Issue 50

M. Eremin et alii, Frattura ed Integrità Strutturale, 50 (2019) 38-45; DOI: 10.3221/IGF-ESIS.50.05 39 alumina ceramics possess brittleness which decreases significantly the operational functionality of devices. This is due to a decrease of elastic and strength characteristics of materials with an increase of porosity. The multiscale modeling approach has been recently successfully applied for investigation of failure mechanisms of different materials [4]. It appears to be useful since it provides a bridge between the microstructure of the material and effective mechanical characteristics utilized for macroscopic simulation. Recently [5] the mesoscale models of a representative volume of porous alumina ceramics were built on the basis of grain and pore distribution patterns and subjected to uniaxial loading in order to determine effective mechanical characteristics which are utilized for macroscopic simulation in this work. In the next sections, we provide a microstructural analysis of sintered specimens using scanning electron microscopy. We provide a mathematical statement of the boundary value problem (BVP). FEM simulation-based approach is utilized to investigate the failure mechanisms of Al 2 O 3 ceramic specimens subjected to three-point bending. We also performed a comprehensive numerical analysis of the failure mechanism. The results of a macroscopic simulation are compared with experimental data and give a good agreement in terms of loading diagram and crack path. (a) (b) (c) Figure 1: Fracture surface of Al 2 O 3 sample after etching, sintered at 1600° C (a), the pore size (b) and the grain size distributions (c) of the ceramic specimen. Images obtained using a scanning electron microscope in SE mode (SD means standard deviation, d stands for average dimension). M ATERIAL CHARACTERIZATION AND EXPERIMENTAL SETUP ectangular shaped specimens of Al 2 O 3 were obtained from technically pure alumina powder by slip casting and sintering, the rate of temperature increase was 3.5°C/min and the specimens were kept at the temperature of 1600°C in a conventional oven during one hour. A detailed study of the microstructure of the samples was carried out. Analysis of the structure allowed us to identify the morphological features of the pore space and the size of structural elements such as grains and pores. Porosity was determined by ImageJ software [2] from photos obtained with the help of SEM Vega 3 LMU. Photos of the etched surface of the samples are presented in Fig. 1a. The average porosity of the samples is 17%. The average pore size is 3.9 microns (Fig. 1b). The pore size varies from 1 to 8 microns, and the maximum is R