Witold Węglewski

Chemically Assisted Damage of Concrete: A Model of Expansion Under External Sulfate Attack:

A micromechanical model is proposed to simulate the deformation of cementitious composites exposed to external sulfate attack. The model involves coupled physico-chemical processes of nonsteady diffusion with reaction, topochemical reaction of ettringite formation, expansion of ettringite inclusions, microcracking of hardened cement paste and percolation of sulfates through heavily deteriorated mortar. The Ficks second law with reaction term is assumed to govern the transport of the sulfate ions. The Eshelby solution and the equivalent inclusion method are used to determine the eigenstrain of expanding ettringite crystals in microcracked hardened cement paste. The degradation of transport properties is studied in the effective medium and the percolation regime. An initial boundary value problem (2D) of expansion of a mortar specimen immersed in a sodium sulfate solution is solved and compared with available test data.

The Influence of Al2O3 Powder Morphology on the Properties of Cu-Al2O3 Composites Designed for Functionally Graded Materials (FGM)

In order to meet the requirements of an increased efficiency applying to modern devices and in more general terms science and technology, it is necessary to develop new materials. Combining various types of materials (such as metals and ceramics) and developing composite materials seem to be suitable solutions. One of the most interesting materials includes Cu-Al2O3 composite and gradient materials (FGMs). Due to their potential properties, copper-alumina composites could be used in aerospace industry as rocket thrusters and components in aircraft engines. The main challenge posed by copper matrix composites reinforced by aluminum oxide particles is obtaining the uniform structure with no residual porosity (existing within the area of the ceramic phase). In the present paper, Cu-Al2O3 composites (also in a gradient form) with 1, 3, and 5 vol.% of aluminum oxide were fabricated by the hot pressing and spark plasma sintering methods. Two forms of aluminum oxide (αAl2O3 powder and electrocorundum) were used as a reinforcement. Microstructural investigations revealed that near fully dense materials with low porosity and a clear interface between the metal matrix and ceramics were obtained in the case of the SPS method. In this paper, the properties (mechanical, thermal, and tribological) of composite materials were also collected and compared. Technological tests were preceded by finite element method analyses of thermal stresses generated in the gradient structure, and additionally, the role of porosity in the formation process of composite properties was modeled. Based on the said modeling, technological conditions for obtaining FGMs were proposed.

Thermal Residual Stresses Generated during Processing of Cr-Al2O3 Composites and their Influence on Macroscopic Elastic Properties

This work is focused on the modeling of thermal stresses induced during the fabrication of the metal/ceramic composites. On example of Cr-Al2O3 composite processed by powder metallurgy, thermal stresses after fabrication are determined by FEM model for different contents of metal and ceramic phases. Numerical model of microcracking induced by thermal stresses is then proposed and applied to compute the overall elastic properties of the damaged composite. Comparison of the model predictions with the measured data for Youngs modulus is presented.