Analysis of Creep in a Variable Thickness Rotating Disc Made of Functionally Graded Composite

Abstract

Metal matrix composites consisting of aluminum/aluminum alloy matrix reinforced with ceramics like silicon carbide (SiC) exhibit higher specific strength and stiffness, and superior thermal resistance and hence may be employed in rotating disc of turbine rotor and disc brakes. The conventional metal matrix composites sometimes fail under extreme service conditions of temperature and mechanical loads. To meet such stringent loading condition, a new class of composites, known as Functionally Graded Materials (FGMs), have been developed. The contents of constituent phases in FGM are gradually varied with respect to position coordinates to attain smooth and continuous variation in the desired properties. The present study is an attempt to investigate the steady state creep behavior of a variable thickness rotating disc made of aluminum or its alloy matrix reinforced with SiC (particles or whiskers). The first segment of the study deals with the analysis of the steady state creep in a rotating FGM disc yielding according to Tresca criterion. The creep behavior of the disc has been described by a threshold stress based law, with the value of stress exponent equals to 5. The disc thickness and distribution of SiCp reinforcement are assumed to decrease linearly on moving from the inner to outer disc radius. The stresses and strain rates are estimated from the analysis and compared with those available in literature for a similar FGM disc yielding according to von Mises criterion. The study reveals that the use of Tresca criterion gives much safer design of a variable thickness rotating FGM disc as compared to FGM disc designed on the basis of von Mises criterion. The second segment of the study investigates the effects of varying disc geometry, radial distribution of SiCp and radial thermal gradient on the steady state creep behavior of a rotating disc, yielding according to Tresca criterion. The study indicates that by varying the disc thickness gradient from 0 to 29.9 mm, the strain rates in a uniform composite disc