292 Creep Response of Rotating Composite Discs having Exponential, Hyperbolic, Linear and Constant Thickness Profles Rajinder Singh # , Ravindra K. Saxena @ , Kishore Khanna * , and V.K. Gupta # # Department of Mechanical Engineering, Punjabi University, Patiala - 147 002, India @ Sant Longowal Institute of Engineering and Technology, Longowal, Sangrur - 148 106, India * Department of Mechanical Engineering, Thapar Institute of Engineering & Technology, Patiala - 147 004, India * E-mail: kishore.khanna@thapar.edu AbstRACt The study compares the steady state creep response of rotating Al-SiC discs having constant, linear, hyperbolic and exponential thickness with diferent thickness profles. All the discs are assumed to have equal volume with the same average thickness. The creep behaviour of the disc material is described by threshold stress based law while the yielding is assumed to follow Tresca criterion. The variable thickness disc is observed to have superior creep response, expressed in terms of stresses and strain rates, to a constant thickness disc. Amongst variable thickness discs, the creep response is observed to be superior for linear thickness disc, when the inner thickness of all the discs is kept the same. However, for the same outer thickness, the disc having hyperbolic thickness profle exhibits the best creep response. Keywords: Creep modelling; Rotating disc; Aluminium composites; Variable thickness; Strain rates Defence Science Journal, Vol. 70, No. 3, May 2020, pp. 292-298, DOI : 10.14429/dsj.70.14913 © 2020, DESIDOC 1. INtRODUCtION Rotating disc is a vital component that fnds use in various structural and engineering devices like turbine rotors, ship propellers, jet engines, automotive brakes, fywheels 1 . In most of these applications, the disc is subjected to severe thermo-mechanical loadings and hence vulnerable to creep 2-5 . Under such loading conditions, the use of Al-SiC p (p refers to particle shape) composite has been suggested by several investigators, owing to their light weight, high specifc strength and high temperature stability 6-8 . A number of studies have been performed to investigate elastic, elastic-plastic and creep response of rotating discs having diferent thickness profles. The stresses and strains produced in the disk due to centrifugal loading are noticed to decrease signifcantly by using radially decreasing thickness profle (viz. linear or hyperbolic), as compared to constant thickness disc 9-13 . It has been attributed to decrease in disc weight with increasing radius, which results in lower centrifugal loading. Deepak, 14-15 , et al. analysed creep stresses and creep strain rates in uniform and functionally graded (FG) discs made of Al-SiC p . Garg 16 , et al. revealed that the creep stresses and creep rates in a linear thickness Al-SiC p FG disc are signifcantly lower than a similar disc of constant thickness. Khanna 17 , et al. compared creep performance of a linear thickness FG disc using Tresca and von-Mises criteria. Jalali & Shahriari 18 , used fnite diference method to analyse elastic stress in a variable thickness rotating FG disc. Sharma 19 , et al. used seth’s transition theory to analyse creep in a rotating disc having exponential thickness. The variable thickness disc was noticed to have less circumferential stress than the fat disk. In a similar study, Sharma & Maheshwari 20 , noticed that FG rotating disk made of isotropic material performs better than that made of orthotropic material. The literature consulted reveals that studies have been undertaken to investigate creep in rotating disc having linear, hyperbolic and constant thickness profles. The studies on rotating disc having exponential profle are rather scant. It would be interesting to estimate creep in exponential disc and compare the results with that estimated for discs having linear, hyperbolic and constant thickness profles, so as to select suitable thickness profles for given operating conditions. In this light, the present study attempts to analyse creep in a rotating Al-SiC p disc having exponential thickness profle. The stresses and strain rates estimated are compared with those available/estimated for similar discs having constant, linear and hyperbolic thickness profles. The investigation is carried out for discs having the same (i) inner thickness and (ii) outer thickness. 2. MAtHEMAtICAL MODELLING 2.1 Disc thickness Profiles and Distribution of Reinforcement The creep analysis is carried out for rotating disc made of Al-20 % SiC p (by Vol.) composite having four diferent thickness profles, viz. constant, linear, hyperbolic and exponential. The inner and outer radii of the discs are kept as 31.75 mm and 152.4 mm, similar to that taken in previous work 11 . The thickness h(r) of the exponential disc, at any radius r, is assumed to vary as, Received : 06 August 2019, Revised : 02 March 2020 Accepted : 20 March 2020, Online published : 27 April 2020