Papers by Author: Maria Berkes Maros

Abstract: A comprehensive experimental and theoretical work aiming at studying the dynamic failure process of silicon nitride ceramics has been recently started. The main goal of this research programme consists in characterizing the mechanical behaviour of the material under dynamic loading as well as investigating the dynamic failure process using micro- and macro-fractography. The current paper deals with the phenomenon of special rate dependence of KId dynamic fracture toughness of Si3N4 based ceramics. The KId values have been determined during instrumented impact test on the one hand based on the dynamic key curve method using notched specimens, on the other hand based on fractographic analyses of fracture surface of impacted unnotched samples.

Abstract: Residual stresses of production origin superimposed with the operational stresses influences the reliability of glass products. The most widely used procedures for their detection and qualification are optical methods that can not be utilized for testing of non-transparent glasses. A recently developed glass qualifying procedure based on scratch test with integrated image processing is applicable for evaluating the residual stresses in surface of both the transparent and non-transparent glasses. The reliability of the suggested test method is greatly dependent on the information content provided by the involved image analysis procedure. The current paper introduces the principle, and methodology of the test method, furthermore presents the latest results gained by applying an improved algorithm of the image processing.

Abstract: The main topic of the current work consists in analysing the tribological behaviour of graphite reinforced Si3N4 nanocomposites. The basic aim was to investigate the influence of microstructural features, i.e. amount and grain size of the added reinforcing graphite, as well as the effect of applied load on the wearing characteristics like wearing profile, wear rate, friction coefficient or mechanism of the wear damage process. Tribological tests were performed on a pinon- disc tribometer with on-line measurement of friction coefficient and the wear profile. Wear tests were completed with traditional micro-hardness and instrumented hardness tests, furthermore fractographical analyses of the wear tracks using scanning electron microscopy.

Abstract: Residual stresses significantly influence the strength and lifetime of the glass products, therefore their qualification and quantification during production is basically important for evaluating their probable reliability in application. The current paper aims at introducing a novel procedure of the suggested automatic glass quality test based on instrumented scratch test completed with computer aided image analysis. A special emphasis is put on the problem of limited reproducibility and reliability of the image processing, arisen in the first stage of the research work. The latest results consisting in the development of a new algorithm, providing a more reliable evaluation of the test data will be described.

Abstract: Si3N4 is widely used as a structural ceramic, therefore mechanical characterization, especially in dynamic loading conditions is important task. In the framework of a comprehensive research work aiming at characterizing the dynamic failure process of Si3N4 based ceramics we executed instrumented impact tests. Beside determining various mechanical characteristics we executed failure analysis by fractography, as well. The current paper focuses on the fractographic analysis of the dynamic failure processes of the investigated Si3N4 based ceramics. A detailed morphological analysis has been carried out determining qualitative and quantitative features using macro- and micro-fractography.

Abstract: The current paper give a brief overview over the principle and information content of the instrumented impact test completed by electro-emission measurement. Introducing over experiences taken by applying these test on a high-tech SiAlON ceramic a novel method for the determination of the dynamic fracture toughness of silicon nitride ceramics is suggested.

Abstract: Si3N4 based ceramics that made by hot isostatic press, were implanted at room temperature with N+ - and C+ - ions with energy of 500 keV and 2 MeV, respectively. The specimens were irradiated at a fluence of 1017 ion/cm2. The microstructure changes after ionimplantation in the surface layer were investigated by transmission electron microscopy (TEM). The effect of ion-implantation on the tribological properties was also studied. After N+ and C+ ionimplantation an amorphous layer near to the surface has been formed which was observed by electron diffraction measurement. The wear tests were performed by means of a ball-on-disk configuration using commercially available Si3N4 ball. The friction coefficient was measured online, the wear coefficient was determined on the base of the wear scar sizes. The specific wear rate was reduced by N+-implantation and the coefficient of friction was lower in the initial stage in both cases.