testing.
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