Finite element modeling of the residual stresses in the ceramic-elastomer infiltrated composites
Kamil Babski*, Anna Boczkowska*, Katarzyna Konopka*, Grzegorz Krzesiński**, Krzysztof J. Kurzydłowski*** *Politechnika Warszawska, Wydział Inżynierii Materiałowej, ul. Wołoska 141, 02-507 Warszawa **Politechnika Warszawska, Instytut Techniki Lotniczej i Mechaniki Stosowanej, ul. Nowowiejska 24, 00-665 Warszawa ***Politechnika Warszawska, Wydział Inżynierii Materiałowej, ul. Wołoska 141, 02-507 Warszawa
Quarterly No. 3, 2005 pages 40-44
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abstract The ceramic-elastomer composites obtained via infiltration of porous SiO2 ceramics by urea-urethane elastomer were obtained and studied (Fig. 1). Such composites are distinguished by the high compression strength and ability to achieve large deformations. The liquid mixture of the substrates is incorporated into ceramic pores using the vacuum pressure and temperature of 120oC. Since the thermal expansions of the elastomer and ceramics are different upon cooling to ambient temperature thermal stresses are generated (Tab. 1). Moreover, the elastomer shrinks as a consequence of its transformation from the mixture of substrates in the liquid to the solid states. These two phenomena result in buildup of residual stresses in the composite what can affect on the composite mechanical properties. In this work numerical models of composite were developed and analysis of the residual stresses arising during fabrication process was reported. To calculate the residual stresses the Finite Element Method (FEM) was used. In the models the shape ratio was involved with a change of elastomeric particles shape from spherical to ellipsoidal (Fig. 2). The volume fraction was constant for all cases and equal to 0.40. The unit cells were subjected to thermal load simulating the cooling from fabrication (120oC) to room temperature (20oC). The stresses distributions in dual phases component material were calculated using Ansys software. The analysis of distribution of principal stresses shows that change of temperature leads to buildup of high tensile stresses in elastomeric phase and tensile and compressive stresses in ceramic phase (Fig. 3). The simulation of both thermal and tensile load of unit cell were made. It was found that the thermal stresses present in composite mostly reduce the maximum values of tensile stresses in ceramic (Fig. 5). The elastomeric particles shape changes can lead to local increase of compressive stresses on parallel direction to ceramic-elastomer interface (Fig. 6). It can be advantageous from the mechanical point of view and can lead to increasing of the resistance for brittle cracking and composite strength. Key words: ceramic-elastomer composites, residual stresses, Finite Element Method, infiltration