Influence of Anisotropy on Creep in a Whisker Reinforced MMC Rotating Disc

Abstract

Whisker reinforced MMC may be employed in rotating disc , a common component in friction drives , turbines and a number of other machine components, often exposed to elevated temperatures . Creep characteristics of these composites have been studied analytically using von Mises flow rule and Norton 's steady state creep equations . The results for isotropic A16061 alloy and for isotropic composite containing 20 vol% SiCµ in a matrix of A16061 alloy have been compared with those obtained for anisotropic composites with characteristic parameters a = 0.7 and 1. 31, indicating respectively relative strengthening and weakening in the tangential direction presumably introduced by either processing or inhomogeneous distribution of reinforcement.The creep strain rates resulting in the isotropic rotating disc made of composite as well as the aluminum alloy, are tensile in the tangential direction but compressive in the axial and radial directions, also conforming to the condition of volume constancy.The creep rates in the composite are significantly reduced (by about three orders of magnitude) in all the directions compared to those observed in the base alloy. In case of anisotropy lowering the strength in the tangential direction (a> 1.0), the radial stresses in the region near inner periphery of the disc, increase while those near the outer periphery decrease in comparison to those for the isotropic composite . But the tangential stresses reduce in the middle region of the disc and enhances near the inner and the outer periphery, when compared to those for the isotropic composite . The magnitude of stress distribution , however, changes by a small extent due to ani sotropy in the disc introduced through processing or reinforcement distribution . The radial strain rate which always remained compressive for the isotropic composite and for a = 1.3,becomes tensile in the middle region of the disc when a = 0.7. If a is reduced from 1.3 to 0 . 7, the variation of tensile strain rate in the tangential direction remains similar but the magnitude reduces by five orders of magnitude . Anisotropy therefore, introduces significant change in the strain rates although its effect on the resulting stress distribution may be relatively small.